Driving Pressure and Transpulmonary Pressure: How Do We Guide Safe Mechanical Ventilation?

Association of mechanical power and postoperative pulmonary complications among young children undergoing video-assisted thoracic surgery: A retrospective study

BACKGROUND

Previous studies have discussed the correlation between mechanical power (MP) and lung injury. However, evidence regarding the relationship between MP and postoperative pulmonary complications (PPCs) in children remains limited, specifically during one-lung ventilation (OLV).

OBJECTIVES

Propensity score matching was employed to generate low MP and high MP groups to verify the relationship between MP and PPCs. Multivariable logistic regression was performed to identify risk factors of PPCs in young children undergoing video-assisted thoracic surgery (VATS).

DESIGN

A retrospective study.

SETTING

Single-site tertiary children's hospital.

PATIENTS

Children aged ≤2 years who underwent VATS between January 2018 and February 2023.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The incidence of PPCs.

RESULTS

Overall, 581 (median age, 6 months [interquartile range: 5-9.24 months]) children were enrolled. The median [interquartile range] MP during OLV were 2.17 [1.84 to 2.64) J min-1. One hundred and nine (18.76%) children developed PPCs. MP decreased modestly during the study period (2.63 to 1.99 J min-1; P < 0.0001). In the propensity score matched cohort for MP (221 matched pairs), MP (median MP 2.63 vs. 1.84 J min-1) was not associated with a reduction in PPCs (adjusted odds ratio, 1.43; 95% CI, 0.87 to 2.37; P = 0.16). In the propensity score matched cohort for dynamic components of MP (139 matched pairs), dynamic components (mean 2.848 vs. 4.162 J min-1) was not associated with a reduction in PPCs (adjusted odds ratio, 1.62; 95% CI, 0.85 to 3.10; P  = 0.15).The multiple logistic analysis revealed PPCs within 7 days of surgery were associated with male gender, OLV duration >90 min, less surgeon's experience and lower positive end-expiratory pressure (PEEP) value.

CONCLUSIONS

MP and dynamic components were not associated with PPCs in young children undergoing VATS, whereas PPCs were associated with male gender, OLV duration >90 min, less surgeon's experience and lower PEEP value.

TRIAL REGISTRATION

ChiCTR2300074649.

Electrical Impedance Tomography-Based Evaluation of Anesthesia-Induced Development of Atelectasis in Obese Patients

Background/Objectives: The induction of general anesthesia leads to the development of atelectasis and redistribution of ventilation to non-dependent lung regions with subsequent impairment of gas exchange. However, it remains unclear how rapidly atelectasis occurs after the induction of anesthesia in obese patients. We therefore investigated the extent of atelectasis formation in obese patients in the first few minutes after the induction of general anesthesia and initiation of mechanical ventilation in the operating room. Methods: In 102 patients with morbid obesity (BMI ≥ 35 kg m-2) scheduled for laparoscopic intrabdominal surgery, induction of general anesthesia was performed while continuously monitoring regional pulmonary ventilation using electrical impedance tomography. Distribution of ventilation to non-dependent lung areas as a surrogate for atelectasis formation was determined by taking the mean value of five consecutive breaths for each minute starting five minutes before to five minutes after intubation. Ventilation inhomogeneity was assessed using the Global Inhomogeneity Index. Results: Median tidal volume in non-dependent lung areas was 58.3% before and 71.5% after intubation and increased by a median of 13.79% after intubation (p < 0.001). Median Global Inhomogeneity Index was 49.4 before and 71.4 after intubation and increased by a median of 21.99 units after intubation (p < 0.001). Conclusions: Atelectasis forms immediately after the induction of general anesthesia and increases the inhomogeneity of lung ventilation.

Effect of inspiratory oxygen fraction during driving pressure-guided ventilation strategy on pulmonary complications following open abdominal surgery: A randomized controlled trial

STUDY OBJECTIVE

The aim of the present study was to determine the effect of 30 % fraction of inspired oxygen (FIO2) compared with 80 % FIO2 in the context of driving pressure-guided ventilation strategy on pulmonary complications following open abdominal surgery.

DESIGN

A single-center, prospective, randomized controlled trial.

SETTING

Tertiary university hospital in China.

PATIENTS

514 adult patients, ASA I-III and scheduled for major open abdominal surgery under general anesthesia.

INTERVENTIONS

Patients were randomly assigned to receive either 30 % or 80 % FIO2 during the intraoperative period. All patients received driving pressure-guided ventilation strategy, including low tidal volume and individualized PEEP set at lowest driving pressure.

MEASUREMENTS

The primary outcome was the incidence of a composite of pulmonary complications within the 7 days postoperatively. The severity of pulmonary complications, extrapulmonary complications, and other secondary outcomes were also assessed.

MAIN RESULTS

Of 1553 patients assessed for eligibility, 514 patients were randomly assigned and analyzed with intention-to-treat principle. Patients receiving 30 % FIO2 had a significantly lower incidence of postoperative pulmonary complications (PPCs) compared to those receiving 80 % FIO2 (46.3 %vs. 64.6 %; RR, 0.72; 95 % CI, 0.61-0.84; P < 0.001). The severity score of PPCs was significantly reduced in the 30 % FIO2 group compared with that in the 80 % FIO2 group within the 7 postoperative days (P < 0.001). Dynamic compliance was significantly greater in 30 % FIO2 group at the end of surgery (56 [48-66] vs. 53 [46-62], P = 0.027). More patients in the 80 % FIO2 group developed oxygen desaturation (SpO2 < 94 %) on air intake during PACU stay (18.5 %vs. 30.4 %; RR, 0.61; 95 % CI, 0.44-0.84; P = 0.002; 30 % FIO2 group vs.80 % FIO2 group).

CONCLUSIONS

In patients undergoing open abdominal surgery, using a 30 % FIO2, compared with 80 % FIO2, in context of driving pressure-guided ventilation strategy, intraoperatively reduced the incidence and severity of pulmonary complications within the first 7 postoperative days.

Lung-protective ventilation and postoperative pulmonary complications during pulmonary resection in children: A prospective, single-centre, randomised controlled trial

BACKGROUND

Children are more susceptible to postoperative pulmonary complications (PPCs) due to their smaller functional residual capacity and higher closing volume; however, lung-protective ventilation (LPV) in children requiring one-lung ventilation (OLV) has been relatively underexplored.

OBJECTIVES

To evaluate the effects of LPV and driving pressure-guided ventilation on PPCs in children with OLV.

DESIGN

Randomised, controlled, double-blind study.

SETTING

Single-site tertiary hospital, 6 May 2022 to 31 August 2023.

PATIENTS

213 children aged < 6 years, planned for lung resection secondary to congenital cystic adenomatoid malformation.

INTERVENTIONS

Children were randomly assigned to LPV ( n  = 142) or control ( n  = 71) groups. Children in LPV group were randomly assigned to either driving pressure group ( n  = 70) receiving individualised positive end-expiratory pressure (PEEP) to deliver the lowest driving pressure or to conventional protective ventilation group ( n  = 72) with fixed PEEP of 5 cmH 2 O.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of PPCs within 7 days after surgery. Secondary outcomes were pulmonary mechanics, oxygenation and mechanical power.

RESULTS

The incidence of PPCs did not differ between the LPV (24/142, 16.9%) and the control groups (15/71, 21.1%) ( P  = 0.45). The driving pressure was lower in the driving pressure group than in the 5 cmH 2 O PEEP group (15 vs. 17 cmH 2 O; P   =  0.001). Lung compliance and oxygenation were higher while the dynamic component of mechanical power was lower in the driving pressure group than in the 5 cmH 2 O PEEP group. The incidence of PPCs did not differ between the driving pressure (11/70, 15.7%) and the 5 cmH 2 O PEEP groups (13/72, 18.1%) ( P   =  0.71).

CONCLUSIONS

LPV did not decrease the occurrence of PPCs compared to non-protective ventilation. Although lung compliance and oxygenation were higher in the driving pressure group than in the 5 cmH 2 O PEEP group, these benefits did not translate into significant reductions in PPCs. However, the study is limited by a small sample size, which may affect the interpretation of the results. Future research with larger sample sizes is necessary to confirm these findings.

TRIAL REGISTRATION

ChiCTR2200059270.

The impact of a lung-protective ventilation mode using transpulmonary driving pressure titrated positive end-expiratory pressure on the prognosis of patients with acute respiratory distress syndrome

OBJECTIVE

This study aimed to assess the impact of a lung-protective ventilation strategy utilizing transpulmonary driving pressure titrated positive end-expiratory pressure (PEEP) on the prognosis [mechanical ventilation duration, hospital stay, 28-day mortality rate and incidence of ventilator-associated pneumonia (VAP), survival outcome] of patients with Acute Respiratory Distress Syndrome (ARDS).

METHODS

A total of 105 ARDS patients were randomly assigned to either the control group (n = 51) or the study group (n = 53). The control group received PEEP titration based on tidal volume [A tidal volume of 6 mL/kg, flow rate of 30-60 L/min, frequency of 16-20 breaths/min, constant flow rate, inspiratory-to-expiratory ratio of 1:1 to 1:1.5, and a plateau pressure ≤ 30-35 cmH2O. PEEP was adjusted to maintain oxygen saturation (SaO2) at or above 90%, taking into account blood pressure], while the study group received PEEP titration based on transpulmonary driving pressure (Esophageal pressure was measured as a surrogate for pleural pressure using an esophageal pressure measurement catheter connected to the ventilator. Tidal volume and PEEP were adjusted based on the observed end-inspiratory and end-expiratory transpulmonary pressures, aiming to maintain a transpulmonary driving pressure below 15 cmH2O during mechanical ventilation. Adjustments were made 2-4 times per day). Statistical analysis and comparison were conducted on lung function indicators [oxygenation index (OI), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2)] as well as other measures such as heart rate, mean arterial pressure, and central venous pressure in two groups of patients after 48 h of mechanical ventilation. The 28-day mortality rate, duration of mechanical ventilation, length of hospital stay, and ventilator-associated pneumonia (VAP) incidence were compared between the two groups. A 60-day follow-up was performed to record the survival status of the patients.

RESULTS

In the control group, the mean age was (55.55 ± 10.51) years, with 33 females and 18 males. The pre-ICU hospital stay was (32.56 ± 9.89) hours. The mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was (19.08 ± 4.67), and the mean Murray Acute Lung Injury score was (4.31 ± 0.94). In the study group, the mean age was (57.33 ± 12.21) years, with 29 females and 25 males. The pre-ICU hospital stay was (33.42 ± 10.75) hours. The mean APACHE II score was (20.23 ± 5.00), and the mean Murray Acute Lung Injury score was (4.45 ± 0.88). They presented a homogeneous profile (all P > 0.05). Following intervention, significant improvements were observed in PaO2 and OI compared to pre-intervention values. The study group exhibited significantly higher PaO2 and OI compared to the control group, with statistically significant differences (all P < 0.05). After intervention, the study group exhibited a significant increase in PaCO2 (43.69 ± 6.71 mmHg) compared to pre-intervention levels (34.19 ± 5.39 mmHg). The study group's PaCO2 was higher than the control group (42.15 ± 7.25 mmHg), but the difference was not statistically significant (P > 0.05). There were no significant differences in hemodynamic indicators between the two groups post-intervention (all P > 0.05). The study group demonstrated significantly shorter mechanical ventilation duration and hospital stay, while 28-day mortality rate and incidence of ventilator-associated pneumonia (VAP) showed no significant differences. Kaplan-Meier survival analysis revealed a significantly better survival outcome in the study group at the 60-day follow-up (HR = 0.565, 95% CI: 0.320-0.999).

CONCLUSION

Lung-protective mechanical ventilation using transpulmonary driving pressure titrated PEEP effectively improves lung function, reduces mechanical ventilation duration and hospital stay, and enhances survival outcomes in patients with ARDS. However, further study is needed to facilitate the wider adoption of this approach.

Association between thoracic epidural anesthesia and driving pressure in adult patients undergoing elective major upper abdominal surgery: a randomized controlled trial

BACKGROUND

Thoracic epidural anesthesia (TEA) is associated with a knowledge gap regarding its mechanisms in lung protection and reduction of postoperative pulmonary complications (PPCs). Driving pressure (ΔP), an alternative indicator of alveolar strain, is closely linked to reduced PPCs with lower ΔP values. We aim to investigate whether TEA contributes to lung protection by lowering ΔP during mechanical ventilation.

METHODS

In this prospective, randomized, patient and evaluator-blinded parallel study, adult patients scheduled for elective major upper abdominal surgery were assigned to either the TEA group with combined thoracic epidural anesthesia and general anesthesia (TEA-GA) (n = 30) or the control group with only general anesthesia (GA) (n = 30).

MEASUREMENTS

The primary outcome was the minimum ΔP determined based on positive end-expiratory pressure (PEEP) after intubation. Secondary outcomes included the incidence of PPCs within seven days, the minimum ΔP at various time points, blood gas analysis, intensive care unit (ICU) admission rates, length of hospital stay, and 30-day mortality rate.

RESULTS

The TEA group had a significantly lower minimum ΔP titrated based on PEEP compared to the control group (11.23 ± 2.19 cmH2O vs. 12.67 ± 2.70 cmH2O; P = 0.028). Multivariate linear regression analysis showed that intraoperative TEA application (compared with its absence; unstandardized beta coefficient (B) = -1.289; P = 0.008) significantly correlated with ΔP. The incidence of PPCs did not differ significantly between the two groups (8 of 30 [26.7%] vs. 12 of 30 [40%]; P = 0.273), but the incidence of atelectasis in the TEA group was significantly lower than in the control group (5 of 30 [16.7%] vs. 12 of 30 [40.7%]; P = 0.012). Multivariate logistic regression analysis indicated that ΔP was the only variable significantly associated with PPCs (Adjusted Odds Ratio [OR] = 2.190; 95% Confidence Interval [CI]: 1.300 to 3.689; P = 0.003).

CONCLUSION

Compared to GA, TEA-GA can reduce intraoperative ΔP in patients undergoing major upper abdominal surgery, especially those undergoing laparoscopic surgery. However, compared to GA combined with ΔP-guided ventilation, TEA-GA combined with ΔP-guided ventilation does not reduce the risk of PPCs. There was no significant difference in the total use of various vasoactive drugs between the two groups.

TRIAL REGISTRATION

This study was registered in the Chinese Clinical Trial Registry (registration number ChiCTR2300068778 date of registration February 28, 2023).

Mechanisms of mechanical stimulation in the development of respiratory system diseases

During respiration, mechanical stress can initiate biological responses that impact the respiratory system. Mechanical stress plays a crucial role in the development of the respiratory system. However, pathological mechanical stress can impact the onset and progression of respiratory diseases by influencing the extracellular matrix and cell transduction processes. In this article, we explore the mechanisms by which mechanical forces communicate with and influence cells. We outline the basic knowledge of respiratory mechanics, elucidating the important role of mechanical stimulation in influencing respiratory system development and differentiation from a microscopic perspective. We also explore the potential mechanisms of mechanical transduction in the pathogenesis and development of respiratory diseases such as asthma, lung injury, pulmonary fibrosis, and lung cancer. Finally, we look forward to new research directions in cellular mechanotransduction, aiming to provide fresh insights for future therapeutic research on respiratory diseases.

The association between intraoperative low driving pressure ventilation and perioperative healthcare-associated costs: A retrospective multicenter cohort study

STUDY OBJECTIVE

A low dynamic driving pressure during mechanical ventilation for general anesthesia has been associated with a lower risk of postoperative respiratory complications (PRC), a key driver of healthcare costs. It is, however, unclear whether maintaining low driving pressure is clinically relevant to measure and contain costs. We hypothesized that a lower dynamic driving pressure is associated with lower costs.

DESIGN

Multicenter retrospective cohort study.

SETTING

Two academic healthcare networks in New York and Massachusetts, USA.

PATIENTS

46,715 adult surgical patients undergoing general anesthesia for non-ambulatory (inpatient and same-day admission) surgery between 2016 and 2021.

INTERVENTIONS

The primary exposure was the median intraoperative dynamic driving pressure.

MEASUREMENTS

The primary outcome was direct perioperative healthcare-associated costs, which were matched with data from the Healthcare Cost and Utilization Project-National Inpatient Sample (HCUP-NIS) to report absolute differences in total costs in United States Dollars (US$). We assessed effect modification by patients' baseline risk of PRC (score for prediction of postoperative respiratory complications [SPORC] ≥ 7) and effect mediation by rates of PRC (including post-extubation saturation < 90%, re-intubation or non-invasive ventilation within 7 days) and other major complications.

MAIN RESULTS

The median intraoperative dynamic driving pressure was 17.2cmH2O (IQR 14.0-21.3cmH2O). In adjusted analyses, every 5cmH2O reduction in dynamic driving pressure was associated with a decrease of -0.7% in direct perioperative healthcare-associated costs (95%CI -1.3 to -0.1%; p = 0.020). When a dynamic driving pressure below 15cmH2O was maintained, -US$340 lower total perioperative healthcare-associated costs were observed (95%CI -US$546 to -US$132; p = 0.001). This association was limited to patients at high baseline risk of PRC (n = 4059; -US$1755;97.5%CI -US$2495 to -US$986; p < 0.001), where lower risks of PRC and other major complications mediated 10.7% and 7.2% of this association (p < 0.001 and p = 0.015, respectively).

CONCLUSIONS

Intraoperative mechanical ventilation targeting low dynamic driving pressures could be a relevant measure to reduce perioperative healthcare-associated costs in high-risk patients.

Risk of pulmonary complications after video-assisted thoracoscopic pulmonary resection in children

BACKGROUND

Postoperative pulmonary complications (PPCs) are associated with high mortality and morbidity rates. Children are more susceptible to PPCs owing to smaller functional residual capacity and greater closing volume. Risk factors of PPCs in children undergoing lung resection remain unclear.

METHODS

This retrospective study enrolled children who underwent video-assisted thoracoscopic surgery between January 2018 and February 2023. The primary outcome was PPC occurrence. Multivariate logistic regression was used to analyze risk factors for PPCs.

RESULTS

Overall, 640 children were analyzed; their median age was 7 (interquartile range: 5-11) months, and the median tidal volume was 7.66 (6.59-8.49) mL/kg. One hundred and seventeen (18.3%) developed PPCs. PPCs were independently associated with male sex (odds ratio [OR], 1.83; 95% confidence interval [CI], 1.17-2.88; P=0.008), longer OLV duration (OR, 1.01; 95% CI, 1.0-1.01; P=0.001), and less surgeon's experience (OR, 1.67; 95% CI, 1.03-2.7; P=0.036). When low-tidal-volume cutoff was defined as <8 mL/kg, PEEP level was a protective factor for PPCs (OR, 0.83; 95% CI, 0.69-1.00; P=0.046). Additionally, PPCs were associated with increased hospital stay (P<0.001).

CONCLUSIONS

Male sex, longer OLV duration, less surgeon's experience, and lower PEEP were risk factors of PPCs in children undergoing video-assisted thoracoscopic surgery. Our findings may serve as targets for prospective studies investigating specific ventilation strategies for children.

Time Course of Mechanical Ventilation Driving Pressure Levels in Pediatric Acute Respiratory Distress Syndrome: Outcomes in a Prospective, Multicenter Cohort Study From Colombia, 2018-2022

OBJECTIVES

High driving pressure (DP, ratio of tidal volume (V t ) over respiratory system compliance) is a risk for poor outcomes in patients with pediatric acute respiratory distress syndrome (PARDS). We therefore assessed the time course in level of DP (i.e., 24, 48, and 72 hr) after starting mechanical ventilation (MV), and its association with 28-day mortality.

DESIGN

Multicenter, prospective study conducted between February 2018 and December 2022.

SETTING

Twelve tertiary care PICUs in Colombia.

PATIENTS

One hundred eighty-four intubated children with moderate to severe PARDS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The median (interquartile range [IQR]) age of the PARDS cohort was 11 (IQR 3-24) months. A total of 129 of 184 patients (70.2%) had a pulmonary etiology leading to PARDS, and 31 of 184 patients (16.8%) died. In the first 24 hours after admission, the plateau pressure in the nonsurvivor group, compared with the survivor group, differed (28.24 [IQR 24.14-32.11] vs. 23.18 [IQR 20.72-27.13] cm H 2 O, p < 0.01). Of note, children with a V t less than 8 mL/kg of ideal body weight had lower adjusted odds ratio (aOR [95% CI]) of 28-day mortality (aOR 0.69, [95% CI, 0.55-0.87]; p = 0.02). However, we failed to identify an association between DP level and the oxygenation index (aOR 0.58; 95% CI, 0.21-1.58) at each of time point. In a diagnostic exploratory analysis, we found that DP greater than 15 cm H 2 O at 72 hours was an explanatory variable for mortality, with area under the receiver operating characteristic curve of 0.83 (95% CI, 0.74-0.89); there was also increased hazard for death with hazard ratio 2.5 (95% CI, 1.07-5.92). DP greater than 15 cm H 2 O at 72 hours was also associated with longer duration of MV (10 [IQR 7-14] vs. 7 [IQR 5-10] d; p = 0.02).

CONCLUSIONS

In children with moderate to severe PARDS, a DP greater than 15 cm H 2 O at 72 hours after the initiation of MV is associated with greater odds of 28-day mortality and a longer duration of MV. DP should be considered a variable worth monitoring during protective ventilation for PARDS.

Mechanical ventilation guided by driving pressure optimizes local pulmonary biomechanics in an ovine model

Mechanical ventilation exposes the lung to injurious stresses and strains that can negatively affect clinical outcomes in acute respiratory distress syndrome or cause pulmonary complications after general anesthesia. Excess global lung strain, estimated as increased respiratory system driving pressure, is associated with mortality related to mechanical ventilation. The role of small-dimension biomechanical factors underlying this association and their spatial heterogeneity within the lung are currently unknown. Using four-dimensional computed tomography with a voxel resolution of 2.4 cubic millimeters and a multiresolution convolutional neural network for whole-lung image segmentation, we dynamically measured voxel-wise lung inflation and tidal parenchymal strains. Healthy or injured ovine lungs were evaluated as the mechanical ventilation positive end-expiratory pressure (PEEP) was titrated from 20 to 2 centimeters of water. The PEEP of minimal driving pressure (PEEPDP) optimized local lung biomechanics. We observed a greater rate of change in nonaerated lung mass with respect to PEEP below PEEPDP compared with PEEP values above this threshold. PEEPDP similarly characterized a breaking point in the relationships between PEEP and SD of local tidal parenchymal strain, the 95th percentile of local strains, and the magnitude of tidal overdistension. These findings advance the understanding of lung collapse, tidal overdistension, and strain heterogeneity as local triggers of ventilator-induced lung injury in large-animal lungs similar to those of humans and could inform the clinical management of mechanical ventilation to improve local lung biomechanics.

Driving pressure association with mortality in post-lung transplant patients: A prospective observational study

OBJECTIVE

To investigate the association between driving pressure (ΔP) and 90-day mortality in patients following lung transplantation (LTx) in patients who developed primary graft dysfunction (PGD).

METHODS

This prospective, observational study involved consecutive patients who, following LTx, were admitted to our intensive care unit (ICU) from January 2022 to January 2023. Patients were separated into two groups according to ΔP at time of admission (i.e., low, ≤15 cmH2O or high, >15 cmH2O). Postoperative outcomes were compared between groups.

RESULTS

In total, 104 patients were involved in the study, and of these, 69 were included in the low ΔP group and 35 in the high ΔP group. Kaplan-Meier analysis of 90-day mortality showed a statistically significant difference between groups with survival better in the low ΔP group compared with the high ΔP group. According to Cox proportional regression model, the variables independently associated with 90-day mortality were ΔP and pneumonia. Significantly more patients in the high ΔP group than the low ΔP group had PGD grade 3 (PGD3), pneumonia, required tracheostomy, and had prolonged postoperative extracorporeal membrane oxygenation (ECMO) time, postoperative ventilator time, and ICU stay.

CONCLUSIONS

Driving pressure appears to have the ability to predict PGD3 and 90-day mortality of patients following LTx. Further studies are required to confirm our results.

Guide to Lung-Protective Ventilation in Cardiac Patients

The incidence of acute respiratory insufficiency has continued to increase among patients admitted to modern-day cardiovascular intensive care units. Positive pressure ventilation (PPV) remains the mainstay of treatment for these patients. Alterations in intrathoracic pressure during PPV has distinct effects on both the right and left ventricles, affecting cardiovascular performance. Lung-protective ventilation (LPV) minimizes the risk of further lung injury through ventilator-induced lung injury and, hence, an understanding of LPV and its cardiopulmonary interactions is beneficial for cardiologists.

Differential Effects of Intra-Abdominal Hypertension and ARDS on Respiratory Mechanics in a Porcine Model

Background and Objectives: Intra-abdominal hypertension (IAH) and acute respiratory distress syndrome (ARDS) are common concerns in intensive care unit patients with acute respiratory failure (ARF). Although both conditions lead to impairment of global respiratory parameters, their underlying mechanisms differ substantially. Therefore, a separate assessment of the different respiratory compartments should reveal differences in respiratory mechanics. Materials and Methods: We prospectively investigated alterations in lung and chest wall mechanics in 18 mechanically ventilated pigs exposed to varying levels of intra-abdominal pressures (IAP) and ARDS. The animals were divided into three groups: group A (IAP 10 mmHg, no ARDS), B (IAP 20 mmHg, no ARDS), and C (IAP 10 mmHg, with ARDS). Following induction of IAP (by inflating an intra-abdominal balloon) and ARDS (by saline lung lavage and injurious ventilation), respiratory mechanics were monitored for six hours. Statistical analysis was performed using one-way ANOVA to compare the alterations within each group. Results: After six hours of ventilation, end-expiratory lung volume (EELV) decreased across all groups, while airway and thoracic pressures increased. Significant differences were noted between group (B) and (C) regarding alterations in transpulmonary pressure (TPP) (2.7 ± 0.6 vs. 11.3 ± 2.1 cmH2O, p < 0.001), elastance of the lung (EL) (8.9 ± 1.9 vs. 29.9 ± 5.9 cmH2O/mL, p = 0.003), and elastance of the chest wall (ECW) (32.8 ± 3.2 vs. 4.4 ± 1.8 cmH2O/mL, p < 0.001). However, global respiratory parameters such as EELV/kg bodyweight (-6.1 ± 1.3 vs. -11.0 ± 2.5 mL/kg), driving pressure (12.5 ± 0.9 vs. 13.2 ± 2.3 cmH2O), and compliance of the respiratory system (-21.7 ± 2.8 vs. -19.5 ± 3.4 mL/cmH2O) did not show significant differences among the groups. Conclusions: Separate measurements of lung and chest wall mechanics in pigs with IAH or ARDS reveals significant differences in TPP, EL, and ECW, whereas global respiratory parameters do not differ significantly. Therefore, assessing the compartments of the respiratory system separately could aid in identifying the underlying cause of ARF.

Association of Mechanical Energy and Power with Postoperative Pulmonary Complications in Lung Resection Surgery: A Post Hoc Analysis of Randomized Clinical Trial Data

BACKGROUND

Mechanical power (MP), the rate of mechanical energy (ME) delivery, is a recently introduced unifying ventilator parameter consisting of tidal volume, airway pressures, and respiratory rates, which predicts pulmonary complications in several clinical contexts. However, ME has not been previously studied in the perioperative context, and neither parameter has been studied in the context of thoracic surgery utilizing one-lung ventilation.

METHODS

The relationships between ME variables and postoperative pulmonary complications were evaluated in this post hoc analysis of data from a multicenter randomized clinical trial of lung resection surgery conducted between 2020 and 2021 (n = 1,170). Time-weighted average MP and ME (the area under the MP time curve) were obtained for individual patients. The primary analysis was the association of time-weighted average MP and ME with pulmonary complications within 7 postoperative days. Multivariable logistic regression was performed to examine the relationships between energy variables and the primary outcome.

RESULTS

In 1,055 patients analyzed, pulmonary complications occurred in 41% (431 of 1,055). The median (interquartile ranges) ME and time-weighted average MP in patients who developed postoperative pulmonary complications versus those who did not were 1,146 (811 to 1,530) J versus 924 (730 to 1,240) J (P < 0.001), and 6.9 (5.5 to 8.7) J/min versus 6.7 (5.2 to 8.5) J/min (P = 0.091), respectively. ME was independently associated with postoperative pulmonary complications (ORadjusted, 1.44 [95% CI, 1.16 to 1.80]; P = 0.001). However, the association between time-weighted average MP and postoperative pulmonary complications was time-dependent, and time-weighted average MP was significantly associated with postoperative pulmonary complications in cases utilizing longer periods of mechanical ventilation (210 min or greater; ORadjusted, 1.46 [95% CI, 1.11 to 1.93]; P = 0.007). Normalization of ME and time-weighted average MP either to predicted body weight or to respiratory system compliance did not alter these associations.

CONCLUSIONS

ME and, in cases requiring longer periods of mechanical ventilation, MP were independently associated with postoperative pulmonary complications in thoracic surgery.

EDITOR’S PERSPECTIVE

Intraoperative lung protection: strategies and their impact on outcomes

PURPOSE OF REVIEW

The present review summarizes the current knowledge and the barriers encountered when implementing tailoring lung-protective ventilation strategies to individual patients based on advanced monitoring systems.

RECENT FINDINGS

Lung-protective ventilation has become a pivotal component of perioperative care, aiming to enhance patient outcomes and reduce the incidence of postoperative pulmonary complications (PPCs). High-quality research has established the benefits of strategies such as low tidal volume ventilation and low driving pressures. Debate is still ongoing on the most suitable levels of positive end-expiratory pressure (PEEP) and the role of recruitment maneuvers. Adapting PEEP according to patient-specific factors offers potential benefits in maintaining ventilation distribution uniformity, especially in challenging scenarios like pneumoperitoneum and steep Trendelenburg positions. Advanced monitoring systems, which continuously assess patient responses and enable the fine-tuning of ventilation parameters, offer real-time data analytics to predict and prevent impending lung complications. However, their impact on postoperative outcomes, particularly PPCs, is an ongoing area of research.

SUMMARY

Refining protective lung ventilation is crucial to provide patients with the best possible care during surgery, reduce the incidence of PPCs, and improve their overall surgical journey.

Linking preoperative and early intensive care unit data for prolonged intubation prediction

Objectives

Prolonged intubation (PI) is a frequently encountered severe complication among patients following cardiac surgery (CS). Solely concentrating on preoperative data, devoid of sufficient consideration for the ongoing impact of surgical, anesthetic, and cardiopulmonary bypass procedures on subsequent respiratory system function, could potentially compromise the predictive accuracy of disease prognosis. In response to this challenge, we formulated and externally validated an intelligible prediction model tailored for CS patients, leveraging both preoperative information and early intensive care unit (ICU) data to facilitate early prophylaxis for PI.

Methods

We conducted a retrospective cohort study, analyzing adult patients who underwent CS and utilizing data from two publicly available ICU databases, namely, the Medical Information Mart for Intensive Care and the eICU Collaborative Research Database. PI was defined as necessitating intubation for over 24 h. The predictive model was constructed using multivariable logistic regression. External validation of the model's predictive performance was conducted, and the findings were elucidated through visualization techniques.

Results

The incidence rates of PI in the training, testing, and external validation cohorts were 11.8%, 12.1%, and 17.5%, respectively. We identified 11 predictive factors associated with PI following CS: plateau pressure [odds ratio (OR), 1.133; 95% confidence interval (CI), 1.111-1.157], lactate level (OR, 1.131; 95% CI, 1.067-1.2), Charlson Comorbidity Index (OR, 1.166; 95% CI, 1.115-1.219), Sequential Organ Failure Assessment score (OR, 1.096; 95% CI, 1.061-1.132), central venous pressure (OR, 1.052; 95% CI, 1.033-1.073), anion gap (OR, 1.075; 95% CI, 1.043-1.107), positive end-expiratory pressure (OR, 1.087; 95% CI, 1.047-1.129), vasopressor usage (OR, 1.521; 95% CI, 1.23-1.879), Visual Analog Scale score (OR, 0.928; 95% CI, 0.893-0.964), pH value (OR, 0.757; 95% CI, 0.629-0.913), and blood urea nitrogen level (OR, 1.011; 95% CI, 1.003-1.02). The model exhibited an area under the receiver operating characteristic curve (AUROC) of 0.853 (95% CI, 0.840-0.865) in the training cohort, 0.867 (95% CI, 0.853-0.882) in the testing cohort, and 0.704 (95% CI, 0.679-0.727) in the external validation cohort.

Conclusions

Through multicenter internal and external validation, our model, which integrates early ICU data and preoperative information, exhibited outstanding discriminative capability. This integration allows for the accurate assessment of PI risk in the initial phases following CS, facilitating timely interventions to mitigate adverse outcomes.

Driving pressure in mechanical ventilation: A review

Driving pressure (∆P) is a core therapeutic component of mechanical ventilation (MV). Varying levels of ∆P have been employed during MV depending on the type of underlying pathology and severity of injury. However, ∆P levels have also been shown to closely impact hard endpoints such as mortality. Considering this, conducting an in-depth review of ∆P as a unique, outcome-impacting therapeutic modality is extremely important. There is a need to understand the subtleties involved in making sure ∆P levels are optimized to enhance outcomes and minimize harm. We performed this narrative review to further explore the various uses of ∆P, the different parameters that can affect its use, and how outcomes vary in different patient populations at different pressure levels. To better utilize ∆P in MV-requiring patients, additional large-scale clinical studies are needed.

A High Respiratory Drive Is Associated with Weaning Failure in Patients with COVID-19-Associated Acute Respiratory Distress Syndrome: The Role of the Electrical Activity of the Diaphragm

BACKGROUND

Mechanical ventilation is the main supportive treatment of severe cases of COVID-19-associated ARDS (C-ARDS). Weaning failure is common and associated with worse outcomes. We investigated the role of respiratory drive, assessed by monitoring the electrical activity of the diaphragm (EAdi), as a predictor of weaning failure.

METHODS

Consecutive, mechanically ventilated patients admitted to the ICU for C-ARDS with difficult weaning were enrolled. Blood gas, ventilator, and respiratory mechanic parameters, as well as EAdi, were recorded at the time of placement of EAdi catheter, and then after 1, 2, 3, 7, and 10 days, and compared between patients with weaning success and weaning failure.

RESULTS

Twenty patients were enrolled: age 66 (60-69); 85% males; PaO2/FiO2 at admission 148 (126-177) mmHg. Thirteen subjects (65%) were classified as having a successful weaning. A younger age (OR(95%CI): 0.02 (0.01-0.11) per year), a higher PaO2/FiO2 ratio (OR(95%CI): 1.10 (1.01-1.21) per mmHg), and a lower EAdi (OR(95%CI): 0.16 (0.08-0.34) per μV) were associated with weaning success.

CONCLUSION

In critically ill patients with moderate-severe C-ARDS and difficult weaning from mechanical ventilation, a successful weaning was associated with a lower age, a higher oxygenation, and a lower respiratory drive, as assessed at the bedside via EAdi monitoring.

Mechanical Ventilation, Past, Present, and Future

Mechanical ventilation (MV) has played a crucial role in the medical field, particularly in anesthesia and in critical care medicine (CCM) settings. MV has evolved significantly since its inception over 70 years ago and the future promises even more advanced technology. In the past, ventilation was provided manually, intermittently, and it was primarily used for resuscitation or as a last resort for patients with severe respiratory or cardiovascular failure. The earliest MV machines for prolonged ventilatory support and oxygenation were large and cumbersome. They required a significant amount of skills and expertise to operate. These early devices had limited capabilities, battery, power, safety features, alarms, and therefore these often caused harm to patients. Moreover, the physiology of MV was modified when mechanical ventilators moved from negative pressure to positive pressure mechanisms. Monitoring systems were also very limited and therefore the risks related to MV support were difficult to quantify, predict and timely detect for individual patients who were necessarily young with few comorbidities. Technology and devices designed to use tracheostomies versus endotracheal intubation evolved in the last century too and these are currently much more reliable. In the present, positive pressure MV is more sophisticated and widely used for extensive period of time. Modern ventilators use mostly positive pressure systems and are much smaller, more portable than their predecessors, and they are much easier to operate. They can also be programmed to provide different levels of support based on evolving physiological concepts allowing lung-protective ventilation. Monitoring systems are more sophisticated and knowledge related to the physiology of MV is improved. Patients are also more complex and elderly compared to the past. MV experts are informed about risks related to prolonged or aggressive ventilation modalities and settings. One of the most significant advances in MV has been protective lung ventilation, diaphragm protective ventilation including noninvasive ventilation (NIV). Health care professionals are familiar with the use of MV and in many countries, respiratory therapists have been trained for the exclusive purpose of providing safe and professional respiratory support to critically ill patients. Analgo-sedation drugs and techniques are improved, and more sedative drugs are available and this has an impact on recovery, weaning, and overall patients' outcome. Looking toward the future, MV is likely to continue to evolve and improve alongside monitoring techniques and sedatives. There is increasing precision in monitoring global "patient-ventilator" interactions: structure and analysis (asynchrony, desynchrony, etc). One area of development is the use of artificial intelligence (AI) in ventilator technology. AI can be used to monitor patients in real-time, and it can predict when a patient is likely to experience respiratory distress. This allows medical professionals to intervene before a crisis occurs, improving patient outcomes and reducing the need for emergency intervention. This specific area of development is intended as "personalized ventilation." It involves tailoring the ventilator settings to the individual patient, based on their physiology and the specific condition they are being treated for. This approach has the potential to improve patient outcomes by optimizing ventilation and reducing the risk of harm. In conclusion, MV has come a long way since its inception, and it continues to play a critical role in anesthesia and in CCM settings. Advances in technology have made MV safer, more effective, affordable, and more widely available. As technology continues to improve, more advanced and personalized MV will become available, leading to better patients' outcomes and quality of life for those in need.

Intraoperative individualization of positive-end-expiratory pressure through electrical impedance tomography or esophageal pressure assessment: a systematic review and meta-analysis of randomized controlled trials

PURPOSE

This systematic review of randomized-controlled trials (RCTs) with meta-analyses aimed to compare the effects on intraoperative arterial oxygen tension to inspired oxygen fraction ratio (PaO2/FiO2), exerted by positive end-expiratory pressure (PEEP) individualized trough electrical impedance tomography (EIT) or esophageal pressure (Pes) assessment (intervention) vs. PEEP not tailored on EIT or Pes (control), in patients undergoing abdominal or pelvic surgery with an open or laparoscopic/robotic approach.

METHODS

PUBMED®, EMBASE®, and Cochrane Controlled Clinical trials register were searched for observational studies and RCTs from inception to the end of August 2022. Inclusion criteria were: RCTs comparing PEEP titrated on EIT/Pes assessment vs. PEEP not individualized on EIT/Pes and reporting intraoperative PaO2/FiO2. Two authors independently extracted data from the enrolled investigations. Data are reported as mean difference and 95% confidence interval (CI).

RESULTS

Six RCTs were included for a total of 240 patients undergoing general anesthesia for surgery, of whom 117 subjects in the intervention group and 123 subjects in the control group. The intraoperative mean PaO2/FiO2 was 69.6 (95%CI 32.-106.4 ) mmHg higher in the intervention group as compared with the control group with 81.4% between-study heterogeneity (p < 0.01). However, at meta-regression, the between-study heterogeneity diminished to 44.96% when data were moderated for body mass index (estimate 3.45, 95%CI 0.78-6.11, p = 0.011).

CONCLUSIONS

In patients undergoing abdominal or pelvic surgery with an open or laparoscopic/robotic approach, PEEP personalized by EIT or Pes allowed the achievement of a better intraoperative oxygenation compared to PEEP not individualized through EIT or Pes.

PROSPERO REGISTRATION NUMBER

CRD 42021218306, 30/01/2023.

One-Lung Ventilation and Postoperative Pulmonary Complications After Major Lung Resection Surgery. A Multicenter Randomized Controlled Trial

OBJECTIVES

The effect of one-lung ventilation (OLV) strategy based on low tidal volume (TV), application of positive end-expiratory pressure (PEEP), and alveolar recruitment maneuvers (ARM) to reduce postoperative acute respiratory distress syndrome (ARDS) and pulmonary complications (PPCs) compared with higher TV without PEEP and ARM strategy in adult patients undergoing lobectomy or pneumonectomy has not been well established.

DESIGN

Multicenter, randomized, single-blind, controlled trial.

SETTING

Sixteen Italian hospitals.

PARTICIPANTS

A total of 880 patients undergoing elective major lung resection.

INTERVENTIONS

Patients were randomized to receive lower tidal volume (LTV group: 4 mL/kg predicted body weight, PEEP of 5 cmH2O, and ARMs) or higher tidal volume (HTL group: 6 mL/kg predicted body weight, no PEEP, and no ARMs). After OLV, until extubation, both groups were ventilated using a tidal volume of 8 mL/kg and a PEEP value of 5 cmH2O. The primary outcome was the incidence of in-hospital ARDS. Secondary outcomes were the in-hospital rate of PPCs, major cardiovascular events, unplanned intensive care unit (ICU) admission, in-hospital mortality, ICU length of stay, and in-hospital length of stay.

MEASUREMENTS AND MAIN RESULTS

ARDS occurred in 3 of 438 patients (0.7%, 95% CI 0.1-2.0) and in 1 of 442 patients (0.2%, 95% CI 0-1.4) in the LTV and HTV group, respectively (Risk ratio: 3.03 95% CI 0.32-29, p = 0.372). Pulmonary complications occurred in 125 of 438 patients (28.5%, 95% CI 24.5-32.9) and in 136 of 442 patients (30.8%, 95% CI 26.6-35.2) in the LTV and HTV group, respectively (risk ratio: 0.93, 95% CI 0.76-1.14, p = 0.507). The incidence of major complications, in-hospital mortality, and unplanned ICU admission, ICU and in-hospital length of stay were comparable in both groups.

CONCLUSIONS

In conclusion, among adult patients undergoing elective lung resection, an OLV with lower tidal volume, PEEP 5 cmH2O, and ARMs and a higher tidal volume strategy resulted in low ARDS incidence and comparable postoperative complications, in-hospital length of stay, and mortality.

Effect of driving pressure-guided positive end-expiratory pressure on postoperative pulmonary complications in patients undergoing laparoscopic or robotic surgery: a randomised controlled trial

BACKGROUND

Individualised positive end-expiratory pressure (PEEP) improves respiratory mechanics. However, whether PEEP reduces postoperative pulmonary complications (PPCs) remains unclear. We investigated whether driving pressure-guided PEEP reduces PPCs after laparoscopic/robotic abdominal surgery.

METHODS

This single-centre, randomised controlled trial enrolled patients at risk for PPCs undergoing laparoscopic or robotic lower abdominal surgery. The individualised group received driving pressure-guided PEEP, whereas the comparator group received 5 cm H2O fixed PEEP during surgery. Both groups received a tidal volume of 8 ml kg-1 ideal body weight. The primary outcome analysed per protocol was a composite of pulmonary complications (defined by pre-specified clinical and radiological criteria) within 7 postoperative days after surgery.

RESULTS

Some 384 patients (median age: 67 yr [inter-quartile range: 61-73]; 66 [18%] female) were randomised. Mean (standard deviation) PEEP in patients randomised to individualised PEEP (n=178) was 13.6 cm H2O (2.1). Individualised PEEP resulted in lower mean driving pressures (14.7 cm H2O [2.6]), compared with 185 patients randomised to standard PEEP (18.4 cm H2O [3.2]; mean difference: -3.7 cm H2O [95% confidence interval (CI): -4.3 to -3.1 cm H2O]; P<0.001). There was no difference in the incidence of pulmonary complications between individualised (25/178 [14.0%]) vs standard PEEP (36/185 [19.5%]; risk ratio [95% CI], 0.72 [0.45-1.15]; P=0.215). Pulmonary complications as a result of desaturation were less frequent in patients randomised to individualised PEEP (8/178 [4.5%], compared with standard PEEP (30/185 [16.2%], risk ratio [95% CI], 0.28 [0.13-0.59]; P=0.001).

CONCLUSIONS

Driving pressure-guided PEEP did not decrease the incidence of pulmonary complications within 7 days of laparoscopic or robotic lower abdominal surgery, although uncertainty remains given the lower than anticipated event rate for the primary outcome.

CLINICAL TRIAL REGISTRATION

KCT0004888 (http://cris.nih.go.kr, registration date: April 6, 2020).

Effects of individualised positive end-expiratory pressure titration on respiratory and haemodynamic parameters during the Trendelenburg position with pneumoperitoneum: A randomised crossover physiologic trial

BACKGROUND

The Trendelenburg position with pneumoperitoneum during surgery promotes dorsobasal atelectasis formation, which impairs respiratory mechanics and increases lung stress and strain. Positive end-expiratory pressure (PEEP) can reduce pulmonary inhomogeneities and preserve end-expiratory lung volume (EELV), resulting in decreased inspiratory strain and improved gas-exchange. The optimal intraoperative PEEP strategy is unclear.

OBJECTIVES

To compare the effects of individualised PEEP titration strategies on set PEEP levels and resulting transpulmonary pressures, respiratory mechanics, gas-exchange and haemodynamics during Trendelenburg position with pneumoperitoneum.

DESIGN

Prospective, randomised, crossover single-centre physiologic trial.

SETTING

University hospital.

PATIENTS

Thirty-six patients receiving robot-assisted laparoscopic radical prostatectomy.

INTERVENTIONS

Randomised sequence of three different PEEP strategies: standard PEEP level of 5 cmH 2 O (PEEP 5 ), PEEP titration targeting a minimal driving pressure (PEEP ΔP ) and oesophageal pressure-guided PEEP titration (PEEP Poeso ) targeting an end-expiratory transpulmonary pressure ( PTP ) of 0 cmH 2 O.

MAIN OUTCOME MEASURES

The primary endpoint was the PEEP level when set according to PEEP ΔP and PEEP Poeso compared with PEEP of 5 cmH 2 O. Secondary endpoints were respiratory mechanics, lung volumes, gas-exchange and haemodynamic parameters.

RESULTS

PEEP levels differed between PEEP ΔP , PEEP Poeso and PEEP5 (18.0 [16.0 to 18.0] vs. 20.0 [18.0 to 24.0]vs. 5.0 [5.0 to 5.0] cmH 2 O; P  < 0.001 each). End-expiratory PTP and lung volume were lower in PEEP ΔP compared with PEEP Poeso ( P  = 0.014 and P  < 0.001, respectively), but driving pressure, lung stress, as well as respiratory system and dynamic elastic power were minimised using PEEP ΔP ( P  < 0.001 each). PEEP ΔP and PEEP Poeso improved gas-exchange, but PEEP Poeso resulted in lower cardiac output compared with PEEP 5 and PEEP ΔP .

CONCLUSION

PEEP ΔP ameliorated the effects of Trendelenburg position with pneumoperitoneum during surgery on end-expiratory PTP and lung volume, decreased driving pressure and dynamic elastic power, as well as improved gas-exchange while preserving cardiac output.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00028559, date of registration 2022/04/27). https://drks.de/search/en/trial/DRKS00028559.

Minimizing Lung Injury During Laparoscopy in Head-Down Tilt: A Physiological Cohort Study

BACKGROUND

Increased intra-abdominal pressure during laparoscopy induces atelectasis. Positive end-expiratory pressure (PEEP) can alleviate atelectasis but may cause hyperinflation. Cyclic opening of collapsed alveoli and hyperinflation can lead to ventilator-induced lung injury and postoperative pulmonary complications. We aimed to study the effect of PEEP on atelectasis, lung stress, and hyperinflation during laparoscopy in the head-down (Trendelenburg) position.

METHODS

An open-label, repeated-measures, interventional, physiological cohort trial was designed. All participants were recruited from a single tertiary Belgian university hospital. Twenty-three nonobese patients scheduled for laparoscopy in the Trendelenburg position were recruited.We applied a decremental PEEP protocol: 15 (high), 10 and 5 (low) cm H 2 O. Atelectasis was studied with the lung ultrasound score, the end-expiratory transpulmonary pressure, the arterial oxygen partial pressure to fraction of inspired oxygen concentration (P ao2 /Fi o2 ) ratio, and the dynamic respiratory system compliance. Global hyperinflation was evaluated by dead space volume, and regional ventilation was evaluated by lung ultrasound. Lung stress was estimated using the transpulmonary driving pressure and dynamic compliance. Data are reported as medians (25th-75th percentile).

RESULTS

At 15, 10, and 5 cm H 2 O PEEP, the respective measurements were: lung ultrasound scores (%) 11 (0-22), 27 (11-39), and 53 (42-61) ( P < .001); end-expiratory transpulmonary pressures (cm H 2 O) 0.9 (-0.6 to 1.7), -0.3 (-2.0 to 0.7), and -1.9 (-4.6 to -0.9) ( P < .001); P ao2 /Fi o2 ratios (mm Hg) 471 (435-538), 458 (410-537), and 431 (358-492) ( P < .001); dynamic respiratory system compliances (mL/cm H 2 O) 32 (26-36), 30 (25-34), and 27 (22-30) ( P < .001); driving pressures (cm H 2 O) 8.2 (7.5-9.5), 9.3 (8.5-11.1), and 11.0 (10.3-12.2) ( P < .001); and alveolar dead space ventilation fractions (%) 10 (9-12), 10 (9-12), and 9 (8-12) ( P = .23). The lung ultrasound score was similar between apical and basal lung regions at each PEEP level ( P = .76, .37, and .76, respectively).

CONCLUSIONS

Higher PEEP levels during laparoscopy in the head-down position facilitate lung-protective ventilation. Atelectasis and lung stress are reduced in the absence of global alveolar hyperinflation.

Regulation of cell proliferation and transdifferentiation compensates for ventilator-induced lung injury mediated by NLRP3 inflammasome activation

BACKGROUND

Mechanical ventilation is an important means of respiratory support and treatment for various diseases. However, its use can lead to serious complications, especially ventilator-induced lung injury (VILI). The mechanisms underlying this disease are complex, but activation of inflammatory signalling pathways results in activation of cytokines and inflammatory mediators, which play key roles in VILI. Recent studies have demonstrated that nod-like receptor protein 3 (NLRP3) inflammasome activation mediates VILI and also accompanied by cell proliferation and transdifferentiation to compensate for alveolar membrane damage. Type I alveolar epithelial cells (AECs I), which are involved in the formation of the blood-air barrier, are vulnerable to damage but cannot proliferate by themselves; thus, replacing AECs I relies on type II alveolar epithelial cells (AECs II).

OBJECTIVE

The review aims to introduce the mechanisms of NLRP3 inflammasome activation and its inhibitors, as well as the mechanisms that regulate cell proliferation and transdifferentiation.

METHODS

A large number of relevant literature was searched, then the key content was summarized and figures were also made.

RESULTS

The mechanism of NLRP3 inflammasome activation has been further explored, including but not limited to pathogenic and aseptic inflammatory signals, such as, pathogenic molecular patterns and host-derived danger-associated molecular patterns activate toll-like receptor 4/nuclear factor-kappaB pathway or reactive oxygen species, cyclic stretch, adenosine triphosphate induce K+ efflux through P2X7, Ca2+ inflow, mitochondrial damage, etc, eventually induce NIMA-related kinase 7/NLRP3 binding and NLRP3 inflammasome activation. Not only that, the review also described in detail the inhibitors of NLRP3 inflammasome. And the mechanisms regulating cell proliferation and transdifferentiation are complex and unclear, including the Wnt/β-catenin, Yap/Taz, BMP/Smad and Notch signalling pathways.

CONCLUSIONS

NLRP3 inflammasome activation mediated VILI, and VILI is alleviated after interfering with its activation, and inflammation and repair exist simultaneously in VILI. Clarifying these mechanisms is expected to provide theoretical guidance for alleviating VILI by inhibiting the inflammatory response and accelerating alveolar epithelial cell regeneration in the early stage.

The effect of driving pressure-guided versus conventional mechanical ventilation strategy on pulmonary complications following on-pump cardiac surgery: A randomized clinical trial

STUDY OBJECTIVE

Postoperative pulmonary complications occur frequently and are associated with worse postoperative outcomes in cardiac surgical patients. The advantage of driving pressure-guided ventilation strategy in decreasing pulmonary complications remains to be definitively established. We aimed to investigate the effect of intraoperative driving pressure-guided ventilation strategy compared with conventional lung-protective ventilation on pulmonary complications following on-pump cardiac surgery.

DESIGN

Prospective, two-arm, randomized controlled trial.

SETTING

The West China university hospital in Sichuan, China.

PATIENTS

Adult patients who were scheduled for elective on-pump cardiac surgery were enrolled in the study.

INTERVENTIONS

Patients undergoing on-pump cardiac surgery were randomized to receive driving pressure-guided ventilation strategy based on positive end-expiratory pressure (PEEP) titration or conventional lung-protective ventilation strategy with fixed 5 cmH2O of PEEP.

MEASUREMENTS

The primary outcome of pulmonary complications (including acute respiratory distress syndrome, atelectasis, pneumonia, pleural effusion, and pneumothorax) within the first 7 postoperative days were prospectively identified. Secondary outcomes included pulmonary complication severity, ICU length of stay, and in-hospital and 30-day mortality.

MAIN RESULTS

Between August 2020 and July 2021, we enrolled 694 eligible patients who were included in the final analysis. Postoperative pulmonary complications occurred in 140 (40.3%) patients in the driving pressure group and 142 (40.9%) in the conventional group (relative risk, 0.99; 95% confidence interval, 0.82-1.18; P = 0.877). Intention-to-treat analysis showed no significant difference between study groups regarding the incidence of primary outcome. The driving pressure group had less atelectasis than the conventional group (11.5% vs 17.0%; relative risk, 0.68; 95% confidence interval, 0.47-0.98; P = 0.039). Secondary outcomes did not differ between groups.

CONCLUSION

Among patients who underwent on-pump cardiac surgery, the use of driving pressure-guided ventilation strategy did not reduce the risk of postoperative pulmonary complications when compared with conventional lung-protective ventilation strategy.

Conducting Prospective Research as a Trainee: Experiences with the DRIVE-SAFE Study

Conducting clinical research during a 2-year critical care fellowship is a challenging endeavor. Fellows are often met with multiple barriers when considering clinical research projects during fellowship, including time, mentorship, resources, and clinical support. This paper presents the perspective and experiences of a group of critical care fellows who conducted the DRIVE-SAFE (Driving Pressure in Assisted Ventilation as a Predictor for Successful Liberation from Invasive Mechanical Ventilation) feasibility study, which aimed to determine measurable physiological variables that could be associated with lung injury and affect duration of mechanical ventilation. This paper provides a guide for trainees on how to conduct prospective clinical research at the bedside. We describe three key steps, including formulating a research question, developing appropriate methodology, and establishing outcomes. We also present the challenges that trainees may encounter when conducting prospective studies and how to overcome these challenges with proper mentorship, training, and collaboration with key stakeholders. These perspectives may provide useful guidance for current and future trainees interested in conducting prospective clinical research at the bedside.

Individualized Positive End-expiratory Pressure Titration Strategies in Superobese Patients Undergoing Laparoscopic Surgery: Prospective and Nonrandomized Crossover Study

BACKGROUND

Superobesity and laparoscopic surgery promote negative end-expiratory transpulmonary pressure that causes atelectasis formation and impaired respiratory mechanics. The authors hypothesized that end-expiratory transpulmonary pressure differs between fixed and individualized positive end-expiratory pressure (PEEP) strategies and mediates their effects on respiratory mechanics, end-expiratory lung volume, gas exchange, and hemodynamic parameters in superobese patients.

METHODS

In this prospective, nonrandomized crossover study including 40 superobese patients (body mass index 57.3 ± 6.4 kg/m2) undergoing laparoscopic bariatric surgery, PEEP was set according to (1) a fixed level of 8 cm H2O (PEEPEmpirical), (2) the highest respiratory system compliance (PEEPCompliance), or (3) an end-expiratory transpulmonary pressure targeting 0 cm H2O (PEEPTranspul) at different surgical positioning. The primary endpoint was end-expiratory transpulmonary pressure at different surgical positioning; secondary endpoints were respiratory mechanics, end-expiratory lung volume, gas exchange, and hemodynamic parameters.

RESULTS

Individualized PEEPCompliance compared to fixed PEEPEmpirical resulted in higher PEEP (supine, 17.2 ± 2.4 vs. 8.0 ± 0.0 cm H2O; supine with pneumoperitoneum, 21.5 ± 2.5 vs. 8.0 ± 0.0 cm H2O; and beach chair with pneumoperitoneum; 15.8 ± 2.5 vs. 8.0 ± 0.0 cm H2O; P < 0.001 each) and less negative end-expiratory transpulmonary pressure (supine, -2.9 ± 2.0 vs. -10.6 ± 2.6 cm H2O; supine with pneumoperitoneum, -2.9 ± 2.0 vs. -14.1 ± 3.7 cm H2O; and beach chair with pneumoperitoneum, -2.8 ± 2.2 vs. -9.2 ± 3.7 cm H2O; P < 0.001 each). Titrated PEEP, end-expiratory transpulmonary pressure, and lung volume were lower with PEEPCompliance compared to PEEPTranspul (P < 0.001 each). Respiratory system and transpulmonary driving pressure and mechanical power normalized to respiratory system compliance were reduced using PEEPCompliance compared to PEEPTranspul.

CONCLUSIONS

In superobese patients undergoing laparoscopic surgery, individualized PEEPCompliance may provide a feasible compromise regarding end-expiratory transpulmonary pressures compared to PEEPEmpirical and PEEPTranspul, because PEEPCompliance with slightly negative end-expiratory transpulmonary pressures improved respiratory mechanics, lung volumes, and oxygenation while preserving cardiac output.

EDITOR’S PERSPECTIVE

Setting the optimal positive end-expiratory pressure: a narrative review

The primary goals of positive end-expiratory pressure (PEEP) are to restore functional residual capacity through recruitment and prevention of alveolar collapse. Through these mechanisms, PEEP improves arterial oxygenation and may reduce the risk of ventilator-induced lung injury (VILI). Because of the many potential negative effects associated with the use of PEEP, much research has concentrated on determining the optimal PEEP setting. Arterial oxygenation targets and pressure-volume loops have been utilized to set the optimal PEEP for decades. Several other techniques have been suggested, including the use of PEEP tables, compliance, driving pressure (DP), stress index (SI), transpulmonary pressures, imaging, and electrical impedance tomography. Each of these techniques has its own benefits and limitations and there is currently not one technique that is recommended above all others.

Individualized positive end-expiratory pressure guided by respiratory mechanics during anesthesia for the prevention of postoperative pulmonary complications: a systematic review and meta-analysis

The optimization of positive end-expiratory pressure (PEEP) according to respiratory mechanics [driving pressure or respiratory system compliance (Crs)] is a simple and straightforward strategy. However, its validity to prevent postoperative pulmonary complications (PPCs) remains unclear. Here, we performed a meta-analysis to assess such efficacy. We searched PubMed, Embase, and the Cochrane Library to identify randomized controlled trials (RCTs) that compared personalized PEEP based on respiratory mechanics and constant PEEP to prevent PPCs in adults. The primary outcome was PPCs. Fourteen studies with 1105 patients were included. Compared with those who received constant PEEP, patients who received optimized PEEP exhibited a significant reduction in the incidence of PPCs (RR = 0.54, 95% CI 0.42 to 0.69). The results of commonly happened PPCs (pulmonary infections, hypoxemia, and atelectasis but not pleural effusion) also supported individualized PEEP group. Moreover, the application of PEEP based on respiratory mechanics improved intraoperative respiratory mechanics (driving pressure and Crs) and oxygenation. The PEEP titration method based on respiratory mechanics seems to work positively for lung protection in surgical patients undergoing general anesthesia.

Extracorporeal Membrane Oxygenation for Refractory Asthma Exacerbations With Respiratory Failure

BACKGROUND

Asthma exacerbations with respiratory failure (AERF) are associated with hospital mortality of 7% to 15%. Extracorporeal membrane oxygenation (ECMO) has been used as a salvage therapy for refractory AERF, but controlled studies showing its association with mortality have not been performed.

RESEARCH QUESTION

Is treatment with ECMO associated with lower mortality in refractory AERF compared with standard care?

STUDY DESIGN AND METHODS

This is a retrospective, epidemiologic, observational cohort study using a national, administrative data set from 2010 to 2020 that includes 25% of US hospitalizations. People were included if they were admitted to an ECMO-capable hospital with an asthma exacerbation, and were treated with short-acting bronchodilators, systemic corticosteroids, and invasive ventilation. People were excluded for age < 18 years, no ICU stay, nonasthma chronic lung disease, COVID-19, or multiple admissions. The main exposure was ECMO vs No ECMO. The primary outcome was hospital mortality. Key secondary outcomes were ICU length of stay (LOS), hospital LOS, time receiving invasive ventilation, and total hospital costs.

RESULTS

The study analyzed 13,714 patients with AERF, including 127 with ECMO and 13,587 with No ECMO. ECMO was associated with reduced mortality in the covariate-adjusted (OR, 0.33; 95% CI, 0.17-0.64; P = .001), propensity score-adjusted (OR, 0.36; 95% CI, 0.16-0.81; P = .01), and propensity score-matched models (OR, 0.48; 95% CI, 0.24-0.98; P = .04) vs No ECMO. Sensitivity analyses showed that mortality reduction related to ECMO ranged from OR 0.34 to 0.61. ECMO was also associated with increased hospital costs in all three models (P < .0001 for all) vs No ECMO, but not with decreased ICU LOS, hospital LOS, or time receiving invasive ventilation.

INTERPRETATION

ECMO was associated with lower mortality and higher hospital costs, suggesting that it may be an important salvage therapy for refractory AERF following confirmatory clinical trials.

Driving pressure-guided ventilation and postoperative pulmonary complications in thoracic surgery: a multicentre randomised clinical trial

BACKGROUND

Airway driving pressure, easily measured as plateau pressure minus PEEP, is a surrogate for alveolar stress and strain. However, the effect of its targeted reduction remains unclear.

METHODS

In this multicentre trial, patients undergoing lung resection surgery were randomised to either a driving pressure group (n=650) receiving an alveolar recruitment/individualised PEEP to deliver the lowest driving pressure or to a conventional protective ventilation group (n=650) with fixed PEEP of 5 cm H₂O. The primary outcome was a composite of pulmonary complications within 7 days postoperatively.

RESULTS

The modified intention-to-treat analysis included 1170 patients (mean [standard deviation, sd]; age, 63 [10] yr; 47% female). The mean driving pressure was 7.1 cm H₂O in the driving pressure group vs 9.2 cm H₂O in the protective ventilation group (mean difference [95% confidence interval, CI]; -2.1 [-2.4 to -1.9] cm H₂O; P<0.001). The incidence of pulmonary complications was not different between the two groups: driving pressure group (233/576, 40.5%) vs protective ventilation group (254/594, 42.8%) (risk difference -2.3%; 95% CI, -8.0% to 3.3%; P=0.42). Intraoperatively, lung compliance (mean [sd], 42.7 [12.4] vs 33.5 [11.1] ml cm H₂O^-1; P<0.001) and Pa_o2 (median [inter-quartile range], 21.5 [14.5 to 30.4] vs 19.5 [13.5 to 29.1] kPa; P=0.03) were higher and the need for rescue ventilation was less frequent (6.8% vs 10.8%; P=0.02) in the driving pressure group.

CONCLUSIONS

In lung resection surgery, a driving pressure-guided ventilation improved pulmonary mechanics intraoperatively, but did not reduce the incidence of postoperative pulmonary complications compared with a conventional protective ventilation.

CLINICAL TRIAL REGISTRATION

NCT04260451.

The impact of driving pressure on postoperative pulmonary complication in patients with different respiratory spirometry

Risk factors for postoperative pulmonary complication (PPC) have not been determined according to preoperative respiratory spirometry. Thus, we aimed to find contributors for PPC in patients with restrictive or normal spirometric pattern. We analyzed 654 patients (379 with normal and 275 with restrictive spirometric pattern). PPCs comprised respiratory failure, pleural effusion, atelectasis, respiratory infection, and bronchospasm. We analyzed the association between perioperative factors and PPC using binary logistic regression. In particular, we conducted subgroup analysis on the patients stratified according to preoperative spirometry. Of 654 patients, 27/379 patients (7.1%) with normal spirometric pattern and 33/275 patients (12.0%) with restrictive spirometric pattern developed PPCs. Multivariable analysis demonstrated that high driving pressure was the only intraoperative modifiable factor increasing PPC risk (OR = 1.13 [1.02-1.25], p = 0.025). In the subgroup of patients with restrictive spirometric pattern, intraoperative driving pressure was significantly associated with PPC (OR = 1.21 [1.05-1.39], p = 0.009), whereas driving pressure was not associated with PPC in patients with normal spirometric pattern (OR = 1.04 [0.89-1.21], p = 0.639). In patients with restrictive spirometric pattern, greater intraoperative driving pressure is significantly associated with increased PPC risk. In contrast, intraoperative driving pressure is not associated with PPC in patients with normal spirometric pattern.

An Updated Review of Driving-Pressure Guided Ventilation Strategy and Its Clinical Application

Traditional lung-protective ventilation strategies (LPVS) are currently used to reduce the incidence of postoperative pulmonary complications (PPCs), including low tidal volume (VT), positive end-expiratory pressure (PEEP), low inspiratory plateau pressure (Pplat), permissive hypercapnia, and recruitment maneuver (RM). However, a meta-analysis showed that high driving pressure was closely associated with the incidence of PPCs, but not with PEEP or VT, which led to the driving pressure-guided ventilation strategy. Some studies have proved that the driving pressure-guided ventilation strategy is superior to the traditional LPVS in reducing the incidence of PPCs. The purpose of this review is to present the current research progress and application of driving pressure-guided ventilation strategy.

Phrenic Nerve Block and Respiratory Effort in Pigs and Critically Ill Patients with Acute Lung Injury

BACKGROUND

Strong spontaneous inspiratory efforts can be difficult to control and prohibit protective mechanical ventilation. Instead of using deep sedation and neuromuscular blockade, the authors hypothesized that perineural administration of lidocaine around the phrenic nerve would reduce tidal volume (VT) and peak transpulmonary pressure in spontaneously breathing patients with acute respiratory distress syndrome.

METHODS

An established animal model of acute respiratory distress syndrome with six female pigs was used in a proof-of-concept study. The authors then evaluated this technique in nine mechanically ventilated patients under pressure support exhibiting driving pressure greater than 15 cm H2O or VT greater than 10 ml/kg of predicted body weight. Esophageal and transpulmonary pressures, electrical activity of the diaphragm, and electrical impedance tomography were measured in pigs and patients. Ultrasound imaging and a nerve stimulator were used to identify the phrenic nerve, and perineural lidocaine was administered sequentially around the left and right phrenic nerves.

RESULTS

Results are presented as median [interquartile range, 25th to 75th percentiles]. In pigs, VT decreased from 7.4 ml/kg [7.2 to 8.4] to 5.9 ml/kg [5.5 to 6.6] (P < 0.001), as did peak transpulmonary pressure (25.8 cm H2O [20.2 to 27.2] to 17.7 cm H2O [13.8 to 18.8]; P < 0.001) and driving pressure (28.7 cm H2O [20.4 to 30.8] to 19.4 cm H2O [15.2 to 22.9]; P < 0.001). Ventilation in the most dependent part decreased from 29.3% [26.4 to 29.5] to 20.1% [15.3 to 20.8] (P < 0.001). In patients, VT decreased (8.2 ml/ kg [7.9 to 11.1] to 6.0 ml/ kg [5.7 to 6.7]; P < 0.001), as did driving pressure (24.7 cm H2O [20.4 to 34.5] to 18.4 cm H2O [16.8 to 20.7]; P < 0.001). Esophageal pressure, peak transpulmonary pressure, and electrical activity of the diaphragm also decreased. Dependent ventilation only slightly decreased from 11.5% [8.5 to 12.6] to 7.9% [5.3 to 8.6] (P = 0.005). Respiratory rate did not vary. Variables recovered 1 to 12.7 h [6.7 to 13.7] after phrenic nerve block.

CONCLUSIONS

Phrenic nerve block is feasible, lasts around 12 h, and reduces VT and driving pressure without changing respiratory rate in patients under assisted ventilation.

EDITOR’S PERSPECTIVE

Extracorporeal Membrane Oxygenation for Respiratory Failure Related to COVID-19: A Nationwide Cohort Study

BACKGROUND

Despite expanding use, knowledge on extracorporeal membrane oxygenation support during the COVID-19 pandemic remains limited. The objective was to report characteristics, management, and outcomes of patients receiving extracorporeal membrane oxygenation with a diagnosis of COVID-19 in France and to identify pre-extracorporeal membrane oxygenation factors associated with in-hospital mortality. A hypothesis of similar mortality rates and risk factors for COVID-19 and non-COVID-19 patients on venovenous extracorporeal membrane oxygenation was made.

METHODS

The Extracorporeal Membrane Oxygenation for Respiratory Failure and/or Heart failure related to Severe Acute Respiratory Syndrome-Coronavirus 2 (ECMOSARS) registry included COVID-19 patients supported by extracorporeal membrane oxygenation in France. This study analyzed patients included in this registry up to October 25, 2020, and supported by venovenous extracorporeal membrane oxygenation for respiratory failure with a minimum follow-up of 28 days after cannulation. The primary outcome was in-hospital mortality. Risk factors for in-hospital mortality were analyzed.

RESULTS

Among 494 extracorporeal membrane oxygenation patients included in the registry, 429 were initially supported by venovenous extracorporeal membrane oxygenation and followed for at least 28 days. The median (interquartile range) age was 54 yr (46 to 60 yr), and 338 of 429 (79%) were men. Management before extracorporeal membrane oxygenation cannulation included prone positioning for 411 of 429 (96%), neuromuscular blockage for 419 of 427 (98%), and NO for 161 of 401 (40%). A total of 192 of 429 (45%) patients were cannulated by a mobile extracorporeal membrane oxygenation unit. In-hospital mortality was 219 of 429 (51%), with a median follow-up of 49 days (33 to 70 days). Among pre-extracorporeal membrane oxygenation modifiable exposure variables, neuromuscular blockage use (hazard ratio, 0.286; 95% CI, 0.101 to 0.81) and duration of ventilation (more than 7 days compared to less than 2 days; hazard ratio, 1.74; 95% CI, 1.07 to 2.83) were independently associated with in-hospital mortality. Both age (per 10-yr increase; hazard ratio, 1.27; 95% CI, 1.07 to 1.50) and total bilirubin at cannulation (6.0 mg/dl or more compared to less than 1.2 mg/dl; hazard ratio, 2.65; 95% CI, 1.09 to 6.5) were confounders significantly associated with in-hospital mortality.

CONCLUSIONS

In-hospital mortality was higher than recently reported, but nearly half of the patients survived. A high proportion of patients were cannulated by a mobile extracorporeal membrane oxygenation unit. Several factors associated with mortality were identified. Venovenous extracorporeal membrane oxygenation support should be considered early within the first week of mechanical ventilation initiation.

EDITOR’S PERSPECTIVE

Overcoming supply disruptions during pandemics by utilizing found hardware for open source gentle ventilation

This article details the design of an open source emergency gentle ventilator (gentle-vent) framework that can be used in periods of scarcity. Although it is not a medical device, the system utilizes a wide range of commonly-available components that are combined using basic electronics skills to achieve the desired performance. The main function of the gentle-vent is to generate a calibrated pressure wave at the pump to provide support to the patient's breathing. Each gentle-vent permutation was tested using a DIY manometer as it would be utilized in the field in low-resource settings and validated with an open source VentMon. The most rudimentary implementation costs less than $40.

Computed Tomography Assessment of Tidal Lung Overinflation in Domestic Cats Undergoing Pressure-Controlled Mechanical Ventilation During General Anesthesia

Objective

This study aimed to evaluate lung overinflation at different airway inspiratory pressure levels using computed tomography in cats undergoing general anesthesia.

Study Design

Prospective laboratory study.

Animals

A group of 17 healthy male cats, aged 1.9–4.5 years and weighing 3.5 ± 0.5 kg.

Methods

Seventeen adult male cats were ventilated in pressure-controlled mode with airway pressure stepwise increased from 5 to 15 cmH₂O in 2 cmH₂O steps every 5 min and then stepwise decreased. The respiratory rate was set at 15 movements per min and end-expiratory pressure at zero (ZEEP). After 5 min in each inspiratory pressure step, a 4 s inspiratory pause was performed to obtain a thoracic juxta-diaphragmatic single slice helical CT image and to collect respiratory mechanics data and an arterial blood sample. Lung parenchyma aeration was defined as overinflated, normally-aerated, poorly-aerated, and non-aerated according to the CT attenuation number (−1,000 to −900 HU, −900 to −500 HU, −500 to −100 HU, and −100 to +100 HU, respectively).

Result

At 5 cmH₂O airway pressure, tidal volume was 6.7± 2.2 ml kg⁻¹, 2.1% (0.3–6.3%) of the pulmonary parenchyma was overinflated and 84.9% (77.6%−87.6%) was normally inflated. Increases in airway pressure were associated with progressive distention of the lung parenchyma. At 15 cmH₂O airway pressure, tidal volume increased to 31.5± 9.9 ml kg⁻¹ (p < 0.001), overinflated pulmonary parenchyma increased to 28.4% (21.2–30.6%) (p < 0.001), while normally inflated parenchyma decreased 57.9% (53.4–62.8%) (p < 0.001). Tidal volume and overinflated lung fraction returned to baseline when airway pressure was decreased. A progressive decrease was observed in arterial carbon dioxide partial pressure (PaCO₂) and end-tidal carbon dioxide (ETCO₂) when the airway pressures were increased above 9 cmH₂O (p < 0.001). The increase in airway pressure promoted an elevation in pH (p < 0.001).

Conclusions and Clinical Relevance

Ventilation with 5 and 7 cmH₂O of airway pressure prevents overinflation in healthy cats with highly compliant chest walls, despite presenting acidemia by respiratory acidosis. This fact can be controlled by increasing or decreasing respiratory rate and inspiratory time.

Lung and diaphragm protective ventilation: a synthesis of recent data

INTRODUCTION

: To adhere to the Hippocratic Oath, to "first, do no harm", we need to make every effort to minimize the adverse effects of mechanical ventilation. Our understanding of the mechanisms of ventilator-induced lung injury (VILI) and ventilator-induced diaphragm dysfunction (VIDD) has increased in recent years. Research focuses now on methods to monitor lung stress and inhomogeneity and targets we should aim for when setting the ventilator. In parallel, efforts to promote early assisted ventilation to prevent VIDD have revealed new challenges, such as titrating inspiratory effort and synchronizing the mechanical with the patients' spontaneous breaths, while at the same time adhering to lung-protective targets.

AREAS COVERED

This is a narrative review of the key mechanisms contributing to VILI and VIDD and the methods currently available to evaluate and mitigate the risk of lung and diaphragm injury.

EXPERT OPINION

Implementing lung and diaphragm protective ventilation requires individualizing the ventilator settings, and this can only be accomplished by exploiting in everyday clinical practice the tools available to monitor lung stress and inhomogeneity, inspiratory effort, and patient-ventilator interaction.

Effects of dynamic individualized PEEP guided by driving pressure in laparoscopic surgery on postoperative atelectasis in elderly patients: a prospective randomized controlled trial

Background

Driving pressure (ΔP = Plateau pressure-PEEP) is highly correlated with postoperative pulmonary complications (PPCs) and appears to be a promising indicator for optimizing ventilator settings. We hypothesized that dynamic, individualized positive end-expiratory pressure (PEEP) guided by ΔP could reduce postoperative atelectasis and improve intraoperative oxygenation, respiratory mechanics, and reduce the incidence of PPCs on elderly patients undergoing laparoscopic surgery.

Methods

Fifty-one elderly patients who were subject to laparoscopic surgery participated in this randomized trial. In the PEEP titration group (DV group), the PEEP titration was decremented to the lowest ΔP and repeated every 1 h. Additional procedures were also performed when performing predefined events that may be associated with lung collapse. In the constant PEEP group (PV group), a PEEP of 6 cmH₂O was used throughout the surgery. Moreover, zero PEEP was applied during the entire procedure in the conventional ventilation group (CV group). The primary objective of this study was lung ultrasound score noted at the end of surgery and 15 min after admission to the post-anesthesia care unit (PACU) at 12 lung areas bilaterally. The secondary endpoints were perioperative oxygenation function, expiratory mechanics, and the incidence of the PPCs.

Results

The lung ultrasound scores of the DV group were significantly lower than those in the PV group and CV group (P < 0.05), whereas there was no significant difference between the PV group and CV group (P > 0.05). The lung static compliance (Cstat) and ΔP at all the intraoperative time points in the DV group were significantly better compared to the PV group and the CV group (p < 0.05).

Conclusions

Intraoperative titrated PEEP reduced postoperative lung atelectasis and improved respiratory mechanics in elderly patients undergoing laparoscopic surgery. Meanwhile, standard PEEP strategy is not superior to conventional ventilation in reducing postoperative pulmonary atelectasis in laparoscopic surgery.

Evidence-Based Mechanical Ventilatory Strategies in ARDS

Acute respiratory distress syndrome (ARDS) remains one of the leading causes of morbidity and mortality in critically ill patients despite advancements in the field. Mechanical ventilatory strategies are a vital component of ARDS management to prevent secondary lung injury and improve patient outcomes. Multiple strategies including utilization of low tidal volumes, targeting low plateau pressures to minimize barotrauma, using low FiO₂ (fraction of inspired oxygen) to prevent injury related to oxygen free radicals, optimization of positive end expiratory pressure (PEEP) to maintain or improve lung recruitment, and utilization of prone ventilation have been shown to decrease morbidity and mortality. The role of other mechanical ventilatory strategies like non-invasive ventilation, recruitment maneuvers, esophageal pressure monitoring, determination of optimal PEEP, and appropriate patient selection for extracorporeal support is not clear. In this article, we review evidence-based mechanical ventilatory strategies and ventilatory adjuncts for ARDS.

Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

Positive end-expiratory pressure individualization guided by continuous end-expiratory lung volume monitoring during laparoscopic surgery

To determine whether end-expiratory lung volume measured with volumetric capnography (EELV_CO2) can individualize positive end-expiratory pressure (PEEP) setting during laparoscopic surgery. We studied patients undergoing laparoscopic surgery subjected to Fowler (F-group; n = 20) or Trendelenburg (T-group; n = 20) positions. EELV_CO2 was measured at 0° supine (baseline), during capnoperitoneum (CP) at 0° supine, during CP with Fowler (head up + 20°) or Trendelenburg (head down - 30°) positions and after CP back to 0° supine. PEEP was adjusted to preserve baseline EELV_CO2 during and after CP. Baseline EELV_CO2 was statistically similar to predicted FRC in both groups. At supine and CP, EELV_CO2 decreased from baseline values in F-group [median and IQR 2079 (768) to 1545 (725) mL; p = 0.0001] and in T-group [2164 (789) to 1870 (940) mL; p = 0.0001]. Change in body position maintained EELV_CO2 unchanged in both groups. PEEP adjustments from 5.6 (1.1) to 10.0 (2.5) cmH₂O in the F-group (p = 0.0001) and from 5.6 (0.9) to 10.0 (2.6) cmH₂O in T-group (p = 0.0001) were necessary to reach baseline EELV_CO2 values. EELV_CO2 increased close to baseline with PEEP in the F-group [1984 (600) mL; p = 0.073] and in the T-group [2175 (703) mL; p = 0.167]. After capnoperitoneum and back to 0° supine, PEEP needed to maintain EELV_CO2 was similar to baseline PEEP in F-group [5.9 (1.8) cmH₂O; p = 0.179] but slightly higher in the T-group [6.5 (2.2) cmH₂O; p = 0.006]. Those new PEEP values gave EELV_CO2 similar to baseline in the F-group [2039 (980) mL; p = 0.370] and in the T-group [2150 (715) mL; p = 0.881]. Breath-by-breath noninvasive EELV_CO2 detected changes in lung volume induced by capnoperitoneum and body position and was useful to individualize the level of PEEP during laparoscopy.Trial registry: Clinicaltrials.gov NCT03693352. Protocol started 1st October 2018.

Intraoperative ventilatory pressures during robotic assisted vs open radical cystectomy

OBJECTIVE

To investigate whether Robotic assisted radical cystectomy (RARC) is associated with increased postoperative pulmonary complications compared to open radical cystectomy (ORC). RARC poses challenges for ventilation with positioning and abdominal insufflation. Conventionally protective mechanical ventilation may be challenging, especially in patients with obesity or pulmonary comorbidities. Given the proven benefits of RARC compared to ORC, the risk of postoperative pulmonary complications merits further investigation.

MATERIALS AND METHODS

Adult patients consented for research who underwent RARC and ORC for invasive bladder cancer from 2013-2018 were identified for retrospective chart review. Perioperative and patient variables were looked at along with postoperative course and outcomes.

RESULTS

328 patients who underwent ORC and 108 patients who underwent RARC were identified. Despite findings of higher peak airway pressures throughout surgery, patients who underwent RARC did not have a higher rate of pulmonary complications than patients who underwent ORC. Patients with obstructive sleep apnea (OSA) who underwent ORC had a higher rate of postoperative pulmonary complications. Patients who underwent RARC had a less intraoperative fluid administration, fewer ICU admissions, and decreased length of hospital stay.

CONCLUSIONS

Despite mechanical ventilation challenges, RARC was not associated with increased post-operative pulmonary complications compared to ORC. This was also found in patients with BMI>30 or with diagnosis or high suspicion of OSA. These findings suggest ventilation at higher pressures does not increase risk for ventilator induced lung injury in patients undergoing RARC, even in conventionally higher risk patients.