Novel Oxygenation and Saturation Indices for Mortality Prediction in COVID-19 ARDS Patients: The Impact of Driving Pressure and Mechanical Power

Background: The oxygenation index (OI) and oxygen saturation index (OSI) are proven mortality predictors in pediatric and adult patients, traditionally using mean airway pressure (Pmean). We introduce novel indices, replacing Pmean with DP (ΔPinsp), MPdyn, and MPtot, assessing their potential for predicting COVID-19 acute respiratory distress syndrome (ARDS) mortality, comparing them to traditional indices. Methods: We studied 361 adult COVID-19 ARDS patients for 7 days, collecting ΔPinsp, MPdyn, and MPtot, OI-ΔPinsp, OI-MPdyn, OI-MPtot, OSI-ΔPinsp, OSI-MPdyn, and OSI-MPtot. We compared these in surviving and non-surviving patients over the first 7 intensive care unit (ICU) days using Mann-Whitney U test. Logistic regression receiver operating characteristic (ROC) analysis assessed AUC and CI values for ICU mortality on day three. We determined cut-off values using Youden's method and conducted multivariate Cox regression on parameter limits. Results: All indices showed significant differences between surviving and non-surviving patients on the third day of ICU care. The AUC values of OI-ΔPinsp were significantly higher than those of P/F and OI-Pmean (P values .0002 and <.0001, respectively). Similarly, AUC and CI values of OSI-ΔPinsp and OSI-MPdyn were significantly higher than those of SpO2/FiO2 and OSI-Pmean values (OSI-ΔPinsp: P < .0001, OSI-MPdyn: P values .047 and .028, respectively). OI-ΔPinsp, OSI-ΔPinsp, OI-MPdyn, OSI-MPdyn, OI-MPtot, and OSI-MPtot had AUC values of 0.72, 0.71, 0.69, 0.68, 0.66, and 0.64, respectively, with cut-off values associated with hazard ratios and P values of 7.06 (HR = 1.84, P = .002), 8.04 (HR = 2.00, P ≤ .0001), 7.12 (HR = 1.68, P = .001), 5.76 (HR = 1.70, P ≤ .0001), 10.43 (HR = 1.52, P = .006), and 10.68 (HR = 1.66, P = .001), respectively. Conclusions: Critical values of all indices were associated to higher ICU mortality rates and extended mechanical ventilation durations. The OI-ΔPinsp, OSI-ΔPinsp, and OSI-MPdyn indices displayed the strongest predictive capabilities for ICU mortality. These novel indices offer valuable insights for intensivists in the clinical management and decision-making process for ARDS patients.

Effect of Individualized PEEP Guided by Driving Pressure on Diaphragm Function in Patients Undergoing Laparoscopic Radical Resection of Colorectal Cancer: A Randomized Controlled Trial

BACKGROUND The concept of driving pressure (ΔP) has been established to optimize mechanical ventilation-induced lung injury. However, little is known about the specific effects of setting individualized positive end-expiratory pressure (PEEP) with driving pressure guidance on patient diaphragm function. MATERIAL AND METHODS Ninety patients were randomized into 3 groups, with PEEP set to 0 in group C; 5 cmH₂O in group F; and individualized PEEP in group I, based on esophageal manometry. Diaphragm ultrasound was performed in the supine position at 6 consecutive time points from T0-T5: diaphragm excursion, end-expiratory diaphragm thickness (Tdi-ee), and diaphragm thickening fraction (DTF) were measured. Primary indicators included diaphragm excursion, Tdi-ee, and DTF at T0-T5, and the correlation between postoperative DTF and ΔP. Secondary indicators included respiratory mechanics, hemodynamic changes at intraoperative d0-d4 time points, and postoperative clinical pulmonary infection scores. RESULTS (1) Diaphragm function parameters reached the lowest point at T1 in all groups (P<0.001). (2) Compared with group C, diaphragm excursion decreased, Tdi-ee increased, and DTF was lower in groups I and F at T1-T5, with significant differences (P<0.05), but the differences between groups I and F were not significant (P>0.05). (3) DTF was significantly and positively correlated with mean intraoperative ΔP in each group at T3, and the correlation was stronger at higher levels of ΔP. CONCLUSIONS Individualized PEEP, achieved by esophageal manometry, minimizes diaphragmatic injury caused by mechanical ventilation based on lung protection, but its protection of the diaphragm during laparoscopic surgery is not superior to that of conventional ventilation strategies.

Soundless Trouble: Syringe Pump Malfunction and the Hypotension Threat

Drug infusion devices have become indispensable tools in ICU patient care, drug delivery, and operation rooms (OR) and for controlled fluid delivery. Syringe pump safety is paramount in healthcare and laboratory settings to ensure accurate medication delivery and prevent adverse events. Healthcare professionals must receive thorough training on syringe pump operation, including loading syringes, programming infusion rates, and responding to alarms. Using the correct syringe size and type is essential to prevent inaccuracies in drug/fluid delivery. Regular calibration and maintenance checks are necessary to ensure the accuracy and reliability of the syringe pumps. Two cases of refractory hypotension are reported here, which were resolved by careful inspection of the infusion pumps.

Feasibility of Setting the Tidal Volume Based on End-Expiratory Lung Volume: A Pilot Clinical Study

OBJECTIVES

To assess the feasibility of setting the tidal volume (TV) as 25% of the actual aerated lung volume (rather than on ideal body weight) in patients with Acute Respiratory Distress Syndrome (ARDS).

DESIGN

Physiologic prospective single-center pilot study.

SETTING

Medical ICU specialized in the care of patients with ARDS.

PATIENTS

Patients with moderate-severe ARDS deeply sedated or paralyzed, undergoing controlled mechanical ventilation with a ventilator able to measure the end-expiratory lung volume (EELV) with a washin, washout technique.

INTERVENTIONS

Three-phase study (baseline, strain-selected TV setting, ventilation with strain-selected TV for 24 hr). The TV was calculated as 25% of the measured EELV minus the static strain due to the applied positive end-expiratory pressure.

MEASUREMENTS AND MAIN RESULTS

Gas exchanges and respiratory mechanics were measured and compared in each phase. In addition, during the TV setting phase, driving pressure (DP) and lung strain (TV/EELV) were measured at different TVs to assess the correlation between the two measurements. The maintenance of the set strain-selected TV for 24 hours was safe and feasible in 76% of the patients enrolled. Three patients dropped out from the study because of the need to set a respiratory rate higher than 35 breaths per minute to avoid respiratory acidosis. The DP of the respiratory system was a satisfactory surrogate for strain in this population.

CONCLUSIONS

In our population of 17 patients with moderate to severe ARDS, setting TV based on the actual lung size was feasible. DP was a reliable surrogate of strain in these patients, and DP less than or equal to 8 cm H2O corresponded to a strain less than 0.25.

Comparison of limited driving pressure ventilation and low tidal volume strategies in adults with acute respiratory failure on mechanical ventilation: a randomized controlled trial

BACKGROUND

Ventilator-induced lung injury (VILI) presents a grave risk to acute respiratory failure patients undergoing mechanical ventilation. Low tidal volume (LTV) ventilation has been advocated as a protective strategy against VILI. However, the effectiveness of limited driving pressure (plateau pressure minus positive end-expiratory pressure) remains unclear.

OBJECTIVES

This study evaluated the efficacy of LTV against limited driving pressure in preventing VILI in adults with respiratory failure.

DESIGN

A single-centre, prospective, open-labelled, randomized controlled trial.

METHODS

This study was executed in medical intensive care units at Siriraj Hospital, Mahidol University, Bangkok, Thailand. We enrolled acute respiratory failure patients undergoing intubation and mechanical ventilation. They were randomized in a 1:1 allocation to limited driving pressure (LDP; ⩽15 cmH2O) or LTV (⩽8 mL/kg of predicted body weight). The primary outcome was the acute lung injury (ALI) score 7 days post-enrolment.

RESULTS

From July 2019 to December 2020, 126 patients participated, with 63 each in the LDP and LTV groups. The cohorts had the mean (standard deviation) ages of 60.5 (17.6) and 60.9 (17.9) years, respectively, and they exhibited comparable baseline characteristics. The primary reasons for intubation were acute hypoxic respiratory failure (LDP 49.2%, LTV 63.5%) and shock-related respiratory failure (LDP 39.7%, LTV 30.2%). No significant difference emerged in the primary outcome: the median (interquartile range) ALI scores for LDP and LTV were 1.75 (1.00-2.67) and 1.75 (1.25-2.25), respectively (p = 0.713). Twenty-eight-day mortality rates were comparable: LDP 34.9% (22/63), LTV 31.7% (20/63), relative risk (RR) 1.08, 95% confidence interval (CI) 0.74-1.57, p = 0.705. Incidences of newly developed acute respiratory distress syndrome also aligned: LDP 14.3% (9/63), LTV 20.6% (13/63), RR 0.81, 95% CI 0.55-1.22, p = 0.348.

CONCLUSIONS

In adults with acute respiratory failure, the efficacy of LDP and LTV in averting lung injury 7 days post-mechanical ventilation was indistinguishable.

CLINICAL TRIAL REGISTRATION

The study was registered with the ClinicalTrials.gov database (identification number NCT04035915).

Safety and Feasibility of Intraoperative High PEEP Titrated to the Lowest Driving Pressure (ΔP)-Interim Analysis of DESIGNATION

Uncertainty remains about the best level of intraoperative positive end-expiratory pressure (PEEP). An ongoing RCT ('DESIGNATION') compares an 'individualized high PEEP' strategy ('iPEEP')-titrated to the lowest driving pressure (ΔP) with recruitment maneuvers (RM), with a 'standard low PEEP' strategy ('low PEEP')-using 5 cm H2O without RMs with respect to the incidence of postoperative pulmonary complications. This report is an interim analysis of safety and feasibility. From September 2018 to July 2022, we enrolled 743 patients. Data of 698 patients were available for this analysis. Hypotension occurred more often in 'iPEEP' vs. 'low PEEP' (54.7 vs. 44.1%; RR, 1.24 (95% CI 1.07 to 1.44); p < 0.01). Investigators were compliant with the study protocol 285/344 patients (82.8%) in 'iPEEP', and 345/354 patients (97.5%) in 'low PEEP' (p < 0.01). Most frequent protocol violation was missing the final RM at the end of anesthesia before extubation; PEEP titration was performed in 99.4 vs. 0%; PEEP was set correctly in 89.8 vs. 98.9%. Compared to 'low PEEP', the 'iPEEP' group was ventilated with higher PEEP (10.0 (8.0-12.0) vs. 5.0 (5.0-5.0) cm H2O; p < 0.01). Thus, in patients undergoing general anesthesia for open abdominal surgery, an individualized high PEEP ventilation strategy is associated with hypotension. The protocol is feasible and results in clear contrast in PEEP. DESIGNATION is expected to finish in late 2023.

Impact of ventilation strategies on pulmonary and cardiovascular complications in patients undergoing general anaesthesia for elective surgery: a systematic review and meta-analysis

BACKGROUND

Many RCTs have evaluated the influence of intraoperative tidal volume (tV), PEEP, and driving pressure on the occurrence of postoperative pulmonary complications, cardiovascular complications, and mortality in adult patients. Our meta-analysis aimed to investigate the association between tV, PEEP, and driving pressure and the above-mentioned outcomes.

METHODS

We conducted a systematic review and meta-analysis of RCTs from inception to May 19, 2022. The primary outcome was the incidence of postoperative pulmonary complications; the secondary outcomes were intraoperative cardiovascular complications and 30-day mortality. Primary and secondary outcomes were evaluated stratifying patients in the following groups: (1) low tV (LV, tV 6-8 ml kg-1 and PEEP ≥5 cm H2O) vs high tV (HV, tV >8 ml kg-1 and PEEP=0 cm H2O); (2) higher PEEP (HP, ≥6 cm H2O) vs lower PEEP (LP, <6 cm H2O); and (3) driving pressure-guided PEEP (DP) vs fixed PEEP (FP).

RESULTS

We included 16 RCTs with a total sample size of 4993. The incidence of postoperative pulmonary complications was lower in patients treated with LV than with HV (OR=0.402, CI 0.280-0.577, P<0.001) and lower in DP than in FP group (OR=0.358, CI 0.187-0.684, P=0.002). Postoperative pulmonary complications did not differ between HP and LP groups; the incidence of intraoperative cardiovascular complications was higher in HP group (OR=1.385, CI 1.027-1.867, P=0.002). The 30-day mortality was not influenced by the ventilation strategy.

CONCLUSIONS

Optimal intraoperative mechanical ventilation is unclear; however, our meta-analysis showed that low tidal volume and driving pressure-guided PEEP strategies were associated with a reduction in postoperative pulmonary complications.

Neurally Adjusted Ventilatory Assist Versus Pressure Support Ventilation: A Comprehensive Review

Mechanical ventilation serves as crucial life support for critically ill patients. Although it is life-saving prolonged ventilation carries risks and complications like barotrauma, Ventilator-associated pneumonia, sepsis, and many others. Optimizing patient-ventilator interactions and facilitating early weaning is necessary for improved intensive care unit (ICU) outcomes. Traditionally Pressure support ventilation (PSV) mode is widely used for weaning patients who are intubated and mechanically ventilated. Neurally adjusted ventilatory assist (NAVA) mode of the ventilator is an emerging ventilator mode that delivers pressure depending on the patient's respiratory drive, which in turn prevents over-inflation and improves the patient's ventilator interactions. Our article revises and compares the effectiveness of NAVA compared to PSV ventilation under different contexts. Overall we conclude that NAVA level of ventilation can be safely administered in a patient with acute respiratory failure, provided diaphragmatic paralysis is not considered. NAVA improves asynchrony index, wean-off time, and sleep quality and is associated with increased ventilator-free days. These results are based on small-scale studies with low power, and further studies are warranted in large-scale cohorts with more diverse populations to confirm these results.

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).

[Driving pressure-guided lung protective ventilation strategy reduces postoperative pulmonary complications in patients recovered from COVID-19]

OBJECTIVE

To investigate the value of lung protective ventilation strategy (LPVS) guided by driving pressure for preventing postoperative pulmonary complications (PPCs) in patients recovered from COVID-19 and optimize intraoperative respiratory management.

METHODS

From December, 2022 to February, 2023, a total of 118 patients recovered from COVID-19 within a month (ASA Ⅰ~Ⅲ, aged ≥18 years) undergoing elective non-cardiac surgeries under general anesthesia in our hospital were randomized equally into LPVS group and control group.The patients in LPVS group received a tidal volume of 6 mL/kg with an individualized PEEP guided by minimum driving pressure and lung re-expansion every 30 min, and those in the control group received conventional mechanical ventilation.The incidence of PPCs and hypoxemia and pulmonary ultrasound score of the patients were compared between the two groups.

RESULTS

There was no significant difference in the baseline data between LPVS group and the control group (P>0.05).Compared with the control group, LPVS group showed significantly lower incidences of PPCs (16.95%vs 35.59%, χ2=5.294, P=0.021) and hypoxemia (15.25%vs 30.51%, χ2=3.890, P=0.049) with also lower pulmonary ultrasound scores (5.31±1.07 vs 8.32±2.34, t=8.986, P<0.001).The PEEP value, airway pressure and plateau pressure in LPVS group were significantly higher, but the driving pressure and the tidal volume were lower than those in the control group (P<0.05).

CONCLUSION

LPVS guided by driving pressure can improve oxygenation and reduce the risk of PPCs in patients recently recovered from COVID-19.

American Association for the Surgery of Trauma/American College of Surgeons Committee on Trauma clinical protocol for management of acute respiratory distress syndrome and severe hypoxemia

LEVEL OF EVIDENCE

Therapeutic/Care Management: Level V.

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.

Development and Internal Validation of a Novel Prognostic Score to Predict Mortality in Acute Respiratory Distress Syndrome - Driving Pressure, Oxygenation and Nutritional Evaluation - "DRONE Score"

Introduction

There are few scores for mortality prediction in acute respiratory distress syndrome (ARDS) incorporating comprehensive ventilatory, acute physiological, organ dysfunction, oxygenation, and nutritional parameters. This study aims to determine the risk factors of ARDS mortality from the above-mentioned parameters at 48 h of invasive mechanical ventilation (IMV), which are feasible across most intensive care unit settings.

Methods

Prospective, observational, single-center study with 150 patients with ARDS defined by Berlin definition, receiving IMV with lung protective strategy.

Results

Our study had a mortality of 41.3% (62/150). We developed a 9-point novel prediction score, the driving pressure oxygenation and nutritional evaluation (DRONE) score comprising of driving pressure (DP), oxygenation accessed by the ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) ratio and nutritional evaluation using the modified nutrition risk in the critically ill (mNUTRIC) score. Each component of the DRONE score with the cutoff value to predict mortality was assigned a particular score (the lowest DP within 48 h in a patient being always ≥15 cmH2O a score of 2, the highest achievable PaO2/FiO2 <208 was assigned a score of 4 and the mNUTRIC score ≥4 was assigned a score of (3). We obtained the DRONE score ≥4, area under the curve 0.860 to predict mortality. Cox regression for the DRONE score >4 was highly associated with mortality (P < 0.001, hazard ratio 5.43, 95% confidence interval [2.94-10.047]). Internal validation was done by bootstrap analysis. The clinical utility of the DRONE score ≥4 was assessed by Kaplan-Meier curve which showed significance.

Conclusions

The DRONE score ≥4 could be a reliable predictor of mortality at 48 h in ARDS patients receiving IMV.

Driving Pressure-Guided Ventilation in Obese Patients Undergoing Laparoscopic Sleeve Gastrectomy: A Randomized Controlled Trial

Purpose

This study aims to compare the conventional lung protective ventilation strategy (LPVS) with driving pressure-guided ventilation in obese patients undergoing laparoscopic sleeve gastrectomy (LSG).

Methods

Forty-five patients undergoing elective LSG under general anesthesia were randomly assigned to the conventional LPVS group (group L) or the driving pressure-guided ventilation group (group D) using random numbers generated by Excel. The primary outcome was the driving pressure of both groups 90 min after pneumoperitoneum.

Results

After 30 min of pneumoperitoneum, 90 min of pneumoperitoneum, 10 min of closing the pneumoperitoneum, and restoring the supine position, the driving pressure of group L and group D were 20.0 ± 2.9 cm H2O vs 16.6 ± 3.0 cm H2O (P < 0.001), 20.7 ± 3.2 cm H2O vs 17.3 ± 2.8 cm H2O (P < 0.001), and 16.3 ± 3.1 cm H2O vs 13.3 ± 2.5 cm H2O (P = 0.001), respectively; the respiratory compliance of groups L and D were 23.4 ± 3.7 mL/cm H2O vs 27.6 ± 5.1 mL/cm H2O (P = 0.003), 22.7 ± 3.8 mL/cm H2O vs 26.4 ± 3.5 mL/cm H2O (P = 0.005), and 29.6 ± 6.8 mL/cm H2O vs 34.7 ± 5.3 mL/cm H2O (P = 0.007), respectively. The intraoperative PEEP in groups L and group D was 5 (5-5) cm H2O vs 10 (9-11) cm H2O (P < 0.001).

Conclusion

An individualized peep-based driving pressure-guided ventilation strategy can reduce intraoperative driving pressure and increase respiratory compliance in obese patients undergoing LSG.

Lung Injury Risk in Traumatic Brain Injury Managed With Optimal Cerebral Perfusion Pressure Guided-Therapy

Introduction

Management of traumatic brain injury (TBI) has to counterbalance prevention of secondary brain injury without systemic complications, namely lung injury. The potential risk of developing acute respiratory distress syndrome (ARDS) leads to therapeutic decisions such as fluid balance restriction, high PEEP and other lung protective measures, that may conflict with neurologic outcome. In fact, low cerebral perfusion pressure (CPP) may induce secondary ischemic injury and mortality, but disproportionate high CPP may also increase morbidity and worse lung compliance and hypoxia with the risk of developing ARDS and fatal outcome. The evaluation of cerebral autoregulation at bedside and individualized (optimal CPP) CPPopt-guided therapy, may not only be a relevant measure to protect the brain, but also a safe measure to avoid systemic complications.

Aim of the study

We aimed to study the safety of CPPopt-guided-therapy and the risk of secondary lung injury association with bad outcome.

Methods and results

Single-center retrospective analysis of 92 severe TBI patients admitted to the Neurocritical Care Unit managed with CPPopt-guided-therapy by PRx (pressure reactivity index). During the first 10 days, we collected data from blood gas, ventilation and brain variables. Evolution along time was analyzed using linear mixed-effects regression models. 86% were male with mean age 53±21 years. 49% presented multiple trauma and 21% thoracic trauma. At hospital admission, median GCS was 7 and after 3-months GOS was 3. Monitoring data was CPP 86±7mmHg, CPP-CPPopt -2.8±10.2mmHg and PRx 0.03±0.19. The average PFratio (PaO2/FiO2) was 305±88 and driving pressure 15.9±3.5cmH2O. PFratio exhibited a significant quadratic dependence across time and PRx and driving pressure presented significant negative association with PFRatio. CPP and CPPopt did not present significant effect on PFratio (p=0.533; p=0.556). A significant positive association between outcome and the difference CPP-CPPopt was found.

Conclusion

Management of TBI using CPPopt-guided-therapy was associated with better outcome and seems to be safe regarding the development of secondary lung injury.

Role of Changes in Driving Pressure and Mechanical Power in Predicting Mortality in Patients with Acute Respiratory Distress Syndrome

Driving pressure (ΔP) and mechanical power (MP) are associated with increased mortality in patients with acute respiratory distress syndrome (ARDS). We aimed to investigate which was better to predict mortality between changes in ΔP and MP. We reanalyzed data from a prospective observational cohort study of patients with ARDS in our hospital. Serial ΔP and MP values were calculated. The factors associated with survival were analyzed. Binary logistic regression showed that age (odds ratio (OR), 1.012; 95% confidence interval (CI), 1.003-1.022), Sequential Organ Failure assessment (SOFA) score (OR, 1.144; 95% CI, 1.086-1.206), trauma (OR, 0.172; 95% CI, 0.035-0.838), ΔP (OR, 1.077; 95% CI, 1.044-1.111), change in ΔP (OR, 1.087; 95% CI, 1.054-1.120), and change in MP (OR, 1.018; 95% CI, 1.006-1.029) were independently associated with 30-day mortality. Change in MP, change in ΔP, and SOFA scores were superior to ΔP in terms of the accuracy of predicting 30-day mortality. In conclusion, calculating change in ΔP is easy for respiratory therapists in clinical practice and may be used to predict mortality in patients with ARDS.

Relationship of Extravascular Lung Water and Pulmonary Vascular Permeability to Respiratory Mechanics in Patients with COVID-19-Induced ARDS

During acute respiratory distress syndrome (ARDS), the increase in pulmonary vascular permeability and lung water induced by pulmonary inflammation may be related to altered lung compliance. A better understanding of the interactions between respiratory mechanics variables and lung water or capillary permeability would allow a more personalized monitoring and adaptation of therapies for patients with ARDS. Therefore, our main objective was to investigate the relationship between extravascular lung water (EVLW) and/or pulmonary vascular permeability index (PVPI) and respiratory mechanic variables in patients with COVID-19-induced ARDS. This is a retrospective observational study from prospectively collected data in a cohort of 107 critically ill patients with COVID-19-induced ARDS from March 2020 to May 2021. We analyzed relationships between variables using repeated measurements correlations. We found no clinically relevant correlations between EVLW and the respiratory mechanics variables (driving pressure (correlation coefficient [CI 95%]: 0.017 [-0.064; 0.098]), plateau pressure (0.123 [0.043; 0.202]), respiratory system compliance (-0.003 [-0.084; 0.079]) or positive end-expiratory pressure (0.203 [0.126; 0.278])). Similarly, there were no relevant correlations between PVPI and these same respiratory mechanics variables (0.051 [-0.131; 0.035], 0.059 [-0.022; 0.140], 0.072 [-0.090; 0.153] and 0.22 [0.141; 0.293], respectively). In a cohort of patients with COVID-19-induced ARDS, EVLW and PVPI values are independent from respiratory system compliance and driving pressure. Optimal monitoring of these patients should combine both respiratory and TPTD variables.

Do we have the 'power' to 'drive' down the incidence of pulmonary complications after thoracic surgery

The concept, mechanisms, and physical and physiological determinants of ventilator-induced lung injury, as well as the influence of lung-protective ventilation strategies, are novel paradigms of modern intensive care and perioperative medicine. Driving pressure and mechanical power have emerged as meaningful and modifiable targets with specific relevance to thoracic anaesthesia and one-lung ventilation. The relationship between these factors and postoperative pulmonary complications remains complex because of the methodological design and outcome selection. Larger observational studies are required to better understand the characteristics of driving pressure and power in current practice of thoracic anaesthesia in order to design future trials in high-risk thoracic populations at risk of acute lung injury.

Airway driving pressure is associated with postoperative pulmonary complications after major abdominal surgery: a multicentre retrospective observational cohort study

Background

High airway driving pressure is associated with adverse outcomes in critically ill patients receiving mechanical ventilation, but large multicentre studies investigating airway driving pressure during major surgery are lacking. We hypothesised that increased driving pressure is associated with postoperative pulmonary complications in patients undergoing major abdominal surgery.

Methods

In this preregistered multicentre retrospective observational cohort study, the authors reviewed major abdominal surgical procedures in 11 hospitals from 2004 to 2018. The primary outcome was a composite of postoperative pulmonary complications, defined as postoperative pneumonia, unplanned tracheal intubation, or prolonged mechanical ventilation for more than 48 h. Associations between intraoperative dynamic driving pressure and outcomes, adjusted for patient and procedural factors, were evaluated.

Results

Among 14 218 qualifying cases, 389 (2.7%) experienced postoperative pulmonary complications. After adjustment, the mean dynamic driving pressure was associated with postoperative pulmonary complications (adjusted odds ratio for every 1 cm H₂O increase: 1.04; 95% confidence interval [CI], 1.02-1.06; P<0.001). Neither tidal volume nor PEEP was associated with postoperative pulmonary complications. Increased BMI, shorter height, and female sex were predictors for higher dynamic driving pressure (β=0.35, 95% CI 0.32-0.39, P<0.001; β=-0.01, 95% CI -0.02 to 0.00, P=0.005; and β=0.74, 95% CI 0.63-0.86, P<0.001, respectively).

Conclusions

Dynamic airway driving pressure, but not tidal volume or PEEP, is associated with postoperative pulmonary complications in models controlling for a large number of risk predictors and covariates. Such models are capable of risk prediction applicable to individual patients.

Adaptive Support Ventilation and Lung-Protective Ventilation in ARDS

BACKGROUND

Adaptive support ventilation (ASV) is a partially closed-loop ventilation mode that adjusts tidal volume (V_T) and breathing frequency (f) to minimize mechanical work and driving pressure. ASV is routinely used but has not been widely studied in ARDS.

METHODS

The study was a crossover study with randomization to intervention comparing a pressure-regulated, volume-targeted ventilation mode (adaptive pressure ventilation [APV], standard of care at Beth Israel Deaconess Medical Center) set to V_T 6 mL/kg in comparison with ASV mode where V_T adjustment is automated. Subjects received standard of care (APV) or ASV and then crossed over to the alternate mode, maintaining consistent minute ventilation with 1-2 h in each mode. The primary outcome was V_T corrected for ideal body weight (IBW) before and after crossover. Secondary outcomes included driving pressure, mechanics, gas exchange, mechanical power, and other parameters measured after crossover and longitudinally.

RESULTS

Twenty subjects with ARDS were consented, with 17 randomized and completing the study (median P_aO2 /F_IO2 146.6 [128.3-204.8] mm Hg) and were mostly passive without spontaneous breathing. ASV mode produced marginally larger V_T corrected for IBW (6.3 [5.9-7.0] mL/kg IBW vs 6.04 [6.0-6.1] mL/kg IBW, P = .035). Frequency was lower with patients in ASV mode (25 [22-26] breaths/min vs 27 [22-30)] breaths/min, P = .01). In ASV, lower respiratory-system compliance correlated with smaller delivered V_T/IBW (R² = 0.4936, P = .002). Plateau (24.7 [22.6-27.6] cm H₂O vs 25.3 [23.5-26.8] cm H₂O, P = .14) and driving pressures (12.8 [9.0-15.8] cm H₂O vs 11.7 [10.7-15.1] cm H₂O, P = .29) were comparable between conventional ventilation and ASV. No adverse events were noted in either ASV or conventional group related to mode of ventilation.

CONCLUSIONS

ASV targeted similar settings as standard of care consistent with lung-protective ventilation strategies in mostly passive subjects with ARDS. ASV delivered V_T based upon respiratory mechanics, with lower V_T and mechanical power in subjects with stiffer lungs.

Association between intraoperative tidal volume and postoperative respiratory complications is dependent on respiratory elastance: a retrospective, multicentre cohort study

BACKGROUND

The impact of high vs low intraoperative tidal volumes on postoperative respiratory complications remains unclear. We hypothesised that the effect of intraoperative tidal volume on postoperative respiratory complications is dependent on respiratory system elastance.

METHODS

We retrospectively recorded tidal volume (Vt; ml kg^-1 ideal body weight [IBW]) in patients undergoing elective, non-cardiothoracic surgery from hospital registry data. The primary outcome was respiratory failure (requiring reintubation within 7 days of surgery, desaturation after extubation, or both). The primary exposure was defined as the interaction between Vt and standardised respiratory system elastance (driving pressure divided by Vt; cm H₂O/[ml kg^-1]). Multivariable logistic regression models, with and without interaction terms (which categorised Vt as low [Vt ≤8 ml kg^-1] or high [Vt >8 ml kg^-1]), were adjusted for potential confounders. Additional analyses included path mediation analysis and fractional polynomial modelling.

RESULTS

Overall, 10 821/197 474 (5.5%) patients sustained postoperative respiratory complications. Higher Vt was associated with greater risk of postoperative respiratory complications (adjusted odds ratio=1.42 per ml kg^-1; 95% confidence interval [CI], 1.35-1.50]; P<0.001). This association was modified by respiratory system elastance (P<0.001); in patients with low compliance (<42.4 ml cm H₂O^-1), higher Vt was associated with greater risk of postoperative respiratory complications (adjusted risk difference=0.3% [95% CI, 0.0-0.5] at 41.2 ml cm H₂O^-1 compliance, compared with 5.8% [95% CI, 3.8-7.8] at 14 ml cm H₂O^-1 compliance). This association was absent when compliance exceeded 41.2 ml cm H₂O^-1. Adverse effects associated with high Vt were entirely mediated by driving pressures (P<0.001).

CONCLUSIONS

The association of harm with higher tidal volumes during intraoperative mechanical ventilation is modified by respiratory system elastance. These data suggest that respiratory elastance should inform the design of perioperative trials testing intraoperative ventilatory strategies.

Effects of Driving Pressure-Guided Ventilation on Postoperative Pulmonary Complications in Prone-Positioned Patients Undergoing Spinal Surgery: A Randomized Controlled Clinical Trial

BACKGROUND

Prolonged spinal surgery in the prone position may lead to postoperative pulmonary complications (PPCs). We aimed to compare the effects of driving pressure-guided ventilation versus conventional protective ventilation on postoperative pulmonary complications in patients undergoing spinal surgery in the prone position. We hypothesized that driving pressure-guided ventilation would be associated with a decreased incidence of PPC.

METHODS

We enrolled 78 patients into this single-center, double-blind, randomized controlled trial. The driving pressure (DP) group (n = 40) received a tidal volume of 6 ml/kg of predicted body weight, individualized positive end-expiratory pressure (PEEP) which produced the lowest driving pressure (plateau pressure-PEEP), and a recruitment maneuver. The protective ventilation (PV) group (n = 38) received the same tidal volume and recruitment maneuver but with a fixed PEEP of 5 cm H₂O. Our primary outcome was postoperative pulmonary complications based on Lung Ultrasound Scores (LUS) at the end of the surgery and the simplified Clinical Pulmonary Infection Score (sCPIS) on postoperative days (POD) 1 and 3.

RESULTS

DP patients had lower LUS and POD1 sCPIS than the PV group (p < 0.01). DP patients had lower driving pressure during the surgery than PV patients (p < 0.01). Perioperative arterial blood gases and hemodynamic parameters were comparable between the two groups (p > 0.05). The visual pain score (VAS) in postoperative days, drainage, and lengths of stay (LOS) were also similar between the two groups (p > 0.05).

CONCLUSIONS

Driving pressure-guided ventilation during spinal surgery with a prolonged prone patient position may reduce the incidence of early postoperative pulmonary complications, compared with conventional protective ventilation.

Venovenous extracorporeal CO2 removal to support ultraprotective ventilation in moderate-severe acute respiratory distress syndrome: A systematic review and meta-analysis of the literature

BACKGROUND

A strategy that limits tidal volumes and inspiratory pressures, improves outcomes in patients with the acute respiratory distress syndrome (ARDS). Extracorporeal carbon dioxide removal (ECCO₂R) may facilitate ultra-protective ventilation. We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of venovenous ECCO₂R in supporting ultra-protective ventilation in moderate-to-severe ARDS.

METHODS

MEDLINE and EMBASE were interrogated for studies (2000-2021) reporting venovenous ECCO₂R use in patients with moderate-to-severe ARDS. Studies reporting ≥10 adult patients in English language journals were included. Ventilatory parameters after 24 h of initiating ECCO₂R, device characteristics, and safety outcomes were collected. The primary outcome measure was the change in driving pressure at 24 h of ECCO₂R therapy in relation to baseline. Secondary outcomes included change in tidal volume, gas exchange, and safety data.

RESULTS

Ten studies reporting 421 patients (PaO₂:FiO₂ 141.03 mmHg) were included. Extracorporeal blood flow rates ranged from 0.35-1.5 L/min. Random effects modelling indicated a 3.56 cmH₂O reduction (95%-CI: 3.22-3.91) in driving pressure from baseline (p < .001) and a 1.89 mL/kg (95%-CI: 1.75-2.02, p < .001) reduction in tidal volume. Oxygenation, respiratory rate and PEEP remained unchanged. No significant interactions between driving pressure reduction and baseline driving pressure, partial pressure of arterial carbon dioxide or PaO₂:FiO₂ ratio were identified in metaregression analysis. Bleeding and haemolysis were the commonest complications of therapy.

CONCLUSIONS

Venovenous ECCO₂R permitted significant reductions in ∆P in patients with moderate-to-severe ARDS. Heterogeneity amongst studies and devices, a paucity of randomised controlled trials, and variable safety reporting calls for standardisation of outcome reporting. Prospective evaluation of optimal device operation and anticoagulation in high quality studies is required before further recommendations can be made.

Driving Pressure Is Associated With Outcome in Pediatric Acute Respiratory Failure

OBJECTIVES

Driving pressure (ratio of tidal volume over respiratory system compliance) is associated with mortality in acute respiratory distress syndrome. We sought to evaluate if such association could be identified in critically ill children.

DESIGN

We studied the association between driving pressure on day 1 of mechanical ventilation and ventilator-free days at day 28 through secondary analyses of prospectively collected physiology data.

SETTING

Medical-surgical university hospital PICU.

PATIENTS

Children younger than 18 years (stratified by Pediatric Mechanical Ventilation Consensus Conference clinical phenotype definitions) without evidence of spontaneous respiration.

INTERVENTIONS

Inspiratory hold maneuvers.

MEASUREMENTS AND MAIN RESULTS

Data of 222 patients with median age 11 months (2-51 mo) were analyzed. Sixty-five patients (29.3%) met Pediatric Mechanical Ventilation Consensus Conference criteria for restrictive and 78 patients (35.1%) for mixed lung disease, and 10.4% of all patients had acute respiratory distress syndrome. Driving pressure calculated by the ratio of tidal volume over respiratory system compliance for the whole cohort was 16 cm H2O (12-21 cm H2O) and correlated with the static airway pressure gradient (plateau pressure minus positive end-expiratory pressure) (Spearman correlation coefficient = 0.797; p < 0.001). Bland-Altman analysis showed that the dynamic pressure gradient (peak inspiratory pressure minus positive end-expiratory pressure) overestimated driving pressure (levels of agreement -2.295 to 7.268). Rematching the cohort through a double stratification procedure (obtaining subgroups of patients with matched mean levels for one variable but different mean levels for another ranking variable) showed a reduction in ventilator-free days at day 28 with increasing driving pressure in patients ventilated for a direct pulmonary indication. Competing risk regression analysis showed that increasing driving pressure remained independently associated with increased time to extubation (p < 0.001) after adjusting for Pediatric Risk of Mortality III 24-hour score, presence of direct pulmonary indication jury, and oxygenation index.

CONCLUSIONS

Higher driving pressure was independently associated with increased time to extubation in mechanically ventilated children. Dynamic assessments of driving pressure should be cautiously interpreted.

Agreement Between Peak Inspiratory Pressure in Decelerating-Flow Ventilation and Plateau Pressure in Square-Flow Ventilation in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Acute respiratory distress syndrome guidelines suggest limiting plateau pressures to 28-30 cm H2O. Plateau pressure is most accurately measured in square-flow modes, such as volume control. In children, decelerating-flow modes, such as pressure-regulated volume control and pressure control, are more common. Consequently, plateau pressures are rarely obtained, and pressure limits are instead provided for peak inspiratory pressure. The degree to which peak inspiratory pressure in decelerating-flow overestimates plateau pressure is unknown. Therefore, we assessed the correlation and accuracy of peak inspiratory pressure in decelerating-flow ventilation for approximating plateau pressure during square-flow ventilation.

DESIGN

Prospective, observational study.

SETTING

Tertiary, academic PICU.

PATIENTS

Fifty-two intubated children with acute respiratory distress syndrome enrolled between January 2020 and May 2021.

INTERVENTIONS

Measurement of peak inspiratory pressure in decelerating-flow ventilation and plateau pressure after transition to square-flow ventilation.

MEASUREMENTS AND MAIN RESULTS

Peak inspiratory pressure in decelerating-flow was highly correlated (r2 = 0.99; p < 0.001) with plateau pressure in square-flow. Peak inspiratory pressure was 1.0 ± 0.6 cm H2O higher than plateau pressure, with 96% of values within 2 cm H2O. The single outlier had coexistent asthma and inspiratory flows that did not reach zero.

CONCLUSIONS

Peak inspiratory pressure measured during decelerating-flow ventilation may be an adequate surrogate of plateau pressure in pediatric acute respiratory distress syndrome when inspiratory flow approaches zero. Practitioners should be aware that peak inspiratory pressures in decelerating-flow may not be substantially higher than plateau pressures.

Lower Driving Pressure and Neuromuscular Blocker Use Are Associated With Decreased Mortality in Patients With COVID-19 ARDS

BACKGROUND

The impact of mechanical ventilation parameters and management on outcomes of patients with coronavirus disease 2019 (COVID-19) ARDS is unclear.

METHODS

This multi-center observational study enrolled consecutive mechanically ventilated patients with COVID-19 ARDS admitted to one of 7 Korean ICUs between February 1, 2020-February 28, 2021. Patients who were age < 17 y or had missing ventilation parameters for the first 4 d of mechanical ventilation were excluded. Multivariate logistic regression was used to identify which strategies or ventilation parameters that were independently associated with ICU mortality.

RESULTS

Overall, 129 subjects (males, 60%) with a median (interquartile range) age of 69 (62-78) y were included. Neuromuscular blocker (NMB) use and prone positioning were applied to 76% and 16% of subjects, respectively. The ICU mortality rate was 37%. In the multivariate analysis, higher dynamic driving pressure (ΔP) values during the first 4 d of mechanical ventilation were associated with increased mortality (adjusted odds ratio 1.16 [95% CI 1.00-1.33], P = .046). NMB use was associated with decreased mortality (adjusted odds ratio 0.27 [95% CI 0.09-0.81], P = .02). The median tidal volume values during the first 4 d of mechanical ventilation and the ICU mortality rate were significantly lower in the NMB group than in the no NMB group. However, subjects who received NMB for ≥ 6 d (vs < 6 d) had higher ICU mortality rate.

CONCLUSIONS

In subjects with COVID-19 ARDS receiving mechanical ventilation, ΔP during the first 4 d of mechanical ventilation was independently associated with mortality. The short-term use of NMB facilitated lung-protective ventilation and was independently associated with decreased mortality.

Positive End-Expiratory Pressure and Respiratory Rate Modify the Association of Mechanical Power and Driving Pressure With Mortality Among Patients With Acute Respiratory Distress Syndrome

Supplemental Digital Content is available in the text.

IMPORTANCE:

Mechanical power and driving pressure have known associations with survival for patients with acute respiratory distress syndrome.

OBJECTIVES:

To further understand the relative importance of mechanical power and driving pressure as clinical targets for ventilator management.

DESIGN:

Secondary observational analysis of randomized clinical trial data.

SETTING AND PARTICIPANTS:

Patients with the acute respiratory distress syndrome from three Acute Respiratory Distress Syndrome Network trials.

MAIN OUTCOMES AND MEASURES:

After adjusting for patient severity in a multivariate Cox proportional hazards model, we examined the relative association of driving pressure and mechanical power with hospital mortality. Among 2,410 patients, the relationship between driving pressure and mechanical power with mortality was modified by respiratory rate, positive end-expiratory pressure, and flow.

RESULTS:

Among patients with low respiratory rate (< 26), only power was significantly associated with mortality (power [hazard ratio, 1.82; 95% CI, 1.41–2.35; p < 0.001] vs driving pressure [hazard ratio, 1.01; 95% CI, 0.84–1.21; p = 0.95]), while among patients with high respiratory rate, neither was associated with mortality. Both power and driving pressure were associated with mortality at high airway flow (power [hazard ratio, 1.28; 95% CI, 1.15–1.43; p < 0.001] vs driving pressure [hazard ratio, 1.15; 95% CI, 1.01–1.30; p = 0.041]) and neither at low flow. At low positive end-expiratory pressure, neither was associated with mortality, whereas at high positive end-expiratory pressure (≥ 10 cm H₂O), only power was significantly associated with mortality (power [hazard ratio, 1.22; 95% CI, 1.09–1.37; p < 0.001] vs driving pressure [hazard ratio, 1.16; 95% CI, 0.99–1.35; p = 0.059]).

CONCLUSIONS AND RELEVANCE:

The relationship between mechanical power and driving pressure with mortality differed within severity subgroups defined by positive end-expiratory pressure, respiratory rate, and airway flow.

Association of Time-Varying Intensity of Ventilation With Mortality in Patients With COVID-19 ARDS: Secondary Analysis of the PRoVENT-COVID Study

Background: High intensity of ventilation has an association with mortality in patients with acute respiratory failure. It is uncertain whether similar associations exist in patients with acute respiratory distress syndrome (ARDS) patients due to coronavirus disease 2019 (COVID-19). We investigated the association of exposure to different levels of driving pressure (ΔP) and mechanical power (MP) with mortality in these patients. Methods: PRoVENT-COVID is a national, retrospective observational study, performed at 22 ICUs in the Netherlands, including COVID-19 patients under invasive ventilation for ARDS. Dynamic ΔP and MP were calculated at fixed time points during the first 4 calendar days of ventilation. The primary endpoint was 28-day mortality. To assess the effects of time-varying exposure, Bayesian joint models adjusted for confounders were used. Results: Of 1,122 patients included in the PRoVENT-COVID study, 734 were eligible for this analysis. In the first 28 days, 29.2% of patients died. A significant increase in the hazard of death was found to be associated with each increment in ΔP (HR 1.04, 95% CrI 1.01-1.07) and in MP (HR 1.12, 95% CrI 1.01-1.36). In sensitivity analyses, cumulative exposure to higher levels of ΔP or MP resulted in increased risks for 28-day mortality. Conclusion: Cumulative exposure to higher intensities of ventilation in COVID-19 patients with ARDS have an association with increased risk of 28-day mortality. Limiting exposure to high ΔP or MP has the potential to improve survival in these patients. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT04346342.

Effect of INTELLiVENT-ASV versus Conventional Ventilation on Ventilation Intensity in Patients with COVID-19 ARDS-An Observational Study

Driving pressure (ΔP) and mechanical power (MP) are associated with outcomes in critically ill patients, irrespective of the presence of Acute Respiratory Distress Syndrome (ARDS). INTELLiVENT-ASV, a fully automated ventilatory mode, controls the settings that affect ΔP and MP. This study compared the intensity of ventilation (ΔP and MP) with INTELLiVENT-ASV versus conventional ventilation in a cohort of COVID-19 ARDS patients in two intensive care units in the Netherlands. The coprimary endpoints were ΔP and MP before and after converting from conventional ventilation to INTELLiVENT-ASV. Compared to conventional ventilation, INTELLiVENT-ASV delivered ventilation with a lower ΔP and less MP. With conventional ventilation, ΔP was 13 cmH₂O, and MP was 21.5 and 24.8 J/min, whereas with INTELLiVENT-ASV, ΔP was 11 and 10 cmH₂O (mean difference –2 cm H2O (95 %CI –2.5 to –1.2 cm H₂O), p < 0.001) and MP was 18.8 and 17.5 J/min (mean difference –7.3 J/Min (95% CI –8.8 to –5.8 J/min), p < 0.001). Conversion from conventional ventilation to INTELLiVENT-ASV resulted in a lower intensity of ventilation. These findings may favor the use of INTELLiVENT-ASV in COVID-19 ARDS patients, but future studies remain needed to see if the reduction in the intensity of ventilation translates into clinical benefits.

The Association between Mechanical Power and Mortality in Patients with Pneumonia Using Pressure-Targeted Ventilation

Recent studies have reported that mechanical power (MP) is associated with increased mortality in patients with acute respiratory distress syndrome (ARDS). We aimed to investigate the association between 28-day mortality and MP in patients with severe pneumonia. In total, the data of 313 patients with severe pneumonia were used for analysis. Serial MP was calculated daily for either 21 days or until ventilator support was no longer required. Compared with the non-ARDS group, the ARDS group (106 patients) demonstrated lower age, a higher Acute Physiology and Chronic Health Evaluation II score, lower history of diabetes mellitus, elevated incidences of shock and jaundice, higher MP and driving pressure on Day 1, and more deaths within 28 days. Regression analysis revealed that MP was an independent factor associated with 28-day mortality (odds ratio, 1.048; 95% confidence interval, 1.020-1.077). MP was persistently high in non-survivors and low in survivors among the ARDS group, the non-ARDS group, and all patients. These findings indicate that MP is associated with the 28-day mortality in ventilated patients with severe pneumonia, both in the ARDS and non-ARDS groups. MP had a better predicted value for the 28-day mortality than the driving pressure.

ARDS - Paradigms Lost and Found

Therefore, we inevitably increase tidal volume, driving pressure, and MP in individuals with the most severe lung injury such that these parameters may be associated with, but not causal to, the outcomes in acute lung injury. However, I remember all too well the assumptions that drove the paradigm in which I trained and am in favor of pushing to better understand at the tissue and even cellular level how much 'volutrauma' we are causing in individual patients, and testing whether or not new therapeutic 'targets' beyond the current '6 cc/kg tidal volume' will enable us to better care for patients with ARDS and improve on the survival gains we have made in the past two decades.

Response to Ventilator Adjustments for Predicting Acute Respiratory Distress Syndrome Mortality. Driving Pressure versus Oxygenation

Rationale: Clinicians commonly use short-term physiologic markers to assess the benefit of ventilator adjustments. Improved arterial oxygen tension/pressure (Pa_O2)/fraction of inspired oxygen (Fi_O2) after ventilator adjustment in acute respiratory distress syndrome is associated with lower mortality. However, as driving pressure (ΔP) reflects lung stress and strain, changes in ΔP may more accurately reflect benefits or harms of ventilator adjustments compared with changes in oxygenation.Objectives: We aimed to compare the association between mortality and the changes in Pa_O2/Fi_O2 and ΔP following protocolized ventilator changes.Methods: We assessed associations between mortality and changes in Pa_O2/Fi_O2 (ΔPa_O2/Fi_O2) and ΔP (ΔΔP) after postrandomization positive end-expiratory pressure (PEEP) and tidal volume adjustment in reanalyses of the ALVEOLI (Assessment of Low Tidal Volume and Elevated End-Expiratory Volume to Obviate Lung Injury) and ExPress (Expiratory Pressure) trials. We included subjects with available pre- and postintervention Pa_O2/Fi_O2 and ΔP (372 in ALVEOLI and 596 in ExPress). In each separate trial cohort, we performed multivariable Cox regression testing the association between ΔPa_O2/Fi_O2 and ΔΔP with mortality.Results: In ALVEOLI, when analyzed as separate variables, ΔPa_O2/Fi_O2 was associated with mortality only in subjects in whom PEEP increased, whereas ΔΔP was associated with mortality irrespective of direction of PEEP change. When modeled together, improved ΔPa_O2/Fi_O2 was not associated with mortality, whereas ΔΔP remained associated with mortality (adjusted hazard ratio [aHR], 1.50 per 5 cm H₂O increase; 95% confidence interval [95% CI], 1.21-1.85). When modeled together in ExPress, ΔΔP (aHR, 1.42; 95% CI, 1.14-1.78) was more strongly associated with mortality than ΔPa_O2/Fi_O2 (aHR, 0.95 per 25 mm Hg increase; 95% CI, 0.90-1.00).Conclusions: Reduced ΔP following protocolized ventilator changes was more strongly and consistently associated with lower mortality than was increased Pa_O2/Fi_O2, making ΔΔP more informative about benefit from ventilator adjustments. Our results reinforce the primacy of ΔP, rather than oxygenation, as the key variable associated with outcome.

Effect of Lowering Vt on Mortality in Acute Respiratory Distress Syndrome Varies with Respiratory System Elastance

Rationale: If the risk of ventilator-induced lung injury in acute respiratory distress syndrome (ARDS) is causally determined by driving pressure rather than by Vt, then the effect of ventilation with lower Vt on mortality would be predicted to vary according to respiratory system elastance (Ers). Objectives: To determine whether the mortality benefit of ventilation with lower Vt varies according to Ers. Methods: In a secondary analysis of patients from five randomized trials of lower- versus higher-Vt ventilation strategies in ARDS and acute hypoxemic respiratory failure, the posterior probability of an interaction between the randomized Vt strategy and Ers on 60-day mortality was computed using Bayesian multivariable logistic regression. Measurements and Main Results: Of 1,096 patients available for analysis, 416 (38%) died by Day 60. The posterior probability that the mortality benefit from lower-Vt ventilation strategies varied with Ers was 93% (posterior median interaction odds ratio, 0.80 per cm H₂O/[ml/kg]; 90% credible interval, 0.63-1.02). Ers was classified as low (<2 cm H₂O/[ml/kg], n = 321, 32%), intermediate (2-3 cm H₂O/[ml/kg], n = 475, 46%), and high (>3 cm H₂O/[ml/kg], n = 224, 22%). In these groups, the posterior probabilities of an absolute risk reduction in mortality ≥ 1% were 55%, 82%, and 92%, respectively. The posterior probabilities of an absolute risk reduction ≥ 5% were 29%, 58%, and 82%, respectively. Conclusions: The mortality benefit of ventilation with lower Vt in ARDS varies according to elastance, suggesting that lung-protective ventilation strategies should primarily target driving pressure rather than Vt.

Associations Between Expiratory Flow Limitation and Postoperative Pulmonary Complications in Patients Undergoing Cardiac Surgery

OBJECTIVES

To determine whether driving pressure and expiratory flow limitation are associated with the development of postoperative pulmonary complications (PPCs) in cardiac surgery patients.

DESIGN

Prospective cohort study.

SETTING

University Hospital San Raffaele, Milan, Italy.

PARTICIPANTS

Patients undergoing elective cardiac surgery.

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was the occurrence of a predefined composite of PPCs. The authors determined the association among PPCs and intraoperative ventilation parameters, mechanical power and energy load, and occurrence of expiratory flow limitation (EFL) assessed with the positive end-expiratory pressure test. Two hundred patients were enrolled, of whom 78 (39%) developed one or more PPCs. Patients with PPCs, compared with those without PPCs, had similar driving pressure (mean difference [MD] -0.1 [95% confidence interval (CI), -1.0 to 0.7] cmH₂O, p = 0.561), mechanical power (MD 0.5 [95% CI, -0.3 to 1.1] J/m, p = 0.364), and total energy load (MD 95 [95% CI, -78 to 263] J, p = 0.293), but they had a higher incidence of EFL (51% v 38%, p = 0.005). Only EFL was associated independently with the development of PPCs (odds ratio 2.46 [95% CI, 1.28-4.80], p = 0.007).

CONCLUSIONS

PPCs occurred frequently in this patient population undergoing cardiac surgery. PPCs were associated independently with the presence of EFL but not with driving pressure, total energy load, or mechanical power.

Calculation of Transpulmonary Pressure From Regional Ventilation Displayed by Electrical Impedance Tomography in Acute Respiratory Distress Syndrome

Transpulmonary driving pressure (DP_L) corresponds to the cyclical stress imposed on the lung parenchyma during tidal breathing and, therefore, can be used to assess the risk of ventilator-induced lung injury (VILI). Its measurement at the bedside requires the use of esophageal pressure (Peso), which is sometimes technically challenging. Recently, it has been demonstrated how in an animal model of ARDS, the transpulmonary pressure (P_L) measured with Peso calculated with the absolute values method (P_L = Paw—Peso) is equivalent to the transpulmonary pressure directly measured using pleural sensors in the central-dependent part of the lung. We hypothesized that, since the P_L derived from Peso reflects the regional behavior of the lung, it could exist a relationship between regional parameters measured by electrical impedance tomography (EIT) and driving P_L (DP_L). Moreover, we explored if, by integrating airways pressure data and EIT data, it could be possible to estimate non-invasively DP_L and consequently lung elastance (EL) and elastance-derived inspiratory P_L (PI). We analyzed 59 measurements from 20 patients with ARDS. There was a significant intra-patient correlation between EIT derived regional compliance in regions of interest (ROI1) (r = 0.5, p = 0.001), ROI2 (r = −0.68, p < 0.001), and ROI3 (r = −0.4, p = 0.002), and DP_L. A multiple linear regression successfully predicted DP_L based on respiratory system elastance (Ers), ideal body weight (IBW), roi1%, roi2%, and roi3% (R² = 0.84, p < 0.001). The corresponding Bland-Altmann analysis showed a bias of −1.4e-007 cmH₂O and limits of agreement (LoA) of −2.4–2.4 cmH₂O. EL and PI calculated using EIT showed good agreement (R² = 0.89, p < 0.001 and R² = 0.75, p < 0.001) with the esophageal derived correspondent variables. In conclusion, DP_L has a good correlation with EIT-derived parameters in the central lung. DP_L, PI, and EL can be estimated with good accuracy non-invasively combining information coming from EIT and airway pressure.

ECCO2R in 12 COVID-19 ARDS Patients With Extremely Low Compliance and Refractory Hypercapnia

Purpose: A phenotype of COVID-19 ARDS patients with extremely low compliance and refractory hypercapnia was found in our ICU. In the context of limited number of ECMO machines, feasibility of a low-flow extracorporeal carbon dioxide removal (ECCO₂R) based on the renal replacement therapy (RRT) platform in these patients was assessed. Methods: Single-center, prospective study. Refractory hypercapnia patients with COVID-19-associated ARDS were included and divided into the adjusted group and unadjusted group according to the level of PaCO₂ after the application of the ECCO₂R system. Ventilation parameters [tidal volume (VT), respiratory rate, and PEEP], platform pressure (Pplat) and driving pressure (DP), respiratory system compliance, arterial blood gases, and ECCO₂R system characteristics were collected. Results: Twelve patients with refractory hypercapnia were enrolled, and the PaCO₂ was 64.5 [56-88.75] mmHg. In the adjusted group, VT was significantly reduced from 5.90 ± 0.16 to 5.08 ± 0.43 ml/kg PBW; DP and Pplat were also significantly reduced from 23.5 ± 2.72 mmHg and 29.88 ± 3.04 mmHg to 18.5 ± 2.62 mmHg and 24.75 ± 3.41 mmHg, respectively. In the unadjusted group, PaCO₂ decreased from 94 [86.25, 100.3] mmHg to 80 [67.50, 85.25] mmHg but with no significant difference, and the DP and Pplat were not decreased after weighing the pros and cons. Conclusions: A low-flow ECCO₂R system based on the RRT platform enabled CO₂ removal and could also decrease the DP and Pplat significantly, which provided a new way to treat these COVID-19 ARDS patients with refractory hypercapnia and extremely low compliance. Clinical Trial Registration: https://www.clinicaltrials.gov/, identifier NCT04340414.

Validity of Empirical Estimates of the Ratio of Dead Space to Tidal Volume in ARDS

BACKGROUND

The ratio of dead space to tidal volume (V_D/V_T) is a clinically relevant parameter in ARDS; it has been shown to predict mortality, and it determines the extent to which extracorporeal CO₂ removal reduces tidal volume (V_T) and driving pressure (ΔP). V_D/V_T can be estimated with volumetric capnography, but empirical formulas using demographic and physiological information have been proposed to estimate V_D/V_T without the need of additional equipment. It is unknown whether estimated and measured V_D/V_T produce similar estimates of the predicted effect of extracorporeal CO₂ removal on ΔP.

METHODS

We performed a secondary analysis of data from a previous clinical trial including subjects with ARDS in whom V_D/V_T and CO₂ production ([Formula: see text]) were measured with volumetric capnography. The estimated ratio of dead space to tidal volume (V_D,est/V_T) was calculated using standard empiric formulas. Agreement between measured and estimated values was evaluated with Bland-Altman analysis. Agreement between the predicted change in ΔP with extracorporeal CO₂ removal as computed using the measured ratio of alveolar dead space to tidal volume (V_Dalv/V_T) or estimated V_Dalv/V_T (V_Dalv,est/V_T) was also evaluated.

RESULTS

V_D,est/V_T was higher than measured V_D/V_T, and agreement between them was low (bias 0.05, limits of agreement -0.21 to 0.31). Differences between measured and estimated [Formula: see text] accounted for 57% of the error in V_D,est/V_T. The predicted reduction in ΔP with extracorporeal CO₂ removal computed using V_Dalv,est/V_T was in reasonable agreement with the expected reduction using V_Dalv/V_T (bias -0.7 cm H₂O, limits of agreement -1.87 to 0.47 cm H₂O). In multivariable regression, measured V_D/V_T was associated with mortality (odds ratio 1.9, 95% CI 1.2-3.1, P = .01), but V_D,est/V_T was not (odds ratio 1.2, 95% CI 0.8-1.8, P = .3).

CONCLUSIONS

V_D/V_T and V_D,est/V_T showed low levels of agreement and cannot be used interchangeably in clinical practice. Nevertheless, the predicted decrease in ΔP due to extracorporeal CO₂ removal was similar when computed from either estimated or measured V_Dalv/V_T.

Direction and Magnitude of Change in Plateau From Peak Pressure During Inspiratory Holds Can Identify the Degree of Spontaneous Effort and Elastic Workload in Ventilated Patients

OBJECTIVES

Inspiratory holds with measures of airway pressure to estimate driving pressure (elastic work) are often limited to patients without respiratory effort. We sought to evaluate if measures of airway pressure during inspiratory holds could be used for patients with spontaneous respiratory effort during mechanical ventilation to estimate the degree of spontaneous effort and elastic work.

DESIGN

We compared the direction and degree of change in airway pressure during inspiratory holds versus esophageal pressure through secondary analysis of physiologic data.

SETTING

ICUs at Children's Hospital Los Angeles.

PATIENTS

Children with pediatric acute respiratory distress syndrome with evidence of spontaneous respiration while on pressure control or pressure support ventilation.

INTERVENTIONS

Inspiratory hold maneuvers.

MEASUREMENTS AND MAIN RESULTS

From airway pressure, we defined "plateau - peak pressure" as Pmusc, index, which was divided into three categories for analysis (< -1 ["negative"], between -1 and 1 ["neutral"], and > 1 cm H2O ["positive"]). A total of 30 children (age 36.8 mo [16.1-70.3 mo]) from 65 study days, comprising 118 inspiratory holds were included. Pmusc, index was "negative" in 29 cases, was "neutral" in 17 cases, and was "positive" in 72 cases. As Pmusc, index went from negative to neutral to positive, there was larger negative deflection in esophageal pressure -5.0 (-8.2 to 1.9), -5.9 (-7.6 to 4.3), and -10.7 (-18.1 to 7.9) cm H2O (p < 0.0001), respectively. There was a correlation between max negative esophageal pressure and Pmusc, index (r = -0.52), and when Pmusc, index was greater than or equal to 7 cm H2O, the max negative esophageal pressure was greater than 10 cm H2O. There was a stronger correlation between Pmusc, index and markers of elastic work from esophageal pressure (r = 0.84).

CONCLUSIONS

The magnitude of plateau minus peak pressure during an inspiratory hold is correlated with the degree of inspiratory effort, particularly for those with high elastic work. It may be useful to identify patients with excessively high effort or high driving pressure.

Dynamic Airway Driving Pressure and Outcomes in Children With Acute Hypoxemic Respiratory Failure

BACKGROUND

Limited adult data suggest that airway driving pressure might better reflect the potential risk for lung injury than tidal volume based on ideal body weight, and the parameter correlates with mortality in ARDS. There is a lack of data about the effect of driving pressure on mortality in pediatric ARDS. This study aimed to evaluate the effect of driving pressure on morbidity and mortality of children with acute hypoxemic respiratory failure.

METHODS

This retrospective cohort study was performed in a tertiary level pediatric ICU. Children who received invasive mechanical ventilation for acute hypoxemic respiratory failure (defined as [Formula: see text] < 300 within 24 h after intubation), in a 2-y period were included. The cohort was divided into 2 groups based on the highest dynamic driving pressure (ΔP, calculated as the difference between peak inspiratory pressure and PEEP) in the first 24 h, with a cutoff value of 15 cm H₂O.

RESULTS

Of the 380 children who were mechanically ventilated during the study period, 101 children who met eligibility criteria were enrolled. Common diagnoses were pneumonia (n = 51), severe sepsis (n = 24), severe dengue (n = 10), and aspiration pneumonia (n = 7). In comparison to the group with high ΔP (ie, ≥ 15 cm H₂O), children in the group with low ΔP (ie, < 15 cm H₂O) had significantly lower median (interquartile range) duration of ventilation (5 [4-6] d vs 8 [6-11] d, P < .001], ICU length of stay (6 [5-8] d vs 12 [8-15] d, P < .001], and more ventilator-free days at day 28 (23 [20-24] vs 17 [0-22] d, P < .001). Logistic regression analysis also suggested driving pressure as an independent predictor of morbidity after adjusting for confounding variables. However, there was no statistically significant difference in mortality between the 2 groups (17% in low ΔP vs 24% in high ΔP, P = .38). Subgroup analysis of 65 subjects who fulfilled ARDS criteria yielded similar results with respect to mortality and morbidity.

CONCLUSIONS

Below a threshold of 15 cm H₂O, ΔP was associated with significantly decreased morbidity in children with acute hypoxemic respiratory failure.

Monitoring During Mechanical Ventilation

Mechanical ventilation is an indispensable form of life support for patients undergoing general anesthesia or experiencing respiratory failure in the setting of critical illness. These patients are at risk for a number of complications related to both their underlying disease states and the mechanical ventilation itself. Intensive monitoring is required to identify early signs of clinical worsening and to minimize the risk of iatrogenic harm. Pulse oximetry and capnography are used to ensure that appropriate oxygenation and ventilation are achieved and maintained. Assessments of driving pressure, transpulmonary pressure, and the pressure-volume loop are performed to ensure that adequate PEEP is applied and excess distending pressure is minimized. Finally, monitoring and frequent adjustment of airway cuff pressures is performed to minimize the risk of airway injury and ventilator-associated pneumonia. We will discuss monitoring during mechanical ventilation with a focus on the accuracy, ease of use, and effectiveness in preventing harm for each of these monitoring modalities.

Fluctuations of driving pressure during mechanical ventilation indicates elevated central venous pressure and poor outcomes

Inappropriate mechanical ventilation may induce hemodynamic alterations through cardiopulmonary interactions. The aim of this study was to explore the relationship between airway pressure and central venous pressure during the first 72 h of mechanical ventilation and its relevance to patient outcomes. We conducted a retrospective study of the Department of Critical Care Medicine of Peking Union Medical College Hospital and a secondary analysis of the MIMIC-III clinical database. The relationship between the ranges of driving pressure and central venous pressure during the first 72 h and their associations with prognosis were investigated. Data from 2790 patients were analyzed. Wide range of driving airway pressure (odds ratio, 1.0681; 95% CI, 1.0415-1.0953; p < 0.0001) were independently associated with mortality, ventilator-free time, intensive care unit and hospital length of stay. Furthermore, wide range of driving pressure and elevated central venous pressure exhibited a close correlation. The area under receiver operating characteristic demonstrated that range of driving pressure and central venous pressure were measured at 0.689 (95% CI, 0.670-0.707) and 0.681 (95% CI, 0.662-0.699), respectively. Patients with high ranges of driving pressure and elevated central venous pressure had worse outcomes. Post hoc tests showed significant differences in 28-day survival rates (log-rank (Mantel-Cox), 184.7; p < 0.001). In conclusion, during the first 72 h of mechanical ventilation, patients with hypoxia with fluctuating driving airway pressure have elevated central venous pressure and worse outcomes.

The Association Between the Mechanical Ventilator Pressures and Outcomes in a Cohort of Patients with Acute Respiratory Failure

Background

Pressures measured during mechanical ventilation provide important information about the respiratory system mechanics and can help predict outcomes.

Methods

The electronic medical records of patients hospitalized between 2010 and 2016 with sepsis who required mechanical ventilation were reviewed to collect demographic information, clinical information, management requirements, and outcomes, such as mortality, ICU length of stay, and hospital length of stay. Mechanical ventilation pressures were recorded on the second full day of hospitalization.

Results

This study included 312 adult patients. The mean age is 59.1 ± 16.3 years; 57.4% were men. The mean BMI was 29.3 ± 10.7. Some patients had pulmonary infections (46.2%), and some patients had extrapulmonary infections (34.9%). The overall mortality was 42.6%. In a multi-variable model that included age, gender, number of comorbidities, APACHE 2 score, and PaO₂/FiO₂ ratio, peak pressure, plateau pressure, driving pressure, and PEEP all predicted mortality when entered into the model separately. There was an increase in peak pressure, plateau pressure, and driving pressure across BMI categories ranging from underweight to obese.

Conclusions

This study demonstrates that ventilator pressure measurements made early during the management of patients with acute respiratory failure requiring mechanical ventilation provide prognostic information regarding outcomes, including mortality. Patients with high mechanical ventilator pressures during the early course of their acute respiratory failure require more attention to identify reversible disease processes when possible. In addition, increased BMIs are associated with increased ventilator pressures, and this increases the complexity of the clinical evaluation in the management of obese patients.

A narrative review of driving pressure as a monitoring indicator during mechanical ventilation with spontaneous breathing

The mortality of acute respiratory distress syndrome (ARDS) remains high, and mechanical ventilation (MV) is an essential means of treatment. During MV, people realize the benefits of spontaneous breathing and the disadvantages of uncontrolled spontaneous breathing. Current methods of monitoring spontaneous breathing include oesophageal manometry, P0.1, and diaphragm function monitoring. However, these methods have limitations and deficiencies. The driving pressure is a new indicator that reflects the strain of the lung, which indicates the volumetric injury of the lung and is independently associated with mortality in ARDS patients. Moreover, in recent studies, driving pressure monitoring has been shown to be feasible in assisted support ventilation. This review summarizes the current state of spontaneous breathing and examines whether it is convenient to monitor driving pressure during spontaneous breathing to achieve lung protection ventilation.

Comparison of the Oxygenation Factor and the Oxygenation Ratio in Subjects With ARDS

BACKGROUND

The oxygenation ratio (ie, [Formula: see text]/[Formula: see text]) remains the most commonly used index for assessing oxygenation and disease severity in patients with acute ARDS. However, the oxygenation ratio does not account for mechanical ventilation settings. We hypothesized that the oxygenation factor (ie, oxygenation ratio/mean airway pressure) is superior to the oxygenation ratio in reflecting oxygenation in patients with ARDS and results in a different classification of ARDS severity.

METHODS

In 150 subjects with ARDS (50 severe, 50 moderate, and 50 mild), arterial blood gas, mean airway pressure, static lung compliance, driving pressure, and mechanical power were obtained. The oxygenation ratio and the oxygenation factor were then calculated. Receiver operating characteristic curves were constructed for oxygenation ratio and oxygenation factor at lung compliance > 40 mL/cm H₂O, driving pressure < 15 cm H₂O, and mechanical power < 17 J/min, thresholds that are known to predict survival in patients with ARDS. Subjects were reclassified for ARDS severity on the basis of the oxygenation factor and compared to classification on the basis of the oxygenation ratio.

RESULTS

Areas under the receiver operating characteristic curves for the oxygenation factor were significantly higher than for the oxygenation ratio. Reclassification of ARDS severity using the oxygenation factor did not affect subjects classified as having severe ARDS per the oxygenation ratio. However, 52% of subjects with moderate ARDS per the oxygenation ratio criteria were reclassified as either severe (25 subjects) or mild ARDS (1 subject) on the basis of oxygenation factor criteria. Also, 54% of subjects with mild ARDS per the oxygenation ratio criteria were reclassified as severe (4 subjects), moderate (21 subjects), or non-ARDS (2 subjects) on the basis of oxygenation factor criteria.

CONCLUSIONS

The oxygenation factor was a superior ARDS oxygenation index compared to the oxygenation ratio and should be considered as a substitute criteria for classification of the severity of ARDS. (ClinicalTrials.gov registration NCT03946189.).

Respiratory Mechanics and Outcomes in Immunocompromised Patients With ARDS: A Secondary Analysis of the EFRAIM Study

BACKGROUND

In view of the high mortality rate of immunocompromised patients with ARDS, it is important to identify targets for improvement.

RESEARCH QUESTION

This study investigated factors associated with mortality in this specific ARDS population, including factors related to respiratory mechanics (plateau pressure [Pplat,rs], compliance [Crs], and driving pressure [ΔPrs]).

STUDY DESIGN AND METHODS

This study consisted of a predefined secondary analysis of the EFRAIM data. Overall, 789 of 1,611 patients met the Berlin criteria for ARDS, and Pplat,rs, ΔPrs, and Crs were available for 494 patients. A hierarchical model was used to assess factors at ARDS onset independently associated with hospital mortality.

RESULTS

Hospital mortality was 56.3%. After adjustment, variables independently associated with hospital mortality included ARDS of undetermined etiology (OR, 1.66; 95% CI, 1.01-2.72), need for vasopressors (OR, 1.91; 95% CI, 1.27-2.88), and need for renal replacement therapy (OR, 2.02; 95% CI, 1.37-2.97). ARDS severity according to the Berlin definition, neutropenia on admission, and the type of underlying disease were not significantly associated with mortality. Before adjustment, higher Pplat,rs, higher ΔPrs, and lower Crs were associated with higher mortality. Addition of each of these individual variables to the final hierarchical model revealed a significant association with mortality: ΔPrs (OR, 1.08; 95% CI, 1.05-1.12), Pplat,rs (OR, 1.07; 95% CI, 1.04-1.11), and Crs (OR, 0.97; 95% CI, 0.95-0.98). Tidal volume was not associated with mortality.

INTERPRETATION

In immunocompromised patients with ARDS, respiratory mechanics provide additional prognostic information to predictors of hospital mortality. Studies designed to define lung-protective ventilation guided by these physiological variables may be warranted in this specific population.

The effect of positive-end-expiratory pressure on stroke volume variation: An experimental study in dogs

Stroke volume variation (SVV) may be affected by ventilation settings. However, it is unclear whether positive-end-expiratory pressure (PEEP) affects SVV independently of the effect of driving pressure. We aimed to investigate the effect of driving pressure and PEEP on SVV under various preload conditions using beagle dogs as the animal model. We prepared three preload model, baseline, mild and moderate haemorrhage model. Mild and moderate haemorrhage models were created in nine anaesthetized, mechanically ventilated dogs by sequentially removing 10 mL/kg, and then an additional 10 mL/kg of blood, respectively. We measured cardiac output, stroke volume (SV), SVV, heart rate, central venous pressure, pulmonary capillary wedge pressure and the mean arterial pressure under varying ventilation settings. Peak inspiratory pressure (PIP) was incrementally increased by 4 cmH₂ O, from 9 cmH₂ O to 21 cmH₂ O, under PEEP values of 4, 8, and 12 cmH₂ O. The driving pressure did not significantly decrease SV under each preload condition and PEEP; however, significantly increased SVV. In contrast, the increased PEEP decreased SV and increased SVV under each preload condition and driving pressure, but these associations were not statistically significant. According to multiple regression analysis, an increase in PEEP and decrease in preload significantly decreased SV (P < .05). In addition, an increase in the driving pressure and decrease in preload significantly increased SVV (P < .05). Driving pressure had more influence than PEEP on SVV.

Associations between changes in oxygenation, dead space and driving pressure induced by the first prone position session and mortality in patients with acute respiratory distress syndrome

Background

Outcome prediction in acute respiratory distress syndrome (ARDS) is challenging, especially in patients with severe hypoxemia. The aim of the current study was to determine the prognostic capacity of changes in PaO₂/FiO₂, dead space fraction (V_D/V_T) and respiratory system driving pressure (ΔP_RS) induced by the first prone position (PP) session in patients with ARDS.

Methods

This was a post hoc analysis of the conveniently-sized 'Molecular Diagnosis and Risk Stratification of Sepsis' study (MARS). The current analysis included ARDS patients who were placed in the PP. The primary endpoint was the prognostic capacity of the PP-induced changes in PaO₂/FiO₂, V_D/V_T, and ΔP_RS for 28-day mortality. PaO₂/FiO₂, V_D/V_T, and ΔP_RS was calculated using variables obtained in the supine position before and after completion of the first PP session. Receiving operator characteristic curves (ROC) were constructed, and sensitivity, specificity positive and negative predictive value were calculated based on the best cutoffs.

Results

Ninety patients were included; 28-day mortality was 46%. PP-induced changes in PaO₂/FiO₂ and V_D/V_T were similar between survivors vs. non-survivors [+83 (+24 to +137) vs. +58 (+21 to +113) mmHg, and -0.06 (-0.17 to +0.05) vs. -0.08 (-0.16 to +0.08), respectively]. PP-induced changes in ΔP_RS were different between survivors vs. non-survivors [-3 (-7 to 2) vs. 0 (-3 to +3) cmH₂O; P=0.03]. The area under the ROC of PP-induced changes in ΔP_RS for mortality, however, was low [0.63 (95% confidence interval (CI), 0.50 to 0.75]; PP-induced changes in ΔP_RS had a sensitivity and specificity of 76% and 56%, and a positive and negative predictive value of 60% and 73%.

Conclusions

Changes in PaO₂/FiO₂, V_D/V_T, and ΔP_RS induced by the first PP session have poor prognostic capacities for 28-day mortality in ARDS patients.

PEEP Titration to Minimize Driving Pressure in Subjects With ARDS: A Prospective Physiological Study

BACKGROUND

Observational studies report that lower driving pressure (ie, the difference between plateau pressure and PEEP) is associated with improved survival in patients with ARDS and may be a key mediator of lung-protective ventilation strategies. The primary objective of this study was to characterize reductions in driving pressure that could be achieved through changes in PEEP.

METHODS

In this prospective physiological pilot study, 10 subjects with ARDS were placed on PEEP according to the ARDS Network Lower PEEP/F_IO2 Table. PEEP was adjusted in small increments and decrements above and below this initial PEEP, and driving pressure was measured at each PEEP level. Subsequently, PEEP was set at the level resulting in the lowest driving pressure, and driving pressure was measured after 1, 5, 15, and 30 min to assess stability over time at constant PEEP.

RESULTS

All subjects had ARDS with a median (interquartile range [IQR]) P_aO2 /F_IO2 of 116 (98-132) at enrollment. Median (IQR) driving pressure at baseline was 14 (13-17) cm H₂O. After PEEP titration, median driving pressure decreased to 13 (12-14) cm H₂O. The largest reduction in driving pressure was 4 cm H₂O. Two subjects had no change in driving pressure at multiple PEEP levels. To achieve the lowest driving pressure, final PEEP was increased in 6 subjects and decreased in 4 subjects from the baseline PEEP prescribed by the ARDS Network Lower PEEP/F_IO2 Table. Driving pressure reached equilibrium within 1-5 min and remained stable for 30 min following PEEP titration.

CONCLUSIONS

PEEP titration had a variable effect in changing driving pressure across this small sample of ARDS subjects. In some subjects, PEEP was decreased from values given in the ARDS Network Lower PEEP/F_IO2 Table to minimize driving pressure. Changes in driving pressure stabilized within a few minutes of PEEP titration.

Effects of positive end-expiratory pressure alone or an open-lung approach on recruited lung volumes and respiratory mechanics of mechanically ventilated horses

OBJECTIVE

To evaluate the effects of positive end-expiratory pressure (PEEP) alone and PEEP preceded by lung recruitment manoeuvre (LRM) on lung volumes and respiratory system mechanics in healthy horses undergoing general anaesthesia.

STUDY DESIGN

Controlled, prospective clinical study.

ANIMALS

A group of 15 horses undergoing arthroscopy.

METHODS

Following anaesthetic induction, initial ventilatory settings were: tidal volume 15 mL kg^-1, inspiratory:expiratory ratio 1:2, respiratory rate to maintain end-tidal CO₂ between 5.3-6.6 kPa (40-50 mmHg). The following settings were implemented sequentially: zero PEEP (ZEEP); PEEP 10 cmH₂O (PEEP); LRM (50 cmH₂O for 20 seconds) followed by 10 cmH₂O of PEEP (LRM + PEEP). Static compliance (C_st), driving pressure, delta end-expiratory (ΔEELV) and recruited lung volumes (RLV) were obtained 30 minutes after initiating each ventilatory strategy. Data were analyzed with paired t test or analysis of variance followed by Tukey's post hoc test. Data are shown as mean ± standard deviation; p < 0.05 was considered significant.

RESULTS

PEEP induced ΔEELV of 6.68 ± 3.36 mL kg^-1; ΔEELV during LRM + PEEP was 14.28 ± 5.59 mL kg^-1 (p < 0.0001). The RLV was greater during the LRM + PEEP phase (12.30 ± 5.85 mL kg^-1) than during PEEP (4.47 ± 3.97 mL kg^-1; p < 0.0001). The C_st was unchanged from ZEEP to PEEP (0.75 ± 0.21 and 0.85 ± 0.22 mL cmH₂O^-1 kg^-1, respectively, p = 0.36) but increased using LRM + PEEP (1.11 ± 0.25 mL cmH₂O^-1 kg^-1, p = 0.0004). Driving pressure was lower during LRM + PEEP than during PEEP and ZEEP (16 ± 2, 19 ± 2 and 21 ± 4 cmH₂O, respectively, p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Unlike PEEP alone, PEEP preceded by LRM increased RLV and C_st and reduced driving pressure in horses under anaesthesia.

Driving Pressure: Defining the Range

BACKGROUND

Recent literature suggests that optimization of tidal driving pressure (ΔP) would be a better variable to target for lung protection at the bedside than tidal volume (V_T) or plateau pressure (P_plat), the traditional indicators of ventilator-induced lung injury. However, the usual range or variability of ΔP over time for any subject category have not been defined. This study sought to document the ΔP ranges observed in current practice among mechanically ventilated subjects receiving routine care for diverse acute conditions in a community hospital environment.

METHODS

This was a retrospective, observational study in a university-affiliated and house staff-aided institution with respiratory care protocols based on extant lung-protective guidelines for V_T. Demographic characteristics and measured parameters related to mechanical ventilation and hemodynamics were extracted from electronic records of intubated subjects for each 8-h period of the first 24 h in the ICU. P_plat values reported by the ventilator were validated by the respiratory therapist before those data were entered into the electronic medical record.

RESULTS

The mean ΔP was significantly higher at Time 1 (mean 16.1, range 7.0-31.0 cm H₂O) compared to both Time 2 (mean 14.5, range 7.0-35.0 cm H₂O) (P < .001) and Time 3 (mean 14.8, range 8.0-32 cm H₂O) (P < .001). At all time points, the median ΔP was higher for completely passive breathing compared to triggered breathing. The widest difference between presumed entirely passive and presumed intermittently or consistently triggered breaths occurred at Time 1 (mean ΔP = 17.2 vs 14.9 cm H₂O, respectively) (P = .01).

CONCLUSIONS

Suggested safety thresholds for ΔP are often violated by a strategy that focuses on only V_T and P_plat. Our data suggest that ΔP is lower for passive versus triggered breathing cycles. Vigilance is especially important in the initial stages of mechanical ventilator support, and attention should be paid to triggering efforts when interpreting and comparing machine-determined numerical values for ΔP.