Expiratory Flow Limitation as a Risk Factor for Pulmonary Complications After Major Abdominal Surgery

Combining Spirometry and the ARISCAT Respiratory Risk Assessment Can Improve Postoperative Outcomes and Reduce Mortality Risk in Mexico

Introduction

Although a major goal of preoperative evaluation is to identify risk factors and improve postoperative outcomes, current clinical guidelines in Mexico indicate that preoperative spirometry should only be performed on patients with pulmonary disease. The aim of this study was to compare the incidence of postoperative complications (POC), mortality, and risk factors among adults who did or did not undergo preoperative spirometry, based on their Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) risk level.

Material and methods

An observational, retrospective and comparative study design was used to identify 2059 patients from the General Hospital of Mexico who had an ARISCAT assessment during 2013-2017. Patients were classified in two groups: ARISCAT with spirometry (n = 1306) and ARISCAT without spirometry (n = 753). Chi-square, Fisher's exact test and the Student's t-tests were used to compare groups. Logistic regression was used to identify factors associated with an increased risk of POC and mortality.

Results

In the ARISCAT with spirometry group, 11% of patients had POC, compared with 48% of patients in the ARISCAT without spirometry group. High-risk ARISCAT patients who did not receive spirometry had higher mortality (18%), than those who underwent spirometry (0.4%). Logistic regression results indicate that not performing preoperative spirometry increases the probability of POC and mortality.

Conclusions

Our findings suggest that the combined use of preoperative spirometry and ARISCAT is associated with reduced POC and mortality. Future clinical guidelines should recommend the use of preoperative spirometry for patients with a moderate or high ARISCAT level in Mexico.

Effect of expiratory flow limitation on ventilation/perfusion mismatch and perioperative lung function during pneumoperitoneum and Trendelenburg position

BACKGROUND

Laparoscopic surgery and Trendelenburg position may affect the respiratory function and alter the gas exchange. Further the reduction of the lung volumes may contribute to the development of expiratory flow limitation (EFL). The latter is associated with an increased risk of postoperative pulmonary complications. Our aim was to investigate the incidence of EFL and to evaluate its effect on pulmonary function and intraoperative V/Q mismatch.

METHODS

This is a prospective study on patients undergoing elective laparoscopic gynecological surgery. We evaluated respiratory mechanics, V/Q mismatch and presence of EFL after anesthesia induction, during pneumoperitoneum and Trendelenburg position and at the end of surgery. Intraoperative gas exchange and hemodynamic were also recorded. Clinical data were collected until seven days after surgery to evaluate the onset of pulmonary postoperative complications (PPCs).

RESULTS

Among the 66 patients enrolled, 25/66 (38%) exhibited EFL during surgery, of whom 10/66 (15%) after anesthesia induction, and the remaining 15 patients after pneumoperitoneum and Trendelenburg position. Median PEEP able to reverse flow limitation was 7 [7-10] cmH2O after anesthesia induction and 9 [8-15] cmH2O after pneumoperitoneum and Trendelenburg position. Patients with EFL had significantly higher shunt (17 [2-25] vs. 9 [1-19]; P=0.05), low V̇/Q̇ (27 [20-70] vs. 15 [10-22]; P=0.05) and high V̇/Q̇ (10 [7-14] vs. 6 [4-7]; P=0.024). At the end of surgery, only high V/Q was significantly higher in EFL patients. Further, they exhibited higher incidence of postoperative pulmonary complication (48% (12/25) vs. 15% (6/41), P=0.005), hypoxemia and hypercapnia (80% [20/25] vs. 32% [13/41]; P<0.001).

CONCLUSIONS

Expiratory flow limitation is a common phenomenon during gynecological laparoscopic surgery associated with worsen gas exchange, increased V/Q mismatch and altered lung mechanics. Our study showed that patients experiencing EFL during surgery showed a higher risk for PPCs.

Efficacy of maintaining low-tidal volume mechanical ventilation as compared to resting lung strategy during coronary artery bypass graft cardiopulmonary bypass surgery: A post-hoc analysis of the MECANO trial

STUDY OBJECTIVE

To compare a low-tidal-volume with positive end-expiratory pressure strategy (VENT strategy) to a resting-lung-strategy (i.e., no-ventilation (noV) strategy) during cardiopulmonary bypass for coronary artery bypass graft surgery on the incidence of postoperative pulmonary complications.

DESIGN

Post-hoc analysis of the MECANO trial which was a prospective single-center, blind, randomized, parallel-group controlled trial.

SETTING

Tertiary care cardiac surgery center.

PATIENTS

Patients who underwent isolated on-pump coronary bypass surgery were randomized either to VENT or noV group.

INTERVENTION

During the cardiopulmonary bypass phase of the cardiac surgery procedure, mechanical ventilation in the VENT group consisted of a tidal volume of 3 mL/kg, a respiratory rate of 5 per minute and a positive end-expiratory pressure of 5 cmH₂O. Patients in the noV group received no ventilation during this phase.

MEASUREMENTS

Primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2 and reintubation.

MAIN RESULTS

In this post-hoc analysis, we retained 725 patients who underwent isolated CABG surgery, from the 1501 patients included in the original study. There were 352 in the VENT group and 373 patients in the noV group. Post-hoc comparison yielded no differences in baseline characteristics between these two groups. The primary outcome occurred less frequently in the VENT group than in the noV group, with 44 (12.5%) and 76 (20.4%) respectively (odds-ratio (OR) = 0.56 (0.37-0.84), p = 0.004). There were fewer early respiratory dysfunctions and prolonged respiratory support in the VENT group (respectively, OR = 0.34 (0.12-0.96) p = 0.033 and OR = 0.51 (0.27-0.94) p = 0.029). Complications related to mechanical ventilation were similar in the two groups.

CONCLUSIONS

In this post-hoc analysis, maintaining low-tidal ventilation compared to a resting-lung strategy was associated with fewer pulmonary postoperative complications in patients who underwent isolated CABG procedures.

Different positive end expiratory pressure and tidal volume controls on lung protection and inflammatory factors during surgical anesthesia

BACKGROUND

Mechanical ventilation can lead to the severe impairment of the metabolic pathway of alveolar surfactants, inactivating alveolar surfactants and significantly reducing lung-chest compliance. The cardiopulmonary function of elderly patients usually reduced to a certain extent, and there are lung complications after surgical anesthesia, just like lung barotrauma caused by mechanical ventilation, atelectasis and postoperative hypoxemia.

AIM

To investigate the effects of different positive end expiratory pressures (PEEPs) and tidal volumes (VTs) on respiratory function, the degree of the inflammatory response and hemodynamic indexes in patients undergoing surgery under general anesthesia.

METHODS

A total of 120 patients undergoing surgery for gastric or colon cancer under general anesthesia in Xinghua People's Hospital from January 2017 to January 2021 were randomly divided into Group A and Group B, with 60 cases in each group. The ventilation mode in Group A was VT (6.0 mL/kg) + PEEP (5.0 cmH2O), while that in Group B was VT (6.0 mL/kg) + PEEP (8.0 cmH2O). Blood gas parameters, respiratory mechanical parameters, inflammatory response indicators, hemodynamic indicators and related complications were compared between the two groups.

RESULTS

There were no significant differences in PaCO2, PaO2, oxygen or the examined indexes at T0 between group A and group B (P > 0.05). The measured PaO2 value of patients in group A at T3 was higher than that in group B, and the difference was significant (P < 0.05). There were no significant differences in peak airway pressure (Ppeak), mean airway pressure or dynamic pulmonary compliance (Cdyn) at T0 between group A and group B (P > 0.05). The measured Ppeak value of patients in group A at T1 was higher than that in group B, and the difference was significant (P < 0.05). The measured Cdyn value at T1 and T2 was greater than that in group B (P < 0.05). Before surgery, there were no significant differences in tumor necrosis factor-α (TNF-α), interleukin (IL)-6 or IL-10 between group A and group B (P > 0.05). After 4 h, the measured values of TNF-α and IL-6 in group A were lower than those in group B, and the differences were significant (P < 0.05). The IL-10 Level in group A was higher than that in group B (P < 0.05). At T0, there were no significant differences in cardiac output, cardiac index (CI), stroke volume index (SVI) or mean arterial pressure between group A and group B (P > 0.05). The measured values of CI and SVI at T2 in patients in group A were higher than those in group B, and the differences were significant (P < 0.05).

CONCLUSION

For patients undergoing surgery for gastric or colon cancer under general anesthesia, the VT (6.0 mL/kg) + PEEP (5.0 cmH2O) regimen was more effective than the VT (6.0 mL/kg) + PEEP (8.0 cmH2O) regimen in protecting the lung function and ventilatory function of patients, and it had better effects on maintaining hemodynamic stability and reducing inflammatory reactions.

Frailty is an independent risk factor for postoperative pulmonary complications in elderly patients undergoing video-assisted thoracoscopic pulmonary resections

BACKGROUND

Although frailty as a common geriatric syndrome is associated with postoperative complications, its relationship with postoperative pulmonary complications (PPCs) following pulmonary resections in elderly patients is unclear.

AIMS

To investigate the relationship between frailty and PPCs in elderly patients undergoing video-assisted thoracoscopic pulmonary resections and explore the effect of the addition of frailty assessment to PPC risk index and ASA on their predictive ability.

METHODS

In a prospective cohort study, we measured frailty status using the FRAIL scale in elderly patients undergoing video-assisted thoracoscopic pulmonary resections. Multivariate analysis was used to identify the relationship between frailty and PPCs. Receiver operating characteristic curves were used to examine the predictive power of frailty and other assessment tools.

RESULTS

227 patients were analyzed in the study. The prevalence of PPCs was 24.7%. Significant differences between patients with and without PPCs were observed in the following aspects: BMI, smoking, COPD, respiratory infection within the last month, FEV1/FVC ratio, creatinine, ASA, frailty and PPC risk index (p < 0.05, respectively). After adjusting for all covariates, frailty was significantly related to PPCs in elderly patients (odds ratio: 6.33, 95% confidence interval: 2.45-16.37). Combined with frailty assessment, the area under the curve for ASA class and PPC risk index was increased to 0.759 (95% CI 0.687-0.831) and 0.821 (95% CI 0.758-0.883).

CONCLUSIONS

Frailty was associated with PPCs in elderly patients undergoing video-assisted thoracoscopic pulmonary resections. Combined with the frailty assessment, the predictive power of the PPC risk index and ASA class was improved.

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.

Management of Intraoperative Mechanical Ventilation to Prevent Postoperative Complications after General Anesthesia: A Narrative Review

Mechanical ventilation (MV) is still necessary in many surgical procedures; nonetheless, intraoperative MV is not free from harmful effects. Protective ventilation strategies, which include the combination of low tidal volume and adequate positive end expiratory pressure (PEEP) levels, are usually adopted to minimize the ventilation-induced lung injury and to avoid post-operative pulmonary complications (PPCs). Even so, volutrauma and atelectrauma may co-exist at different levels of tidal volume and PEEP, and therefore, the physiological response to the MV settings should be monitored in each patient. A personalized perioperative approach is gaining relevance in the field of intraoperative MV; in particular, many efforts have been made to individualize PEEP, giving more emphasis on physiological and functional status to the whole body. In this review, we summarized the latest findings about the optimization of PEEP and intraoperative MV in different surgical settings. Starting from a physiological point of view, we described how to approach the individualized MV and monitor the effects of MV on lung function.

Impact of Facilitation of Early Mobilization on Postoperative Pulmonary Outcomes After Colorectal Surgery: A Randomized Controlled Trial

OBJECTIVE

To estimate the extent to which staff-directed facilitation of early mobilization impacts recovery of pulmonary function and 30-day postoperative pulmonary complications (PPCs) after colorectal surgery.

SUMMARY BACKGROUND DATA

Early mobilization after surgery is believed to improve pulmonary function and prevent PPCs; however, adherence is low. The value of allocating resources (eg, staff time) to increase early mobilization is unknown.

METHODS

This study involved the analysis of a priori secondary outcomes of a pragmatic, observer-blind, randomized trial. Consecutive patients undergoing colorectal surgery were randomized 1:1 to usual care (preoperative education) or facilitated mobilization (staff dedicated to assist transfers and walking during hospital stay). Forced vital capacity, forced expiratory volume in 1 second (FEV1), and peak cough flow were measured preoperatively and at 1, 2, 3 days and 4 weeks after surgery. PPCs were defined according to the European Perioperative Clinical Outcome Taskforce.

RESULTS

Ninety-nine patients (57% male, 80% laparoscopic, median age 63, and predicted FEV1 97%) were included in the intention-to-treat analysis (usual care 49, facilitated mobilization 50). There was no between-group difference in recovery of forced vital capacity [adjusted difference in slopes 0.002 L/d (95% CI -0.01 to 0.01)], FEV1 [-0.002 L/d (-0.01 to 0.01)] or peak cough flow [-0.002 L/min/d (-0.02 to 0.02)]. Thirty-day PPCs were also not different between groups [adjusted odds ratio 0.67 (0.23-1.99)].

CONCLUSIONS

In this randomized controlled trial, staff-directed facilitation of early mobilization did not improve postoperative pulmonary function or reduce PPCs within an enhanced recovery pathway for colorectal surgery.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02131844.

Physiological effects of two driving pressure-based methods to set positive end-expiratory pressure during one lung ventilation

During one-lung ventilation (OLV), titrating the positive end-expiratory pressure (PEEP) to target a low driving pressure (∆P) could reduce postoperative pulmonary complications. However, it is unclear how to conduct PEEP titration: by stepwise increase starting from zero PEEP (PEEP_INCREMENTAL) or by stepwise decrease after a lung recruiting manoeuvre (PEEP_DECREMENTAL). In this randomized trial, we compared the physiological effects of these two PEEP titration strategies on respiratory mechanics, ventilation/perfusion mismatch and gas exchange. Patients undergoing video-assisted thoracoscopic surgery in OLV were randomly assigned to a PEEP_INCREMENTAL or PEEP_DECREMENTAL strategy to match the lowest ∆P. In the PEEP_INCREMENTAL group, PEEP was stepwise titrated from ZEEP up to 16 cm H₂O, whereas in the PEEP_DECREMENTAL group PEEP was decrementally titrated, starting from 16 cm H₂O, immediately after a lung recruiting manoeuvre. Respiratory mechanics, ventilation/perfusion mismatch and blood gas analyses were recorded at baseline, after PEEP titration and at the end of surgery. Sixty patients were included in the study. After PEEP titration, shunt decreased similarly in both groups, from 50 [39-55]% to 35 [28-42]% in the PEEP_INCREMENTAL and from 45 [37-58]% to 33 [25-45]% in the PEEP_DECREMENTAL group (both p < 0.001 vs baseline). The resulting ∆P, however, was lower in the PEEP_DECREMENTAL than in the PEEP_INCREMENTAL group (8 [7-11] vs 10 [9-11] cm H₂O; p = 0.03). In the PEEP_DECREMENTAL group the PaO₂/ FIO₂ ratio increased significantly after intervention (from 140 [99-176] to 186 [152-243], p < 0.001). Both the PEEP_INCREMENTAL and the PEEP_DECREMENTAL strategies were able to decrease intraoperative shunt, but only PEEP_DECREMENTAL improved oxygenation and lowered intraoperative ΔP.Clinical trial number NCT03635281; August 2018; "retrospectively registered".

Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse

Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.

Airway Closure during Surgical Pneumoperitoneum in Obese Patients

BACKGROUND

Airway closure causes lack of communication between proximal airways and alveoli, making tidal inflation start only after a critical airway opening pressure is overcome. The authors conducted a matched cohort study to report the existence of this phenomenon among obese patients undergoing general anesthesia.

METHODS

Within the procedures of a clinical trial during gynecological surgery, obese patients underwent respiratory/lung mechanics and lung volume assessment both before and after pneumoperitoneum, in the supine and Trendelenburg positions, respectively. Among patients included in this study, those exhibiting airway closure were compared to a control group of subjects enrolled in the same trial and matched in 1:1 ratio according to body mass index.

RESULTS

Eleven of 50 patients (22%) showed airway closure after intubation, with a median (interquartile range) airway opening pressure of 9 cm H2O (6 to 12). With pneumoperitoneum, airway opening pressure increased up to 21 cm H2O (19 to 28) and end-expiratory lung volume remained unchanged (1,294 ml [1,154 to 1,363] vs. 1,160 ml [1,118 to 1,256], P = 0.155), because end-expiratory alveolar pressure increased consistently with airway opening pressure and counterbalanced pneumoperitoneum-induced increases in end-expiratory esophageal pressure (16 cm H2O [15 to 19] vs. 27 cm H2O [23 to 30], P = 0.005). Conversely, matched control subjects experienced a statistically significant greater reduction in end-expiratory lung volume due to pneumoperitoneum (1,113 ml [1,040 to 1,577] vs. 1,000 ml [821 to 1,061], P = 0.006). With airway closure, static/dynamic mechanics failed to measure actual lung/respiratory mechanics. When patients with airway closure underwent pressure-controlled ventilation, no tidal volume was inflated until inspiratory pressure overcame airway opening pressure.

CONCLUSIONS

In obese patients, complete airway closure is frequent during anesthesia and is worsened by Trendelenburg pneumoperitoneum, which increases airway opening pressure and alveolar pressure: besides preventing alveolar derecruitment, this yields misinterpretation of respiratory mechanics and generates a pressure threshold to inflate the lung that can reach high values, spreading concerns on the safety of pressure-controlled modes in this setting.

Point of Care Ultrasound to Identify Diaphragmatic Dysfunction after Thoracic Surgery

BACKGROUND

Postoperative diaphragmatic dysfunction after thoracic surgery is underestimated due to the lack of reproducible bedside diagnostic methods. We used point of care ultrasound to assess diaphragmatic function bedside in patients undergoing video-assisted thoracoscopic or thoracotomic lung resection. Our main hypothesis was that the thoracoscopic approach may be associated with lower incidence of postoperative diaphragm dysfunction as compared to thoracotomy. Furthermore, we assessed the association between postoperative diaphragmatic dysfunction and postoperative pulmonary complications.

METHODS

This was a prospective observational cohort study. Two cohorts of patients were evaluated: those undergoing video-assisted thoracoscopic surgery versus those undergoing thoracotomy. Diaphragmatic dysfunction was defined as a diaphragmatic excursion less than 10 mm. The ultrasound evaluations were carried out before (preoperative) and after (i.e., 2 h and 24 h postoperatively) surgery. The occurrence of postoperative pulmonary complications was assessed up to 7 days after surgery.

RESULTS

Among the 75 patients enrolled, the incidence of postoperative diaphragmatic dysfunction at 24 h was higher in the thoracotomy group as compared to video-assisted thoracoscopic surgery group (29 of 35, 83% vs. 22 of 40, 55%, respectively; odds ratio = 3.95 [95% CI, 1.5 to 10.3]; P = 0.005). Patients with diaphragmatic dysfunction on the first day after surgery had higher percentage of postoperative pulmonary complications (odds ratio = 5.5 [95% CI, 1.9 to 16.3]; P = 0.001). Radiologically assessed atelectasis was 46% (16 of 35) in the thoracotomy group versus 13% (5 of 40) in the video-assisted thoracoscopic surgery group (P = 0.040). Univariate logistic regression analysis indicated postoperative diaphragmatic dysfunction as a risk factor for postoperative pulmonary complications (odds ratio = 5.5 [95% CI, 1.9 to 16.3]; P = 0.002).

CONCLUSIONS

Point of care ultrasound can be used to evaluate postoperative diaphragmatic function. On the first postoperative day, diaphragmatic dysfunction was less common after video-assisted than after the thoracotomic surgery and is associated with postoperative pulmonary complications.

Expiratory flow limitation in intensive care: prevalence and risk factors

BACKGROUND

Expiratory flow limitation (EFL) is characterised by a markedly reduced expiratory flow insensitive to the expiratory driving pressure. The presence of EFL can influence the respiratory and cardiovascular function and damage the small airways; its occurrence has been demonstrated in different diseases, such as COPD, asthma, obesity, cardiac failure, ARDS, and cystic fibrosis. Our aim was to evaluate the prevalence of EFL in patients requiring mechanical ventilation for acute respiratory failure and to determine the main clinical characteristics, the risk factors and clinical outcome associated with the presence of EFL.

METHODS

Patients admitted to the intensive care unit (ICU) with an expected length of mechanical ventilation of 72 h were enrolled in this prospective, observational study. Patients were evaluated, within 24 h from ICU admission and for at least 72 h, in terms of respiratory mechanics, presence of EFL through the PEEP test, daily fluid balance and followed for outcome measurements.

RESULTS

Among the 121 patients enrolled, 37 (31%) exhibited EFL upon admission. Flow-limited patients had higher BMI, history of pulmonary or heart disease, worse respiratory dyspnoea score, higher intrinsic positive end-expiratory pressure, flow and additional resistance. Over the course of the initial 72 h of mechanical ventilation, additional 21 patients (17%) developed EFL. New onset EFL was associated with a more positive cumulative fluid balance at day 3 (103.3 ml/kg) compared to that of patients without EFL (65.8 ml/kg). Flow-limited patients had longer duration of mechanical ventilation, longer ICU length of stay and higher in-ICU mortality.

CONCLUSIONS

EFL is common among ICU patients and correlates with adverse outcomes. The major determinant for developing EFL in patients during the first 3 days of their ICU stay is a positive fluid balance. Further studies are needed to assess if a restrictive fluid therapy might be associated with a lower incidence of EFL.

Regional air trapping in acute exacerbation of obstructive lung diseases measured with electrical impedance tomography: a feasibility study

BACKGROUND

Since bronchial abnormalities often exhibit spatial non-uniformity which may be not correctly assessed by conventional global lung function measures, regional information may help to characterize the disease progress. We hypothesized that regional air trapping during mechanical ventilation could be characterized by regional end-expiratory flow (EEF) derived from electrical impedance tomography (EIT).

METHODS

Twenty-five patients suffering from chronic obstructive pulmonary disease (COPD grade 3 or 4) or severe asthma with acute exacerbation were examined prospectively. Patients were ventilated under assist-control mode. EIT measurements were conducted before and one hour after inhaled combined corticosteroid and long-acting β2 agonist, on two consecutive days. Regional EEF was calculated as derivative of relative impedance for every image pixel in the lung regions. The results were normalized to global flow values measured by the ventilator.

RESULTS

Regional and global EEF were highly correlated (P<0.00001) and regional effects of medication and disease progression were visible in the regional EEF maps. The sums of regional EEF in lung regions were 3.8 [2.0, 5.1] and 3.6 [1.9, 4.5] L/min in COPD patients before and after medication (median [lower, upper quartiles]; P=0.37). The corresponding values in asthma patients were 3.0 [2.5, 4.2] and 2.2 [1.7, 3.2] L/min (P<0.05). Histograms of regional EEF showed high spatial heterogeneity of EEF before medication. After one day of treatment, the histograms exhibited less heterogeneous and a decrease in EEF level.

CONCLUSIONS

Regional EEF characterizes air trapping and intrinsic PEEP, which could provide diagnostic information for monitoring the disease progress during treatment.

Dynamic hyperinflation and intrinsic positive end-expiratory pressure in ARDS patients

Background

In ARDS patients, changes in respiratory mechanical properties and ventilatory settings can cause incomplete lung deflation at end-expiration. Both can promote dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEP). The aim of this study was to investigate, in a large population of ARDS patients, the presence of intrinsic PEEP, possible associated factors (patients’ characteristics and ventilator settings), and the effects of two different external PEEP levels on the intrinsic PEEP.

Methods

We made a secondary analysis of published data. Patients were ventilated with a tidal volume of 6–8 mL/kg of predicted body weight, sedated, and paralyzed. After a recruitment maneuver, a PEEP trial was run at 5 and 15 cmH₂O, and partitioned mechanics measurements were collected after 20 min of stabilization. Lung computed tomography scans were taken at 5 and 45 cmH₂O. Patients were classified into two groups according to whether or not they had intrinsic PEEP at the end of an expiratory pause.

Results

We enrolled 217 sedated, paralyzed patients: 87 (40%) had intrinsic PEEP with a median of 1.1 [1.0–2.3] cmH₂O at 5 cmH₂O of PEEP. The intrinsic PEEP significantly decreased with higher PEEP (1.1 [1.0–2.3] vs 0.6 [0.0–1.0] cmH₂O; p < 0.001). The applied tidal volume was significantly lower (480 [430–540] vs 520 [445–600] mL at 5 cmH₂O of PEEP; 480 [430–540] vs 510 [430–590] mL at 15 cmH₂O) in patients with intrinsic PEEP, while the respiratory rate was significantly higher (18 [15–20] vs 15 [13–19] bpm at 5 cmH₂O of PEEP; 18 [15–20] vs 15 [13–19] bpm at 15 cmH₂O). At both PEEP levels, the total airway resistance and compliance of the respiratory system were not different in patients with and without intrinsic PEEP. The total lung gas volume and lung recruitability were also not different between patients with and without intrinsic PEEP (respectively 961 [701–1535] vs 973 [659–1433] mL and 15 [0–32] % vs 22 [0–36] %).

Conclusions

In sedated, paralyzed ARDS patients without a known obstructive disease, the amount of intrinsic PEEP during lung-protective ventilation is negligible and does not influence respiratory mechanical properties.

Electrical impedance tomography in perioperative medicine: careful respiratory monitoring for tailored interventions

BACKGROUND

Electrical impedance tomography (EIT) is a non-invasive radiation-free monitoring technique that provides images based on tissue electrical conductivity of the chest. Several investigations applied EIT in the context of perioperative medicine, which is not confined to the intraoperative period but begins with the preoperative assessment and extends to postoperative follow-up.

MAIN BODY

EIT could provide careful respiratory monitoring in the preoperative assessment to improve preparation for surgery, during anaesthesia to guide optimal ventilation strategies and to monitor the hemodynamic status and in the postoperative period for early detection of respiratory complications. Moreover, EIT could further enhance care of patients undergoing perioperative diagnostic procedures. This narrative review summarizes the latest evidence on the application of this technique to the surgical patient, focusing also on possible future perspectives.

CONCLUSIONS

EIT is a promising technique for the perioperative assessment of surgical patients, providing tailored adaptive respiratory and haemodynamic monitoring. Further studies are needed to address the current technological limitations, confirm the findings and evaluate which patients can benefit more from this technology.

Delayed Respiratory Distress in a Patient With Chronic Obstructive Pulmonary Disease After Abdominal Surgery

Patients with chronic obstructive pulmonary disease (COPD) are at increased risk for perioperative complications. The frequency of complications depends on the severity of COPD, the type of anesthesia used, the surgical site, and other comorbidities. Patients undergoing upper abdominal surgery have significant changes in lung volumes, likely secondary to changes in diaphragm function and abdominal pain, and these changes increase the risk for complications, including acute respiratory failure, atelectasis, pneumonia and unplanned reintubation. We discuss a patient with COPD who did well for the first 3 days following an open incisional hernia repair. However, on the fourth day he noted significant dyspnea and radiographic studies revealed atelectasis. Over the next week the patient remained symptomatic and dependent on noninvasive ventilation; he eventually had a rapid response to corticosteroids. This case indicates that atelectasis can develop late following a surgical procedure and that multiple factors potentially influence development of this complication.

Expiratory flow-limitation in mechanically ventilated patients: A risk for ventilator-induced lung injury?

Expiratory flow limitation (EFL), that is the inability of expiratory flow to increase in spite of an increase of the driving pressure, is a common and unrecognized occurrence during mechanical ventilation in a variety of intensive care unit conditions. Recent evidence suggests that the presence of EFL is associated with an increase in mortality, at least in acute respiratory distress syndrome (ARDS) patients, and in pulmonary complications in patients undergoing surgery. EFL is a major cause of intrinsic positive end-expiratory pressure (PEEPi), which in ARDS patients is heterogeneously distributed, with a consequent increase of ventilation/perfusion mismatch and reduction of arterial oxygenation. Airway collapse is frequently concomitant to the presence of EFL. When airways close and reopen during tidal ventilation, abnormally high stresses are generated that can damage the bronchiolar epithelium and uncouple small airways from the alveolar septa, possibly generating the small airways abnormalities detected at autopsy in ARDS. Finally, the high stresses and airway distortion generated downstream the choke points may contribute to parenchymal injury, but this possibility is still unproven. PEEP application can abolish EFL, decrease PEEPi heterogeneity, and limit recruitment/derecruitment. Whether increasing PEEP up to EFL disappearance is a useful criterion for PEEP titration can only be determined by future studies.

Positive end-expiratory pressure (PEEP) level to prevent expiratory flow limitation during cardiac surgery: study protocol for a randomized clinical trial (EFLcore study)

Background

Lung dysfunction commonly occurs after cardiopulmonary bypass (CPB). Randomized evidence suggests that the presence of expiratory flow limitation (EFL) in major abdominal surgery is associated with postoperative pulmonary complications. Appropriate lung recruitment and a correctly set positive end-expiratory pressure (PEEP) level may prevent EFL. According to the available data in the literature, an adequate ventilation strategy during cardiac surgery is not provided. The aim of this study is to assess whether a mechanical ventilation strategy based on optimal lung recruitment with a best PEEP before and after CPB and with a continuous positive airway pressure (CPAP) during CPB would reduce the incidence of respiratory complications after cardiac surgery.

Methods/design

This will be a single-center, single-blind, parallel-group, randomized controlled trial. Using a 2-by-2 factorial design, high-risk adult patients undergoing elective cardiac surgery will be randomly assigned to receive either a best PEEP (calculated with a PEEP test) or zero PEEP before and after CPB and CPAP (equal to the best PEEP) or no ventilation (patient disconnected from the circuit) during CPB.

The primary endpoint will be a composite endpoint of the incidence of EFL after the weaning from CPB and postoperative pulmonary complications.

Discussion

This study will help to establish a correct ventilatory strategy before, after, and during CPB. The main purpose is to establish if a ventilation based on a simple and feasible respiratory test may preserve lung function in cardiac surgery.

Trial registration

ClinicalTrials.gov, ID: NCT02633423. Registered on 6 December 2017.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-3046-0) contains supplementary material, which is available to authorized users.

Respiratory mechanics during general anaesthesia

Intraoperative mechanical ventilation is mandatory during many surgical procedures. Knowledge in this field has been widely derived from the experience in the treatment of patients with acute respiratory distress syndrome in the intensive care unit. However, also in surgical patients without lung injury, mechanical ventilation settings affect the clinical outcome, and in particular the occurrence of postoperative pulmonary complications (PPCs). A deep understanding of respiratory physiology is mandatory for the clinician, in order to tailor ventilation settings based on the specific characteristics of each patient. In this paper we will discuss the basis of lung physiology applied to the mechanical ventilation in the operating room. The role of compliance, tidal volume, positive end-expiratory pressure (PEEP), plateau pressure, driving pressure, stress index, mechanical power and other ventilator-derived parameters will be discussed. The above-mentioned physiological parameters are easy to measure and can guide the clinician to assess and titrate mechanical ventilation parameters, but the clinical impact of guiding mechanical ventilation based on these parameters has yet to be determined.

Expiratory Flow Limitation During Mechanical Ventilation

Expiratory flow limitation (EFL) is present when the flow cannot rise despite an increase in the expiratory driving pressure. The mechanisms of EFL are debated but are believed to be related to the collapsibility of small airways. In patients who are mechanically ventilated, EFL can exist during tidal ventilation, representing an extreme situation in which lung volume cannot decrease, regardless of the expiratory driving forces. It is a key factor for the generation of auto- or intrinsic positive end-expiratory pressure (PEEP) and requires specific management such as positioning and adjustment of external PEEP. EFL can be responsible for causing dyspnea and patient-ventilator dyssynchrony, and it is influenced by the fluid status of the patient. EFL frequently affects patients with COPD, obesity, and heart failure, as well as patients with ARDS, especially at low PEEP. EFL is, however, most often unrecognized in the clinical setting despite being associated with complications of mechanical ventilation and poor outcomes such as postoperative pulmonary complications, extubation failure, and possibly airway injury in ARDS. Therefore, prompt recognition might help the management of patients being mechanically ventilated who have EFL and could potentially influence outcome. EFL can be suspected by using different means, and this review summarizes the methods to specifically detect EFL during mechanical ventilation.

Lower airways inflammation in patients with ARDS measured using endotracheal aspirates: a pilot study

Introduction

Our knowledge of acute respiratory distress syndrome (ARDS) pathogenesis is incomplete. The goal of this pilot study is to investigate the feasibility of measuring lower airways inflammation in patients with ARDS using repeated endotracheal aspirates (ETAs).

Methods

ETAs were obtained within 24 hours by intensive care unit admission from 25 mechanically ventilated patients with ARDS and 10 of them underwent a second ETA within 96 hours after the first sampling. In each sample, cell viability was assessed using trypan blue exclusion method and the total and differential cell counts were measured using Neubauer-improved cell counting chamber and cytospins stained with Diff-Quik.

Results

The median cell viability was 89 (IQR 80–93)%, with a median total cell count of 305 (IQR 130–1270)×10³/mL and a median macrophage, neutrophil, lymphocyte and eosinophil count, respectively, of 19.8 (IQR 5.4–71.6)×10³/mL; 279 (IQR 109–1213)×10³/mL; 0 (IQR 0–0.188)×10³/mL; 0 (IQR 0–1.050)×10³/mL. Eosinophil count in the ETA correlated with the number of blood eosinophils (r=0.4840, p=0.0142). Cell viability and total and differential cell counts were neither significantly different in the second ETA compared with the first ETA nor were unaffected by the presence or absence of bacteria in the blood and/or ETA, or by the ARDS aetiology, apart from the macrophage count which was significantly increased in patients with ARDS associated with acute pancreatitis compared with those associated with pneumonia (p=0.0143).

Conclusions

ETA can be used to investigate the cellularity of the lower airways in patients with ARDS and it is an easy-to-perform and non-invasive procedure. Eosinophil counts in ETA and blood are significantly correlated. The number of macrophages in ETA may be affected by the aetiology of the ARDS.

The Epidemiology and Risk Factors for Postoperative Pneumonia

Postoperative pneumonia is a common complication of surgery, and is associated with marked morbidity and mortality. Despite advances in surgical and anesthetic technique, it persists as a frequent postoperative complication. Many studies have aimed to assess its burden, as well as associated risk factors. However, this complication varies among the different surgical specialties, and there is a paucity of reports that comprehensively evaluate this complication. Therefore, the purpose of this study was to review the epidemiology and risk factors of postoperative pneumonia in the setting of: 1) general surgery; 2) cardiothoracic surgery; 3) orthopedic and spine surgery; and 4) head and neck surgery.

Characteristics and Associated Factors of Postoperative Pulmonary Complications in Patients Undergoing Radical Cystectomy for Bladder Cancer: A National Surgical Quality Improvement Program Study

INTRODUCTION

The purpose of this study was to summarize the characteristics and identify associated factors of postoperative pulmonary complications (PPCs) in patients undergoing radical cystectomy (RC).

MATERIALS AND METHODS

The National Surgical Quality Improvement Project (NSQIP) database (2005-2014) was used to identify patients who underwent RC for bladder cancer. PPCs were defined as pneumonia, unplanned reintubation, and ventilator support > 48 hours within 30 days of RC. Incidence, timing, and outcomes of PPCs were described and analyzed. Multivariable logistic regression was used to evaluate associated factors of PPCs.

RESULTS

Among 3790 patients included, 213 (5.6%) had at least 1 PPC. Patients with PPCs had a significantly higher 30-day mortality (17.4% vs. 0.7%; P < .001) and longer hospital stay (13 vs. 8 days; P < .001). Logistic regression showed that age ≥ 75 years (odds ratio [OR], 2.07; P = .001), body mass index < 18.5 kg/m² (OR, 2.48; P = .017), body mass index ≥ 30 kg/m² (OR, 1.71; P = .009), dependent functional status (OR, 2.77; P = .006), current smoker (OR, 1.57; P = .011), chronic obstructive pulmonary disease (OR, 1.70; P = .018), insulin-treated diabetes (OR, 1.70; P = .042), and albumin < 3.5 g/dL (OR, 1.72; P = .015) were associated with increased risk of overall PPCs.

CONCLUSION

Approximately 5.6% of patients have at least one PPC within 30 days of RC. Several preoperative associated factors for PPCs were identified, which should be helpful for risk stratification, patient counseling, and perioperative care.