Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery

Maintaining moderate versus lower PEEP after cardiac surgery: a propensity-scored matched analysis

BACKGROUND

Setting positive end-expiratory pressure (PEEP) at around 5 cm H2O in the early postoperative period seems a common practice for most patients. It remains unclear if the routine application of higher levels of PEEP confers any meaningful clinical benefit for cardiac surgical patients. The aim of this study was to compare moderate versus conventional lower PEEP on patient-centered outcomes in the intensive care unit (ICU).

METHODS

This is a single-center retrospective study involving patients receiving cardiac surgery from June 2022 to May 2023. Propensity-score matching (PSM) was used to balance the baseline differences. Primary outcomes were the duration of mechanical ventilation and ICU length of stay. Secondary outcomes included PaO2/FiO2 ratio at 24 h and the need for prone positioning during ICU stay.

RESULTS

A total of 334 patients were included in the study, 102 (31%) of them received moderate PEEP (≥ 7 cm H2O) for the major time in the early postoperative period (12 h). After PSM, 79 pairs of patients were matched with balanced baseline data. The results showed that there was marginal difference in the distribution of mechanical ventilation duration (p = 0.05) and the Moderate PEEP group had a higher extubation rate at the day of T-piece trial (65 [82.3%] vs 52 [65.8%], p = 0.029). Applying moderate PEEP was also associated with better oxygenation. No differences were found regarding ICU length of stay and patients requiring prone positioning between groups.

CONCLUSION

In selective cardiac surgical patients, using moderate PEEP compared with conventional lower PEEP in the early postoperative period correlated to better oxygenation, which may have potential for earlier liberation of mechanical ventilation.

Capnodynamic monitoring of lung volume and pulmonary blood flow during alveolar recruitment: a prospective observational study in postoperative cardiac patients

Alveolar recruitment manoeuvres may mitigate ventilation and perfusion mismatch after cardiac surgery. Monitoring the efficacy of recruitment manoeuvres should provide concurrent information on pulmonary and cardiac changes. This study in postoperative cardiac patients applied capnodynamic monitoring of changes in end-expiratory lung volume and effective pulmonary blood flow. Alveolar recruitment was performed by incremental increases in positive end-expiratory pressure (PEEP) to a maximum of 15 cmH2O from a baseline of 5 cmH2O over 30 min. The change in systemic oxygen delivery index after the recruitment manoeuvre was used to identify responders (> 10% increase) with all other changes (≤ 10%) denoting non-responders. Mixed factor ANOVA using Bonferroni correction for multiple comparisons was used to denote significant changes (p < 0.05) reported as mean differences and 95% CI. Changes in end-expiratory lung volume and effective pulmonary blood flow were correlated using Pearson's regression. Twenty-seven (42%) of 64 patients were responders increasing oxygen delivery index by 172 (95% CI 61-2984) mL min-1 m-2 (p < 0.001). End-expiratory lung volume increased by 549 (95% CI 220-1116) mL (p = 0.042) in responders associated with an increase in effective pulmonary blood flow of 1140 (95% CI 435-2146) mL min-1 (p = 0.012) compared to non-responders. A positive correlation (r = 0.79, 95% CI 0.5-0.90, p < 0.001) between increased end-expiratory lung volume and effective pulmonary blood flow was only observed in responders. Changes in oxygen delivery index after lung recruitment were correlated to changes in end-expiratory lung volume (r = 0.39, 95% CI 0.16-0.59, p = 0.002) and effective pulmonary blood flow (r = 0.60, 95% CI 0.41-0.74, p < 0.001). Capnodynamic monitoring of end-expiratory lung volume and effective pulmonary blood flow early in postoperative cardiac patients identified a characteristic parallel increase in both lung volume and perfusion after the recruitment manoeuvre in patients with a significant increase in oxygen delivery.Trial registration This study was registered on ClinicalTrials.gov (NCT05082168, 18th of October 2021).

Effect of intraoperative alveolar recruitment maneuver on intraoperative oxygenation and postoperative pulmonary function tests in patients undergoing robotic-assisted hysterectomy: a single-blind randomized study

BACKGROUND

Robotic-Assisted Hysterectomies (RAH) require Trendelenburg positioning and pneumoperitoneum, which further accentuate alteration in respiratory mechanics induced by general anesthesia. The role of Recruitment Maneuver (RM) as a lung-protective strategy during intraoperative surgical settings has not been much studied. We planned this study to evaluate the effect of RM on perioperative oxygenation and postoperative spirometry using PaO₂/FiO₂ and FEV1/FVC, respectively in patients undergoing RAH.

METHODS

Sixty-six ASA I‒II female patients scheduled for elective RAH were randomized into group R (recruitment maneuver, n = 33) or group C (control, n = 33). Portable spirometry was done one day before surgery. Patients were induced with general anesthesia, and mechanical ventilation started with volume control mode, with Tidal Volume (TV) of 6-8 mL.kg^-1, Respiratory Rate (RR) of 12 min, inspiratory-expiratory ratio (I: E ratio) of 1:2, FiO₂ of 0.4, and Positive End-Expiratory Pressure (PEEP) of 5 cmH₂O. Patients in group R received recruitment maneuvers of 30 cmH₂O every 30 minutes following tracheal intubation. The primary objectives were comparison of oxygenation and ventilation between two groups intraoperatively and portable spirometry postoperatively. Postoperative pulmonary complications, like desaturation, pulmonary edema, pneumonia, were monitored.

RESULTS

Patients who received RM had significantly higher PaO₂ (mmHg) (203.2+-24.3 vs. 167.8+-27.3, p < 0.001) at T2 (30 min after the pneumoperitoneum). However, there was no significant difference in portable spirometry between the groups in the postoperative period (FVC, 1.40 ± 0.5 L vs. 1.32 ± 0.46 L, p = 0.55).

CONCLUSION

This study concluded that intraoperative recruitment did not prevent deterioration of postoperative spirometry values; however, it led to improved oxygenation intraoperatively.

Higher PEEP versus lower PEEP strategies for patients in ICU without acute respiratory distress syndrome: A systematic review and meta-analysis

PURPOSE

To evaluate the effects of high and low levels of PEEP on ICU patients without ARDS.

METHODS

We searched public databases (including PubMed, EMBASE, Cochrane Library and Clinicaltrial.gov). The Cochrane Risk of Bias Assessment tool was used to evaluate the quality of the included studies.

RESULTS

We included 2307 patients from 24 trials. Although no significant difference was found between high and low PEEP applications in in-hospital mortality (risk ratio[RR] 0.98, 95% confidence interval[CI] [0.81, 1.19], P = 0.87), high PEEP indeed decreased the incidence of ARDS, hypoxemia, and increased the level of PaO₂/FIO₂. In addition, although the overall results did not reveal any advantages of high PEEP in terms of secondary outcomes regarding 28-day mortality, the duration of ventilation, atelectasis, pulmonary barotrauma, hypotension, and so forth, the subgroup analysis concerning the level of low PEEP (ZEEP or not) and patient type (postoperative or medical ones) yielded different results. The TSA results suggested that more RCTs are needed.

CONCLUSIONS

Although ventilation with high PEEP in ICU patients without ARDS may not reduce in-hospital mortality, the decreased incidences of ARDS and hypoxemia and the improvement in PaO₂/FIO₂ were found in the high PEEP arm.

Optimal Positive End Expiratory Pressure Levels in Ventilated Patients Without Acute Respiratory Distress Syndrome: A Bayesian Network Meta-Analysis and Systematic Review of Randomized Controlled Trials

Background: To find the optimal positive end expiratory pressure (PEEP) in mechanical ventilated patients without Acute Respiratory Distress Syndrome (ARDS), we conducted a Bayesian network meta-analysis and systematic review of randomized controlled trials (RCTs) comparing different level of PEEP based on a novel classification of PEEP level: ZEEP group (PEEP = 0 cm H2O); lower PEEP group (PEEP = 1–6 cm H2O); intermediate PEEP group (PEEP = 7–10 cm H2O); higher PEEP group (PEEP > 10 cm H2O).

Result: Twenty eight eligible studies with 2,712 patients were included. There were no significant differences in the duration of mechanical ventilation between higher and intermediate PEEP (MD: 0.020, 95% CI: −0.14, 0.28), higher and lower PEEP (MD: −0.010, 95% CI: −0.23, 0.22), higher PEEP and ZEEP (MD: 0.010, 95% CI: −0.40, 0.22), intermediate and lower PEEP (MD: −0.040, 95% CI: −0.18, 0.040), intermediate PEEP and ZEEP (MD: −0.010, 95% CI: −0.42, 0.10), lower PEEP and ZEEP (MD: 0.020, 95% CI: −0.32, 0.13), respectively. Higher PEEP was associated with significantly higher PaO2/FiO2 ratio(PFR) when compared to ZEEP (MD: 73.24, 95% CI: 11.03, 130.7), and higher incidence of pneumothorax when compared to intermediate PEEP, lower PEEP and ZEEP (OR: 2.91e + 12, 95% CI: 40.3, 1.76e + 39; OR: 1.85e + 12, 95% CI: 29.2, 1.18e + 39; and OR: 1.44e + 12, 95% CI: 16.9, 8.70e + 38, respectively). There was no association between PEEP levels and other secondary outcomes.

Conclusion: We identified higher PEEP was associated with significantly higher PFR and higher incidence of pneumothorax. Nonetheless, in terms of other outcomes, no significant differences were detected among four levels of PEEP.

Systematic Review Registration: The study had registered on an international prospective register of systematic reviews, PROSPERO, on 09 April 2021, identifier: [CRD42021241745].

Higher versus lower positive end-expiratory pressure in patients without acute respiratory distress syndrome: a meta-analysis of randomized controlled trials

Background

We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) to assess the association of higher positive end-expiratory pressure (PEEP), as opposed to lower PEEP, with hospital mortality in adult intensive care unit (ICU) patients undergoing invasive mechanical ventilation for reasons other than acute respiratory distress syndrome (ARDS).

Methods

We performed an electronic search of MEDLINE, EMBASE, Scopus, Cochrane Central Register of Controlled Trials, CINAHL, and Web of Science from inception until June 16, 2021 with no language restrictions. In addition, a research-in-progress database and grey literature were searched.

Results

We identified 22 RCTs (2225 patients) comparing higher PEEP (1007 patients) with lower PEEP (991 patients). No statistically significant association between higher PEEP and hospital mortality was observed (risk ratio 1.02, 95% confidence interval 0.89–1.16; I² = 0%, p = 0.62; low certainty of evidence). Among secondary outcomes, higher PEEP was associated with better oxygenation, higher respiratory system compliance, and lower risk of hypoxemia and ARDS occurrence. Furthermore, barotrauma, hypotension, duration of ventilation, lengths of stay, and ICU mortality were similar between the two groups.

Conclusions

In our meta-analysis of RCTs, higher PEEP, compared with lower PEEP, was not associated with mortality in patients without ARDS receiving invasive mechanical ventilation. Further large high-quality RCTs are required to confirm these findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03669-4.

Effect of different levels of PEEP on mortality in ICU patients without acute respiratory distress syndrome: systematic review and meta-analysis with trial sequential analysis

OBJECTIVE

To determine whether higher positive end- expiratory pressure (PEEP) could provide a survival advantage for patients without acute respiratory distress syndrome (ARDS) compared with lower PEEP.

METHODS

Eligible studies were identified through searches of Embase, Cochrane Library, Web of Science, Medline, and Wanfang database from inception up to 1 June 2021. Trial sequential analysis (TSA) was used in this meta-analysis.

DATA SYNTHESIS

Twenty-seven randomized controlled trials (RCTs) were identified for further evaluation. Higher and lower PEEP arms included 1330 patients and 1650 patients, respectively. A mean level of 9.6±3.4 cmH₂O was applied in the higher PEEP groups and 1.9±2.6 cmH₂O was used in the lower PEEP groups. Higher PEEP, compared with lower PEEP, was not associated with reduction of all-cause mortality (RR 1.03; 95% CI 0.91-1.18; P =0.627), and 28-day mortality (RR 1.07 ; 95% CI 0.92-1.24; P =0.365). In terms of risk of ARDS (RR 0.43; 95% CI 0.24-0.78; P =0.005), duration of intensive care unit (MD -1.04; 95%CI-1.36 to -0.73; P < 0.00001), and oxygenation (MD 40.30; 95%CI 0.94 to 79.65; P = 0.045), higher PEEP was superior to lower PEEP. Besides, the pooled analysis showed no significant differences between groups both in the duration of mechanical ventilation (MD 0.00; 95%CI-0.13 to 0.13; P = 0.996) and hospital stay (MD -0.66; 95%CI-1.94 to 0.61; P = 0.309). More importantly, lower PEEP did not increase the risk of pneumonia, atelectasis, barotrauma, hypoxemia, or hypotension among patients compared with higher PEEP. The TSA analysis showed that the results of all-cause mortality and 28-day mortality might be false-negative results.

CONCLUSIONS

Our results suggest that a lower PEEP ventilation strategy was non-inferior to a higher PEEP ventilation strategy in ICU patients without ARDS, with no increased risk of all-cause mortality and 28-day mortality. Further high-quality RCTs should be performed to confirm these findings.

Temporal Changes in Ventilator Settings in Patients With Uninjured Lungs: A Systematic Review

In patients with uninjured lungs, increasing evidence indicates that tidal volume (VT) reduction improves outcomes in the intensive care unit (ICU) and in the operating room (OR). However, the degree to which this evidence has translated to clinical changes in ventilator settings for patients with uninjured lungs is unknown. To clarify whether ventilator settings have changed, we searched MEDLINE, Cochrane Central Register of Controlled Trials, and Web of Science for publications on invasive ventilation in ICUs or ORs, excluding those on patients <18 years of age or those with >25% of patients with acute respiratory distress syndrome (ARDS). Our primary end point was temporal change in VT over time. Secondary end points were changes in maximum airway pressure, mean airway pressure, positive end-expiratory pressure, inspiratory oxygen fraction, development of ARDS (ICU studies only), and postoperative pulmonary complications (OR studies only) determined using correlation analysis and linear regression. We identified 96 ICU and 96 OR studies comprising 130,316 patients from 1975 to 2014 and observed that in the ICU, VT size decreased annually by 0.16 mL/kg (-0.19 to -0.12 mL/kg) (P < .001), while positive end-expiratory pressure increased by an average of 0.1 mbar/y (0.02-0.17 mbar/y) (P = .017). In the OR, VT size decreased by 0.09 mL/kg per year (-0.14 to -0.04 mL/kg per year) (P < .001). The change in VTs leveled off in 1995. Other intraoperative ventilator settings did not change in the study period. Incidences of ARDS (ICU studies) and postoperative pulmonary complications (OR studies) also did not change over time. We found that, during a 39-year period, from 1975 to 2014, VTs in clinical studies on mechanical ventilation have decreased significantly in the ICU and in the OR.

Impact of Lung Expansion Therapy Using Positive End-Expiratory Pressure in Mechanically Ventilated Patients Submitted to Coronary Artery Bypass Grafting

OBJECTIVE

To evaluate the impact of different levels of positive end-expiratory pressure (PEEP) on gas exchange in patients undergoing coronary artery bypass grafting (CABG).

METHODS

A randomized clinical trial was conducted with patients undergoing CABG surgery. Patients were randomized into three groups: Group 10, PEEP of 10 cmH2O; Group 12, PEEP of 12 cmH2O; and Group 15, PEEP of 15 cmH2O. After the randomization, all patients underwent gas analysis at three moments: (1) before lung expansion therapy (LET); (2) 30 minutes after LET; and (3) one hour after extubation.

RESULTS

Sixty-six patients were studied, of which 61.7% were men, with mean age of 64 ± 8.9 years. Patients allocated to Group 15 showed a significant improvement in gas exchange comparing pre- and post-expansion values (239±21 vs. 301±19, P<0,001) and the increase was maintained after extubation (278±26). Despite the use of high levels of PEEP, no significant hemodynamic change was evidenced.

CONCLUSION

It is concluded that high levels of PEEP (15 cmH2O) are beneficial for the improvement of gas exchange in patients undergoing CABG.

Optimising mechanical ventilation through model-based methods and automation

Mechanical ventilation (MV) is a core life-support therapy for patients suffering from respiratory failure or acute respiratory distress syndrome (ARDS). Respiratory failure is a secondary outcome of a range of injuries and diseases, and results in almost half of all intensive care unit (ICU) patients receiving some form of MV. Funding the increasing demand for ICU is a major issue and MV, in particular, can double the cost per day due to significant patient variability, over-sedation, and the large amount of clinician time required for patient management. Reducing cost in this area requires both a decrease in the average duration of MV by improving care, and a reduction in clinical workload. Both could be achieved by safely automating all or part of MV care via model-based dynamic systems modelling and control methods are ideally suited to address these problems. This paper presents common lung models, and provides a vision for a more automated future and explores predictive capacity of some current models. This vision includes the use of model-based methods to gain real-time insight to patient condition, improve safety through the forward prediction of outcomes to changes in MV, and develop virtual patients for in-silico design and testing of clinical protocols. Finally, the use of dynamic systems models and system identification to guide therapy for improved personalised control of oxygenation and MV therapy in the ICU will be considered. Such methods are a major part of the future of medicine, which includes greater personalisation and predictive capacity to both optimise care and reduce costs. This review thus presents the state of the art in how dynamic systems and control methods can be applied to transform this core area of ICU medicine.

Post–suction Recruitment Manoeuvre Restores Lung Function in Healthy, Anaesthetized Pigs

Endotracheal suction can cause partial lung collapse and hypoxia and alter lung mechanics. We investigated the effects of adding a recruitment manoeuvre directly after endotracheal suction to restore lung volume in volume-controlled ventilation and pressure-controlled ventilation modes. Five anaesthetized pigs were investigated. The effects of endotracheal suction with or without a recruitment manoeuvre were compared in random order. In volume-controlled ventilation, compliance decreased after suction from 33±5 to 26±6 ml.cmH2O–1 (P<0.05), and 30 minutes later it remained decreased at 25±6 ml.cmH2O–1. Venous admixture increased after suction from 5±2 to 8±4% (P<0.05), but had recovered at 30 minutes. In pressure-controlled ventilation, compliance decreased after suction from 34±3 to 25±7 ml.cmH2O–1 (P<0.05), and 30 minutes later it remained decreased at 25±7 ml.cmH2O–1. Venous admixture increased after suction from 5±2 to 13±7% (P<0.05), and had not recovered after 30 minutes, 10±4%. When a recruitment manoeuvre was applied directly after suction, no negative side-effects were registered in volume-controlled ventilation or pressure-controlled ventilation. We conclude that the impairment of lung mechanics and gas exchange induced by endotracheal suction can be prevented by a simple post-suction recruitment manoeuvre. Further studies are needed to identify a suitable suction recruitment manoeuvre in patients with diseased lungs.

RELAx - REstricted versus Liberal positive end-expiratory pressure in patients without ARDS: protocol for a randomized controlled trial

BACKGROUND

Evidence for benefit of high positive end-expiratory pressure (PEEP) is largely lacking for invasively ventilated, critically ill patients with uninjured lungs. We hypothesize that ventilation with low PEEP is noninferior to ventilation with high PEEP with regard to the number of ventilator-free days and being alive at day 28 in this population.  METHODS/DESIGN: The "REstricted versus Liberal positive end-expiratory pressure in patients without ARDS" trial (RELAx) is a national, multicenter, randomized controlled, noninferiority trial in adult intensive care unit (ICU) patients with uninjured lungs who are expected not to be extubated within 24 h. RELAx will run in 13 ICUs in the Netherlands to enroll 980 patients under invasive ventilation. In all patients, low tidal volumes are used. Patients assigned to ventilation with low PEEP will receive the lowest possible PEEP between 0 and 5 cm H2O, while patients assigned to ventilation with high PEEP will receive PEEP of 8 cm H2O. The primary endpoint is the number of ventilator-free days and being alive at day 28, a composite endpoint for liberation from the ventilator and mortality until day 28, with a noninferiority margin for a difference between groups of 0.5 days. Secondary endpoints are length of stay (LOS), mortality, and occurrence of pulmonary complications, including severe hypoxemia, major atelectasis, need for rescue therapies, pneumonia, pneumothorax, and development of acute respiratory distress syndrome (ARDS). Hemodynamic support and sedation needs will be collected and compared.

DISCUSSION

RELAx will be the first sufficiently sized randomized controlled trial in invasively ventilated, critically ill patients with uninjured lungs using a clinically relevant and objective endpoint to determine whether invasive, low-tidal-volume ventilation with low PEEP is noninferior to ventilation with high PEEP.

TRIAL REGISTRATION

ClinicalTrials.gov , ID: NCT03167580 . Registered on 23 May 2017.

Early Open-Lung Ventilation Improves Clinical Outcomes in Patients with Left Cardiac Dysfunction Undergoing Off-Pump Coronary Artery Bypass: a Randomized Controlled Trial

Objective

To compare pulmonary function, functional capacity and clinical outcomes amongst three groups of patients with left ventricular dysfunction following off-pump coronary artery bypass, namely: 1) conventional mechanical ventilation (CMV); 2) late open lung strategy (L-OLS); and 3) early open lung strategy (E-OLS).

Methods

Sixty-one patients were randomized into 3 groups: 1) CMV (n=21); 2) L-OLS (n=20) initiated after intensive care unit arrival; and 3) E-OLS (n=20) initiated after intubation. Spirometry was performed at bedside on preoperative and postoperative days (PODs) 1, 3, and 5. Partial pressure of arterial oxygen (PaO₂) and pulmonary shunt fraction were evaluated preoperatively and on POD1. The 6-minute walk test was applied on the day before the operation and on POD5.

Results

Both the open lung groups demonstrated higher forced vital capacity and forced expiratory volume in 1 second on PODs 1, 3 and 5 when compared to the CMV group (P<0.05). The 6-minute walk test distance was more preserved, shunt fraction was lower, and PaO₂ was higher in both open-lung groups (P<0.05). Open-lung groups had shorter intubation time and hospital stay and also fewer respiratory events (P<0.05). Key measures were significantly more favorable in the E-OLS group compared to the L-OLS group.

Conclusion

Both OLSs (L-OLS and E-OLS) were able to promote higher preservation of pulmonary function, greater recovery of functional capacity and better clinical outcomes following off-pump coronary artery bypass when compared to conventional mechanical ventilation. However, in this group of patients with reduced left ventricular function, initiation of the OLS intra-operatively was found to be more beneficial and optimal when compared to OLS initiation after intensive care unit arrival.

Monitoring of breath VOCs and electrical impedance tomography under pulmonary recruitment in mechanically ventilated patients

Analysis of exhaled VOCs can provide information on physiology, metabolic processes, oxidative stress and lung diseases. In critically ill patients, VOC analysis may be used to gain complimentary information beyond global clinical parameters. This seems especially attractive in mechanically ventilated patients frequently suffering from impairment of gas exchange. This study was intended to assess (a) the effects of recruitment maneuvers onto VOC profiles, (b) the correlations between electrical impedance tomography (EIT) data and VOC profiles and (c) the effects of recruitment onto distribution of ventilation. Eleven mechanically ventilated patients were investigated during lung recruitment after cardiac surgery. Continuous breath gas analysis by means of PTR-ToF-MS, EIT and blood gas analyses were performed simultaneously. More than 300 mass traces could be detected and monitored continuously by means of PTR-ToF-MS in every patient. Exhaled VOC concentrations varied with recruitment induced changes in minute ventilation and cardiac output. Ammonia exhalation depended on blood pH. The improvement in dorsal lung ventilation during recruitment ranged from 9% to 110%. Correlations between exhaled concentrations of acetone, isoprene, benzene sevoflurane and improvement in regional ventilation during recruitment were observed. Extent and quality of these correlations depended on physico-chemical properties of the VOCs. Combination of continuous real-time breath analysis and EIT revealed correlations between exhaled VOC concentrations and distribution of ventilation. This setup enabled immediate recognition of physiological and therapeutic effects in ICU patients. In a perspective, VOC analysis could be used for non-invasive control and optimization of ventilation strategies.

Low-positive pressure ventilation improves non-hypoxaemic apnoea tolerance during ear, nose and throat pan-endoscopy: A randomised controlled trial

BACKGROUND

It has been suggested that oxygenation using pressure support ventilation (PSV) before general anaesthesia can reduce the duration of non-hypoxaemic apnoea.

OBJECTIVE

The objective was to determine whether or not pre-oxygenation with PSV increases the duration of non-hypoxaemic apnoea in non-obese patients during pan-endoscopy.

DESIGN

A randomised, controlled trial.

SETTING

Amiens University Hospital, France.

PATIENTS

Fifty patients scheduled for ENT pan-endoscopy with a BMI lower than 35  kg  m(-2).

INTERVENTION

Patients scheduled for pan-endoscopy were enrolled to receive either 100% oxygen at neutral pressure (the control group) or 100% oxygen with positive-pressure ventilation (a positive inspiratory pressure of 4  cmH2O and a positive end-expiratory pressure of 4  cmH2O; the PSV group) during spontaneous ventilation with a face mask. The goal of pre-oxygenation was to obtain an end-tidal oxygen concentration of more than 90% prior to induction of anaesthesia.

MAIN OUTCOME MEASURES

The primary efficacy criterion was the duration of non-hypoxaemic apnoea (i.e. before the peripheral capillary oxygen saturation fell to 90%). Secondary outcomes were duration of pre-oxygenation, pre-oxygenation failure and tolerance.

RESULTS

The mean (interquartile range) duration of non-hypoxaemic apnoea was longer in the PSV group [598 (447 to 717) s] than in the control group [310 (217 to 451) s] (P < 0.001). Oxygenation time was shorter in the PSV group [190 (159 to 225) s] than in the control group [245 (151 to 435) s] (P = 0.037). Pre-oxygenation was unsuccessful (i.e. end-tidal oxygen concentration was < 90%) in 20% of the patients in the control group but none in the PSV group. The intergroup difference in the duration of pan-endoscopy was not significant. Tolerance was good or very good in all patients.

CONCLUSION

Our results show that pre-oxygenation with PSV is associated with a longer duration of non-hypoxaemic apnoea and a lower frequency of manual reventilation during ENT pan-endoscopy. CLINICALTRIALS.

GOV REGISTRATION NUMBER

NCT02167334.

Associations between positive end-expiratory pressure and outcome of patients without ARDS at onset of ventilation: a systematic review and meta-analysis of randomized controlled trials

Background

The aim of this investigation was to compare ventilation at different levels of positive end-expiratory pressure (PEEP) with regard to clinical important outcomes of intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) at onset of ventilation.

Methods

Meta-analysis of randomized controlled trials (RCTs) comparing a lower level of PEEP with a higher level of PEEP was performed. The primary outcome was in-hospital mortality.

Results

Twenty-one RCTs (1393 patients) were eligible. PEEP ranged from 0 to 10 cmH₂O and from 5 to 30 cmH₂O in the lower PEEP and the higher PEEP arms of included RCTs, respectively. In-hospital mortality was not different between the two PEEP arms in seven RCTs (risk ratio [RR] 0.87; 95% confidence interval [CI] 0.62–1.21; I² = 26%, low quality of evidence [QoE]), as was duration of mechanical ventilation in three RCTs (standardized mean difference [SMD] 0.68; 95% CI −0.24 to 1.61; I² = 82%, very low QoE). PaO₂/FiO₂ was higher in the higher PEEP arms in five RCTs (SMD 0.72; 95% CI 0.10–1.35; I² = 86%, very low QoE). Development of ARDS and the occurrence of hypoxemia (2 RCTs) were lower in the higher PEEP arms in four RCTs and two RCTs, respectively (RR 0.43; 95% CI 0.21–0.91; I² = 56%, low QoE; RR 0.42; 95%–CI 0.19–0.92; I² = 19%, low QoE). There was no association between the level of PEEP and any hemodynamic parameter (four RCTs).

Conclusion

Ventilation with higher levels of PEEP in ICU patients without ARDS at onset of ventilation was not associated with lower in-hospital mortality or shorter duration of ventilation, but with a lower incidence of ARDS and hypoxemia, as well as higher PaO₂/FiO₂. These findings should be interpreted with caution, as heterogeneity was moderate to high, the QoE was low to very low, and the available studies prevented us from addressing the effects of moderate levels of PEEP.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0208-7) contains supplementary material, which is available to authorized users.

Preoxygenation and intraoperative ventilation strategies in obese patients: a comprehensive review

PURPOSE OF REVIEW

Obesity along with its pathophysiological changes increases risk of intraoperative and perioperative respiratory complications. The aim of this review is to highlight recent updates in preoxygenation techniques and intraoperative ventilation strategies in obese patients to optimize gas exchange and pulmonary mechanics and reduce pulmonary complications.

RECENT FINDINGS

There is no gold standard in preoxygenation or intraoperative ventilatory management protocol for obese patients. Preoxygenation in head up or sitting position has been shown to be superior to supine position. Apneic oxygenation and use of continuous positive airway pressure increases safe apnea duration. Recent evidence encourages the intraoperative use of low tidal volume to improve oxygenation and lung compliance without adverse effects. Contrary to nonobese patients, some studies have reported the beneficial effect of recruitment maneuvers and positive end-expiratory pressure in obese patients. No difference has been observed between volume controlled and pressure controlled ventilation.

SUMMARY

The ideal ventilatory plan for obese patients is indeterminate. A multimodal preoxygenation and intraoperative ventilation plan is helpful in obese patients to reduce perioperative respiratory complications. More studies are needed to identify the role of low tidal volume, positive end-expiratory pressure, and recruitment maneuvers in obese patients undergoing general anesthesia.

Pulmonary Complications After Cardiac Surgery

Over the past two decades there has been a steady evolution in the practice of adult cardiac surgery with the introduction of “off-pump” surgery. However, respiratory complications remain a leading cause of postcardiac surgical morbidity and can prolong hospital stays and increase costs. The high incidence of pulmonary complications is in part due to the disruption of normal ventilatory function that is inherent to surgery in the thoracic region. Furthermore, patients undergoing such surgery often have underlying illnesses such as intrinsic lung disease (e.g., chronic obstructive pulmonary disease) and pulmonary dysfunction secondary to cardiac disease (e.g., congestive heart failure) that increase their susceptibility to postoperative respiratory problems. Given that many patients undergoing cardiac surgery are thus susceptiple to pulmonary complications, it is remarkable that more patients do not suffer from them during and after cardiac surgery. This is to a large degree because of advances in anesthetic, surgical and critical care that, for example, have reduced the physiological insults of surgery (e.g., better myocardial preservation techniques) and streamlined care in the immediate postoperative period (e.g., early extubation). Moreover, the development of minimally invasive surgery and nonbypass techniques are further evidence of the attempts at reducing the homeostatic disruptions of cardiac surgery. This review examines the available information on the incidences, consequences, and treatments of postcardiac surgery respiratory complications.

Mechanical ventilation strategies for intensive care unit patients without acute lung injury or acute respiratory distress syndrome: a systematic review and network meta-analysis

Background

It has been shown that the application of a lung-protective mechanical ventilation strategy can improve the prognosis of patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). However, the optimal mechanical ventilation strategy for intensive care unit (ICU) patients without ALI or ARDS is uncertain. Therefore, we performed a network meta-analysis to identify the optimal mechanical ventilation strategy for these patients.

Methods

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, EMBASE, MEDLINE, CINAHL, and Web of Science for studies published up to July 2015 in which pulmonary compliance or the partial pressure of arterial oxygen/fraction of inspired oxygen (PaO₂/FIO₂) ratio was assessed in ICU patients without ALI or ARDS, who received mechanical ventilation via different strategies. The data for study characteristics, methods, and outcomes were extracted. We assessed the studies for eligibility, extracted the data, pooled the data, and used a Bayesian fixed-effects model to combine direct comparisons with indirect evidence.

Results

Seventeen randomized controlled trials including a total of 575 patients who received one of six ventilation strategies were included for network meta-analysis. Among ICU patients without ALI or ARDS, strategy C (lower tidal volume (VT) + higher positive end-expiratory pressure (PEEP)) resulted in the highest PaO₂/FIO₂ ratio; strategy B (higher VT + lower PEEP) was associated with the highest pulmonary compliance; strategy A (lower VT + lower PEEP) was associated with a shorter length of ICU stay; and strategy D (lower VT + zero end-expiratory pressure (ZEEP)) was associated with the lowest PaO₂/FiO₂ ratio and pulmonary compliance.

Conclusions

For ICU patients without ALI or ARDS, strategy C (lower VT + higher PEEP) was associated with the highest PaO₂/FiO₂ ratio. Strategy B (higher VT + lower PEEP) was superior to the other strategies in improving pulmonary compliance. Strategy A (lower VT + lower PEEP) was associated with a shorter length of ICU stay, whereas strategy D (lower VT + ZEEP) was associated with the lowest PaO₂/FiO₂ ratio and pulmonary compliance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1396-0) contains supplementary material, which is available to authorized users.

Comparison of intraoperative volume and pressure-controlled ventilation modes in patients who undergo open heart surgery

Respiratory problems occur more frequently in patients who undergo open heart surgery. Intraoperative and postoperative ventilation strategies can prevent these complications and reduce mortality. We hypothesized that PCV would have better effects on gas exchange, lung mechanics and hemodynamics compared to VCV in CABG surgery. Our primary outcome was to compare the PaO₂/FiO₂ ratio. Patients were randomized into two groups, (VCV, PCV) consisting of 30 individuals each. Two patients were excluded from the study. I/E ratio was adjusted to 1:2 and, RR:10/min fresh air gas flow was set at 3L/min in all patients. In the VCV group TV was set at 8 mL/kg of the predicted body weight. In the PCV group, peak inspiratory pressure was adjusted to the same tidal volume with the VCV group. PaO2/FiO2 was found to be higher with PCV at the end of the surgery. Time to extubation and ICU length of stay was shorter with PCV. Ppeak was similar in both groups. Pplateau was lower and Pmean was higher at the and of the surgery with PCV compared to VCV. The hemodynamic effects of both ventilation modes were found to be similar. PVC may be preferable to VCV in patients who undergo open heart surgery. However, it would be convenient if our findings are supported by similar studies.

Effect of Ultrafiltration on Pulmonary Function and Interleukins in Patients Undergoing Cardiopulmonary Bypass

OBJECTIVE

To evaluate the effect of ultrafiltration on interleukins, TNF-α levels, and pulmonary function in patients undergoing coronary artery bypass grafting (CABG).

DESIGN

Prospective, randomized, controlled trial.

SETTING

University hospital.

PARTICIPANTS

Forty patients undergoing CABG were randomized into a group assigned to receive ultrafiltration (UF) during cardiopulmonary bypass (CPB) or into another group (control) that underwent the same procedure but without ultrafiltration.

METHODS

Interleukins and TNF-α levels, pulmonary gas exchange, and ventilatory mechanics were measured in the preoperative, intraoperative, and postoperative periods. Interleukins and TNF-α also were analyzed in the perfusate of the test group.

MEASUREMENTS AND MAIN RESULTS

There were increases in IL-6 and IL-8 at 30 minutes after CPB and 6, 12, 24, and 36 hours after surgery, along with an increase in TNF-α at 30 minutes after CPB and 24, 36, and 48 hours after surgery in both groups. IL-1 increased at 30 minutes after CPB and 12 hours after surgery, while IL-6 increased 24 and 36 hours after surgery in the UF group. The analysis of the ultrafiltrate showed the presence of TNF-α and traces of IL-1β, IL-6, and IL-8. There were alterations in the oxygen index, alveolar-arterial oxygen difference, deadspace, pulmonary static compliance and airway resistance after anesthesia and sternotomy, as well as in airway resistance at 6 hours after surgery in both groups, with no difference between them.

CONCLUSIONS

Ultrafiltration increased the serum level of IL-1 and IL-6, while it did not interfere with gas exchange and pulmonary mechanics in CABG.

Cardiorespiratory effects of recruitment maneuvers and positive end expiratory pressure in an experimental context of acute lung injury and pulmonary hypertension

Background

Recruitment maneuvers (RM) and positive end expiratory pressure (PEEP) are the cornerstone of the open lung strategy during ventilation, particularly during acute lung injury (ALI). However, these interventions may impact the pulmonary circulation and induce hemodynamic and respiratory effects, which in turn may be critical in case of pulmonary hypertension (PHT). We aimed to establish how ALI and PHT influence the cardiorespiratory effects of RM and PEEP.

Methods

Rabbits control or with monocrotaline-induced PHT were used. Forced oscillatory airway and tissue mechanics, effective lung volume (ELV), systemic and right ventricular hemodynamics and blood gas were assessed before and after RM, during baseline and following surfactant depletion by whole lung lavage.

Results

RM was more efficient in improving respiratory elastance and ELV in the surfactant-depleted lungs when PHT was concomitantly present. Moreover, the adverse changes in respiratory mechanics and ELV following ALI were lessened in the animals suffering from PHT.

Conclusions

During ventilation with open lung strategy, the role of PHT in conferring protection from the adverse respiratory consequences of ALI was evidenced. This finding advocates the safety of RM and PEEP in improving elastance and advancing lung reopening in the simultaneous presence of PHT and ALI.

Postoperative pulmonary dysfunction and mechanical ventilation in cardiac surgery

Postoperative pulmonary dysfunction (PPD) is a frequent and significant complication after cardiac surgery. It contributes to morbidity and mortality and increases hospitalization stay and its associated costs. Its pathogenesis is not clear but it seems to be related to the development of a systemic inflammatory response with a subsequent pulmonary inflammation. Many factors have been described to contribute to this inflammatory response, including surgical procedure with sternotomy incision, effects of general anesthesia, topical cooling, and extracorporeal circulation (ECC) and mechanical ventilation (VM). Protective ventilation strategies can reduce the incidence of atelectasis (which still remains one of the principal causes of PDD) and pulmonary infections in surgical patients. In this way, the open lung approach (OLA), a protective ventilation strategy, has demonstrated attenuating the inflammatory response and improving gas exchange parameters and postoperative pulmonary functions with a better residual functional capacity (FRC) when compared with a conventional ventilatory strategy. Additionally, maintaining low frequency ventilation during ECC was shown to decrease the incidence of PDD after cardiac surgery, preserving lung function.

Pressure safety range of barotrauma with lung recruitment manoeuvres: a randomised experimental study in a healthy animal model

CONTEXT

Recruitment manoeuvres aim at reversing atelectasis during general anaesthesia but are associated with potential risks such as barotrauma.

OBJECTIVE

To explore the range of pressures that can be used safely to fully recruit the lung without causing barotrauma in an ex-vivo healthy lung rabbit model.

DESIGN

Prospective, randomised, experimental study.

SETTING

Experimental Unit, La Paz University Hospital, Madrid, Spain.

ANIMALS

Fourteen healthy young New Zealand rabbits of 12 weeks of age.

INTERVENTIONS

Animals were euthanised, the thorax and both pleural spaces were opened and the animals were allocated randomly into one of two groups submitted to two distinct recruitment manoeuvre strategies: PEEP-20 group, in which positive end-expiratory pressure (PEEP) was increased in 5-cmH2O steps from 0 to 20 cmH2O and PEEP-50 group, in which PEEP was increased in 5-cmH2O steps from 0 to 50 cmH2O. In both groups, a driving pressure of 15 cmH2O was maintained until maximal PEEP and its corresponding maximal inspiratory pressures (MIPs) were reached. From there on, driving pressure was progressively increased in 5-cmH2O steps until detectable barotrauma occurred. Two macroscopic conditions were defined: anatomically open lung and barotrauma.

MAIN OUTCOME MEASURES

We measured open lung and barotrauma MIP, PEEP and driving pressure obtained using each strategy. A pressure safety range, defined as the difference between barotrauma MIP and anatomically open lung MIP, was also determined in both groups.

RESULTS

Open lung MIP was similar in both groups: 23.6 ± 3.8 and 23.3 ± 4.1 cmH2O in the PEEP-50 and PEEP-20 groups, respectively (P = 0.91). However, barotrauma MIP in the PEEP-50 group was higher (65.7 ± 3.4 cmH2O) than in the PEEP-20 group (56.7 ± 5 0.2 cmH2O) (P = 0.003) resulting in a safety range of pressures of respectively 33.3 ± 8.7 and 42.1 ± 3.9 cmH2O (P = 0.035).

CONCLUSION

In this ex-vivo model, we found a substantial difference between recruitment and barotrauma pressures using both recruitment strategies. However, a higher margin of safety was obtained when a higher PEEP and lower driving pressure strategy was used for recruiting the lung.

Lung recruitment in acute respiratory distress syndrome: what is the best strategy?

PURPOSE OF REVIEW

Supporting patients with acute respiratory distress syndrome (ARDS) using a low tidal volume strategy is a standard practice in the ICU. Recruitment maneuvers can be used to augment other methods, like positive end-expiratory pressure and positioning, to improve aerated lung volume. Clinical practice varies widely, and optimal method and patient selection for recruitment maneuvers have not been determined.

RECENT FINDINGS

Recent developments include experimental and clinical evidence that a stepwise extended recruitment maneuver may match the improvement in aerated lung volume seen with sustained inflation traditionally used, with less adverse effects. Positioning and other chest wall modifications may be useful adjuncts to recruitment maneuvers. In addition, evidence from clinical studies in the operating room suggests that recruitment maneuvers, as a component of an open lung strategy, may be helpful for mechanically ventilated patients with normal lungs.

SUMMARY

As a component of ventilation strategy for patients with ARDS, the use of recruitment maneuvers, especially a stepwise maneuver, in addition to adequate positive end-expiratory pressure and appropriate positioning, is suggested by currently available data. Until their effect on clinical outcomes is further defined, the use of recruitment maneuvers in ARDS and other settings will continue to be guided by individual clinician experience and patient factors.

Positive end-expiratory pressure (PEEP) during anaesthesia for prevention of mortality and postoperative pulmonary complications

BACKGROUND

General anaesthesia causes atelectasis, which can lead to impaired respiratory function. Positive end-expiratory pressure (PEEP) is a mechanical manoeuvre that increases functional residual capacity (FRC) and prevents collapse of the airways, thereby reducing atelectasis. It is not known whether intraoperative PEEP alters the risks of postoperative mortality and pulmonary complications. This review was originally published in 2010 and was updated in 2013.

OBJECTIVES

To assess the benefits and harms of intraoperative PEEP in terms of postoperative mortality and pulmonary outcomes in all adult surgical patients.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) 2013, Issue 10, part of The Cochrane Library, as well as MEDLINE (via Ovid) (1966 to October 2013), EMBASE (via Ovid) (1980 to October 2013), CINAHL (via EBSCOhost) (1982 to October 2013), ISI Web of Science (1945 to October 2013) and LILACS (via BIREME interface) (1982 to October 2010). The original search was performed in January 2010.

SELECTION CRITERIA

We included randomized clinical trials assessing the effects of PEEP versus no PEEP during general anaesthesia on postoperative mortality and postoperative respiratory complications in adults, 16 years of age and older.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected papers, assessed trial quality and extracted data. We contacted study authors to ask for additional information, when necessary. We calculated the number of additional participants needed (information size) to make reliable conclusions.

MAIN RESULTS

This updated review includes two new randomized trials. In total, 10 randomized trials with 432 participants and four comparisons are included in this review. One trial had a low risk of bias. No differences were demonstrated in mortality, with risk ratio (RR) of 0.97 (95% confidence interval (CI) 0.20 to 4.59; P value 0.97; 268 participants, six trials, very low quality of evidence (grading of recommendations assessment, development and evaluation (GRADE)), and in pneumonia, with RR of 0.40 (95% CI 0.11 to 1.39; P value 0.15; 120 participants, three trials, very low quality of evidence (GRADE)). Statistically significant results included the following: The PEEP group had higher arterial oxygen pressure (PaO2)/fraction of inspired oxygen (FiO2) on day one postoperatively, with a mean difference of 22.98 (95% CI 4.40 to 41.55; P value 0.02; 80 participants, two trials, very low quality of evidence (GRADE)), and postoperative atelectasis (defined as an area of collapsed lung, quantified by computerized tomography scan) was less in the PEEP group (standard mean difference -1.2, 95% CI -1.78 to -0.79; P value 0.00001; 88 participants, two trials, very low quality of evidence (GRADE)). No adverse events were reported in the three trials that adequately measured these outcomes (barotrauma and cardiac complications). Using information size calculations, we estimated that a further 21,200 participants would have to be randomly assigned to allow a reliable conclusion about PEEP and mortality.

AUTHORS' CONCLUSIONS

Evidence is currently insufficient to permit conclusions about whether intraoperative PEEP alters risks of postoperative mortality and respiratory complications among undifferentiated surgical patients.

Respiratory function during anesthesia: effects on gas exchange

Anaesthesia causes a respiratory impairment, whether the patient is breathing spontaneously or is ventilated mechanically. This impairment impedes the matching of alveolar ventilation and perfusion and thus the oxygenation of arterial blood. A triggering factor is loss of muscle tone that causes a fall in the resting lung volume, functional residual capacity. This fall promotes airway closure and gas adsorption, leading eventually to alveolar collapse, that is, atelectasis. The higher the oxygen concentration, the faster will the gas be adsorbed and the aleveoli collapse. Preoxygenation is a major cause of atelectasis and continuing use of high oxygen concentration maintains or increases the lung collapse, that typically is 10% or more of the lung tissue. It can exceed 25% to 40%. Perfusion of the atelectasis causes shunt and cyclic airway closure causes regions with low ventilation/perfusion ratios, that add to impaired oxygenation. Ventilation with positive end-expiratory pressure reduces the atelectasis but oxygenation need not improve, because of shift of blood flow down the lung to any remaining atelectatic tissue. Inflation of the lung to an airway pressure of 40 cmH2O recruits almost all collapsed lung and the lung remains open if ventilation is with moderate oxygen concentration (< 40%) but recollapses within a few minutes if ventilation is with 100% oxygen. Severe obesity increases the lung collapse and obstructive lung disease and one-lung anesthesia increase the mismatch of ventilation and perfusion. CO2 pneumoperitoneum increases atelectasis formation but not shunt, likely explained by enhanced hypoxic pulmonary vasoconstriction by CO2. Atelectasis may persist in the postoperative period and contribute to pneumonia.

Effects of fluid load on cardiovascular function during stepwise lung recruitment manoeuvre in healthy dogs

The aim of this study was to evaluate the effects of a stepwise lung recruitment manoeuvre (RM) on cardiac output (CO) in mechanically ventilated dogs, with or without a previous fluid load. Eight healthy adult Beagle dogs were enrolled in a prospective crossover study. Following sedation with dexmedetomidine and methadone, anaesthesia was induced with propofol and maintained with isoflurane. CO (thermodilution method) and direct arterial blood pressure were monitored. The dogs were mechanically ventilated in a volume-controlled mode (tidal volume, VT = 10 mL/kg; positive end-expiratory pressure [PEEP] = 0 cm H2O) until normocapnia was achieved (end tidal CO2 35-45 mmHg). The RM was then performed in a pressure-controlled mode, with progressive increases of the PEEP and end-inspiratory pressure of 5 cm H2O, until 15 cm H2O and 30 cm H2O were reached, respectively. After the RM, the ventilatory mode was returned to volume-control, and the PEEP was sequentially decreased to 10, 5 and 0 cm H2O. Baseline ventilation was maintained for 30 min. Next, 10 mL/kg of lactated Ringer's solution was administered within 10 min, prior to a second RM. The CO was determined before each RM (baseline) and at each pressure step. A repeated measures ANOVA test was used to compare data. Compared to baseline, CO decreased during the RM in both groups. However, there was a significantly higher CO during the second RM at the highest pressure step (P<0.05) and during all decreasing pressure steps (P<0.05). In conclusion, a previous crystalloid fluid load could reduce the impact of a RM on CO in healthy dogs.

Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis

BACKGROUND

Pathophysiological changes due to obesity may complicate mechanical ventilation during general anaesthesia. The ideal ventilation strategy is expected to optimize gas exchange and pulmonary mechanics and to reduce the risk of respiratory complications.

METHODS

Systematic search (databases, bibliographies, to March 2012, all languages) was performed for randomized trials testing intraoperative ventilation strategies in obese patients (BMI ≥ 30 kg m(-2)), and reporting on gas exchange, pulmonary mechanics, or pulmonary complications. Meta-analyses were performed when data from at least three studies or 100 patients could be combined.

RESULTS

Thirteen studies (505 obese surgical patients) reported on a variety of ventilation strategies: pressure- or volume-controlled ventilation (PCV, VCV), various tidal volumes, and different PEEP or recruitment manoeuvres (RM), and combinations thereof. Definitions and reporting of endpoints were inconsistent. In five trials (182 patients), RM added to PEEP compared with PEEP alone improved intraoperative PaO2/FIO2 ratio [weighted mean difference (WMD), 16.2 kPa; 95% confidence interval (CI), 8.0-24.4] and increased respiratory system compliance (WMD, 14 ml cm H(2)O(-1); 95% CI, 8-20). Arterial pressure remained unchanged. In four trials (100 patients) comparing PCV with VCV, there was no difference in PaO2/FIO2 ratio, tidal volume, or arterial pressure. Comparison of further ventilation strategies or combination of other outcomes was not feasible. Data on postoperative complications were seldom reported.

CONCLUSIONS

The ideal intraoperative ventilation strategy in obese patients remains obscure. There is some evidence that RM added to PEEP compared with PEEP alone improves intraoperative oxygenation and compliance without adverse effects. There is no evidence of any difference between PCV and VCV.

Pulmonary mechanics during mechanical ventilation

The use of mechanical ventilation has become widespread in the management of hypoxic respiratory failure. Investigations of pulmonary mechanics in this clinical scenario have demonstrated that there are significant differences in compliance, resistance and gas flow when compared with normal subjects. This paper will review the mechanisms by which pulmonary mechanics are assessed in mechanically ventilated patients and will review how the data can be used for investigative research purposes as well as to inform rational ventilator management.

Evaluation of a CO2 partial rebreathing functional residual capacity measurement method for use during mechanical ventilation

OBJECTIVE

There is a need for an automated bedside functional residual capacity (FRC) measurement method that does not require a step change in inspired oxygen fraction. Such a method can be used for patients who require a high inspired oxygen fraction to maintain arterial oxygenation and for patients ventilated using a circle breathing system commonly found in operating rooms, which is not capable of step changes in oxygen. We developed a CO(2) rebreathing method for FRC measurement that is based on the change in partial pressure of end-tidal carbon dioxide and volume of CO(2) eliminated at the end of a partial rebreathing period. This study was designed to assess the accuracy and precision of the proposed FRC measurement system compared to body plethysmography and nitrogen washout FRC.

METHODS

Accuracy and precision of measurements were assessed by comparing the CO(2) rebreathing FRC values to the gold standard, body plethysmography FRC, in twenty spontaneously breathing volunteers. The CO(2) rebreathing FRC measurements were then compared to nitrogen washout FRC in twenty intensive care patients whose lungs were mechanically ventilated. For each subject, an average value of CO(2) rebreathing FRC was compared to the average gold standard method. Measurements were accepted for statistical analysis if they had been recorded from periods of stable tidal ventilation, defined as a coefficient of variation of tidal volume of <0.13.

RESULTS

Compared to body plethysmography, the accuracy (average error) for the CO(2) rebreathing method during stable ventilation (n = 8) was 0.03 L and precision (1 standard deviation of the error) was 0.29 L (0.8 ± 7.6% of body plethysmography). During stable mechanical ventilation (n = 9), the accuracy was -0.02 L and precision was 0.26 L (-1.1 ± 12.6% of nitrogen washout).

CONCLUSIONS

The CO(2) rebreathing method for FRC measurement provides acceptable accuracy and precision during stable ventilation compared to the gold standards of body plethysmography and nitrogen washout. The results based on periods of stable ventilation best approximate the performance of the system in the likely areas of application during controlled mechanical ventilation. Further study of the CO(2) rebreathing method is needed to evaluate accuracy in a larger group of controlled mechanical ventilation patients, including patients with respiratory insufficiency and significant lung injury.

Effect of the alveolar recruitment manoeuvre on haemodynamic parameters in patients with acute respiratory distress syndrome: relationship with oxygenation

BACKGROUND AND OBJECTIVE

Although the alveolar recruitment manoeuvre (ARM) is considered to be an optimal method of recruiting collapsed alveoli in a short period, the haemodynamic effects of the ARM have not been investigated. The aim of this study was to assess whether the ARM causes haemodynamic instability in patients with ARDS, and any relationship this might have with arterial oxygenation.

METHODS

Twenty-eight patients with ARDS (16 responders and 12 non-responders), who were admitted to the medical intensive care unit of a university-affiliated hospital, were enrolled in the study. ARM, using the extended sigh method, was performed within 48 h of the onset of ARDS. Haemodynamic parameters were measured at baseline, during the ARM, and at 2 min, 30 min and 1 h after the ARM.

RESULTS

Responders and non-responders showed no significant changes in blood pressure or cardiac index during or after ARM. Mean pulmonary artery pressure (MPAP), pulmonary vascular resistance index (PVRI) and right ventricular stroke work index (RVSWI) were transiently increased compared with baseline, in responders and non-responders. During and after ARM, the systemic vascular resistance index was significantly higher in non-responders than in responders.

CONCLUSIONS

Some haemodynamic parameters (MPAP, PVRI and RVSWI) changed significantly during ARM. However, these haemodynamic changes were minimal, transient and probably have no clinical significance.

Effects of positive end-expiratory pressure on anesthesia-induced atelectasis and gas exchange in anesthetized and mechanically ventilated sheep

OBJECTIVE

To evaluate the effects of 10 cm H(2)O of positive end-expiratory pressure (PEEP) on lung aeration and gas exchange in mechanically ventilated sheep during general anesthesia induced and maintained with propofol.

ANIMALS

10 healthy adult Bergamasca sheep.

PROCEDURES

Sheep were sedated with diazepam (0.4 mg/kg, IV). Anesthesia was induced with propofol (5 mg/kg, IV) and maintained with propofol via constant rate infusion (0.4 mg/kg/min). Muscular paralysis was induced by administration of vecuronium (25 microg/kg, bolus IV) to facilitate mechanical ventilation. After intubation, sheep were positioned in right lateral recumbency and mechanically ventilated with pure oxygen and zero end-expiratory pressure (ZEEP). After 60 minutes, 10 cm H(2)O of PEEP was applied for 20 minutes. Spiral computed tomography of the thorax was performed, and data were recorded for hemodynamic and gas exchange variables and indicators of respiratory mechanics after 15 (T(15)), 30 (T(30)), and 60 (T(60)) minutes of ZEEP and after 20 minutes of PEEP (T(PEEP)). Computed tomography images were analyzed to determine the extent of atelectasis before and after PEEP application.

RESULTS

At T(PEEP), the volume of poorly aerated and atelectatic compartments was significantly smaller than at T(15), T(30), and T(60), which indicated that there was PEEP-induced alveolar recruitment and clearance of anesthesia-induced atelectasis. Arterial oxygenation and static respiratory system compliance were significantly improved by use of PEEP.

CONCLUSIONS AND CLINICAL RELEVANCE

Pulmonary atelectasis can develop in anesthetized and mechanically ventilated sheep breathing pure oxygen; application of 10 cm H(2)O of PEEP significantly improved lung aeration and gas exchange.

Positive end-expiratory pressure (PEEP) during anaesthesia for the prevention of mortality and postoperative pulmonary complications

BACKGROUND

General anaesthesia causes atelectasis which can lead to impaired respiratory function. Positive end-expiratory pressure (PEEP) is a mechanical manoeuvre which increases functional residual capacity (FRC) and prevents collapse of the airways thereby reducing atelectasis. It is not known whether intra-operative PEEP alters the risk of postoperative mortality and pulmonary complications.

OBJECTIVES

To assess the benefits and harms of intraoperative PEEP, for all adult surgical patients, on postoperative mortality and pulmonary outcomes.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, Issue 4), MEDLINE (via Ovid) (1966 to January 2010), EMBASE (via Ovid) (1980 to January 2010), CINAHL (via EBSCOhost) (1982 to January 2010), ISI Web of Science (1945 to January 2010) and LILACS (via BIREME interface) (1982 to January 2010).

SELECTION CRITERIA

We included randomized clinical trials that evaluated the effect of PEEP versus no PEEP, during general anaesthesia, on postoperative mortality and postoperative respiratory complications. We included studies irrespective of language and publication status.

DATA COLLECTION AND ANALYSIS

Two investigators independently selected papers, extracted data that fulfilled our outcome criteria and assessed the quality of all included trials. We undertook pooled analyses, where appropriate. For our primary outcome (mortality) and two secondary outcomes (respiratory failure and pneumonia), we calculated the number of further patients needed (information size) in order to make reliable conclusions.

MAIN RESULTS

We included eight randomized trials with a total of 330 patients. Two trials had a low risk of bias. There was no difference demonstrated for mortality (relative risk (RR) 0.95, 95% CI 0.14 to 6.39). Two statistically significant results were found: the PEEP group had a higher PaO(2)/FiO(2) on day 1 postoperatively (mean difference (MD) 22.98, 95% CI 4.40 to 41.55) and postoperative atelectasis (defined as an area of collapsed lung, quantified by computerized tomography (CT) scan) was less in the PEEP group (SMD -1.2, 95% CI -1.78 to -0.79). There were no adverse events reported in the three trials that adequately measured these outcomes (barotrauma and cardiac complications). Using information size calculations, we estimated that a further 21,200 patients would need to be randomized in order to make a reliable conclusion about PEEP and mortality.

AUTHORS' CONCLUSIONS

There is currently insufficient evidence to make conclusions about whether intraoperative PEEP alters the risk of postoperative mortality and respiratory complications among undifferentiated surgical patients.

Perioperative tidal volume and intra-operative open lung strategy in healthy lungs: where are we going?

Tidal volumes have tremendously decreased over the last decades from <15 ml kg(-1) to approximately 6 ml kg(-1) actual body weight. Guidelines, widely agreed and used, exist for patients with acute lung injury or acute respiratory distress syndrome (ARDS). However, it is questionable if data created in patients with acute lung injury or ARDS from ventilation on intensive care units can be transferred to healthy patients undergoing surgery. Consensus criteria regarding this topic are still missing because only a few randomised controlled trials have been performed to date, focussing on the use of the best intra-operative tidal volume. The same problem has been observed regarding the application of positive end-expiratory pressure (PEEP) and intra-operative lung recruitment. This article provides an overview of the current literature addressing the size of tidal volume, the use of PEEP and the application of the open-lung concept in patients without acute lung injury or ARDS. Pathophysiological aspects of mechanical ventilation are elucidated.

Changes of splanchnic perfusion after applying positive end expiratory pressure in patients with acute respiratory distress syndrome

Background:

Positive end-expiratory pressure (PEEP) improves oxygenation and can prevent ventilator- induced lung injury in patients with acute respiratory distress syndrome (ARDS). Nevertheless, PEEP can also induce detrimental effects by its influence on the cardiovascular system. The purpose of this study was to assess the effects of PEEP on gastric mucosal perfusion while applying a protective ventilatory strategy in patients with ARDS.

Materials and Methods:

Thirty-two patients were included in the study. A pressure–volume curve was traced and ideal PEEP, defined as lower inflection point + 2cmH₂O, was determined. Gastric tonometry was measured continuously (Tonocap). After baseline measurements, 10, 15 and 20cmH₂O PEEP and ideal PEEP were applied for 30 min each. By the end of each period, hemodynamics, CO₂ gap (gastric minus arterial partial pressures), and ventilatory measurements were taken.

Results:

PEEP had no effect on CO₂ gap (median [range], baseline: 18 [2–30] mmHg; PEEP 10: 18 [0–40] mmHg; PEEP 15: 17 [0–39] mmHg; PEEP 20: 16 [4–39] mmHg; ideal PEEP: 19 [9–39] mmHg; P = 0.19). Cardiac index also remained unchanged (baseline: 4.7 [2.6–6.2] l min⁻¹ m⁻²; PEEP 10: 4.4 [2.5–7] l min⁻¹ m⁻²; PEEP 15: 4.4 [2.2–6.8] l min⁻¹ m⁻²; PEEP 20: 4.8 [2.4–6.3] l min⁻¹ m⁻²; ideal PEEP: 4.9 [2.4–6.3] l min⁻¹ m⁻²; P = 0.09).

Conclusion:

PEEP of 10–20 cmH₂O does not affect splanchnic perfusion and is hemodynamically well tolerated in most patients with ARDS, including those receiving inotropic supports.

Alveolar recruitment maneuvers in acute lung injury/acute respiratory distress syndrome

Mechanical ventilation can worsen lung damage in acute lung injury and acute respiratory distress syndrome. The use of low tidal volumes is one of the strategies that has been shown to reduce lung injury and improve outcomes in this situation. However, low tidal volumes may lead to alveolar derecruitment and worsening of hypoxia. Recruitment maneuvers along with positive end-expiratory pressure may help to prevent derecruitment. Although recruitment maneuvers have been shown to improve oxygenation, improved clinical outcomes have not been demonstrated. The optimal recruitment strategy and the type of patients who might benefit are also unclear. This review summarizes the impact of recruitment maneuvers on lung mechanics and physiology, techniques of application, and the clinical situations in which they may be useful.

CPAP of 10 cmH2O during cardiopulmonary bypass followed by an alveolar recruitment manoeuvre does not improve post-bypass oxygenation compared to a recruitment manoeuvre alone in children

This randomised controlled study assessed whether continuous positive airway pressure (CPAP) of 10 cmH2O during cardiopulmonary bypass improves post-bypass oxygenation in children compared with no CPAP during bypass. We studied children with a ventricular septal defect. CPAP of 10 cmH2O was applied during bypass in the CPAP group (n=24), whereas the lungs were left deflated in the control group (n=20). In both groups, an alveolar recruitment maneuver was performed by applying positive pressure of 30 to 40 cmH2O for five seconds before weaning from bypass. Postoperative ventilation had the peak inflation pressure set to produce an expired tidal volume of 8 ml/kg with positive end expiratory pressure of 5 cmH2O. Arterial blood gas and haemodynamic measurements were performed at skin incision, five minutes after weaning from bypass, five minutes after chest closure and four hours after arrival in the intensive care unit. In four children CPAP was discontinued because it adversely affected the operating field. There was no difference in demographic characteristics, haemodynamic data, bypass time and operation time. No difference was observed between the groups with respect to pH, PaO2, P(A-a) DO2, PaCO2, and ETCO2 at each time. Variability in the data was greater than expected, leading to a decrease in the expected power of the study. CPAP at 10 cmH2O during bypass was not found to improve the post-bypass oxygenation as compared with leaving the lung deflated during bypass in children undergoing ventricular septal defect repair who had an alveolar recruitment maneuver at the end of bypass.

[Peri-operative atelectasis and alveolar recruitment manoeuvres]

Respiratory complications are a significant cause of post-operative morbidity and mortality. Peri-operative atelectasis, in particular, affects 90% of surgical patients and its effects can be prolonged, due to changes in respiratory mechanics, pulmonary circulation and hypoxaemia. Alveolar collapse is caused by certain predisposing factors, mainly by compression and absorption mechanisms. To prevent or treat these atelectasis several therapeutic strategies have been proposed, such as alveolar recruitment manoeuvres, which has become popular in the last few years. Its application in patients with alveolar collapse, but without a previous significant acute lung lesion, has some special features, therefore its use is not free of uncertainties and complications. This review describes the frequency, pathophysiology, importance and treatment of peri-operative atelectasis. Special attention is paid to treatment with recruitment manoeuvres, with the purpose of providing a basis for the their rational and appropriate use.