Prolonged moderate pressure recruitment manoeuvre results in lower optimal positive end-expiratory pressure and plateau pressure

Gas distribution by EIT during PEEP inflation: PEEP response and optimal PEEP with lowest trans-pulmonary driving pressure can be determined without esophageal pressure during a rapid PEEP trial in patients with acute respiratory failure

Objective. Protective ventilation should be based onlungmechanics and transpulmonary driving pressure (ΔPTP), as this 'hits' the lung directly.Approach. The change in end-expiratory lung volume (ΔEELV) is determined by the size of the PEEP step and the elastic properties of the lung (EL), ΔEELV/ΔPEEP. Consequently, EL can be determined as ΔPEEP/ΔEELV. By calibration of tidal inspiratory impedance change with ventilator inspiratory tidal volume, end-expiratory lung impedance changes were converted to volume changes and lung P/V curves were obtained during a PEEP trial in ten patients with acute respiratory failure. The PEEP level where ΔPTP was lowest (optimal PEEP) was determined as the steepest point of the lung P/V curve.Main results. Over-all EL ranged between 7.0-23.2 cmH₂O/L. Optimal PEEP was 12.9 cmH₂O (10-16) with ΔPTP of 4.1 cmH₂O (2.8-7.6). Patients with highest EL were PEEP non-responders, where EL increased in non-dependent and dependent lung at high PEEP, indicating over-distension in all lung. Patients with lower EL were PEEP responders with decreasing EL in dependent lung when increasing PEEP.Significance. PEEP non-responders could be identified by regional lung P/V curves derived from ventilator calibrated EIT. Optimal PEEP could be determined from the equation for the lung P/V curve.

Positive end-expiratory pressure titration with electrical impedance tomography and pressure-volume curve: a randomized trial in moderate to severe ARDS

OBJECTIVE

The aim of the study was to compare titration of positive end-expiratory pressure (PEEP) with electrical impedance tomography (EIT) and with ventilator-embedded pressure-volume (PV) loop in moderate to severe acute respiratory distress syndrome (ARDS).

APPROACH

Eighty-seven moderate to severe ARDS patients (arterial oxygen partial pressure to fractional inspired oxygen ratio, PaO₂/FiO₂ ≤ 200 mmHg) were randomized to either EIT group (n = 42) or PV group (n = 45). All patients received identical medical care using the same general support guidelines and protective mechanical ventilation. In the EIT group, the selected PEEP equaled the airway pressure at the intercept between cumulated collapse and overdistension percentages curves and in the PV group, at the pressure where maximal hysteresis was reached.

MAIN RESULTS

Baseline characteristics and settings were comparable between the groups. After optimization, PEEP was significantly higher in the PV group (17.4 ± 1.7 versus 16.2 ± 2.6 cmH₂O, PV versus EIT groups, p = 0.02). After 48 h, driving pressure was significantly higher in the PV group (12.4 ± 3.6 versus 10.9 ± 2.5 cmH₂O, p = 0.04). Lung mechanics and oxygenation were better in the EIT group but did not statistically differ between the groups. The survival rate was lower in the PV group (44.4% versus 69.0%, p = 0.02; hazard ratio 2.1, confidence interval 1·1-3.9). None of the other pre-specified exploratory clinical endpoints were significantly different.

SIGNIFICANCE

In moderate to severe ARDS, PEEP titration guided with EIT, compared with PV curve, might be associated with improved driving pressure and survival rate.

TRIAL REGISTRATION

NCT03112512, 13 April, 2017.

Intravenous administration of normal saline may be misinterpreted as a change of end-expiratory lung volume when using electrical impedance tomography

Electrical impedance tomography (EIT) is a noninvasive imaging modality that allows real-time monitoring of regional lung ventilation. The aim of the study is to investigate whether fast saline infusion causes changes in lung impedance that could affect the interpretation of EIT data. Eleven pigs were anaesthetized and mechanically ventilated. A bolus of 500 mL of normal saline was administered rapidly. Two PEEP steps were performed to allow quantification of the effect of normal saline on lung impedance. The mean change of end-expiratory lung impedance (EELI) caused by the saline bolus was equivalent to a virtual decrease of end-expiratory lung volume (EELV) by 227 (188–250) mL and decremental PEEP step of 4.40 (3.95–4.59) cmH₂O (median and interquartile range). In contrast to the changes of PEEP, the administration of normal saline did not cause any significant differences in measured EELV, regional distribution of lung ventilation determined by EIT or in extravascular lung water and intrathoracic blood volume. In conclusion, EELI can be affected by the changes of EELV as well as by the administration of normal saline. These two phenomena can be distinguished by analysis of regional distribution of lung ventilation.

Recruitment manoeuvres for adults with acute respiratory distress syndrome receiving mechanical ventilation

BACKGROUND

Recruitment manoeuvres involve transient elevations in airway pressure applied during mechanical ventilation to open ('recruit') collapsed lung units and increase the number of alveoli participating in tidal ventilation. Recruitment manoeuvres are often used to treat patients in intensive care who have acute respiratory distress syndrome (ARDS), but the effect of this treatment on clinical outcomes has not been well established. This systematic review is an update of a Cochrane review originally published in 2009.

OBJECTIVES

Our primary objective was to determine the effects of recruitment manoeuvres on mortality in adults with acute respiratory distress syndrome.Our secondary objective was to determine, in the same population, the effects of recruitment manoeuvres on oxygenation and adverse events (e.g. rate of barotrauma).

SEARCH METHODS

For this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), Embase (OVID), the Cumulative Index to Nursing and Allied Health Literature (CINAHL, EBSCO), Latin American and Caribbean Health Sciences (LILACS) and the International Standard Randomized Controlled Trial Number (ISRCTN) registry from inception to August 2016.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of adults who were mechanically ventilated that compared recruitment manoeuvres versus standard care for patients given a diagnosis of ARDS.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We contacted study authors for additional information.

MAIN RESULTS

Ten trials met the inclusion criteria for this review (n = 1658 participants). We found five trials to be at low risk of bias and five to be at moderate risk of bias. Six of the trials included recruitment manoeuvres as part of an open lung ventilation strategy that was different from control ventilation in aspects other than the recruitment manoeuvre (such as mode of ventilation, higher positive end-expiratory pressure (PEEP) titration and lower tidal volume or plateau pressure). Six studies reported mortality outcomes. Pooled data from five trials (1370 participants) showed a reduction in intensive care unit (ICU) mortality (risk ratio (RR) 0.83, 95% confidence interval (CI) 0.72 to 0.97, P = 0.02, low-quality evidence), pooled data from five trials (1450 participants) showed no difference in 28-day mortality (RR 0.86, 95% CI 0.74 to 1.01, P = 0.06, low-quality evidence) and pooled data from four trials (1313 participants) showed no difference in in-hospital mortality (RR 0.88, 95% CI 0.77 to 1.01, P = 0.07, low-quality evidence). Data revealed no differences in risk of barotrauma (RR 1.09, 95% CI 0.78 to 1.53, P = 0.60, seven studies, 1508 participants, moderate-quality evidence).

AUTHORS' CONCLUSIONS

We identified significant clinical heterogeneity in the 10 included trials. Results are based upon the findings of several (five) trials that included an "open lung ventilation strategy", whereby the intervention group differed from the control group in aspects other than the recruitment manoeuvre (including co-interventions such as higher PEEP, different modes of ventilation and higher plateau pressure), making interpretation of the results difficult. A ventilation strategy that included recruitment manoeuvres in participants with ARDS reduced intensive care unit mortality without increasing the risk of barotrauma but had no effect on 28-day and hospital mortality. We downgraded the quality of the evidence to low, as most of the included trials provided co-interventions as part of an open lung ventilation strategy, and this might have influenced results of the outcome.

Electrical impedance tomography in adult patients undergoing mechanical ventilation: A systematic review

PURPOSE

The purpose of the study is to systematically review and summarize current literature concerning the validation and application of electrical impedance tomography (EIT) in mechanically ventilated adult patients.

MATERIALS AND METHODS

An electronic search of MEDLINE, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials, and the Web of Science was performed up to June 2014. Studies investigating the use of EIT in an adult human patient population treated with mechanical ventilation (MV) were included. Data extracted included study objectives, EIT details, interventions, MV protocol, validation and comparators, population characteristics, and key findings.

RESULTS

Of the 67 included studies, 35 had the primary objective of validating EIT measures including regional ventilation distribution, lung volume, regional respiratory mechanics, and nonventilatory parameters. Thirty-two studies had the primary objective of applying EIT to monitor the response to therapeutic MV interventions including change in ventilation mode, patient repositioning, endotracheal suctioning, recruitment maneuvers, and change in positive end-expiratory pressure.

CONCLUSIONS

In adult patients, EIT has been successfully validated for assessing ventilation distribution, measuring changes in lung volume, studying regional respiratory mechanics, and investigating nonventilatory parameters. Electrical impedance tomography has also been demonstrated to be useful in monitoring regional respiratory system changes during MV interventions, although existing literature lacks clinical outcome evidence.

Recruitment maneuvers modulate epithelial and endothelial cell response according to acute lung injury etiology

OBJECTIVE

To investigate the effects of the rate of increase in airway pressure and duration of lung recruitment maneuvers in experimental pulmonary and extrapulmonary acute lung injury.

DESIGN

Prospective, randomized, controlled experimental study.

SETTINGS

University research laboratory.

SUBJECTS

Fifty adult male Wistar rats.

INTERVENTIONS

Acute lung injury was induced by Escherichia coli lipopolysaccharide either intratracheally (pulmonary acute lung injury) or intraperitoneally (extrapulmonary acute lung injury). After 24 hours, animals were assigned to one of three different recruitment maneuvers, targeted to maximal airway pressure of 30 cm H2O: 1) continuous positive airway pressure for 30 seconds (CPAP-30); 2) stepwise airway pressure increase (5 cm H2O/step, 8.5 s at each step) over 51 seconds (STEP-51) to achieve a pressure-time product similar to that of CPAP-30; and 3) stepwise airway pressure increase (5 cm H2O/step, 5 s at each step) over 30 seconds with maximum pressure sustained for a further 30 seconds (STEP-30/30).

MEASUREMENTS AND MAIN RESULTS

All recruitment maneuvers reduced static lung elastance independent of acute lung injury etiology. In pulmonary acute lung injury, CPAP-30 yielded lower surfactant protein-B and higher type III procollagen expressions compared with STEP-30/30. In extrapulmonary acute lung injury, CPAP-30 and STEP-30/30 increased vascular cell adhesion molecule-1 expression, but the type of recruitment maneuver did not influence messenger ribonucleic acid expression of receptor for advanced glycation end products, surfactant protein-B, type III procollagen, and pro-caspase 3.

CONCLUSIONS

CPAP-30 worsened markers of potential epithelial cell damage in pulmonary acute lung injury, whereas both CPAP-30 and STEP-30/30 yielded endothelial injury in extrapulmonary acute lung injury. In both acute lung injury groups, recruitment maneuvers improved respiratory mechanics, but stepwise recruitment maneuver without sustained airway pressure appeared to associate with less biological impact on lungs.

A comparison between two different alveolar recruitment maneuvers in patients with acute respiratory distress syndrome

Background:

Alveolar recruitment is a physiological process that denotes the reopening of previously gasless lung units exposed to positive pressure ventilation. The current study was aimed to compare two recruitment maneuvers, a high continuous positive airway pressure (CPAP), and an extended sigh in patients with ARDS.

Materials and Methods:

Forty patients with acute respiratory distress syndrome were randomly divided into two groups, 20 patients each. Group I received a CPAP of 40 cm H₂O for 40 seconds and group II received extended sigh (providing a sufficient recruiting pressure × time). In our study, we assessed the effects of both recruitment maneuvers on respiratory mechanics, gas exchange, and hemodynamics. These data were analyzed using two-way analysis of variance (ANOVA) followed by a Student--Newman--Keuls post hoc comparison test. P < 0.05 was considered statistically significant.

Results:

Both methods improved the compliance, increased arterial oxygenation (PaO₂), increased the PaO₂/FiO₂ ratio, and reduced the pulmonary shunt fraction (Q_s/Q_t). However, the extended sigh improved both PaO₂ and PaO₂/FiO₂ ratios more than continuous positive airway pressure. Also the hemodynamic parameters were better maintained during the extended sigh.

Conclusion:

Alveolar recruitment maneuvers are effective in management of mechanically ventilated ARDS patients. We conclude that extended sigh is more effective than continuous positive airway pressure as a recruitment maneuver.

Lung elastance and transpulmonary pressure can be determined without using oesophageal pressure measurements

INTRODUCTION

The aim of the present study was to demonstrate that lung elastance and transpulmonary pressure can be determined without using oesophageal pressure measurements.

METHODS

Studies were performed on 13 anesthetized and sacrificed ex vivo pigs. Tracheal and oesophageal pressures were measured and changes in end-expiratory lung volume (ΔEELV) determined by spirometry as the cumulative inspiratory-expiratory tidal volume difference. Studies were performed with different end-expiratory pressure steps [change in end-expiratory airway pressure (ΔPEEP)], body positions and with abdominal load.

RESULTS

A PEEP increase results in a multi-breath build-up of end-expiratory lung volume. End-expiratory oesophageal pressure did not increase further after the first expiration, constituting half of the change in ΔEELV following a PEEP increase, even though end-expiratory volume continued to increase. This resulted in a successive left shift of the chest wall pressure-volume curve. Even at a PEEP of 12 cmH(2) O did the end-expiratory oesophageal (pleural) pressure remain negative.

CONCLUSIONS

A PEEP increase resulted in a less than expected increase in end-expiratory oesophageal pressure, indicating that the chest wall and abdomen gradually can accommodate changes in lung volume. The rib cage end-expiratory spring-out force stretches the diaphragm and prevents the lung from being compressed by abdominal pressure. The increase in transpulmonary pressure following a PEEP increase was closely related to the increase in PEEP, indicating that lung compliance can be calculated from the ratio of the change in end-expiratory lung volume and the change in PEEP, ΔEELV/ΔPEEP.

Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury: a controlled experimental study in pigs with saline lavage lung injury

Introduction

Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach.

Methods

17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH₂O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH₂O in steps of 2 cmH₂O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis.

Results

The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO₂ and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group.

Conclusions

In a lavage model of lung injury a PEEP optimization strategy based on maximizing Xrs attenuated the signs of ventilator induced lung injury. The respiratory system reactance measured by FOT could thus be an important component in a strategy for delivering protective ventilation to patients with ARDS/acute lung injury.