Positive end-expiratory pressure-induced recruited lung volume measured by volume-pressure curves in acute respiratory distress syndrome: a physiologic systematic review and meta-analysis

Abstract

Purpose: Recruitment of lung volume is often cited as the reason for using positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) patients. We performed a systematic review on PEEP-induced recruited lung volume measured from inspiratory volume-pressure (VP) curves in ARDS patients to assess the prevalence of patients with PEEP-induced recruited lung volume and the mortality in recruiters and non-recruiters.

Methods: We conducted a systematic search of PubMed to identify studies including ARDS patients in which the intervention of an increase in PEEP was accompanied by measurement of the recruited volume (V_rec increase versus no increase) using the VP curve in order to assess the relation between V_rec and mortality at ICU discharge. We first analysed the pooled data from the papers identified and then analysed individual patient level data received from the authors via personal contact. The risk of bias of the included papers was assessed using the quality in prognosis studies tool and the certainty of the evidence regarding the relationship of mortality to V_rec by the GRADE approach. Recruiters were defined as patients with a V_rec > 150 ml. A random effects model was used for the pooled data. Multivariable logistic regression analysis was used for individual patient data.

Results: We identified 16 papers with a total of 308 patients for the pooled data meta-analysis and 14 papers with a total of 384 patients for the individual data analysis. The quality of the articles was moderate. In the pooled data, the prevalence of recruiters was 74% and the mortality was not significantly different between recruiters and non-recruiters (relative risk 1.20 [95% confidence intervals 0.88-1.63]). The certainty of the evidence regarding this association was very low and publication bias evident. In the individual data, the prevalence of recruiters was 70%. In the multivariable logistic regression, V_rec was not associated with mortality but Simplified Acute Physiology Score II and driving pressure at PEEP of 5 cmH₂O were.

Conclusion: After a PEEP increment, most patients are recruiters. V_rec was not associated with ICU mortality. The presence of similar findings in the individual patient level analysis and the driving pressure at PEEP of 5 cmH₂O was associated with mortality as previously reported validate our findings. Publication bias and the lack of prospective studies suggest more research is required.

Keywords: Alveolar recruitment; Lung recruitment; Positive end-expiratory pressure; Positive-pressure respiration/therapeutic use; Respiratory distress syndrome, adult/mortality; Respiratory distress syndrome, adult/physiopathology; Respiratory distress syndrome, adult/therapy.

Fig. 1

The two methods to measure recruited volume (V_rec) from volume-pressure curve of the respiratory system that were investigated in present study. a Occlusion technique at different tidal volume (V_T). Airway pressure (P_aw) is recorded at different V_T during an end-inspiratory occlusion. Each dot is the plateau pressure at a given V_T. The procedure is done at PEEP 0 (red dots) and PEEP14 cmH2O (blue dots). Both curves are referred to the relaxation volume of the respiratory system at PEEP 0 (Vr). V_rec is the change in lung volume at a given pressure, i.e. 20 cmH₂O, between the 2 PEEP (broken horizontal black lines). b Low flow inflation technique. The respiratory system is insufflated from PEEP 5 (blue line) or PEEP10 (grey line) at constant low flow (7 l/min). Volumes are referred to V_r at PEEP 0. V_rec can be obtained as the difference in lung volume at same 20 cmH₂O P_aw (broken horizontal green lines) or from PEEP10 down to PEEP5 (broken horizontal red lines)

Fig. 2

PRISMA flow chart of the inclusion/exclusion process. RM recruited manoeuvers, VP volume-pressure, V_rec recruited volume

Fig. 3

Forest plot of the prevalence of recruiters after positive end-expiratory pressure trials in the pooled analysis. Recruiters were defined as having a recruited volume greater than 150 ml and non-recruiters equal to or below that value

Fig. 4

Forest plot of the prevalence of recruiters according to PaO₂/FiO₂ ratio in the pooled analysis

Fig. 5

Forest plot of the mortality at ICU discharge in recruiters and non-recruiters in the pooled analysis

Fig. 6

Receiver operating curve (ROC) (continuous blue line) of recruited volume for assessing mortality. Area under curve (AUC) of the ROC curve with 95% confidence intervals (broken red lines) is displayed. The broken black line is the identity line