How large is the lung recruitability in early acute respiratory distress syndrome: a prospective case series of patients monitored by computed tomography

Abstract

IntroductionThe benefits of higher positive end expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS) have been modest, but few studies have fully tested the "open-lung hypothesis". This hypothesis states that most of the collapsed lung tissue observed in ARDS can be reversed at an acceptable clinical cost, potentially resulting in better lung protection, but requiring more intensive maneuvers. The short-/middle-term efficacy of a maximum recruitment strategy (MRS) was recently described in a small physiological study. The present study extends those results, describing a case-series of non-selected patients with early, severe ARDS submitted to MRS and followed until hospital discharge or death.MethodsMRS guided by thoracic computed tomography (CT) included two parts: a recruitment phase to calculate opening pressures (incremental steps under pressure-controlled ventilation up to maximum inspiratory pressures of 60 cmH2O, at constant driving-pressures of 15 cmH2O); and a PEEP titration phase (decremental PEEP steps from 25 to 10 cmH2O) used to estimate the minimum PEEP to keep lungs open. During all steps, we calculated the size of the non-aerated (-100 to +100 HU) compartment and the recruitability of the lungs (the percent mass of collapsed tissue re-aerated from baseline to maximum PEEP).ResultsA total of 51 severe ARDS patients, with a mean age of 50.7 years (84% primary ARDS) was studied. The opening plateau-pressure was 59.6 (± 5.9 cmH2O), and the mean PEEP titrated after MRS was 24.6 (± 2.9 cmH2O). Mean PaO2/FiO2 ratio increased from 125 (± 43) to 300 (± 103; P < 0.0001) after MRS and was sustained above 300 throughout seven days. Non-aerated parenchyma decreased significantly from 53.6% (interquartile range (IQR): 42.5 to 62.4) to 12.7% (IQR: 4.9 to 24.2) (P < 0.0001) after MRS. The potentially recruitable lung was estimated at 45% (IQR: 25 to 53). We did not observe major barotrauma or significant clinical complications associated with the maneuver.ConclusionsMRS could efficiently reverse hypoxemia and most of the collapsed lung tissue during the course of ARDS, compatible with a high lung recruitability in non-selected patients with early, severe ARDS. This strategy should be tested in a prospective randomized clinical trial.

Lung recruitment in ARDS patients

“…Some authors have recently described a strategy to fully recruit the lung using high pressure for recruitment maneuver and high PEEP (4). Even if the clinical outcomes seem good (1), the clinician at the bedside should always balance the benefits and risk of such strategy in an individual patient (5). The method we describe in this review is based on an individual approach of the respiratory mechanics and should be applied as soon as possible in the management of ARDS patients.…”

“…The potential of recruitability in ARDS patient is highly variable (5,6) and difficult to predict. Lung recruitability depends mainly on the mechanism (pulmonary versus extrapulmonary injury) (7), the localization (lobar versus nonlobar) and the time from the beginning of the lung disease (early onset if within 48 hours from the beginning or late onset afterward) (8).…”

“…Staircase recruitment maneuvers are usually performed in the pressure control mode with a fixed driving pressure of 15 cmH2O, increasing progressively the PEEP from 20 to 45 cmH 2 O by steps of 5 to 10 cmH 2 O each 5 minutes (5,14). Both methods have not been compared.…”

“…The adequate level of PEEP is difficult to predict from the pressure-volume curve. A decreasing PEEP trial starting from 25 cmH 2 O with steps of 2-3 cmH 2 O each 5 min monitoring SpO 2 is a practical approach (5,14). A more physiological method is based on esophageal pressure monitoring and targets on a transpulmonary pressure (airway pressure minus esophageal pressure) during an end-expiratory pause from 0 to 10 cmH 2 O (22).…”

Titulação da PEEP rápida versus lenta guiadas por tomografia de impedância elétrica em pacientes hipoxêmicos no pós-operatório imediato de cirurgia cardíaca: estudo clínico randomizado

“…Muitas formas de se titular a PEEP têm sido propostas, sem nenhuma evidência de superioridade de alguma delas: baseada em variáveis mecânicas pela curva pressão-volume (P-V) (5,7,8) , de acordo com a oxigenação (SpO2) (18) , por medidas de espaço morto (19,20) , por tabelas PEEP-FiO2 (9,10,12) , de acordo com a aeração medida na tomografia computadorizada (21) ou por índices calculados pela Tomografia de Impedância Elétrica (TIE) (22) .…”