Abstract
IntroductionPositive end-expiratory pressure (PEEP)-induced lung derecruitment can be assessed by a pressure–volume (P–V) curve method or by lung computed tomography (CT). However, only the first method can be used at the bedside. The aim of the study was to compare both methods for assessing alveolar derecruitment after the removal of PEEP in patients with acute lung injury or acute respiratory distress syndrome.MethodsP–V curves (constant-flow method) and spiral CT scans of the whole lung were performed at PEEPs of 15 and 0 cmH2O in 19 patients with acute lung injury or acute respiratory distress syndrome. Alveolar derecruitment was defined as the difference in lung volume measured at an airway pressure of 15 cmH2O on P–V curves performed at PEEPs of 15 and 0 cmH2O, and as the difference in the CT volume of gas present in poorly aerated and nonaerated lung regions at PEEPs of 15 and 0 cmH2O.ResultsAlveolar derecruitments measured by the CT and P–V curve methods were 373 ± 250 and 345 ± 208 ml (p = 0.14), respectively. Measurements by both methods were tightly correlated (R = 0.82, p < 0.0001). The derecruited volume measured by the P–V curve method had a bias of -14 ml and limits of agreement of between -158 and +130 ml in comparison with the average derecruited volume of the CT and P–V curve methods.ConclusionAlveolar derecruitment measured by the CT and P–V curve methods are tightly correlated. However, the large limits of agreement indicate that the P–V curve and the CT method are not interchangeable.
Highlights
Positive end-expiratory pressure (PEEP)-induced lung derecruitment can be assessed by a pressure–volume (P– V) curve method or by lung computed tomography (CT)
ALI = acute lung injury; ARDS = acute respiratory distress syndrome; CT = computed tomography; ∆EELV = changes in end-expiratory lung volume measured by pneumotachography; ∆FRC = change in functional residual capacity measured by the computed tomography method; HU = Hounsfield unit; PaCO2 = arterial partial pressure of CO2; PEEP = positive end-expiratory pressure; P–V = pressure–volume; ZEEP = zero end-expiratory pressure
Comparison of PEEP-induced changes in end-expiratory lung volume measured by pneumotachography and functional residual capacity measured by CT In the 12 patients in whom CT sections at ZEEP were acquired immediately after the disconnecting maneuver, ∆FRC and ∆EELV were similar (1,054 ± 352 ml versus 1,022 ± 315 ml)
Summary
Positive end-expiratory pressure (PEEP)-induced lung derecruitment can be assessed by a pressure–volume (P– V) curve method or by lung computed tomography (CT). The aim of the study was to compare both methods for assessing alveolar derecruitment after the removal of PEEP in patients with acute lung injury or acute respiratory distress syndrome. ALI = acute lung injury; ARDS = acute respiratory distress syndrome; CT = computed tomography; ∆EELV = changes in end-expiratory lung volume measured by pneumotachography; ∆FRC = change in functional residual capacity measured by the computed tomography method; HU = Hounsfield unit; PaCO2 = arterial partial pressure of CO2; PEEP = positive end-expiratory pressure; P–V = pressure–volume; ZEEP = zero end-expiratory pressure. Another critical question is whether the P–V curve method can differentiate recruitment from (over)inflation
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