Abstract
PurposeIt has been suggested that, by recruiting lung regions and enlarging the distribution volume of the cold indicator, increasing the positive end-expiratory pressure (PEEP) may lead to an artefactual overestimation of extravascular lung water (EVLW) by transpulmonary thermodilution (TPTD).MethodsIn 60 ARDS patients, we measured EVLW (PiCCO2 device) at a PEEP level set to reach a plateau pressure of 30 cmH2O (HighPEEPstart) and 15 and 45 min after decreasing PEEP to 5 cmH2O (LowPEEP15′ and LowPEEP45′, respectively). Then, we increased PEEP back to the baseline level (HighPEEPend). Between HighPEEPstart and LowPEEP15′, we estimated the degree of lung derecruitment either by measuring changes in the compliance of the respiratory system (Crs) in the whole population, or by measuring the lung derecruited volume in 30 patients. We defined patients with a large derecruitment from the other ones as patients in whom the Crs changes and the measured derecruited volume were larger than the median of these variables observed in the whole population.ResultsReducing PEEP from HighPEEPstart (14 ± 2 cmH2O) to LowPEEP15′ significantly decreased EVLW from 20 ± 4 to 18 ± 4 mL/kg, central venous pressure (CVP) from 15 ± 4 to 12 ± 4 mmHg, the arterial oxygen tension over inspired oxygen fraction (PaO2/FiO2) ratio from 184 ± 76 to 150 ± 69 mmHg and lung volume by 144 [68–420] mL. The EVLW decrease was similar in “large derecruiters” and the other patients. When PEEP was re-increased to HighPEEPend, CVP, PaO2/FiO2 and EVLW significantly re-increased. At linear mixed effect model, EVLW changes were significantly determined only by changes in PEEP and CVP (p < 0.001 and p = 0.03, respectively, n = 60). When the same analysis was performed by estimating recruitment according to lung volume changes (n = 30), CVP remained significantly associated to the changes in EVLW (p < 0.001).ConclusionsIn ARDS patients, changing the PEEP level induced parallel, small and reversible changes in EVLW. These changes were not due to an artefact of the TPTD technique and were likely due to the PEEP-induced changes in CVP, which is the backward pressure of the lung lymphatic drainage.Trial registration ID RCB: 2015-A01654-45. Registered 23 October 2015
Highlights
Extravascular lung water (EVLW) is the amount of fluid present in the lungs, outside the pulmonary blood vessels [1]
In acute respiratory distress syndrome (ARDS), lung injury leads to increases in the pulmonary capillary permeability and in EVLW, which reflect the severity of the disease [2]
Many studies have investigated the changes in EVLW induced by a positive end-expiratory pressure (PEEP), which is the cornerstone of ARDS treatment (Additional file 1: Table S1)
Summary
Extravascular lung water (EVLW) is the amount of fluid present in the lungs, outside the pulmonary blood vessels [1]. Many studies have investigated the changes in EVLW induced by a positive end-expiratory pressure (PEEP), which is the cornerstone of ARDS treatment (Additional file 1: Table S1) They have provided very discordant results, some showing that EVLW augmented when increasing levels of PEEP were applied [3,4,5,6,7,8], some that it decreased [9,10,11,12,13,14,15,16,17] and some others that it did not change [18,19,20,21,22,23,24,25,26,27,28]. These studies did not investigate the potential artefact that may induce an increase in EVLW along with the PEEP level
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