Hemodynamic effects of lung recruitment maneuvers in acute respiratory distress syndrome.
BACKGROUND
Clinical trials have, so far, failed to establish clear beneficial outcomes of recruitment maneuvers (RMs) on patient mortality in acute respiratory distress syndrome (ARDS), and the effects of RMs on the cardiovascular system remain poorly understood.


METHODS
A computational model with highly integrated pulmonary and cardiovascular systems was configured to replicate static and dynamic cardio-pulmonary data from clinical trials. Recruitment maneuvers (RMs) were executed in 23 individual in-silico patients with varying levels of ARDS severity and initial cardiac output. Multiple clinical variables were recorded and analyzed, including arterial oxygenation, cardiac output, peripheral oxygen delivery and alveolar strain.


RESULTS
The maximal recruitment strategy (MRS) maneuver, which implements gradual increments of positive end expiratory pressure (PEEP) followed by PEEP titration, produced improvements in PF ratio, carbon dioxide elimination and dynamic strain in all 23 in-silico patients considered. Reduced cardiac output in the moderate and mild in silico ARDS patients produced significant drops in oxygen delivery during the RM (average decrease of 423 ml min-1and 526 ml min-1, respectively). In the in-silico patients with severe ARDS, however, significantly improved gas-exchange led to an average increase of 89 ml min-1in oxygen delivery during the RM, despite a simultaneous fall in cardiac output of more than 3 l min-1on average. Post RM increases in oxygen delivery were observed only for the in silico patients with severe ARDS. In patients with high baseline cardiac outputs (>6.5 l min-1), oxygen delivery never fell below 700 ml min-1.


CONCLUSIONS
Our results support the hypothesis that patients with severe ARDS and significant numbers of alveolar units available for recruitment may benefit more from RMs. Our results also indicate that a higher than normal initial cardiac output may provide protection against the potentially negative effects of high intrathoracic pressures associated with RMs on cardiac function. Results from in silico patients with mild or moderate ARDS suggest that the detrimental effects of RMs on cardiac output can potentially outweigh the positive effects of alveolar recruitment on oxygenation, resulting in overall reductions in tissue oxygen delivery.
School of Engineering, University of Warwick, Nottingham, CV4 7AL, UK.
Anup
A
Das
Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, NG7 2UH, UK.
Mainul
M
Haque
Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, NG7 2UH, UK.|Nottingham University Hospitals NHS Trust, Nottingham, NG7 2UH, UK.
Marc
M
Chikhani
Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, NG7 2UH, UK.
Oana
O
Cole
School of Engineering, University of Warwick, Nottingham, CV4 7AL, UK.
Wenfei
W
Wang
Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Nottingham, NG7 2UH, UK. J.Hardman@nottingham.ac.uk.|Nottingham University Hospitals NHS Trust, Nottingham, NG7 2UH, UK. J.Hardman@nottingham.ac.uk.
Jonathan G
JG
Hardman
School of Engineering, University of Warwick, Nottingham, CV4 7AL, UK.
Declan G
DG
Bates
D002245:Carbon Dioxide / Q000097:blood; D006439:Hemodynamics; D006801:Humans; D008170:Lung Compliance; D010102:Oxygen Inhalation Therapy; D066230:Patient-Specific Modeling; D011175:Positive-Pressure Respiration / Q000379:methods*; D011659:Pulmonary Gas Exchange; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D015656:Respiratory Mechanics; D012720:Severity of Illness Index
D002245:Carbon Dioxide
Acute respiratory distress syndrome; Carbon dioxide clearance; Cardiac output; Computational modelling; Mechanical ventilation; Oxygen delivery; Positive end expiratory pressure; Recruitment maneuvers; Strain