Introduction: In the present study, we investigated the behavior of adaptive support ventilation (ASV) in patients after cardiothoracic surgery. We determined tidal volumes (Vt) and factors that influence Vt with this mode of microprocessor-controlled mechanical ventilation (MV).
Methods: This was a prospective, multicenter, observational study in three Dutch intensive care units over a 5-mo period. MV data were collected during steady-state after arrival in the intensive care unit.
Results: Data were collected for 346 consecutive patients after cardiothoracic surgery: 262 patients weaned with ASV, and 84 patients weaned with pressure-controlled/pressure-support MV. With ASV the mean (+/- sd) Vt expressed per kilogram actual body weight was 7.1 +/- 1.6 mL. Expressed per kilogram ideal body weight (IBW), Vt was 8.3 +/- 1.5 mL. In patients with a correctly set body weight (SBW) (i.e., the IBW), Vt was 8.1 +/- 1.4 mL/kg. With pressure-controlled/pressure-support-MV Vt was 7.3 +/- 1.4 mL/kg IBW (P < 0.001 vs ASV). Multivariate logistic regression analysis showed Vt with ASV to be dependent on only two parameters: respiratory rate and the correctness of SBW.
Conclusions: Vt with ASV seems to be dependent on two parameters: respiratory rate and the correctness of SBW. The first factor is not clinically important because respiratory rate is automatically chosen by the microprocessor. The second factor is clinically important because it is the only factor that can be influenced by the operator. Our data show the importance of setting the correct weight with ASV. With ASV, Vt are >8 mL/kg IBW in a substantial number of patients. Randomized clinical trials should be performed to compare ASV with other ventilation modes.