Factors of tidal volume variation during augmented spontaneous ventilation in patients on extracorporeal carbon dioxide removal. A multivariate analysis.

ABSTRACT

BACKGROUND: Extracorporeal carbon dioxide removal (ECCO2-R) allows lung protective ventilation using lower tidal volumes (VT) in patients with acute respiratory failure. The dynamics of spontaneous ventilation under ECCO2-R has not been described previously. This retrospective multivariable analysis examines VT patterns and investigates the factors that influence VT, in particular sweep gas flow and blood flow through the artificial membrane. METHODS: We assessed VT, respiratory rate (RR), minute ventilation (MV), and levels of pressure support (0-24 cm H2O), sweep gas flow (0-14 L/min) and blood flow through the membrane (0.8-1.8 L/min) in 40 patients from the moment they were allowed to breathe spontaneously. Modest hypercapnia was accepted. RESULTS: Patients tolerated moderate hypercapnia well. In a generalized linear model the increase in sweep gas flow (P<0.001), a low PaCO2 (P=0.029), and an increased breathing frequency (P<0.001) were associated with lower VT. Neither blood flow through the membrane (P=0.351) nor the level of pressure support (P=0.595) influenced VT size. CONCLUSION: Higher sweep gas flow is associated with low VT in patients on extracorporeal lung assist and augmented spontaneous ventilation. Such a technique can be used for prolonged lung protective ventilation even in the patient's recovery period.