[Utility of the dead space fraction (Vd/Vt) as a predictor of extubation success]

Abstract

Purpose: To determine the value of Vd/Vt as a predictor of extubation failure in patients with mechanical ventilation admitted to the intensive care units.

Design: A prospective, observational cohort study conducted from 1 September 2010 to 1 March 2011.

Setting: General intensive care unit (G-ICU) of a third level university hospital.

Patients or participants: The study included patients on mechanical ventilation (MV) for over 12 hours, and who in the process of weaning were subjected to low-level pressure support. Exclusion criteria were age under 18 years, ventilation via tracheotomy and patients failing to cooperate for different reasons. During the study, 392 patients were admitted to the G-ICU; of these, 214 required MV. The weaning process was started in 154 cases. Fifty-four patients were excluded from the study, and 24 were not extubated from MV. A total of 76 patients were finally extubated and analyzed.

Variables of interest: Vd/Vt was calculated as the ratio (PaCO(2)-Pє CO(2))/PaCO(2), with the recorded parameters.

Results: Logistic regression analysis showed a significant association between the Vd/Vt and extubation failure, with OR=1.52 (95%CI 1.11 to 2.09, p=0.008). The area under the ROC curve with respect to the prediction of extubation failure according to the Vd/Vt value was 0.94 (95%CI 0.86 to 0.98, p<0.0001).

Conclusions: Vd/Vt is a powerful predictor of extubation failure in patients on MV.