Study objectives: To determine if minute ventilation (V̇e) measured as a trend following the final weaning trial prior to extubation may identify patients ready for extubation and be useful as a predictive measure of extubation outcome.
Design: Prospective observational study.
Setting: Community hospital medical/surgical ICU.
Patients: Sixty-nine patients receiving mechanical ventilation enrolled in an ICU weaning protocol who underwent planned extubation during 6 months of prospective evaluation. The failed extubation group included patients reintubated within 7 days. Patients were excluded if they received ventilation by noninvasive mask, bilevel positive airway pressure, tracheostomy, or were self-extubated.
Interventions: Patients tolerating a spontaneous breathing trial (SBT) and ready for planned extubation were placed back on their pre-SBT ventilator settings for up to 25 min, during which respiratory parameters were recorded. Respiratory parameters (respiratory rate, tidal volume, V̇e, rapid shallow breathing index [f/Vt]) were obtained at three time points: baseline (pre-SBT), posttrial (immediate conclusion of SBT), and recovery (return to baseline). Patients were assumed to recover when V̇e decreased to 110% of the predetermined baseline.
Measurements and results: Fifty-nine patients were successfully extubated, and 10 patients required reintubation after 2.5 ± 2.6 days (mean ± SD). Both groups were similar in age, comorbid status, primary diagnosis, APACHE (acute physiology and chronic health evaluation) II score, mode of weaning, and SBT length (p > 0.1). Respiratory parameters measured were similar at all three time points studied (p > 0.1). V̇e recovery time of successful extubations was significantly shorter than failed extubations (3.6 ± 2.7 min vs 9.6 ± 5.8 min, p < 0.011). Multiple logistic regression adjusted for age, sex, and severity of illness revealed that V̇e recovery time was an independent predictor of extubation outcome (p < 0.01). The area under the receiver operating characteristic curve for V̇e recovery time (0.85 ± 0.07) was larger than that for baseline V̇e, posttrial V̇e, posttrial f/Vt, or Paco2.
Conclusions: V̇e recovery time is an easy-to-measure parameter that may assist in determining respiratory reserve. Preliminary data demonstrates that it may be a useful adjunct in the decision to discontinue mechanical ventilation.