Objective: To compare the respiratory rate to tidal volume ratio with the oxygen cost of breathing to see which could more accurately predict the outcome of ventilator weaning for surgical patients.
Design: Prospective comparison of two modalities used to predict the likelihood of successful ventilator weaning.
Patients: Twenty-eight consecutive patients with chronic respiratory insufficiency requiring long-term mechanical ventilation in the surgical intensive care unit at New England Deaconess Hospital, Boston, Mass, were studied.
Main outcome measures: The oxygen cost of breathing and the respiratory rate to tidal volume ratio were measured during spontaneous breathing. Patients extubated within 2 weeks of being studied were designated as extubated while patients not extubated within this period or requiring reintubation were recorded as not extubated.
Results: The oxygen cost of breathing predicted successful extubation in all five patients who were extubated, and failure in 20 of 23 patients who could not be extubated (sensitivity, 100%; specificity, 87%). In contrast, the respiratory rate to tidal volume ratio predicted extubation for only two of five patients who were extubated and predicted failure in only 12 of 23 patients who could not be extubated (sensitivity, 40%; specificity, 52%).
Conclusion: For this group of patients requiring prolonged ventilation, the oxygen cost of breathing proved to be a more reliable predictor of both successful extubation and failure.