The unassisted respiratory rate-tidal volume ratio accurately predicts weaning outcome

W Chatila, B Jacob, D Guaglionone, C A Manthous
American Journal of Medicine 1996, 101 (1): 61-7

PURPOSE: To assess the accuracies of four commonly used parameters in predicting weaning outcome and whether breathing pattern changes during weaning.

PATIENTS AND METHODS: We prospectively examined the predictive accuracies of four weaning parameters in mechanically ventilated patients in the medical and cardiac intensive care units of a 270-bed community teaching hospital. The spontaneous respiratory rate:tidal volume ratio (RVRi), negative inspiratory force (NIF), and spontaneous minute volume (VE) at the onset of weaning, and the RVR at 30 to 60 minutes of weaning (RVR30) were measured. Weaning decisions were made by patients' primary physicians independent of this study. Threshold values for computations of predictive values were as follows: RVR 100 < or = breaths per minute/L, NIF < or = -20 cm H2O, VE < or = 10 Lpm. Receiver operator curves were generated for each parameter.

RESULTS: One hundred medical/cardiac intensive care unit patients were studied. Their mean age was 64.6 +/- 15.8 years, mean APACHE II score of 15.8 +/- 6.7 and mean duration of mechanical ventilation before the study of 4.9 +/- 8.1 days. RVRi sensitivity was 89%, specificity was 41%, positive predictive value was 72%, negative predictive value was 68%, and accuracy was 71%. The RVR30 sensitivity was 98%, specificity was 59%, positive predictive value was 83%, negative predictive value was 94%, and accuracy was 85%. Accuracies for the NIF and VE were 66% and 62%, respectively. The area under the receiver operator curve of the RVR30 (0.92 +/- 0.03) was higher than the RVRi (0.74 +/- 0.05), NIF (0.68 +/- 0.06) and VE (0.54 +/- 0.06) (p < 0.05).

CONCLUSIONS: The RVR is more accurate than other commonly utilized clinical tools in predicting the outcome of weaning from mechanical ventilation. The RVR measured at 30 minutes is superior to the RVR in the first minute of weaning. The predictive accuracy and unique simplicity of the RVR justify its use in the care of mechanically ventilated patients.

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