THE UNASSISTED RESPIRATORY RATE TIDAL VOLUME RATIO ACCURATELY PREDICTS WEANING OUTCOME

PURPOSE: To assess the accuracies of four commonly used parameters in predicting weaning outcome and whether breathing pattern changes durin g weaning. PATIENTS AND METHODS: We prospectively examined the predict ive accuracies of four weaning parameters in mechanically ventilated p atients in the medical and cardiac intensive care units of a 270-bed c ommunity teaching hospital. The spontaneous respiratory rate:tidal vol ume ratio (RVR(i)), negative inspiratory force (NIF), and spontaneous minute volume (V-E) at the onset of weaning, acid the RVR at 30 to 60 minutes of weaning (RVR(30)) were measured. Weaning decisions were mad e by patients' primary physicians independent of this study. Threshold values: for computations of predictive values were as follows: RVR 10 0 less than or equal to breaths per minute/L, NIF less than or equal t o-20 cm H2O, V-E less than or equal to 10 Lpm. Receiver operator curve s were generated for each parameter. RESULTS: One hundred medical/card iac 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 duratio n of mechanical ventilation before the study of 4.9 +/- 8.1 days. RVR( i) sensitivity was 89%, specificity was 41%, positive predictive value was 72%, negative predictive value was 68%, and accuracy was 71%. The RVR(30) 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 V-E were 66% and 62%, respectively. The area under the receiver operator curve of the RVR(30) (0.92 +/- 0.03) was higher than the RVR(i) (0.74 +/- 0.05), NIF (0.68 +/- 0.06) and V- E (0.54 +/- 0.06) (p < 0.05). CONCLUSIONS: The RVR is more accurate th an other commonly utilized clinical tools in predicting the outcome of weaning from mechanical ventilation. The RVR measured at 30 minutes i s superior to the RVR in the first minute of weaning. The predictive a ccuracy and unique simplicity of the RVR justify its use in the care o f mechanically ventilated patients.