Evaluation of indexes predicting the outcome of ventilator weaning and value of adding supplemental inspiratory load.

OBJECTIVE: To assess the diagnostic accuracy of several measured and calculated indexes for early prediction of weaning outcome, and to study the value of supplemental inspiratory load in improving the accurate prediction of successful weaning.

DESIGN: Prospective study.

SETTING: ICU of a University Hospital.

PATIENTS: Thirty consecutive patients under prolonged mechanical ventilation and without chronic obstructive pulmonary disease (COPD).

INTERVENTIONS: Forty weaning trials were performed. Data were recorded at 15, 30 (adding inspiratory flow resistance), 60 and 120 min.

MEASUREMENTS AND MAIN RESULTS: The threshold values and the accuracy of three indexes were determined: Inspiratory airway occlusion pressure at 0.1 sec. (P01) to maximum inspiratory pressure ratio (P01/MIP), inspiratory effort quotient (IEQ), and the ratio of respiratory frequency to tidal volume (F/Vt). All three were useful predictors for weaning success with a diagnostic accuracy between 82%-87%. At 15 min of spontaneous breathing, a P01/MIP ratio < 0.14 predicts weaning success with a sensitivity of 82% and specificity of 83%. In our group of patients no reintubation was necessary. The application of mechanical inspiratory load significantly increased P01 values (3.16 +/- 1.22 to 3.60 +/- 1.19, p < 0.001). The degree of the P01 increase did not provide prediction of weaning outcome.

CONCLUSIONS: a) P01/MIP, IEQ and F/Vt ratio were accurate, early predictors of weaning outcome. b) The addition of a moderate mechanical inspiratory load did not enhance the diagnostic accuracy of P01 measurements. c) In our patients, a period of two hours seemed to be sufficient for development and detection of weaning failure.