Predicting 3-day and 7-day outcomes of weaning from mechanical ventilation.

OBJECTIVE: To determine the correlation of acute physiology and chronic health evaluation (APACHE) II score and various weaning indexes (WIs) with 3- and 7-day weaning outcomes.
DESIGN: Prospective, observational.
SETTING: The medical ICU of a teaching, urban hospital.
METHODS: The study included 118 adults referred for weaning from mechanical ventilation (MV). Critical care physicians, critical care nurses, and respiratory care practitioners were asked to predict whether it would take < or =3 days, 4 to 7 days, or > or =8 days to wean each patient from MV. The WIs and APACHE II scores were measured or calculated. The causes of respiratory failure, the duration of MV before initiating weaning assessment, and the 3- and 7-day weaning outcomes were obtained. Significance was set at p<0.05.
RESULTS: The most common causes of respiratory failure were pneumonia (38 cases) and acute exacerbation of COPD (29 cases). Fifty-seven patients (48%) were successfully weaned from MV within 3 days of weaning assessment, and 67 (57%) were weaned within 7 days. The percentages of correct prediction of 3-day weaning outcome by critical care physicians, critical care nurses, and respiratory care practitioners were 64%, 62%, and 59%, respectively; for 7-day weaning outcome, 60%, 64%, and 58%, respectively. The successfully weaned groups had significantly lower APACHE II scores and higher maximal inspiratory pressures than the unsuccessfully weaned (failure) groups. There were no significant differences between the two groups for the remaining indexes, including rapid shallow breathing, dynamic compliance, static compliance, spontaneous respiratory rate, and the ratio of PaO2 to the fraction of inspired oxygen.
CONCLUSIONS: The overall severity of illness as assessed by APACHE II score correlates better with 3- and 7-day weaning outcome than the published WIs.