Evaluation of simple criteria to predict successful weaning from mechanical ventilation in intensive care patients.

BACKGROUND: There is increasing evidence that weaning protocols improve outcome from mechanical ventilation, but it is unclear how best to implement such protocols in large intensive care units. We evaluated a checklist of simple bedside criteria to determine whether it could be used reliably to predict successful discontinuation of mechanical ventilation.
METHODS: We carried out a prospective observational cohort study in a 12-bedded general intensive care unit (ICU). We developed a checklist of metabolic, cardiorespiratory and neurological criteria that suggested that patients should start the weaning process. We performed daily assessments throughout ICU stay and recorded whether the criteria were met. Ultimate ventilator independence was used as the reference standard.
RESULTS: We studied 325 sequential admissions to the ICU. Data were available for 98% of patients; 97% of admissions were mechanically ventilated on admission to ICU. Overall, 205 of the 308 ventilated patients (67%) achieved ventilator independence during ICU admission; the other patients died or were transferred ventilated to other ICUs. Eighty-three per cent of the patients who achieved ventilator independence met the set criteria. Fulfilling the criteria was a moderately strong predictor of ultimate ventilator independence: specificity 89%, positive predictive value 94%, positive likelihood ratio (LR) 7.6. When we analysed data by the day from admission on which patients were examined, the test was a strong predictor of subsequent ventilator independence when criteria were met by day 1 (LR 11.1) or day 2 (LR 6.9), but weaker when met by more than/equal to 4 days (LR <3). Patients who met criteria after more than/equal to 4 days often had prolonged weaning and a high incidence of re-intubation. Patients who achieved ventilator independence without fulfilling the criteria (n=35) had a short duration of mechanical ventilation (median 2 days, interquartile range 1-3 days). The most frequent reason for failing criteria before ventilator independence was a Pa(O(2))/FI(O(2)) ratio less than 24 kPa (49% of cases).
CONCLUSIONS: A simple checklist can assist nurse assessment of suitability for weaning and could be used as a trigger to commence a weaning protocol. The day on which criteria are met is a useful way of stratifying patients for likely patterns of weaning.