A randomized, controlled trial of the role of weaning predictors in clinical decision making.

OBJECTIVE: Weaning predictors are often incorporated in protocols to predict weaning outcome for patients on mechanical ventilation. The predictors are used as a decision point in protocols to determine whether a patient may advance to a spontaneous breathing trial. The impact of including predictors in a weaning protocol has not been previously studied. We designed a study to determine the effect of including a weaning predictor (frequency-tidal volume ratio, or f/Vt) in a weaning protocol. DESIGN: Randomized, blinded controlled trial. SETTING: Academic teaching hospitals. PATIENTS: Three hundred and four patients admitted to intensive care units at three academic teaching hospitals. INTERVENTIONS: Patients were screened daily for measures of oxygenation, cough and secretions, adequate mental status, and hemodynamic stability. Patients were randomized to two groups; in one group the f/Vt was measured but not used in the decision to wean (n = 151), but in the other group, f/Vt was measured and used, using a threshold of 105 breaths/min/L (n = 153). Patients passing the screen received a 2-hr spontaneous breathing trial. Patients passing the spontaneous breathing trial were eligible for an extubation attempt. MEASUREMENTS AND MAIN RESULTS: Groups were similar with regard to gender, age, and Acute Physiology and Chronic Health Evaluation II score. The median duration for weaning time was significantly shorter in the group where the weaning predictor was not used (2.0 vs. 3.0 days, p = .04). There was no difference with regard to the extubation failure, in-hospital mortality rate, tracheostomy, or unplanned extubation. CONCLUSIONS: Including a weaning predictor (f/Vt) in a protocol prolonged weaning time. In addition, the predictor did not confer survival benefit or reduce the incidence of extubation failure or tracheostomy. The results of this study indicate that f/Vt should not be used routinely in weaning decision making.

Development and prospective validation of a model for predicting weaning in chronic ventilator dependent patients.

BACKGROUND: Approximately ten percent of patients placed on mechanical ventilation during acute illness will require long-term ventilator support. Unfortunately, despite rehabilitation, some will never be liberated from the ventilator. A method of predicting weaning outcomes for these patients could help conserve resources and minimize frustrating failed weaning attempts for this population. The objective of this investigation was to identify predictors of weaning outcome for patients admitted to a chronic ventilator unit (CVU). METHODS: This was a retrospective analysis with prospective validation. The study setting was a 25 bed CVU within a rehabilitation hospital. The training group consisted of 43 patients referred to our facility for weaning after > 3 weeks of mechanical ventilation. A multivariate model to predict weaning outcome was constructed in this group and applied to a prospective group of 31 patients followed during an 18-month period. RESULTS: A modified Glasgow Coma Scale (GCS) and the presence of sustained spontaneous respirations (SSR), defined as the presence of 2 breaths recorded above the ventilator settings on four occasions, were highly predictive of weaning success within six months of CVU admission. Patients with a modified GCS > or = 8 were 6.5 times more likely to wean than those with a modified GCS < 8 (95% confidence interval 1.6-26.3) and those with SSR were 25.5 times more likely to wean than those without SSR (95% confidence interval 4.3-51.9). CONCLUSIONS: In our population of CVU patients, simple parameters that were available on admission and did not directly reflect cardiopulmonary function were useful predictors of weaning outcome.

Hemodialysis-associated methemoglobinemia in acute renal failure.

Patients on maintenance hemodialysis are vulnerable to chloramine toxicity if chloramines are inadequately removed. We report two critically ill patients with acute renal failure who developed methemoglobinemia during hemodialysis in the intensive care unit. During the same period, methemoglobin levels measured from 30 patients in the outpatient dialysis facility were undetectable. Methemoglobin levels normalized when the carbon filtration system of the portable dialysis machine was replaced with a larger unit to remove chloramines more effectively. Causes, treatment, and prevention of chloramine toxicity in patients receiving dialysis in the intensive care unit are discussed.