icu

The Weaning Process: Traditional Methods of Assessment

　　 In the ICU, up to 20% of mechanically ventilated patients will repeatedly fail attempts at weaning their ventilatory support.[2] Of the intubated patients in the ICU, 14% to 22% will require reintubation after being extubated.[3-5] This carries an associated cost in both dollar terms and an increase in hospital mortality (up to 40%).[3] There would thus appear to be room for techniques that might improve our management in this area of critical care medicine.
　　When does weaning start? This dynamic process usually begins during patient recovery at some undefined point that is determined by the bedside physician. This subjectivity inevitably decreases the reproducibility of any study and makes the results less reliable for extrapolation to clinical practice. Standard indices for assessing patient "weanability" include: resolution of the etiology of respiratory failure (decreased inspired oxygen fraction [FIO2] and need for positive end-expiratory pressure [PEEP]), hemodynamic stability (at least tolerating a reduction in inotropic support), and adequate respiratory muscle function (acceptable respiratory rate).
　　Traditional predictors of weaning success that rely on patient cooperation and effort (including maximum inspiratory effort, vital capacity, and maximum voluntary ventilation) have an understandably high false negative predictive rate.[2] The Table below lists some commonly used weaning criteria. Widely accepted clinical signs and symptoms associated with failure to wean include a respiratory rate greater than 35 breaths/minute, arterial oxygen saturation (SaO2) less than 90%, heart rate higher than 140 beats/minute (or a sustained increase or decrease of > 20% in the heart rate), systolic blood pressure of more than 180 mm Hg, agitation, anxiety, or distress.[1] There is some evidence that spontaneous breathing trials and different modes of ventilation may play a role in the ability to successfully wean mechanical support and the time required for the weaning process.