1996 OPEN FORUM Abstracts
Ventilatory Strategies in the Difficult-to-Wean Patient
Neil R. Maclntyre, MD Monday, November 4, 1996
Weaning a patient from mechanical ventilatory support is determined by three major factors: 1) resolution of disease, 2) development of iatrogenic injuries, 3) aggressiveness of the weaning approach. Ventilator strategies must always be looked at as support strategies, not therapeutic strategies. As such, ventilator strategies can have no impact on resolution of disease. On the other hand, ventilator strategies to minimize iatrogenic injury can be very important. Specific strategies that might be useful in this regard are modes that promote comfort (and therefore reduce sedation needs), modes that reduce volutrauma, and modes that do not result in excessive muscle fatigue. Pressure targeted strategies (pressure support, pressure assist) have been shown to improve patient comfort in dyspneic patients with active ventilatory drives. In this sense, they may reduce the need for sedation.
Modes that facilitate clinician aggressiveness are also important. Specifically, a mode that does not force a clinician to continuously reassess the patient for reductions in support can unnecessarily delay the weaning process.
Regardless of mode, careful assessment of respiratory muscle fatigue must be always done. Perhaps most sensitive indicator of impending fatigue is the respiratory frequency, perhaps the frequency/tidal volume ratio. Regardless of mode use, enough support should be given so that fatigue is not likely to develop. Finally, the ventilatory strategy ought to be one that should promote clinician aggressiveness. In this sense, the t-piece trial is the most aggressive. This, however, must be balanced with the potential for fatigue if left unmonitored. Pressure targeted strategies, while more comfortable, need to be followed carefully by clinicians to make sure aggressive weaning takes place.