Etiology The U.S. Experience

In addition to the cardiopulmonaiy dysfunction, a major factor that influences weaning is the use of sedatives and hypnotics, which depress respiratory drive and level of consciousness, leading to prolonged dependence on mechanical ventilation. Patients admitted to our regional weaning center had a mean of 12 medications prescribed prior to admission whereas on admission this could be reduced to nine medications, a reduction of 33%. Most of these medications were sedatives and h)q)notics. 

Nutritional status is crucial in the care of ventilated patients, as malnutrition reduces respiratory muscle mass and contributes to failure to wean from PMV (22-25). Therefore, 

Other metabolic factors contributing to PMV include hypophosphatemia and hypomagnesemia, both of which have been associated with diminished diaphragmatic function. Hypothyroidism is an uncommon cause of ventilator dependency (27), being associated with respiratory muscle weakness as well as altered ventilatory drive and upper airway obstruction. Hypothyroidism is a potentially treatable cause of failure to wean and it should be considered in patients with prolonged ventilator dependence. 

Acute renal failure in association with respiratory failure has a mortality rate as high as 89% (28), although the influence of renal function on weaning has not been fully investigated. Scheinhorn et al. (29) included renal function in their scoring system, which is devised to predict the chance of weaning success after six weeks of ventilation. Datta and Scalise also reported that renal function correlated indirectly with weaning success (30). 

Dasta JF, McLaughlin TP, Mody SH, et al. Daily cost of an intensive care unit day the contribution of mechanical ventilation. Crit Care Med 2005 33(6) 1266-1271. 

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