Dependence upon prolonged mechanical ventilation and inability to wean may result from a number of factors. The primary reason is failure of resolution of the initial condition that precipitated dependence upon mechanical ventilation. However, in addition to psychological and cognitive factors, patients with critical illness rapidly lose muscle mass and their inability to preserve strength results in decreased respiratory muscle strength. (25)
Metabolic disorders associated with critical illness can negatively impact the ability to wean, (26,27) Because of the difficulty of maintaining a sound nutritional balance, protein catabolism may occur, resulting in decreased respiratory muscle mass. Overfeeding may result in an increased ventilator requirement from production of carbon dioxide. (28, 29)
Frequent infections further weaken patients on mechanical ventilation support. The outcome for patients on long-term mechanical ventilation is generally poor, with high mortality rates and poor quality of life. One observational study of 1419 patients on prolonged mechanical ventilation who were admitted for a year to a ventilator weaning facility revealed a one-year mortality rate of 52 percent. Patients who were admitted for end-of-life care, or who were thought to be incapable of weaning, were excluded from the study. (30)
