Ventilator-associated respiratory muscle dysfunction

New-onset respiratory muscle weakness may result from conditions that are unique to mechanically ventilated patients, such as ventilator-associated respiratory muscle dysfunction, sepsis-associated myopathy, and ICU-acquired paresis (63). New-onset respiratory muscle weakness may also result from conditions that are not unique to critically ill patients, such as acid-base disorders, electrolyte disturbances, decreased oxygen delivery, and medications (63). 

In laboratory animals, controlled mechanical ventilation delivered for 1 to 11 days can decrease diaphragmatic force generation by 20-50% and can cause similar decreases in diaphragmatic endurance (40). Several mechanisms, including stmctural injury, muscle atrophy, and oxidative stress, appear to be responsible for ventilator-associated respiratory muscle dysfunction (40). Of interest, in a study of more than 200 critically ill patients— 80% of whom required acute ventilator support—duration of mechanical ventilation was nearly three days shorter in those who completed a 10-day antioxidant supplementation protocol (vitamins E and C) than in those who completed a 10-day course of placebo (76). 

Whether ventilator-associated respiratory muscle dysfunction occurs in humans is unclear. In 13 infants who received uninterrupted ventilator assistance for at least 12 days before death, most diaphragmatic fibers appeared atrophic (Fig. 9) (77). These data are supported by a recent preliminary report of Levine et al. (78) who compared costal diaphragm biopsies of six brain-dead organ donors maintained on controlled mechanical ventilation for... 

Given the possible relationship between decreases in protein synthesis and ventilator-associated respiratory muscle dysfunction, it would seem plausible that administration of anabolic factors, such as growth hormone, might be beneficial to ventilated patients. Unfortunately, when growth hormone was administered to patients requiring PMV, duration of mechanical ventilation was not decreased nor was muscle strength increased (80). The report that recombinant growth hormone can increase mortality of critically ill patients is a matter of concern (81). 

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