Mechanical ventilation, diaphragm weakness and weaning: a rehabilitation perspective

Abstract

Most patients are easily liberated from mechanical ventilation (MV) following resolution of respiratory failure and a successful trial of spontaneous breathing, but about 25% of patients experience difficult weaning. MV use leads to cellular changes and weakness, which has been linked to weaning difficulties and has been labeled ventilator induced diaphragm dysfunction (VIDD). Aggravating factors in human studies with prolonged weaning include malnutrition, chronic electrolyte abnormalities, hyperglycemia, excessive resistive and elastic loads, corticosteroids, muscle relaxant exposure, sepsis and compromised cardiac function. Numerous animal studies have investigated the effects of MV on diaphragm function. Virtually all these studies have concluded that MV use rapidly leads to VIDD and have identified cellular and molecular mechanisms of VIDD. Molecular and functional studies on the effects of MV on the human diaphragm have largely confirmed the animal results and identified potential treatment strategies. Only recently potential VIDD treatments have been tested in humans, including pharmacologic interventions and diaphragm "training". A limited number of human studies have found that specific diaphragm training can increase respiratory muscle strength in FTW patients and facilitate weaning, but larger, multicenter trials are needed.

Keywords: Diaphragm strength training; Ventilator induced diaphragm dysfunction; Ventilator weaning.

Figure 1

Effects of intermittent spontaneous breathing during controlled MV on diaphragm force – frequency relationship. This figure demonstrates the effects of allowing spontaneous breathing for five minutes out of every six hours on animals receiving controlled MV for 24 hours. The Control animals received no MV. The intermittent spontaneous breathing (ISB) group maintained more diaphragm force than the animals receiving continuous MV, but generated less force than the Control animals. Adapted with permission from Gayan-Ramirez, 2005.

Fig 2

Relationship between duration of pressure support mechanical ventilation (PSV) and twitch trans diaphragmatic pressure (Pdi) generation in ventilated patients. The greatest loss in Pdi occurs in the first 5–7 days of MV and the rate of Pdi loss slows after about 7 days. Adapted from Hermans, 2010.