Diaphragm muscle thinning in patients who are mechanically ventilated

Approximately 40% of patients in medical ICUs require mechanical ventilation (MV). Approximately 20% to 25% of these patients will encounter difficulties in discontinuing MV. Multiple studies have suggested that MV has an unloading effect on the respiratory muscles that leads to diaphragmatic atrophy and dysfunction, a process called ventilator-induced diaphragmatic dysfunction (VIDD). VIDD may be an important factor affecting when and if MV can be discontinued. A sensitive and specific diagnostic test for VIDD could provide the physician with valuable information that might influence decisions regarding extubation or tracheostomy. The purpose of this study was to quantify, using daily sonographic assessments, the rate and degree of diaphragm thinning during MV.

Seven intubated patients receiving MV during acute care were included. Using sonography, diaphragm muscle thickness was measured daily from the day of intubation until the patient underwent extubation or tracheostomy or died. We analyzed our data using standard descriptive statistics, linear regression, and mixed-model effects.

The overall rate of decrease in the diaphragm thickness of all seven patients over time averaged 6% per day of MV, which differed significantly from zero. Similarly, the diaphragm thickness decreased for each patient over time.

Sonographic assessment of the diaphragm provides noninvasive measurement of diaphragmatic thickness and the degree of diaphragm thinning in patients receiving MV. Our data show that diaphragm muscle thinning starts within 48 h after initiation of MV. However, it is unclear if diaphragmatic thinning correlates with diaphragmatic atrophy or pulmonary function. The relationship between diaphragm thinning and diaphragm strength remains to be elucidated.