While mechanical ventilation (MV) is life-saving in patients with acute respiratory failure, prolonged mechanical ventilation is associated with numerous potential complications. Recent studies have suggested that the ventilator is a likely cause of the decreased diaphragm force generating capacity (dFGC) seen in mechanically ventilated patients. Further, mode of ventilation has been associated with diaphragm atrophy, which has been identified as a key factor influencing dFGC. Animal studies suggest that even as little as 18 hours of mandatory modes of ventilation lead to diaphragm-muscle atrophy and weakness. This study utilizes ultrasound to investigate the rate at which diaphragm thickness changes in response to mode of MV in critically ill patients, and validates the reliability of our sonography techniques. We acquired daily ultrasonographic images of the right diaphragm in the zone of apposition in critically ill patients (n=8) in the ICU of the Royal Columbian hospital. As a control for generalized muscle wasting in the critically ill, we acquired daily ultrasonographic images of the quadriceps from each subject. Patients on all modes of ventilation were included. Inter-operator and inter-observer reliability tests were conducted. A mean increase in diaphragm thickness of 8.41±3.88% was detected over a mean of 5.5±4.28 days in all patients on PS ventilation (n=8), a mean increase of 1.53±1.39% per day. Patients ventilated on AC mode (n=4) showed a mean decline in diaphragm thickness of 21.2±10.8% over 4.5±4.4 days, an average decrease of 4.7±5.7% per day. Mean decline in quadriceps thickness for all participants in this study (n=8) was 14.4±13.6% over a mean period of 7.1±4.7 days, an average decline of 2±2.7% per day. Ultrasound provides a reliable non-invasive method of measuring diaphragm thickness and tracking rates of change in thickness in mechanically ventilated critically ill patients. This may be a useful tool in critical care units to identify patients who may be at risk of weaning difficulties secondary to diaphragms that are weakened as a result of atrophy.
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Thesis advisor: Hoffer, Andy
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