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Insights into the increased oxygen demand during chest physiotherapy
K Horiuchi1, D Jordan, D Cohen
1Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, NY, USA.
Critical Care Medicine
|August 1, 1997
Summary
Chest physical therapy increases oxygen consumption (VO2) primarily due to muscular activity, not just patient positioning. Muscle relaxants significantly reduced this increased oxygen demand, confirming exercise-like physiological responses.
Area of Science:
- Physiology
- Critical Care Medicine
Background:
- Chest physical therapy (CPT) is a common intervention in intensive care units.
- The physiological impact of CPT, particularly on metabolic demand, requires further elucidation.
- Understanding the mechanisms behind increased oxygen consumption during CPT is crucial for patient management.
Purpose of the Study:
- To identify the primary mechanism driving the increase in oxygen consumption (VO2) during CPT.
- To test the hypothesis that increased muscular activity is the main contributor to elevated oxygen demand.
- To differentiate between exercise-like and stress-like responses to CPT.
Main Methods:
- A prospective, observational study was conducted in a surgical intensive care unit.
- Phase 1 involved 13 mechanically ventilated patients undergoing turning to the lateral decubitus position.
- Phase 2 involved 7 mechanically ventilated patients receiving midazolam and vecuronium (a muscle relaxant) before CPT sessions.
Main Results:
- Turning patients to the lateral position significantly increased oxygen uptake (VO2) and CO2 elimination (VCO2).
- The muscle relaxant vecuronium completely abolished the increases in VO2 and VCO2 observed during CPT.
- Increases in blood pressure and cardiac output were not affected by vecuronium, suggesting a different underlying mechanism.
Conclusions:
- The elevated metabolic demand during CPT is predominantly caused by increased muscular activity.
- The observed increases in VO2 during CPT are comparable to those seen with physical exertion.
- Elevated blood pressure and cardiac output during CPT likely result from sympathetic nervous system activation.