Metabolic Response to Supine Physiotherapy in Mechanically Ventilated ICU Patients

Critically ill patients who require mechanical ventilation frequently experience rapid loss of muscle mass and physical function during their stay in the intensive care unit (ICU). As part of standard care, physiotherapy and limb mobilization exercises are commonly provided, even in patients who are sedated and confined to bed in a supine position. However, the actual physiological and metabolic intensity of these routine physiotherapy interventions is poorly understood, and current prescriptions are largely based on clinical judgment rather than objective measures of patient effort or tolerance. Oxygen consumption (VO₂) is a direct indicator of metabolic demand and physiological workload. In mechanically ventilated patients, indirect calorimetry integrated into the ventilator allows continuous measurement of VO₂ and carbon dioxide production without adding invasive procedures. While indirect calorimetry is routinely used to individualize nutritional support in the ICU, its potential role in quantifying the metabolic cost of physiotherapy interventions has been scarcely explored. The aim of this prospective observational study is to quantify the acute metabolic response to a standardized session of supine physiotherapy in adult critically ill patients receiving invasive mechanical ventilation. During routine physiotherapy sessions performed as part of usual care, oxygen consumption will be continuously measured using indirect calorimetry integrated into the ventilator circuit. Each session will include a baseline resting period, the physiotherapy intervention itself, and a post-intervention recovery period, allowing patients to act as their own controls. Physiotherapy sessions will consist of passive limb mobilization in deeply sedated patients and passive or active-assisted mobilization in patients who are awake or lightly sedated and able to cooperate. The primary outcome will be the change in oxygen consumption during physiotherapy compared with baseline rest.