Background: Intensive care unit-acquired weakness (ICU-AW) research focuses predominantly on intrinsic muscle pathology rather than integrated systemic interactions, which are commonly studied in exercise science. Peak oxygen uptake (V˙O2peak), V˙O2 on/off kinetics, and skeletal muscle oxygenation provide a quantitative evaluation of exercise capacity and are infrequently measured in intensive care unit (ICU) survivors. Routine cardiopulmonary exercise test (CPET) research separates V˙O2peak and V˙O2 kinetics assessments into multiple sessions. Yet, a combined experimental approach may enhance diagnosis, follow-up retention, and mechanistic insight for patients with ICU-AW. Objective: This prospective cross-sectional observational study aims to develop a standardized, single-session CPET protocol for combined assessment of V˙O2peak, V˙O2 kinetics, and skeletal muscle microvascular oxygenation in ICU survivors, enabling quantitative and integrated assessment of ICU-AW. Methods: Adults mechanically ventilated for ≥7 days will be recruited to participate 6 months post-ICU discharge in a modified CPET exercise session on an upright cycle ergometer. The proposed standardization will involve (1) the estimation of V˙O2peak using a priori formulas with a V˙O2peak correction factor for the ICU population, (2) V˙O2 on-kinetics (constant work rate) targeting relative 30% V˙O2reserve, (3) an incremental ramp exercise based on self-reported functional status, and (4) a 10-minute recovery to quantify V˙O2 off-kinetics. In addition, near-infrared spectroscopy will be placed on the vastus lateralis muscle to simultaneously collect tissue saturation index and deoxyhemoglobin during each phase of the protocol. Results: Recruitment is anticipated to begin in June 2026 and is expected to be completed in 2029/2030. The anticipated sample size will be approximately 48 participants based on the feasibility of recruiting 1 participant per month and a sample size calculation based on Bland-Altman limits of agreement between predicted and measured V˙O2peak. Conclusions: The intensive care unit combined assessment of cardiorespiratory exercise (ICU-CARE) CPET protocol will enable the quantitative evaluation of V˙O2peak, V˙O2 on/off kinetics, and local microvascular skeletal muscle oxygenation during a single exercise session, facilitating the integrated physiological study of ICU-AW.
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Blunderfield et al. (2026) studied this question.
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