Standardized Single-Session Cardiopulmonary Exercise Test for Measuring Peak Oxygen Uptake, Oxygen On/Off Kinetics, and Skeletal Muscle Oxygenation in ICU Survivors-ICU Combined Assessment of Cardiorespiratory Exercise (ICU-CARE) Study: Protocol for a Cross-Sectional Observational Study.

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.