Intensity of physical therapy interventions in the intensive care unit: An exploratory analysis

The optimal "dose" of rehabilitation interventions in patients who are critically ill is unknown due to gaps in the literature. One of the challenges with determining dose is the lack of a feasible method for measuring the intensity (i.e., patient effort) in patients who are critically ill receiving rehabilitation interventions. Percentage of heart rate reserve (%HRR) may offer an objective method to quantify the intervention intensity in this population.

The aim of this study was to evaluate the feasibility of using %HRR to measure intensity during physical therapy (PT) sessions in the intensive care unit.

This was a retrospective observational study conducted in the medical intensive care unit at one academic medical centre. The sample included 106 consecutive adults admitted for >24 h, mechanically ventilated, and collectively receiving 765 PT sessions between June 1, 2021, and January 31, 2022. The %HRR was calculated as (peak heart rate - resting heart rate)/(predicted maximum heart rate - resting heart rate). Mobility level was assessed using the Johns Hopkins Highest Level of Mobility score, a one-item scale with eight ordinal responses scored based on highest level of mobility achieved during a PT session.

Of 765 PT sessions, the %HRR could be calculated for 515 (67%) sessions in which patients' heart rate increased during the session. The median (interquartile range) %HRR per patient was 10% (6-18%), with 381 (74%) of PT sessions consisting of bed activity and sitting at the edge of the bed. The Spearman's rank correlation demonstrated a weak relationship between %HRR and Johns Hopkins Highest Level of Mobility (rho = 0.17; 95% confidence interval: 0.09 to 0.25, p = 0.0001).

This exploratory analysis found that %HRR could be calculated in 67% of PT sessions. Further studies are needed to determine if %HRR is a feasible and valid measure of rehabilitation intensity (i.e., patient effort) for PT sessions among patients who are critically ill.