An Exploratory Study Of Physiologic Responses To A Passive Exercise Intervention In Mechanically-ventilated Critically Ill Adults

Muscle weakness is the most common and persistent problem after a critical illness. Early mobilization of the critically ill patient, beginning with passive exercise and progressing to ambulation, may mitigate muscle effects of the critical illness. However, mobilization may produce adverse effects, especially early in the illness when risk for physiologic deterioration is common. If safe, introducing a mobility intervention early in the illness may facilitate ventilator weaning, shorten intensive care unit and hospitals stays, and improve functional status and quality of life for mechanically ventilated critically ill patients. The aim of this study was assess the cardiopulmonary and inflammatory responses to an early standardized passive exercise protocol (PEP) in mechanically ventilated critically ill patients. Using a quasi-experimental within-subjects repeated measures design, mechanically ventilated critically ill adults who were physiologically stable received a single standardized PEP within 72 hours of intubation. The PEP consisted of 20 minutes of bilateral passive leg movement delivered by continuous passive motion machines at a rate of 20 repetitions per minute, from 5-75 degrees, to simulate very slow walking. Physiologic parameters evaluated included heart rate (HR), mean blood pressure (MBP), oxygen saturation, and cytokine levels (IL-6 and IL-10), obtained before, during, and after the intervention. The Behavioral Pain Scale (BPS), administered before, during and after the intervention was used as a measure of participant comfort. The study sample was comprised of 18 (60%) males and 12 (40%) females, with a mean age of 56.5 years (SD 16.9 years), who were primarily Caucasian (N=18, 64%). Mean APACHE II scores for the sample were 23.8 (SD 6.2) with a mean predicted death rate of 48.8 (SD 19.8), indicating moderate mortality risk related to illness severity. Number of comorbidities ranged iv from 1-10 (X=4). All participants completed the intervention with no adverse events. Using repeated measures analysis of variance (rmANOVA), no significant differences were found in HR, MBP, or oxygen saturation at any of the four time points in comparison to baseline. BPS scores were significantly reduced (F(2.43, 70.42)=4.08, p=.02) at 5 and 10 minutes after the PEP was started, and were sustained at 20 minutes and for one hour after the PEP was completed. IL-6 was significantly reduced (F(1.60, 43.1)=4.351, p=.03) at the end of the intervention but not at the end of the final rest period. IL-10 values were not significantly different at any of the three time points, but IL-6 to IL-10 ratios did decrease significantly (F(1.61, 43.38)=3.42, p=.05) at the end of the PEP and again after a 60 minute rest period. Passive leg exercise was well tolerated by study participants. HR, MBP, and oxygen saturation were maintained within order set-specified ranges during and for one hour after activity, and patient comfort improved during and after the intervention. A downward trend in HR was noted in participants, which is contrary to usual HR response during exercise, and may represent clinical improvement in this population related to reduction in pain. Reduction of mean IL-6 values at the end of the PEP, but not after the rest period, suggests that the PEP was responsible for the initial IL-6 improvement. Improvement of IL-6 to IL-10 ratios from the end of the PEP to the end of the final rest period suggests that IL-10, although non-significant, may have had some effect, indicating that IL-10 increases may occur later than the time period of study. Passive exercise can be used as an approach to facilitating mobilization in mechanically ventilated critically ill adults until they are ready to participate in more active exercise. It could be that more frequent and aggressive exercise, such as passive cycling at faster rates, four times daily, will be tolerated in this population. While the understanding of clinical significance of cytokine profiles in critically ill patients is still evolving, cytokine levels may be useful in v explaining benefits of mobilization in this population. Further study is required to replicate the impact of passive exercise on pain, and it may represent a novel approach to pain management in critically ill patients