Trajectory of Physical Function Recovery May Help Inform Prognosis for Survivors of Acute Respiratory Failure
By Elaine Chen, MD
Assistant Professor, Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, Section of Palliative Medicine, Rush University Medical Center, Chicago
Dr. Chen reports no financial relationships relevant to this field of study.
SYNOPSIS: There are several distinct trajectories of recovery after acute respiratory failure. The group with the highest physical function consisted primarily of younger women who experienced less continuous sedation time and shorter ICU length of stay.
SOURCE: Gandotra S, Lovato J, Case D, et al. Physical function trajectories in survivors of acute respiratory failure. Ann Am Thorac Soc 2019;16:471-477.
Persistent physical function impairment for months to years is common after mechanical ventilation for acute respiratory failure.1 Patients have identified physical strength, fatigue, and decreased walking distance as important outcomes after critical illness. Prior studies have revealed that factors such as hospital length of stay, sex, ethnicity, and prior smoking status may influence physical function recovery after a critical illness. The authors of this study sought to determine whether common patterns of physical function recovery occur over a six-month period after a critical illness and to assess the characteristics of such trajectory groups.
Researchers performed a secondary analysis of a previously designed randomized clinical trial that evaluated standardized rehabilitation therapy among patients with acute respiratory failure.2 In this was single-center trial, investigators recruited 300 mechanically ventilated patients, 18 years of age or older, over a five-year period. The duration of mechanical ventilation was limited to 80 hours or less, and the duration of hospitalization was limited to seven days or less. Patients were previously independently ambulatory, but the use of a cane or walker was allowed. In-person physical function testing was evaluated at hospital discharge and again at two, four, and six months after enrollment. The Short Physical Performance Battery (SPPB), which assesses gait speed, balance, and lower extremity strength with a score from 0 to 12, was chosen as the objective physical function variable. Statistical analysis included group-based trajectory modeling.
Of the 300 patients randomized, 260 were discharged alive and had at least one SPPB data point available for analysis. The mean SPPB score for all patients at the time of discharge was in the “low function” category and increased to a plateau in the “intermediate function” category by month 2. Patients were grouped into four different trajectories based on physical function recovery. Characteristics of the groups were evaluated using chi-square tests, one-way analysis of variance, and multinomial logistic regression. Group 1 included patients discharged with physical function disability that did not improve by six months. Patients in group 2 were discharged with physical function disability with some improvement, but they remained functionally disabled by six months. Group 3 patients exhibited low physical function at discharge and improved to intermediate physical function. Patients in group 4 had intermediate physical function at discharge and improved to high physical function at two months; this level was sustained at six months. The greatest change in physical function appeared to occur within the first two months after discharge. In the final regression model, age, sex, ICU length of stay (LOS), and continuous intravenous (IV) sedation days were found to influence trajectory group membership.
Group 4, the group with highest physical function, was comprised of mostly younger females with shorter ICU LOS and duration of sedation. Group 1, the group with the most persistent physical disability, consisted primarily of older patients who had longer sedation time and longer ICU LOS. Ventilator days and hospital LOS were excluded in this study because of their close correlation with ICU LOS. The median age in group 4 was 45 years, and the youngest patient in group 1 was 40 years old.
In other ICU survivorship studies, pre-existing comorbidities were associated with some factors in recovery. In this study, prehospital oxygen use, dialysis, or Acute Physiology and Chronic Health Evaluation (APACHE) III scores were not associated with recovery trajectory. In this study, female sex showed an advantage for long-term physical function recovery. In other studies, female sex was shown to be associated with higher mortality and increased ICU-acquired weakness. The authors agreed that sex-related differences in ICU outcomes are complex and need further elucidation. The time receiving continuous IV sedation was the only modifiable factor that was shown to influence the recovery trajectory. This finding supports other studies that encourage minimizing the duration of continuous sedation in critically ill patients.
Limitations to this study included missing data due to death or loss to follow-up. Prehospitalization functional status was not well defined, but the patients in this study were younger and less ill at baseline compared to subjects in other studies. Follow-up time of six months, with only a small number of measurements at each follow-up, limits the complexity of the regression models. Additionally, hospitalization time was limited to seven days or less, but the authors of other studies have looked at longer durations of mechanical ventilation or hospitalization.
In summary, this study defined four distinct trajectories of recovery after mechanical ventilation for acute respiratory failure, limited to adult ambulatory patients with a maximum of seven days of hospitalization. Trajectory membership was associated with age, sex, ICU LOS, and continuous IV sedation days. The researchers found that the group with the highest physical function was primarily younger women with a shorter LOS and fewer IV sedation days.
This study adds to the extensive literature on outcomes after critical illness. The authors described four distinct trajectories of recovery over the first six months after hospital discharge. As with many studies of recovery after critical illness, the study is limited by subject selection and loss to follow-up. The inclusion criteria for this study were predetermined to be relatively higher functioning, since the parent study was designed to evaluate standardized rehabilitation therapy. All patients were ambulating independently prior to critical illness, while many critically ill patients have lower levels of premorbid function. APACHE III score at enrollment was used as a surrogate for prehospitalization illness. Although it appeared significant in univariate analysis, the multivariate P value was not significant. Perhaps with a larger cohort, this could become a significant factor in the recovery trajectory. In addition to the limitations described earlier, the number of ICU organ failures was not assessed in this study, and the severity of illness during hospitalization was not evaluated as a factor in recovery. Because these patients were followed for only six months, it would be interesting to see the trajectories of recovery at one and five years after discharge.
This study shows that there are distinct trajectories of physical function recovery after critical illness. Although the information found in this study does not provide targeted interventions to improve function and recovery, it may help identify patients at greater risk of physical function disability after critical illness. It helps inform prognosis in those who are expected to recover and provides a basis for designs of further clinical trials to tailor interventions to specific subgroups.
- Herridge MS, Tansey CM, Matte A, et al. Functional disability 5 years after acute respiratory distress syndrome. N Engl J Med 2011;364:1293-1304.
- Morris PE, Berry MJ, Files DC, et al. Standardized rehabilitation and hospital length of stay among patients with acute respiratory failure: A randomized clinical trial. JAMA 2016;315:2694-2702.
There are several distinct trajectories of recovery after acute respiratory failure. The group with the highest physical function consisted primarily of younger women who experienced less continuous sedation time and shorter ICU length of stay.
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