Physical complications in acute lung injury survivors: a two-year longitudinal prospective study

Abstract

Objective: Survivors of severe critical illness frequently develop substantial and persistent physical complications, including muscle weakness, impaired physical function, and decreased health-related quality of life. Our objective was to determine the longitudinal epidemiology of muscle weakness, physical function, and health-related quality of life and their associations with critical illness and ICU exposures.

Design: A multisite prospective study with longitudinal follow-up at 3, 6, 12, and 24 months after acute lung injury.

Setting: Thirteen ICUs from four academic teaching hospitals.

Patients: Two hundred twenty-two survivors of acute lung injury.

Interventions: None.

Measurements and main results: At each time point, patients underwent standardized clinical evaluations of extremity, hand grip, and respiratory muscle strength; anthropometrics (height, weight, mid-arm circumference, and triceps skin fold thickness); 6-minute walk distance, and the Medical Outcomes Short-Form 36 health-related quality of life survey. During their hospitalization, survivors also had detailed daily evaluation of critical illness and related treatment variables. Over one third of survivors had objective evidence of muscle weakness at hospital discharge, with most improving within 12 months. This weakness was associated with substantial impairments in physical function and health-related quality of life that persisted at 24 months. The duration of bed rest during critical illness was consistently associated with weakness throughout 24-month follow-up. The cumulative dose of systematic corticosteroids and use of neuromuscular blockers in the ICU were not associated with weakness.

Conclusions: Muscle weakness is common after acute lung injury, usually recovering within 12 months. This weakness is associated with substantial impairments in physical function and health-related quality of life that continue beyond 24 months. These results provide valuable prognostic information regarding physical recovery after acute lung injury. Evidence-based methods to reduce the duration of bed rest during critical illness may be important for improving these long-term impairments.

Figure 1

Flow Diagram of Study Participants

Figure 2. Anthropometric, Muscle Strength, Physical Function, and Health-Related Quality of Life Outcomes in ALI Survivors

The dashed line (gray circles) denotes an anthropometric measure (arm muscle area), solid lines (solid markers) denote measures of muscle strength, and the dotted lines (open markers) denote physical function (6MWD) and health-related quality of life (SF-36 PFS) outcomes. All outcomes are scaled as a proportion of normative values. * The marker for MMT at the vertical axis (0 months after ALI onset) represents MMT obtained at hospital discharge. The marker (and corresponding sample size) for SF-36 PFS at the vertical access represents pre-ICU baseline SF-36 PFS obtained retrospectively from patients. Abbreivations: 6MWD, 6-minute walk distance; ALI, acute lung injury; AMA, arm muscle area; MIP, maximal inspiratory pressure; MMT, manual muscle strength testing; SF-36 PFS, Short Form-36 Physical Function Subscale score

Figure 3. Arm Muscle Area and ICU-Acquired Weakness in ALI Survivors

Comparison of arm muscle area (as proportion of normative value) in patients with and without ICU-acquired weakness at each time point: p=0.32 at 3 months, p=0.02 at 6 months, p=0.03 at 12 months, and p=0.86 at 24 months. Markers represent median values, and error bars standard errors. The number of patients at each time point was: 116 at 3 months, 130 at 6 months, 127 at 12 months, and 126 at 24 months. Abbreviations: ICU, intensive care unit; ICUAW, ICU-acquired weakness; MMT, manual muscle strength testing

Figure 4. Association of ICU-Acquired Weakness with Outcomes in ALI Survivors

Outcomes are presented according to the presence or absence of ICUAW (abbreviated composite MMT score <48 out of 60) at each time point. Markers represent median values, and error bars standard errors. All values are presented as proportion of normative values, and p-values correspond to the comparison of participants with versus without ICUAW at the specific time point. The number of patients with ICUAW at each time point after ALI onset was: 28/130 (22%) at 3 months, 21/136 (15%) at 6 months, 18/127 (14%) at 12 months, and 11/127 (9%) at 24 months. A. Hand grip strength, p≤0.01 at all time points. B. Physical function subscale of the SF-36 quality-of-life instrument, p≤0.001 at all time points after ALI. C. Maximum inspiratory pressure, p=0.47 at 3 months, and p≤0.02 at 6, 12, and 24 months post-ALI. D. Six-minute walk distance, p=0.10 at 3 months, and p≤0.01 at 6, 12, and 24 months post-ALI. Abbreviations: 6MWD, 6-minute walk distance; ALI, acute lung injury; ICU, intensive care unit; ICUAW, ICU-acquired weakness; MIP, maximal inspiratory pressure; MMT, manual muscle strength testing; SF-36, Short Form-36 survey