Does intensive care unit severity of illness influence recall of baseline physical function?☆
Introduction
As the mortality of intensive care unit (ICU) patients improves and research focuses on reducing long-term morbidity, understanding ICU patients' baseline quality of life before hospital admission becomes increasingly important. Assessment of baseline quality of life is helpful in prognostication of short-term mortality [1], in evaluating post-ICU measures of quality of life, and in determining whether patients recover to their pre-ICU status [2], [3]. Age- and sex-matched population norms are commonly used as a reference point in understanding patients' recovery from critical illness. However, patients who experience critical illness may have baseline quality-of-life measures that are lower than population norms [4], [5], [6], [7]. Hence, using population norms can potentially overstate patients' post-ICU impairments in quality of life. Consequently, a patient-specific baseline estimate of quality of life may help in establishing a reference point for post-ICU follow-up measurements [2], [8].
Despite its importance, it is difficult to obtain a valid baseline measure of quality of life for ICU patients. Emergent admission and critical illness prevent patients from providing self-reported baseline quality of life at the time of ICU admission. Moreover, proxy assessment of patients' baseline quality of life often differs from the patient's assessment [5], [9], [10], [11]. Proxies may be under great stress at the time of patients' ICU admission, which may contribute to difficulty in accurately estimating patients' baseline status. An alternative is seeking ICU survivors' own retrospective recall of their baseline quality of life. However, such a retrospective quality-of-life measure may be affected by recall bias [12], [13]. Factors such as severity of current symptoms may bias patients' recall of baseline status [12], [14], but these issues have not been empirically explored among critically ill patients [8].
Our objective was to evaluate the relationship between ICU severity of illness and patients' post-ICU retrospective assessment of their baseline quality of life. Specifically, we focused on the physical function domain within the Short Form 36 (SF-36) quality-of-life instrument because it is often severely impaired after critical illness [15], [16]. A significant association between ICU severity of illness and patients' pre-ICU physical function score would help inform our understanding of potential recall bias in patients' retrospective assessment of baseline quality of life. We specifically evaluated this objective using a cohort of patients with acute lung injury (ALI), an archetype of ICU patients with a high severity of illness [17].
Section snippets
Study design and participants
This analysis is part of an ongoing prospective cohort study of patients with ALI [18]. Participants were enrolled from 13 ICUs in 4 hospitals in Baltimore, MD. Eligible patients were mechanically ventilated and met criteria for ALI as defined by the American-European Consensus Conference [19]. Relevant exclusion criteria included (1) baseline language or communication barrier, (2) preexisting cognitive impairment, (3) preexisting illness with a predicted life expectancy of less than 6 months,
Results
Of the 520 subjects enrolled, 269 (52%) survived until the time of post-ICU consent and survey administration, of whom 33 (12%) had no consent for the survey at time of discharge. Consistent with prior research findings [20], [30], approximately 11% of the remaining eligible subjects could not complete the SF-36 because of delirium, assessed using the Confusion Assessment Method for the ICU [30] and other cognitive impairment at hospital discharge, whereas a small proportion of consenting
Discussion
In evaluating for potential recall bias in ALI survivors' retrospective reports of physical function before hospital admission, we investigated whether 4 measures of ICU severity of illness were independently associated with retrospectively patient-reported baseline physical function. Consistent with other quality of life literature, patients' SF-36 physical function score was associated with age, sex, education, BMI, and comorbidity, thus providing some assurance regarding the validity of this
Acknowledgment
The authors thank all patients who participated in the study and the dedicated research staff who assisted with the study: Ms Rachel Bell, Ms Kim Boucher, Dr Sanjay Desai, Ms Carinda Feild, Ms Thelma Harrington, Dr Praveen Kondreddi, Ms Stacey Murray, Dr Abdulla Damluji, Ms Arabela Sampaio, and Ms Kristin Sepulveda.
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This research was supported by the National Institutes of Health (Acute Lung Injury SCCOR Grant no. P050 HL 73994). The funding bodies had no role in the study design, manuscript writing, or decision to submit the manuscript for publication.