Know thy proxy: Using patient proxies to assess functional status after critical illness.

Dr. Ahasic is an Assistant Professor in the Section of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, Yale University School of Medicine. The study described here was performed in collaboration with investigators from the Yale Claude D. Pepper Older Americans Independence Center and the Yale Program on Aging. 

Functional impairment is a measure of disability that can include ability to perform activities of daily living (ADLs). Basic ADLs include self-care such as dressing, bathing and toileting. Instrumental ADLs are important to living independently such as using the telephone, taking medications, and shopping for groceries.

Functional impairment is commonly assessed using patient interviews, but there are many times when patients themselves may be unable or unwilling to be interviewed, particularly when they are ill or recovering from major illness. This may be particularly relevant during critical illness requiring admission to an intensive care unit (ICU), or during recovery after an ICU stay.

When clinicians are unable to obtain information directly from patients, we turn to patient proxies, commonly a spouse, child, other close relative or close friend. Previous studies have shown widely ranging results in terms of whether such proxies can answer questions about a patient in close agreement to what patients themselves would say. We hypothesized that in the case of ADLs, a proxy would need to spend a significant amount of time with the patient to be able to answer accurately. This is important because a proxy may be someone with whom the patient has a close relationship, but if they do not observe the patient in their day-to-day functioning, they may not be able to provide accurate information.

Our study looked at a group of patients who were enrolled in a prospective study of delirium in the ICU. We used a careful screening tool to identify the best available proxy at the time of ICU admission (see Figure 1 in the article). We then interviewed patients and their proxies independently one month after ICU discharge to assess ADLs. We analyzed the agreement between patient and proxy responses for 14 ADLs, and the agreement was very strong overall.

We believe using a systematic proxy screening tool such as the one presented here could enhance the accuracy of information obtained from proxies, particularly in research studies. Clinicians might also consider this tool when obtaining collateral information from proxies. We only studied patient-proxy agreement for ADLs assessed one month after ICU discharge, but systematic proxy screening may be useful beyond this context such as in asking about domains other than ADLs, or in interviewing proxies at the time of ICU admission. Future studies may help elucidate this.

Read the paper in full on the Age and Ageing journal website, here.

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