Elsevier

Journal of Critical Care

Volume 44, April 2018, Pages 196-202
Journal of Critical Care

Clinical Potpourri
Exploring the impact of using measured or estimated values for height and weight on the relationship between BMI and acute hospital mortality

https://doi.org/10.1016/j.jcrc.2017.11.021Get rights and content

Highlights

  • Most ICU patients do not have height and weight measured.

  • Despite extensive case mix adjustment, mortality in ICU is lower in obese patients compared with those of normal weight.

  • The relationship between BMI and mortality is similar regardless of whether weight and/or height are measured or estimated.

  • Estimates of height and weight are valid for epidemiological purposes.

Abstract

Purpose

Studies have demonstrated an association between height and weight and mortality among patients in the Intensive Care Unit (ICU) and the optimal body mass index (BMI) might be well above the optimal values in the general population. Most of these studies have relied on estimated values, the validity of which is not known.

Material and methods

Admissions to adult general ICUs from 1 April 2009 to 31 March 2016 in the Case Mix Programme (CMP) Database were described by height and weight assessment methods (measured or estimated). A multilevel logistic regression model was built, which had acute hospital mortality as the outcome and included standard case mix adjustment, BMI, the assessment method and the interactions between BMI and assessment method.

Results

There were 690,405 eligible admissions and most patients (59.7%) had estimates of height and/or weight recorded. Patients with both height and weight measured had lower severity and mortality. The association between BMI and mortality was reverse J-shaped with the lowest mortality at BMI 34.3 kg/m2. Whether height and weight were measured or estimated did not influence the association between BMI and mortality.

Conclusions

For epidemiological comparisons of mortality among critically ill adults, estimated values of height and weight appear valid.

Introduction

The relationship between body mass index (BMI) and mortality in critical care populations is unclear [1], [2], [3]. While most studies agree that being very underweight, a very low BMI, is disadvantageous, the relationship of being overweight or obese, a high or very high BMI, varies across studies. The variation seen across studies may be due to the degree of adjustment for other confounders and/or the precision of the measurements of height and weight used to calculate BMI.

In the UK, the National Institute for Health and Care Excellence (NICE) guideline specifies that all patients have their height and weight measured on admission to hospital [4], however, these measurements are often not performed [5]. In the ICU setting, the condition of the patient, lack of suitable equipment or high workload may render measurements of height and weight challenging [6]. Most papers discussing the association between BMI and mortality in this setting do not report whether assessments of height and weight were measured or estimated [7].

The Intensive Care National Audit & Research Centre (ICNARC) coordinates the national clinical audit for adult critical care, the Case Mix Programme (CMP), in England, Wales and Northern Ireland. As part of data collection, height and weight are recorded along with whether these values are measured or estimated. The aim of this study was to explore the impact of using measured or estimated values for height and weight on the relationship between BMI and acute hospital mortality.

Section snippets

Case Mix Programme Database

Case mix and outcome data for the Case Mix Programme are collected on consecutive admissions to participating ICUs to precise rules and definitions, by trained data collectors and undergo extensive local and central validation. Details of the data collection and validation have been reported previously [8]. The Case Mix Programme Database has been independently assessed to be of high quality [8] and support for the collection and use of patient-identifiable data without consent has been

Case mix and outcomes

The inclusion criteria were met by 690,405 admissions to 219 ICUs (Fig. 1). Most patients had estimates of height and/or weight rather than actual measurements (59.8%). Height was estimated more often than weight (Table 1).

Patients with both height and weight measured had lower physiology scores, were more likely to have been admitted to ICU following elective surgery and were less likely to have received CPR. They were more likely to have been living independently and their reasons for

Discussion

Methods for estimating height and weight range from formalised algorithms based on easily obtainable measures to subjective guesses, but all of these techniques are prone to variation and bias [15], [16], [17], [18], [19], [20], [21].

Most ICU patients do not have their height and weight measured but practice varies considerably both across ICUs and according to patient characteristics. Our data confirm the previously reported reverse-J-shaped relationship between BMI and mortality with the

Conclusion

In conclusion, our study demonstrates that height and weight are estimated for a substantial proportion of patients admitted to UK ICUs. For epidemiological purposes, heights and weights estimated by the currently used techniques are valid approximations of the actual values.

The following are the supplementary data related to this article.

. The coefficients in the adjusted association between BMI and acute hospital mortality.

Conflicts of interest

On behalf of all authors the corresponding author states that there are no conflicts of interest.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgements

We are very grateful to Amber Tiffany Rucinski for help with the literature searching related to this work.

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