Patient age and outcome following severe traumatic brain injury: an analysis of 5600 patients

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Object. Increasing age is associated with poorer outcome in patients with closed traumatic brain injury (TBI). It is uncertain whether critical age thresholds exist, however, and the strength of the association has yet to be investigated across large series. The authors studied the shape and strength of the relationship between age and outcome, that is, the 6-month mortality rate and unfavorable outcome based on the Glasgow Outcome Scale.

Methods. The shape of the association was examined in four prospective series with individual patient data (2664 cases). All patients had a closed TBI and were of adult age (96% < 65 years of age). The strength of the association was investigated in a metaanalysis of the aforementioned individual patient data (2664 cases) and aggregate data (2948 cases) from TBI studies published between 1980 and 2001 (total 5612 cases). Analyses were performed with univariable and multivariable logistic regression.

Proportions of mortality and unfavorable outcome increased with age: 21 and 39%, respectively, for patients younger than 35 years and 52 and 74%, respectively, for patients older than 55 years. The association between age and both mortality and unfavorable outcome was continuous and could be adequately described by a linear term and expressed even better statistically by a linear and a quadratic term. The use of age thresholds (best fitting threshold 39 years) in the analysis resulted in a considerable loss of information. The strength of the association, expressed as an odds ratio per 10 years of age, was 1.47 (95% confidence interval [CI] 1.34–1.63) for death and 1.49 (95% CI 1.43–1.56) for unfavorable outcome in univariable analyses, and 1.39 (95% CI 1.3–1.5) and 1.46 (95% CI 1.36–1.56), respectively, in multivariable analyses. Thus, the odds for a poor outcome increased by 40 to 50% per 10 years of age.

Conclusions. An older age is continuously associated with a worsening outcome after TBI; hence, it is disadvantageous to define the effect of age on outcome in a discrete manner when we aim to estimate prognosis or adjust for confounding variables.

Article Information

Address reprint requests to: Chantal W. P. M. Hukkelhoven, M.Sc., Erasmus Medical Center, Center for Clinical Decision Sciences, Department of Public Health, Ee2075, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands. email: c.hukkelhoven@erasmusmc.nl.

© AANS, except where prohibited by US copyright law.

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Figures

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    Graph demonstrating the univariable association between age and 6-month outcome in 2664 patients with severe TBI. Age was described as a continuous linear term (age linear), an age linear plus quadratic term, and a smoothing spline. The vertical strokes at the base of the graph indicate the age distribution. For ease of interpretation, the probability scale is presented in this figure, rather than the logistical log-odds scale generally used in logistic regression models. A linear association on the log-odds scale corresponds to a sigmoid curve on the probability scale. Model parameters for age linear (age per 10 years) were as follows: logit (mortality) = −2.18 + 0.34 * age and logit (unfavorable outcome) = −1.34 + 0.37 * age. Model parameters for age linear plus age quadratic (age per 10 years) were as follows: logit (mortality) = −1.26 −0.18 * age +0.06 * age2 and logit (unfavorable outcome) = −0.77 + 0.03 * age + 0.04 * age2.

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    Graph displaying the univariable association between age and 6-month outcome in 2664 patients with severe TBI. Age was described as a discrete variable with a threshold value at 39 years. The vertical strokes at the base of the graph indicate the age distribution.

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    Graphs demonstrating a comparison of the strength of the effect of patient age on mortality (upper) and unfavorable outcome (lower) obtained from individual patient data and aggregate data. Solid squares denote the values for the estimated ORs. Horizontal lines extending to the right and left of the solid squares indicate the 95% CIs. The variation in the CIs is, for the most part, a function of the different sample sizes. aggr. = aggregate; EBIC survey = Murray, et al.; ind. = individual; Int. Tir. trial = Marshall, et al., 1998, and Hukkelhoven, et al., 2002; NA. Tir. trial = Hukkelhoven, et al.; Selfotel trial = Morris, et al.

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