Weight-for-age distribution and case-mix adjusted outcomes of 14,307 paediatric intensive care admissions

Abstract

Aims: To determine whether the paediatric intensive care (PIC) population weight distribution differs from the UK reference population and whether weight-for-age at admission is an independent risk factor for mortality.

Methods: Admission weight-for-age standard deviation scores (SDS) were calculated for all PIC admissions (March 2003-December 2011) to Great Ormond Street Hospital: this is the number of standard deviations (SD) between a child's weight and the UK mean weight-for-age. Categorised into nine SDS groups, standardised mortality ratios (SMR) and logistic regression were used to assess the relationship between weight-for-age at admission and risk-adjusted mortality.

Results: Out of 12,458 admissions, mean weight-for-age was 1.04 SD below the UK reference population mean (p < 0.0001). Based on 942 deaths, risk-adjusted mortality was lowest in those with mild-to-moderately raised weight-for-age (SDS 0.5-2.5) and highest in children with extreme under- or overweight (SDS < -3.5 and SDS > +3.5). Logistic regression indicated that age, gender, ethnicity and weight-for-age are independent risk factors for mortality. South Asian and 'other' ethnicities had significantly increased risk of death compared to children of white and black ethnic origin.

Conclusion: The PIC population mean weight-for-age is significantly lower than the UK reference mean. The extremes of weight-for-age are over-represented, especially underweight. Weight-for-age at admission is an independent risk factor for mortality. A U-shaped association between weight and risk-adjusted mortality exists, with the lowest risk of death in children who are mild-to-moderately overweight. Future studies should determine the impact of malnutrition on risk-adjusted mortality and investigate the aetiology of risk disparities with ethnicity.

Figures

Fig. 1

Stacked histogram of study population admission Weight-for-age standard deviation score compared to UK reference population. Survivors and deaths are differentiated within the histogram. A representative UK reference population curve is superimposed for comparison. The mean weight-for-age at admission of the study population was 1.04 standard deviations less than that of the UK reference population (95 % CI −1.07 to −1.01, p < 0.0001), with an over-representation of outliers, especially extreme underweight. SDS standard deviation score, SD standard deviation

Fig. 2

Plot of standardised mortality ratios (SMRs) vs. weight-for-age at admission standard deviation scores, with 95 % confidence intervals. Expected deaths are estimated by the sum of PIM2 scores for all patients in a group. SMRs are a ratio of observed to expected deaths. A ‘U-shaped’ association is indicated: highest risk of mortality occurs with extreme under- or overweight, which this study has shown to be over-represented in children admitted to PICU. The lowest risk of mortality occurred in children with a weight-for-age at admission between 0.5 and 2.5 standard deviations above the UK mean weight-for-age. Asterisk (*) indicates the overall SMR for the whole study cohort is displayed on the chart at 0.94

Fig. 3

Plot of odds ratio (OR) risk of death comparing categories within subgroups, determined by multivariable logistic regression, with 95 % confidence intervals. The logit form of PIM2 was used for mortality risk adjustment with further sequential adjustment of the model for each covariate (gender, age and ethnicity). One category in each subgroup is used as the reference (OR = 1) (see also Supplementary Appendix 3, Table 2). Age group: A ≤ 1 month, B = 1 month–4.9 years, C = 5–16 years. Wh white, Bl black, SA South Asian, O other