Indication Bias Explains Some of the Observed Increased Mortality Associated With Use of Prehospital Intravenous Fluids in a Pediatric Trauma Population
Authors: Garwe Tabitha , Johnson Jeremy J. , Letton Robert W. 
Published: December 2015

Objectives

Traditionally, in both pediatric and adult trauma patients, management of hemorrhage and shock has included early rapid intravenous fluid (IVF) replacement at the scene or during transport to a definitive care facility. Because prehospital resuscitation can be considered as a lifesaving intervention, severely injured patients are more likely to receiveIVF. Observational studies not adequately adjusting for this confounding by indication (indication bias) while evaluating the impact of prehospitalIVFon mortality in clinically heterogeneous patient populations are likely to find an increased mortality associated with the use of prehospitalIVF, an association that may be spurious even after traditional multivariable risk adjustment. Propensity scores can be used to mitigate the impact of this selection bias on the estimated effect. The authors hypothesized that the effect ofIVFon mortality will differ based on whether propensity scores (based on a set of prehospital indications forIVF) are adjusted for in a multivariable outcome model.

Methods

This was a retrospective cohort study of severely injured pediatric (<18 years) patients consecutively evaluated and treated between January 1, 2008, and June 30, 2011, at Oklahoma's only Level I pediatric trauma center. Patients were divided into those receiving 250 mLor more (GE250 group) and those receiving less (LT250 group) of prehospitalIVFbased on area under curve (AUC) analysis (AUC = 0.7, 95% confidence interval [CI] = 0.6 to 0.80, sensitivity = 0.81 and specificity = 0.56). Propensity scores were used to minimize confounding by indication of the mortality estimate and were calculated based on measurable prehospital factors. Using Cox's regression to minimize survival bias, the independent effect of prehospitalIVFon the risk of 30‐day in‐hospital mortality was evaluated with and without adjusting for the propensity to receive 250 mLof prehospital IVF.

Results

A total of 482 patients met study criteria. Of these, 46.3% (223 of 449) were in theGE250 group. After adjusting for Injury Severity Score, presence of a severe head injury, shock, and a penetrating injury, all of which were significant predictors of mortality, receiving 250 mLor more of prehospitalIVFwas significantly associated with an almost threefold increase in the risk of 30‐day in‐hospital mortality (hazard ratio [HR] = 2.96, 95%CI = 1.1 to 8.2). However, further adjusting for the propensity to be in theGE250 group, in addition to the aforementioned variables, attenuated the effect estimate and resulted in a nonsignificant (p = 0.3408), more precise association between prehospitalIVFand mortality (HR = 1.9, 95%CI = 0.6 to 6.6).

Conclusions

Propensity‐adjusted survival analysis suggests that the observed increased risk in mortality associated with use of prehospitalIVFreplacement may be a spurious association resulting from inadequate control of confounding by indication inherent in observational studies. In the absence of patient subgroup‐specific results from well‐controlled studies,IVFresuscitation should not be a reason to delay patient transport to a definitive care facility. Randomized trials evaluating the effect of prehospital fluids are warranted in the pediatric trauma population, as such studies have shown clinical significance in the adult trauma population.