Association between serum bicarbonate and injury severity among major trauma patients in Mulago National Referral Hospital
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Background: Injuries represent a significant cause of morbidity and mortality worldwide, and more than 90% of injury deaths occur in Low and Middle income countries (LMICs). While the majority of injury related deaths results from the ‘lethal triad’, which includes hypothermia, acidosis and coagulopathy –injury scoring tools, such as the Kampala Trauma Score(KTS-II), do not use acid base parameters to stratify injury, but rather focus on anatomical and physiological parameters that fail to detect other lethal acid base derangements that contribute to occult tissue hypoxia. Evidence is scarce on the level of association between changing serum HCO3 levels and severity of injury. Furthermore, there is no comprehensive data showing the outcomes of major trauma and the predictors of mortality among patients admitted at Mulago National Referral Hospital (MNRH), Uganda. Objective: To determine the association between serum bicarbonate levels and injury severity, and also determine the outcomes of major trauma and the predictors of mortality among major trauma patients in MNRH. Methods: This was an observational prospective study involving major trauma patients admitted to MNRH between February and May, 2018. Data on sociodemographic characteristics, clinical characteristics, serum bicarbonate levels, KTS-II score, and outcomes of major trauma such as death, surgery, ICU admission were collected. Data were entered into Epidata version 3.1 and Analysis was conducted using STATA version 14.1. Descriptive analysis involved obtaining means and medians for continuous variables and proportions and percentages for categorical variables. Predictors of mortality were assessed using logistic regression and odds ratios (OR) were reported alongside their corresponding 95% CI and level of significance set at alpha 0.05. Results: Out of 2750 trauma patients seen at the Mulago A&E Department during the study period, 135 had major trauma. The male/female ratio was 15.9:1 and the mean age was 31.1(SD 11.4). Of the participants, 68 had venous blood samples drawn for measurement of initial levels of bicarbonate (Normal range 22-29mmol/L). Mean initial HCO3 value was 16.7(median 18) and the mean follow up (day 3) value was 22.3(median 22).Range 2-27 mmol/L. Most participants 78(57.8%) had a KTS of 6 and 6.4% had a KTS of <4. Among the participants, 70(51.9%) had ICU admission and 83(61.9%) had emergency surgery done. Eighty (80) participants (77.7%) had an accident as the cause of their injury with the biggest percentage having atleast a craniocerebral injury. The overall mortality was 29.6%. For the association between bicarbonate and KTS, the AUC for the ROC plotted was 0.6500. Conclusions: There was a fairly strong association between Serum HCO3 and KTS and thus venous serum bicarbonate levels may be considered as an alternative predictive marker of injury severity among severely ill patients.