319: Routine Arterial Blood Gases In Trauma Patients: Is It Necessary?

Abstract

Arterial blood gases and serum lactate levels are routinely drawn during trauma activations to demonstrate acidosis and to help predict severity of injury and outcomes. While serum lactate levels are obtained through peripheral IVs, an arterial blood gas requires a separate arterial sample and is frequently considered inconvenient for the practitioner and painful for the patient. The object of this study is to show that routine, arterial blood gas draws on trauma patients may not be necessary since serum lactate levels provide equally accurate information. We conducted a retrospective chart review of trauma activations at a level I trauma center and collected values for base excess/deficit (BED), lactate, Glasgow Coma Scale (GCS), systolic blood pressure (SBP), and injury severity score (ISS) for each encounter. A target sample size of 4100 patients was based on power calculations of a 5-year convenience sample. Our outcome measures included studying base excess/deficit and lactate to establish their relationship. The goal was to demonstrate that lactate was non-inferior to base excess/deficit when predicting: 1) SBP less than 90mmHg, 2) ISS greater than 15, 3) GCS less than 8. Non-inferiority was evaluated using an area under the curve metric with a margin of equivalence of 10%. Of the 10503 charts reviewed, 4831 had complete data and were used for analysis. Of these 4831 patients, 24.53% had an ISS > 15, 5.28% had a SBP < 90, and 8.83% had a GCS < 8. Additionally, 21.7% had an abnormal BED (<−3, as established by our institution), and 58.57% had an abnormal lactate (>2.1, as established by our institution). For all data points, lactate and BED had a correlation coefficient of −0.549 (CI 0.58-0.52). Of the 1062 patients with an abnormal BED, 82.2% also had an abnormal lactate. When looking at the predefined subgroups, the area under the ROC curve for BED and lactate as predictors of ISS > 15 were 0.62 (CI 0.60-0.64) and 0.60 (CI 0.58-0.62), respectively. As predictors of abnormal SBP, the area under the ROC curve for BED was 0.73 (CI 0.69-0.77) and 0.69 (CI 0.65-0.72) for lactate. As predictors of abnormal GCS, the area under the ROC curve for BED was 0.67 (CI 0.64-0.70) and 0.66 (CI 0.63-0.69) for lactate. Lactate was non-inferior to BED for predicting abnormal values of ISS, SBP, and GCS with a margin of equivalence of 10%. When setting the margin of equivalence to 5%, lactate is inferior to BED for predicting an abnormal SBP. Lactate correlated marginally well to base excess/deficit, but this can be easily explained as the vast majority of traumas had normal values. The presence of low SBP, low GCS, and high ISS in trauma patients are proven predictors of poor outcomes. Lactate proved to be non-inferior to base excess/deficit when predicting these important outcomes in trauma patients. Limitations include that our margin of equivalence of 10% seemed very wide considering area under the curve values ranged from 0.6 to 0.7 with 0.5 being accepted as equivalence. Resetting the margin of equivalence to 5%, lactate remained non-inferior in 2 of 3 primary outcome measures. We are also limited by the retrospective design of the study. Additionally, using base excess/deficit as the accepted standard can be debated; however, our goal was to establish lactate as non-inferior to our current practices.