Predicting Response to Naloxone in Patients With Respiratory Depression in the Prehospital Setting

Introduction—The authors sought to determine the utility of using levels of expired EtCO₂ in the prehospital setting as a criterion for determining response to naloxone in patients with respiratory depression and comparing EtCO₂ to current prehospital criteria that use Glasgow Coma Scale score as an indication for treatment.

Methods—This was a retrospective analysis of prospectively collected prehospital EMS data from a single EMS agency in Orange County, Fla., from January 2011 to December 2015. Patients included all patients given naloxone in the prehospital setting by paramedics for respiratory depression defined as a respiratory rate (RR) of <10 breaths/min. The current paramedic protocol by this agency uses a GCS score <12 as criteria to administer naloxone. The main outcome measure was the success of naloxone administration in reversing respiratory depression by increasing RR by ≥10 breaths/min. Data were adjusted to account for the dose of naloxone used. Logistic regression and ROC curve analysis were conducted and expressed using 95%CI.

Results—Of the 608 cases initially identified, 185 cases had both EtCO₂ and GCS recorded and were included in the analysis. The mean patient age was 48 (SD 19). The mean dose of naloxone administered was 1.6 mg (maximum 10 mg), and the routes of administration included IV in 126 (68%), IO in 29 (16%), IM in 4 (2%) and nasal/oral in 26 (14%). Naloxone reversed respiratory depression in 106 (57%) of cases. The area under the ROC curve for predicting response to naloxone using EtCO₂ was 0.72 (95% CI, 0.64–0.80), using GCS score was 0.57 (95% CI, 0.49–0.66) and using a dose of naloxone was 0.51 (0.43–0.60). The optimal cut point for EtCO₂ was determined to be 35. Adjusted odds ratios for successful reversal by naloxone by using a criteria of EtCO₂ >35 mmHg was 6.6 (95% CI, 3.4–13.0), for GCS <12 was 0.7 (95% CI, 0.2–2.7) and for dose of naloxone 1.3 (95% CI, 0.8–2.1).

Conclusion—Controlling for dose of naloxone, EtCO₂ was a better predictor of response to naloxone than GCS score in a prehospital population with respiratory depression.