Fentanyl in the Out-of-Hospital Setting: Variables Associated with Hypotension and Hypoxemia

Background: Previous out-of-hospital fentanyl analgesia studies are limited by retrospective nature or low numbers. Study Objectives: This study sought to prospectively assess fentanyl safety in a large out-of-hospital group, to identify variables associated with post-fentanyl hypotension (HN; systolic blood pressure [SBP] < 90) or hypoxemia (HX; SpO2 < 90%). Methods: As part of a new protocol requiring documentation of peri-dose vital signs and adverse effects associated with fentanyl bolus doses, our Emergency Medical Services helicopter service assessed 500 consecutive patients receiving fentanyl from July through September 2006. By a priori plan, we assessed HN and HX descriptively (median with interquartile range, exact confidence intervals [CIs]) and with multivariate regression. Results: In 1055 patients, post-fentanyl HN was noted 52 times (4.9%), being a continuation of pre-fentanyl HN in 24 patients (46.2%); HN was new in 28 patients (2.7% of 1055, 95% CI 1.8–3.8%). Regression showed no association between dependent variables HN (assessed for 1055 doses) or HX (528 doses in non-intubated) and independent variables age, diagnosis, gender, scene/inter-facility mission, dose, or total transport dose. Pre-and post-fentanyl SpO2 means were unchanged: 98.8% (95% CI 98.5–98.9) vs. 98.6% (95% CI 98.3–99.0), respectively. Post-fentanyl HN was seen in patients with pre-fentanyl intubation (odds ratio [OR] 5.3, p = 0.002) and with pre-fentanyl low SBP (OR 40, p < 0.001). Conclusion: In a closely monitored out-of-hospital population, fentanyl incurs a low risk of significant hypoxemia. The risk of fentanyl-associated hypotension is also very low, but difficult to predict in the absence of acuity markers such as pre-existing hypotension.