Effect of Fentanyl Compared to Morphine on Pain Score and Cardiorespiratory Vital Signs in Out-of-Hospital Adult STEMI Patients

Objective: ST-elevation myocardial infarction (STEMI) is a leading cause of mortality in Australia. Paramedics treating adults with STEMI in the out-of-hospital environment can use fentanyl or morphine to manage the patient’s pain, although there is little research comparing the efficacy and safety of these drugs. Therefore, the objective of this study was to compare the effects of fentanyl to morphine on cardiac chest pain and cardiorespiratory vital signs in adult STEMI patients in the out-of-hospital environment. Methods: We conducted a retrospective analysis of records of 1902 STEMI cases attended by Queensland Ambulance Service paramedics during the 4-year interval from 2013 to 2016. We compared pain score, blood pressure, respiratory rate, and pulse rate between patients administered intravenous fentanyl and intravenous morphine. We used a two-way mixed effects model (drug, time) to assess for main and interaction effects, and where the interaction effect was significant, applied Mann-Whitney U tests to further analyze between-group differences at each time point. Results: We observed a significant main effect of time on pain score (p < 0.001), respiratory rate (p < 0.05), and pulse rate (p = 0.025), such that these variables all decreased over time. Additionally, we observed a significant drug-time interaction for systolic and diastolic blood pressures (both p < 0.01), such that blood pressures decreased over time in the morphine, but not fentanyl, group. Conclusion: We compared the effects of fentanyl to morphine on cardiac chest pain and cardiorespiratory vital signs in out-of-hospital adult STEMI patients and observed differences in blood pressures only. Morphine appeared to have a depressive effect on systolic and diastolic blood pressure, whereas fentanyl did not. An unanticipated behavioural finding of this research is that, in the absence of a definitive guideline, paramedics appear to use fentanyl when patients may be at risk of developing hypotension.