Prehospital analgesia in adults using inhaled methoxyflurane: a feasibility study

BACKGROUND: Acute pain is common and often undertreated prehospitally. Inhaled low-dose methoxyflurane is a rapid, patient-controlled analgesic with internationally reported safety data but has not been studied for prehospital use in Canada; this feasibility study informs a future multicentre stepped-wedge cluster randomized trial. METHODS: We conducted a single-center prospective observational study in a Canadian paramedic service to assess feasibility for a stepped-wedge cluster randomized trial. Adult trauma patients (≥18-years) with Glasgow Coma Scale(GCS) ≥14 and numeric rating scale(NRS) pain ≥4 received self-administered inhaled methoxyflurane (3mls). Feasibility outcomes included regulatory timelines, protocol adherence, and data completeness; secondary outcomes included pain documentation and adverse events. RESULTS: Ethics board approval was obtained in 93 days, slightly exceeding the target, while trial readiness occurred 404 days post-approval and did not meet feasibility targets. Protocol compliance was high (95%) (92/97), and post-treatment pain scores were documented in 90% (83/92) of cases. Median pain decreased from 8/10 pre-treatment to 5/10 post-treatment. Side effects occurred in 23% of patients, were mostly mild, and no serious methoxyflurane-related adverse events were observed. CONCLUSIONS: The results of this feasibility study were used to inform the deployment of an ongoing prospective stepped-wedge open-label, cluster randomized trial to inform clinical care in the real world. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov identifier is NCT04287803.