Psychomotor and cognitive effects of 15-minute inhalation of methoxyflurane in healthy volunteers: implication for post-colonoscopy care

Abstract

Introduction: In addition to its use in ambulance services, portable inhaled methoxyflurane (Penthrox, 3ml) has been successfully used as a form of patientcontrolled analgesia for colonoscopy in both unselected and high-risk patients (Nguyen et al 2013, Nguyen et al 2015). More importantly, the use of Penthrox for colonoscopy has been shown to be safe, cost effective and allowed earlier discharge due its lack of sedation. It remains unclear, however, whether it is safe for patients to drive and/or return to work after short-term Penthrox inhalation. Aims & Methods: The aim is to evaluate the psychomotor and cognitive effects of 15 minutes inhalation of Penthrox in adult healthy volunteers. Each of the 50 healthy volunteers, age from 18 to 80 years, were studied on 2 occasions with either Penthrox or placebo (normal saline with methoxyflurane odor) in a randomized, double-blind fashion. On each occasion, the subject's psychomotor function was examined before, immediately after, and at 30, 60, 120, 180 and 240 min after completion of a 15-min inhalation of the studied drug. Psychomotor and cognitive performance was evaluated by validated Digit Symbol Substitution Test (DSST), auditory reaction time (ART) test, eye-hand coordination (EHC) test trail making test (TMT) and logical reasoning test (LRT). Results: Compared to placebo, a 15-min Penthrox inhalation led to an immediate modest impairment of DSST (P50.001), ART (P50.001), EHC (P50.01), TMT (P=0.02) and LRT (P=0.04). In all subjects, the performance of all five tests normalized by 30 minutes after inhalation, and was comparable to that of placebo. Although increasing age associated with a deterioration in the performance of all five psychomotor tests, the effects of Penthrox remained similar and were comparable amongst all age groups. Conclusion: In all age groups, a 15 minute inhalation of methoxyflurane induces an acute but very short-lasting impairment of psychomotor and cognitive performance, which returns to normal within 30 minutes after inhalation. These findings indicate that subjects who use inhaled Penthrox for colonoscopy can safely return to tasks that require high psychomotor skills such as driving and work on the same day.