Methoxyflurane analgesia by Cyprane inhaler

Evaluation of the effectiveness and costs of inhaled methoxyflurane versus usual analgesia for prehospital injury and trauma: non-randomised clinical study

BACKGROUND

We aimed to investigate clinical benefits and economic costs of inhaled methoxyflurane when used by ambulance staff for prehospital emergency patients with trauma. Comparison is to usual analgesic practice (UAP) in the UK in which patient records were selected if treatment had been with Entonox® or intravenous morphine or intravenous paracetamol.

METHODS

Over a 12-month evaluation period, verbal numerical pain scores (VNPS) were gathered from adults with moderate to severe trauma pain attended by ambulance staff trained in administering and supplied with methoxyflurane. Control VNPS were obtained from ambulance database records of UAP in similar patients for the same period. Statistical modelling enabled comparisons of methoxyflurane to UAP, where we employed an Ordered Probit panel regression model for pain, linked by observational rules to VNPS.

RESULTS

Overall, 96 trained paramedics and technicians from the East Midlands Ambulance Service NHS Trust (EMAS) prepared 510 doses of methoxyflurane for administration to a total of 483 patients. Comparison data extracted from the EMAS database of UAP episodes involved: 753 patients using Entonox®, 802 patients using intravenous morphine, and 278 patients using intravenous paracetamol. Modelling results included demonstration of faster pain relief with inhaled methoxyflurane (all p-values < 0.001). Methoxyflurane's time to achieve maximum pain relief was estimated to be significantly shorter: 26.4 min (95%CI 25.0-27.8) versus Entonox® 44.4 min (95%CI 39.5-49.3); 26.5 min (95%CI 25.0-27.9) versus intravenous morphine 41.8 min (95%CI 38.9-44.7); 26.5 min (95%CI 25.1-28.0) versus intravenous paracetamol 40.8 (95%CI 34.7-46.9). Scenario analyses showed that durations spent in severe pain were significantly less for methoxyflurane. Costing scenarios showed the added benefits of methoxyflurane were achieved at higher cost, eg versus Entonox® the additional cost per treated patient was estimated to be £12.30.

CONCLUSION

When administered to adults with moderate or severe pain due to trauma inhaled methoxyflurane reduced pain more rapidly and to a greater extent than Entonox® and parenteral analgesics. Inclusion of inhaled methoxyflurane to the suite of prehospital analgesics provides a clinically useful addition, but one that is costlier per treated patient.

The Reincarnation of Methoxyflurane

Methoxyflurane was an inhaled agent commonly used for general anesthesia in the 1960s, but its clinical role gradually decreased in the 1970s because of reports of dose-dependent nephrotoxicity. In 1999 its manufacturer, Abbott Laboratories, discontinued distribution of methoxyflurane in the United States and Canada. Outside of North America, however, methoxyflurane has been reborn as an inhaled analgesic used for pain relief in the prehospital setting and for minor surgical procedures. First used in Australia and New Zealand, and subsequently in over thirty-seven other countries, low concentrations of methoxyflurane are administered with a hand-held inhaler which provides conscious sedation, so that patients can self-assess their level of pain and control the amount of inhaled agent. The Penthrox inhaler, originally developed in Australia after several other hand-held vaporizers were tried, is currently being used worldwide as a portable and disposable self-administered agent delivery system. Methoxyflurane-induced nephrotoxicity continues to be a major concern, but with cautious administration of recommended doses methoxyflurane has been established as a remarkably safe analgesic agent with minimal side effects for patients in need of rapid and potent pain relief.

Prehospital analgesia in adults using inhaled methoxyflurane

OBJECTIVE

For many years, ambulance services throughout Australia have been administering methoxyflurane as a first-line analgesic agent. However, there is a paucity of literature regarding its efficacy, safety and usage profile. The present study was designed to examine the efficacy of methoxyflurane in adults.

METHODS

An observational case series was conducted over a 10 month period. Adults to whom methoxyflurane was administered while traveling by ambulance to an urban teaching hospital were enrolled. Data analysed included indications for use, verbal numerical pain scores, depth of sedation and adverse effects. Data were collected via paramedic, patient and ED staff surveys.

RESULTS

Eighty-three adult patients were enrolled over a 10 month period. A mean reduction in verbal numerical rating scale (VNRS) scores of 2.47 +/- 0.24 (on a 10-point scale) was recorded 5 min post methoxyflurane, with a total reduction of 3.21 +/- 0.24 at time of arrival at the ED. Both VNRS scores were significantly different from baseline (P < 0.0001). Fifteen patients (18.1%, 95% CI 9.8-26.4%) reported mild side-effects either during or shortly after administration. A total of 68 (81.9%, 95% CI 72.0-89.5%) of the paramedics and 60 (72.3%, 95% CI 61.4-81.6%) of the patients interviewed said that they felt satisfied with the level of analgesia provided by methoxyflurane.

CONCLUSION

The use of methoxyflurane as a prehospital analgesic significantly reduced pain in patients, with no significant side-effects attributed to its use. The majority of patients and paramedics interviewed were satisfied with its effects and indicated a willingness to use it again.

A pilot study of inhaled methoxyflurane for procedural analgesia in children

BACKGROUND

Methoxyflurane (MF), a potent volatile anesthetic, can be used as an analgesic in subanesthetic concentrations. In Australia, MF is extensively used in children and adults as an analgesic in the prehospital setting via a hand-held inhaler device. We conducted a pilot study to explore its use as a patient controlled analgesic for painful procedures in children in the emergency department (ED).

METHODS

This is a prospective observational case series of children aged 5 years and older requiring procedural analgesia for brief painful procedures. Pain scores, depth of sedation, adverse events and patient, parent and staff satisfaction were assessed as well as consumption of MF measured.

RESULTS

Fourteen patients (aged 6-13 years) received MF mainly for extremity injuries. Amount of MF consumed ranged from 0.36 to 3.06 g per patient inhaled over 4-25 min. There were no serious adverse events. No patient was deeply sedated. Five patients had mild brief self-resolving adverse events including agitation, euphoria, blurry vision, dizziness and cough. Four patients with fractures with initial high pain scores (> or =6) received MF for bridging analgesia with large drops in pain scores. Four patients who required fracture reductions with initial low scores did not achieve adequate analgesia. The remaining six patients had painful procedures undertaken with satisfactory analgesia.

CONCLUSIONS

On the basis of this small pilot study of MF use in children in the ED, this agent appears to be a powerful analgesic. MF seems most useful as a self-titrated bridging analgesic agent in patients after extremity trauma. It appears less useful as a procedural agent when patients are unable to anticipate and achieve a sufficient level of analgesia before painful stimulus infliction. Pre- and intraprocedure coaching is an important aspect of its use especially if initial pain scores are low.

Inhaled methoxyflurane as a prehospital analgesic in children

OBJECTIVE

Despite widespread use of methoxyflurane as an inhaled analgesic by ambulance services in Australia there are no published data as to its use pattern, efficacy and safety in the prehospital setting. We set out to characterize methoxyflurane use in children in the prehospital setting.

METHODS

An observational case series was conducted over an 8 month period. Children who received methoxyflurane while being transported to a tertiary children's hospital by ambulance were enrolled. We analysed indications for use, verbal numerical pain scores, adverse events and depth of sedation based on paramedic, patient, parent and ED staff surveys and review of ambulance care records.

RESULTS

During the study period 105 patients were enrolled with an age range of 15 months to 17 years (median age 11 years). Methoxyflurane was mainly used for extremity injuries (82%). Paramedic pain scores dropped from a mean of 7.9 (95% confidence interval [CI] 7.5-8.3) prior to methoxyflurane use to 4.5 (95% CI 3.9-5.0) at 2-5 min and to 3.2 (95% CI 2.8-3.7) at 10 min. There were no serious adverse events (one-sided 97.5% CI 0-3%). Mild adverse events occurred in 38 patients (36.2%; 95% CI 27.0-46.1%). Five of 15 (33.3%) patients under 5 years of age were deeply sedated.

CONCLUSION

In the present paediatric case series methoxyflurane appears to be an efficacious analgesic with a low adverse events profile. In young children in particular it can briefly lead to deep sedation.