| MAC | Blood:gas coefficient | Oil:gas coefficient | Molecular weight | Boiling point | SVP at 20ºC | Safe ppm |
| 0.16% | 12 | 0.16 | 167 | - | 3kPa | 15 |
Methoxyflurane
Methoxyflurane
- Methoxyflurane was initially produced as a volatile anaesthetic agent, but fell out of favour owing to concerns about renal injury
- Now licensed for and primarily used for analgesia and sedation
Uses
- Analgesia
- Burns dressing changes
- Acute pain from trauma
- Sedation
- Colonoscopy
- Dental extractions
- Biopsies e.g. prostate, bone marrow
Presentation
- Penthrox - single use "green whistle" containing 3ml of methoxyflurane (25 - 30min continuous use)
- Delivers 0.2 - 0.7% methoxyflurane which causes analgesia within a few breaths
- Max 6ml/24hrs and maximum 15ml per week
Respiratory
- When used as an analgesic, does not cause undue respiratory depression
Cardiovascular
- As an anaesthetic agent, demonstrated cardiovascular stability over halothane
- Occasional bradycardia but no major adverse cardiovascular effects when used as an analgesic
Neurological
- Analgesia; equi-analgesic to 25microgram fentanyl IV
- Sedative effect limited by very slow onset
- Can in theory called malignant hyperthermia
- Self-limiting nausea, dizziness and drowsiness following inhaled uses
Nephrotoxicity
- Causes a high-output acute renal failure
- Precise mechanism unclear
- Due to impaired renal tubular concentrating ability
- Leads to excessive diuresis, thirst and severe hyponatraemia
- Resistant to vasopressin
- Contributes to prolonged hospital admission and poor long-term outcome
- Majority recover full renal function
Hepatotoxicity
- Rare; likely an idiosyncratic reaction as with other volatiles
- Appears to cause a self-limiting transaminitis ± clinical features