- Inherited pharmacogenetic disorder, autosomal dominant
- Myopathy with defective Ca2+ release at the sarcoplasmic reticulum within the muscle fiber, setting off a cascade of events on exposure to volatile anesthetics and depolarizing muscle relaxants
- Potentially lethal, but mortality nowadays <5%
- Patients with known MH history
- Diagnosed family members
- Patients with “central core disease” and periodic hyperkalemic paralysis
- Administration of succinylcholine and volatile anesthetics to patients with muscular dystrophies can trigger rhabdomyolysis difficult to distinguish from MH. Volatile anesthetics and depolarizing muscle relaxant should be used cautiously in these patients
- Some individuals with history of clinical MH and positive in vitro contracture test (IVCT) may develop heat or exercise intolerance, but there is no evidence of the reverse, that is, no increased risk of MH in patients with a history of exertional rhabdomyolysis (ER) or exertional heat illness (EI)
- All volatile anesthetics and succinylcholine can trigger MH
- Complete information about previous anesthetics, including complications or adverse events, must be obtained
- NB: A patient can develop MH despite having undergone prior anesthetics with triggering agents in the past without having developed MH
- The apprehensive patient must be reassured during the perioperative evaluation
- Types of anesthesia and alternatives must be explained, including usage of safe drugs and adequate monitoring
- If any suspicion of neuromuscular disease, consultation with a geneticist, neurologist, pediatric specialist should be sought
- It is debatable whether or not further tests such as creatine kinase or blood gas analysis are required following the evaluation
- Prophylaxis with dantrolene is not required
- As per guidelines, decontaminate the anesthesia machine, that is:
- Remove vaporizers
- Change all removable parts of the machine in contact with volatile anesthetics (soda lime, fresh gas outlet hose)
- Wash circuit with 100% oxygen at a gas flow of 10 L/min for 10 minutes
- Avoid triggering agents (volatile anesthetics, succinylcholine)
- What is safe: nitrous oxide, barbiturates, propofol, etomidate, benzodiazepines, nondepolarizing muscle relaxants, and neostigmine
- Regional anesthesia is safe and is preferred as an alternative
- Standard monitors: pulse oximetry, BP, ECG, capnometry, and continuous measurement of temperature should be standard. Invasive monitoring only if otherwise clinically indicated
- With appropriate planning, MH patients can have surgery in ambulatory surgical facilities
Early signs may be acute, or subtle and slow to progress.
- Increase in expired CO2 (most sensitive and early sign):
- Respiratory acidosis
- Then rapidly mixed acidosis with increased arterial lactate
- Muscle rigidity:
- Very specific but inconstant; can be limited to masseter spasm
- Elevated serum K, Ca
- Increased serum and urine myoglobin
- Delayed increase in CK, peak at 24 hours
- Late sign
- Can progress very quickly (1°C/5 minutes)
- Other, less specific:
- Tachycardia, dysrhythmia
- Cyanosis, skin mottling
- Dark blood in surgical field; however, typically normal SpO2
- Thyroid storm
- Communicate with surgical team; terminate surgery; if impossible, continue using nontriggering agents
- Discontinue triggers; remove vaporizers; not necessary to change the whole circuit, CO2 absorber, ...
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