Can a patient develop malignant hyperthermia (MH) during a later surgery if they did not experience it during an initial surgery?

Malignant Hyperthermia Can Develop During Later Surgeries Despite Previous Uneventful Anesthesia

Yes, a patient can absolutely develop malignant hyperthermia (MH) during a later surgery even if they did not experience it during previous anesthetic exposures with triggering agents. This is a critical safety concept in anesthesiology that must be understood to prevent potentially fatal outcomes.

Understanding Variable Penetrance of MH

The European Malignant Hyperthermia Group and Association of Anaesthetists guidelines clearly establish that:

• MH susceptibility shows variable penetrance, meaning susceptible individuals may tolerate triggering agents multiple times before experiencing an MH crisis 1
• There are documented cases of patients receiving multiple apparently uneventful anesthetics before experiencing an MH reaction 2
• The reasons why susceptible individuals may not trigger when exposed to triggering agents are not fully understood 2

Evidence Supporting Variable Expression

The 2021 Association of Anaesthetists guideline explicitly states:

"One reason that diagnosis may be delayed is if the anaesthetist incorrectly assumes that a history of uneventful anaesthesia precludes the possibility that the patient is at risk of developing MH. We know this not to be the case and there are reports of patients who have received multiple apparently uneventful anaesthetics before they have a reaction." 2

Clinical Implications

This variable expression has important clinical implications:

1. Never assume safety based on previous exposures:

   • A history of uneventful anesthesia with triggering agents does not rule out MH susceptibility
   • This misconception can lead to delayed diagnosis and treatment 1

2. Maintain vigilance with every anesthetic:

   • Monitor for early signs of MH (unexplained increase in end-tidal CO₂, tachycardia, rigidity) even in patients with previous uneventful exposures
   • Case reports document MH occurring in elderly patients and after several hours of anesthesia 3

3. Genetic considerations:

   • The discrepancy between the prevalence of genetic variants associated with MH risk (less than 1:2000) and the incidence of clinical MH episodes suggests complex factors affecting expression 2
   • Both genetic and non-genetic factors likely contribute to the reduced penetrance of MH susceptibility 2

Management Recommendations

For patients with suspected or confirmed MH susceptibility:

• Provide trigger-free anesthesia using total intravenous anesthesia (TIVA) when general anesthesia is required 1
• Consider regional or local anesthesia when appropriate 1
• Ensure dantrolene availability (36-48 vials) wherever triggering drugs are used 1
• Properly prepare anesthetic machines through thorough flushing or use of activated charcoal filters 1

Key Pitfalls to Avoid

• Underestimating risk: The lowest vapor concentration that can trigger MH remains unknown, making any exposure potentially dangerous 1
• Delayed recognition: Assuming safety based on previous exposures can delay diagnosis and treatment 2, 1
• Inadequate preparation: Failure to have dantrolene readily available and staff trained in MH management protocols

Bottom Line

The unpredictable nature of MH expression means that every anesthetic exposure to triggering agents carries risk for susceptible individuals, regardless of previous uneventful exposures. This underscores the importance of identifying at-risk patients, using non-triggering anesthetic techniques when indicated, and maintaining vigilance during every anesthetic.