Secondary prevention

Individuals who have susceptibility to MH should not be exposed to potent inhalation anesthetics or succinylcholine.[1] However, they may be cared for safely in both inpatient operative settings and properly resourced ambulatory surgery centers, utilizing non-triggering anesthetic agents.[91] Prophylactic dantrolene is not recommended in these patients.[100][104][105]

The anesthetic workstation used in MH susceptible patients should either be a dedicated workstation for trigger-free anesthetics or a workstation properly prepared by flushing and/or the use of activated charcoal filters.[100][105] Charcoal filters reliably prepare anesthetic workstations in 90 seconds, while the flushing process otherwise varies according to manufacturer guidelines and requires up to 2 hours in some modern workstations.[101][106]

Previous safe exposure to a potent inhalation anesthetic should not be taken as evidence that future exposures will be safe; on average MH does not present until the third inhaled anesthetic exposure in an MH susceptible patient.[6][7] Some myopathic patients can receive inhalation anesthetics safely. All anesthesia providers must have a plan for identifying and means for treating MH in a patient in whom no increased risk was detected preoperatively.

The anesthetic and general medical records of individuals suspected of having experienced an episode of MH or of being susceptible to MH must be reviewed, preferably by an experienced anesthesiologist and ideally by the physicians at an MH Diagnostic Testing Center. The primary care physician of the patient should be involved in this process, and consultation with a neurologist or other specialist may also be indicated.

The Clinical Grading Scale (CGS) is based on observations of muscle tone, respiration, core temperature, family history, and laboratory tests.[55] All these data should be collected because the CGS can be used to estimate the likelihood that an observed episode was due to MH. However, a low CGS does not by itself indicate that the event was not due to MH. The CGS assigns a point score primarily based on evidence of (1) muscle rigidity, (2) muscle breakdown (creatine kinase, myoglobinuria, hyperkalemia), (3) unexpected hypercapnia, (4) inappropriate temperature increase, (5) inappropriate tachycardia, and (6) family history of MH. Most items score 15 points and a score >35 makes MH very likely.[55] Interestingly, rapid reversal of MH signs following intravenous dantrolene only scores 5 points on the CGS. Clearly, a muscle biopsy with contracture testing and/or genetic analysis are important for confirming that MH susceptibility is present.

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