Malignant hyperthermia
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Revision as of 16:25, 6 March 2025 by Aidan (talk | contribs) (Created page with "== Background == * Familial condition characterized by a hypermetabolic response to inhaled general anaesthetic agents, including halothane, sevoflurane, and desflurane, and to the depolarizing muscle relaxant succinylcholine * Autosomal dominant inheretance * Present worldwide == Clinical Grading Scale == * Developed by Larach and colleaguesCiteRef::larach1994a * Used to evaluate an adverse anaesthetic event for the likelihood that it was caused b...")
Background
- Familial condition characterized by a hypermetabolic response to inhaled general anaesthetic agents, including halothane, sevoflurane, and desflurane, and to the depolarizing muscle relaxant succinylcholine
- Autosomal dominant inheretance
- Present worldwide
Clinical Grading Scale
- Developed by Larach and colleagues1
- Used to evaluate an adverse anaesthetic event for the likelihood that it was caused by MH
- Within a single process, only count the points from the indicator that provides the greater number of points
- Except the "Other Indicators", for which all points should be added
- Do not add points for indicators that are used to calculate susceptibility
| Process | Indicator | Points |
|---|---|---|
| Process I: Rigidity | generalized muscular rigidity (in the absence of shivering due to hypothermia, or during or immediately following emergence from inhalational general anaesthesia) | 15 |
| Masseter spasm shortly following succinylcholine administration | 15 | |
| Process II: Muscle Breakdown | Elevated CK greater than 20,000 IU after anaesthetic that included succinylcholine | 15 |
| Elevated CK greater than 10,000 IU after anaesthetic without succinylcholine | 15 | |
| Cola-coloured urine in perioperative period | 10 | |
| Myoglobin in urine greater than 60 µg/L | 5 | |
| Myoglobin in serum greater than 170 µg/L | 5 | |
| Blood, plasma, or serum potassium greater than 6 mEq/L (in the absence of renal failure) | 3 | |
| Process III: Respiratory Acidosis | PETCO2 greater than 55 mmHg with appropriate ventilation | 15 |
| Arterial PaCO2 greater than 60 mmHg with appropriate ventilation | 15 | |
| PETCO2 greater than 60 mmHg with spontaneous ventilation | 15 | |
| Arterial PaCO2 greater than 65 mmHg with spontaneous ventilation | 15 | |
| Inappropriate hypercarbia (in anaesthetist's judgement) | 15 | |
| Inappropriate tachypnea | 10 | |
| Process IV: Temperature Increase | Inappropriately rapid increase in temperature (in anaesthetist's judgement) | 15 |
| Inappropriately increased temperature greater than 38.8 ºC in the perioperative period (in anaesthetist's judgement) | 10 | |
| Process V: Cardiac Involvement | Inappropriate sinus tachycardia | 3 |
| Ventricular tachycardia or fibrillation | 3 | |
| Process VI: Family History* | Family history of MH in a first-degree relative* | 15 |
| Family history of MH in a relative that it's first degree* | 5 | |
| Other Indicators† | Arterial base excess more than -8 mEq/L | 10 |
| Arterial pH less than 7.25 | 10 | |
| Rapid reversal of MH signs with IV dantrolene | 5 | |
| Positive family history together with another indicator from the patient's own anaesthetic experience other than elevated serum CK* | 10 | |
| Positive family history with resting elevated serum CK* | 10 |
- \* Indicators only used to determine MH susceptibility, not for evaluating a specific event
- † Indicators that should be added without regard for double counting
Interpretation
| Score | Interpretation |
|---|---|
| 0 | Almost never |
| 3 to 9 | Unlikely |
| 10 to 19 | Somewhat less than likely |
| 20 to 34 | Somewhat greater than likely |
| 35 to 49 | Very likely |
| 50+ | Almost certain |
Diagnosis
- In vitro contracture test (IVCT) of muscle fibres contracting to the presence of halothane or caffeine
- Expensive test, not often done
Management
Acute Crisis
- Stop the trigger agents (inhalation anaesthetic agents and succinylcholine)
- Increase ventilation to decrease ETCO2
- Administer dantrolene: 2.5 mg/kg IV initial dose, then titrated to tachycardia and hypercarbia
- Thereafter, continue dantolene at 1 mg/kg q4-8h for 24-48 hours
- Cooling measures, including topical ice packs, NG lavage with iced solution, etc, to a target of less than or equal to 38.5 ºC
- Treat any arrhythmias that arise, avoiding CCBs
- Bloodwork, including ABG/VBG, electrolytes, CK, and blood and urine myoglobin, and coagulation panel
- Treat hyperkalemia with glucose and insulin as needed
- Target urine output 2 mL/kg/hour using mannitol, furosemide, and fluids
- Monitor for 48 to 72 hours, as about a quarter of patients will have a relapse
Prevention
- Avoid potent volatile inhalation anaesthetic agents and succinylcholine
- Purge the anaesthesia machine with 100% FiO2 at 10 L/min for at least 20 minutes
- Disable vaporizers and drain or remove if possible
References
- ^ Marilyn Green Larach, A Russell Localio, Gregory C. Allen, Michael A. Denborough, F Richard Ellis, Gerald A. Gronert, Richard F. Kaplan, Sheila M. Muldoon, Thomas E. Nelson, Helle Ørding, Henry Rosenberg, Barbara E. Waud, Denise J. Wedel. A Clinical Grading Scale to Predict Malignant Hyperthermia Susceptibility. Anesthesiology. 1994;80(4):771-779. doi:10.1097/00000542-199404000-00008.
