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Calculator: Clinical indicators for malignant hyperthermia in adults (conventional and SI units)

Calculator: Clinical indicators for malignant hyperthermia in adults (conventional and SI units)


Generalized muscular rigidity without shivering during or immediately following emergence from inhalational anesthesia (15 points)

Masseter muscle spasm shortly following succinylcholine administration (15 points)

CK >20,000 units/L [>333 mcKat/L] after anesthesia with succinylcholine (15 points)

CK >10,000 units/L [>167 mcKat/L] after anesthesia without succinylcholine (15 points)

Cola-colored urine in perioperative period (10 points)

Urine myoglobin >60 mcg/L [>3.5 nmol/L] (5 points)

Serum myoglobin >170 mcg/L [>10.3 nmol/L] (5 points)

Serum K >6 mEq/L [>6 mmol/L] (without renal failure) (3 points)
Respiratory acidosis*

Controlled ventilation ETCO2 >55 mmHg (15 points)

Controlled ventilation PaCO2 >60 mmHg (15 points)

Spontaneous ventilation ETCO2 >60 mmHg (15 points)

Spontaneous ventilation PaCO2 >65 mmHg (15 points)

Inappropriate hypercarbia (judgment) (15 points)

Inappropriate tachypnea (judgment) (10 points)

Inappropriate rapid increase in temperature (judgment) (15 points)

Inappropriate perioperative temperature >38.8°C [>101.8°F] (judgment) (10 points)

Inappropriate sinus tachycardia (3 points)

Ventricular tachycardia or ventricular fibrillation (3 points)
Other **

Base excess below -8 mEq/L [below -8 mmol/L] (10 points)

Arterial pH <7.25 (10 points)

Rapid reversal of MH signs with dantrolene (5 points)

Positive family history together with positive personal anesthetic history (not including elevated resting CK) (10 points)

Resting elevated serum CK (in patient with positive family history) (10 points)

Important: Inputs must be complete to perform calculation.

Total criteria point count:


MH likelihood and rank

0 points: MH Rank = 1; MH likelihood = Almost never
3 to 9 points: MH Rank = 2; MH likelihood = Unlikely
10 to 19 points: MH Rank = 3; MH likelihood = Somewhat less than likely
20 to 34 points: MH Rank = 4; MH likelihood = Somewhat greater than likely
35 to 49 points: MH Rank = 5; MH likelihood = Very likely
50 to 108 points: MH Rank = 6; MH likelihood = Almost certain

  • *Do not double count; choose the indicator with highest score.
  • **Ok to double count; add each applicable.
  • CK: creatine kinase; ETCO2: end-tidal carbon dioxide pressure; PaCO2: arterial partial pressure of carbon dioxide; MH: malignant hyperthermia.
  • In this calculator, mcg is the abbreviation for micrograms.

Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

Information on this page may not appear correctly if printed.

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Topic 13458 Version 15.0