Red flag to remember
Unexplained rising end-tidal CO2 with jaw rigidity during anesthesia is MH until proven otherwise; act immediately.
What is malignant hyperthermia?
Uncontrolled muscle metabolism causes a hypermetabolic crisis with rigidity, rapidly rising temperature, and acidosis. The earliest and most specific sign is unexplained rising end-tidal CO2 and jaw/muscle rigidity, not the high temperature, which appears late. Dantrolene is the antidote.
Key points to remember
- The earliest signs are a rising end-tidal CO2 and masseter (jaw) muscle rigidity after anesthesia induction; temperature elevation is a late sign.
- Extremely high temperature (can exceed 105-107 F / 40+ C) rises rapidly, often more than 1-2 degrees every few minutes.
- Tachycardia, tachypnea, dysrhythmias, hyperkalemia, and metabolic and respiratory acidosis develop quickly.
- It is an autosomal dominant inherited trait, so a family history of anesthesia reactions or unexplained surgical deaths is a major risk factor.
- Muscle breakdown causes rising potassium and myoglobinuria (dark/tea-colored urine), threatening dysrhythmias and renal failure.
- Dantrolene sodium directly relaxes skeletal muscle and is the only specific drug treatment.
Common causes
- Genetic rxn to anesthesia
- Trigger: succinylcholine, inhaled gas
Signs & symptoms
- Early: jaw rigidity, ↑↑CO2
- ↑temp is LATE sign
- Tachycardia, muscle rigidity
Nursing priorities
- Stop the triggering anesthetic agent and surgery immediately and call for the malignant hyperthermia emergency cart.
- Administer IV dantrolene rapidly per protocol and prepare to give repeated doses until the crisis resolves.
- Cool the patient aggressively with iced IV fluids, cooling blankets, and ice packs to groin/axillae; administer 100% oxygen.
- Treat hyperkalemia and dysrhythmias, monitor cardiac rhythm, and insert a catheter to monitor urine output and color.
- Identify the patient with known MH risk preoperatively and ensure a trigger-free anesthetic plan is used.
Labs & values
Potassium:3.5-5.0 mEq/L (rises sharply in MH)
Arterial pH: 7.35-7.45 (falls with acidosis)
CK (creatine kinase): markedly elevated from muscle breakdown
Patient teaching
- Inform every future anesthesia provider of your personal or family history of malignant hyperthermia.
- Wear a medical alert bracelet identifying the MH risk.
- First-degree relatives should be counseled about genetic risk and testing before any surgery.
Red flags: report now
- Unexplained rising end-tidal CO2 with jaw rigidity during anesthesia is MH until proven otherwise; act immediately.
- A rapidly climbing temperature combined with muscle rigidity is a true emergency requiring dantrolene without delay.
- Family or personal history of a severe anesthesia reaction must be reported before surgery to prevent triggering an episode.
- Dark cola-colored urine signals rhabdomyolysis and impending renal failure; escalate at once.
References
Clinical references for this topic
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