👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Reduction of Risk Potential🔖 Free to read, print, and share
Also known as: MH · anesthesia high fever · MH crisis · reaction to anesthesia
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Use this quick-reference guide to spot, treat, and prevent Malignant Hyperthermia on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
⚠️ Cause
Genetic rxn to anesthesia
Trigger: succinylcholine, inhaled gas
🩺 Signs
Early: jaw rigidity, ↑↑CO2
↑temp is LATE sign
Tachycardia, muscle rigidity
✅ Do
Stop trigger agent now
Give dantrolene IV STAT
Cooling, 100% O2, monitor K+
🚩 Report
Hyperkalemia → arrhythmias
📚 Malignant Hyperthermia — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Malignant hyperthermia is a rare, life-threatening genetic reaction to certain anesthetics, most often succinylcholine and volatile inhaled agents like halothane. 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.
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Key points
Understand these first
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.
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Nursing priorities
What to do, in order
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.
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Red flags — report now
Escalate immediately
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.
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Labs & values
Numbers to know
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
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Patient teaching
What patients must know
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.
❓ Malignant Hyperthermia: NCLEX FAQs
What are the priority nursing interventions for Malignant Hyperthermia?
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.
What are the warning signs of Malignant Hyperthermia a nurse must report?
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.
What do I need to know about Malignant Hyperthermia for the NCLEX?
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.
What patient teaching is important for Malignant Hyperthermia?
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.
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Quick Tip
The earliest signs are a rising end-tidal CO2 and masseter (jaw) muscle rigidity after anesthesia induction; temperature elevation is a late sign.