A 28-year-old male from rural Maharashtra is scheduled for emergency appendicectomy under general anesthesia. Induction is uneventful with propofol and succinylcholine. Within 2 minutes of intubation, the anesthesiologist notices the patient's jaw is rigid and muscles are tense. Core temperature rises from 36.8°C to 38.2°C within 5 minutes. Capnography shows a sudden rise in end-tidal CO₂ from 35 to 55 mmHg. Arterial blood gas reveals pH 7.28, PaCO₂ 62 mmHg, HCO₃⁻ 28 mEq/L, and K⁺ 6.2 mEq/L. Urine output is minimal and dark-colored. What is the most appropriate immediate management?

Explanation

## Diagnosis: Malignant Hyperthermia (MH) ### Clinical Recognition **Key Point:** The classic triad of MH includes: 1. Muscle rigidity (jaw clenching, generalized muscle tension) 2. Hypercarbia (elevated end-tidal CO₂ out of proportion to ventilation) 3. Hyperthermia (late sign; core temperature rise) **High-Yield:** Early signs of MH are **muscle rigidity** and **hypercarbia**, NOT fever. Temperature rise occurs late and is a poor early warning sign. ### Pathophysiology MH is a pharmacogenetic disorder of skeletal muscle triggered by volatile anesthetics (sevoflurane, isoflurane, desflurane) and/or succinylcholine. The trigger causes uncontrolled calcium release from the sarcoplasmic reticulum, leading to: - Sustained muscle contraction → rigidity and heat generation - Rhabdomyolysis → myoglobinuria (dark urine) - Hyperkalemia (from muscle breakdown) - Metabolic and respiratory acidosis (from CO₂ production and anaerobic metabolism) ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected MH: Rigidity + Hypercarbia + Rising Temp]:::outcome --> B[STOP all triggering agents immediately]:::urgent B --> C[Hyperventilate with 100% O₂]:::action C --> D[Switch to TIVA if not already done]:::action D --> E[Administer dantrolene 2.5 mg/kg IV]:::action E --> F[Repeat dantrolene q5min up to 10 mg/kg if signs persist]:::action F --> G[Manage complications]:::action G --> H1[Hyperkalemia: Ca²⁺, insulin-dextrose, sodium bicarbonate]:::action G --> H2[Acidosis: hyperventilation, sodium bicarbonate]:::action G --> H3[Myoglobinuria: aggressive IV fluids, maintain UOP > 200 mL/hr]:::action G --> H4[Monitor core temperature, CK, myoglobin, renal function]:::action ``` **Key Point:** Dantrolene sodium is the ONLY specific treatment for MH. It blocks calcium release from the sarcoplasmic reticulum by inhibiting the ryanodine receptor. ### Dantrolene Administration | Parameter | Detail | |-----------|--------| | **Initial dose** | 2.5 mg/kg IV rapid bolus | | **Repeat dosing** | Every 5 minutes if signs persist | | **Maximum cumulative dose** | 10 mg/kg | | **Reconstitution** | Each 20 mg vial requires 60 mL sterile water (no bacteriostatic agents) | | **Onset** | 1–5 minutes IV | **Clinical Pearl:** Have dantrolene prepared and immediately available in all ORs. Pre-calculate the dose (2.5 mg/kg) for all elective cases at risk. ### Post-Crisis Management 1. **Hyperkalemia:** Calcium gluconate 10% (cardioprotection), insulin 0.1 U/kg + dextrose 0.5 g/kg, sodium bicarbonate 1–2 mEq/kg 2. **Acidosis:** Hyperventilation + sodium bicarbonate 3. **Myoglobinuria:** Aggressive IV hydration (target UOP > 200 mL/hr), consider furosemide and mannitol 4. **Monitoring:** Continuous ECG, core temperature, serial ABGs, serum K⁺, CK, myoglobin, creatinine, urine dipstick 5. **ICU admission:** Post-operative dantrolene 1 mg/kg IV q4–6h for 24–48 hours to prevent recrudescence **Mnemonic:** **DANTROLENE** = **D**on't **A**llow **N**euromuscular blockers, **T**rigger **R**emoval, **O**xygen, **L**iquids, **E**lectrolyte management, **N**ursing in ICU, **E**arly recognition **Warning:** Succinylcholine is absolutely contraindicated in MH — it is a trigger agent and will worsen the crisis. Avoid all volatile anesthetics. **High-Yield:** Dantrolene must be reconstituted fresh — it has poor solubility and requires vigorous mixing. Prepare multiple vials in advance if MH is suspected. [cite:Miller's Anesthesia 8e Ch 33]