23.2 Perioperative Crises: Malignant Hyperthermia and Severe Anaphylaxis

23.2 Perioperative Crises: Malignant Hyperthermia and Severe Anaphylaxis

Intraoperative crises such as Malignant Hyperthermia (MH) and acute perioperative anaphylaxis represent life-threatening emergencies that develop precipitously under anaesthesia. Both conditions feature rapid cardiovascular collapse and metabolic decompensation, requiring instant recognition, immediate pharmacological intervention, and adherence to standardized European clinical guidelines.

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1. Malignant Hyperthermia: Genetics and Molecular Pathophysiology

Malignant Hyperthermia is an inherited pharmacogenetic channelopathy of skeletal muscle characterized by hypermetabolism triggered by halogenated volatile anaesthetics or depolarizing neuromuscular blockers.

Molecular Genetics

• Transmission: Autosomal dominant with variable penetrance and expressivity. Incidence is approximately 1 in 10,000 to 1 in 50,000 anaesthetics.
• RYR1 Gene: Mutations in the RYR1 gene on chromosome 19q13.1 account for over 70% of MH-susceptible families. RYR1 encodes the skeletal muscle Ryanodine Receptor 1, the sarcoplasmic reticulum calcium release channel.
• CACNA1S Gene: Mutations in CACNA1S on chromosome 1q32 account for $<2\text{--}3\%$ of cases. It encodes the $\alpha_1$-subunit of the L-type voltage-gated calcium channel (dihydropyridine receptor / DHPR).
• Associated Myopathies: MH susceptibility is genetically linked to Central Core Disease and King-Denborough Syndrome.
• Critical Distinction: Duchenne and Becker Muscular Dystrophies are NOT malignant hyperthermia. In dystrophinopathies, exposure to suxamethonium precipitates massive rhabdomyolysis and life-threatening hyperkalemic cardiac arrest due to sarcolemmal fragility, not abnormal RyR1 calcium channel kinetics. Halogenated volatiles can trigger volatile-induced rhabdomyolysis (anesthetic-induced rhabdomyolysis / AIR) in DMD, but this does not represent true hypermetabolic MH.

Pathophysiological Cascade

In MH-susceptible skeletal muscle, triggering agents induce conformational changes in mutated RyR1 channels, causing uncontrolled, sustained efflux of calcium from the sarcoplasmic reticulum into the myoplasm. Intracellular calcium concentrations surge twenty-fold:

1. Sustained troponin-C activation drives uninhibited actin-myosin cross-bridge cycling and profound muscle contraction / rigidity.
2. Sarcoplasmic reticulum $Ca^{2+}\text{-ATPase}$ (SERCA) and myocellular pumps work at maximum capacity to re-sequester calcium, consuming massive reserves of adenosine triphosphate (ATP).
3. Accelerating glycogenolysis and oxidative phosphorylation exhaust oxygen reserves, shifting to anaerobic metabolism, massive lactic acid generation, and mixed metabolic and respiratory acidosis.
4. Heat generation from uncoupled aerobic/anaerobic ATP hydrolysis overwhelms thermoregulatory capacity, precipitating fulminant hyperthermia.
5. Cellular energy exhaustion leads to myocyte membrane rupture, releasing vast quantities of potassium, myoglobin, and creatine kinase (CK) into the circulation.

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2. Triggering Agents and Clinical Manifestations

+------------------------------------+------------------------------------+
|        TRIGGERING AGENTS           |           SAFE AGENTS              |
+------------------------------------+------------------------------------+
| - All volatile inhalational        | - Intravenous induction agents     |
|   anaesthetics (sevoflurane,       |   (propofol, etomidate, ketamine,  |
|   desflurane, isoflurane,          |   thiopental, methohexital)        |
|   halothane, enflurane)            | - All non-depolarizing NMBAs       |
| - Depolarizing muscle relaxants    |   (rocuronium, vecuronium,         |
|   (suxamethonium / succinylcholine)|   cisatracurium, atracurium)       |
|                                    | - All opioids, local anaesthetics, |
|                                    |   nitrous oxide, benzodiazepines   |
+------------------------------------+------------------------------------+

Clinical Progression and Warning Signs

• Earliest and Most Sensitive Sign: An unexplained, dramatic surge in End-Tidal Carbon Dioxide ($ET\text{CO}_2$) that is completely refractory to massive increases in minute ventilation ($ET\text{CO}_2$ doubling or tripling to $>75\text{--}100\text{ mmHg}$). Sinus tachycardia and tachypnea (in spontaneous breathers) accompany this early hypercapnia.
• Masseter Muscle Rigidity (MMR): Acute spasm of the jaw muscles ("jaws of steel") occurring immediately following suxamethonium administration, preventing laryngoscopy. MMR occurs in approximately 1% of paediatric patients receiving suxamethonium. If MMR is accompanied by generalized axial or peripheral muscle rigidity, it indicates fulminant MH. If MMR occurs in isolation without other hypermetabolic signs, the procedure should ideally be aborted; if emergency surgery is required, anaesthesia must be switched immediately to clean non-triggering intravenous drugs with intensive monitoring.
• Intermediate Signs: Cutaneous mottling, cyanosis, unstable hemodynamic arrhythmias (ventricular ectopy, peaked T waves from hyperkalemia), and generalized muscular rigidity.
• Late Signs: Hyperthermia with core body temperatures climbing at $1\text{--}2\text{°C}$ every 5 minutes (often exceeding $41\text{--}42\text{°C}$), gross myoglobinuria (burgundy/cola-colored urine), profound mixed acidosis ($pH < 7.10$, base excess $< -10\text{ mmol/L}$), disseminated intravascular coagulation (DIC), and hyperkalemic cardiac arrest.

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3. Emergency Management: European Malignant Hyperthermia Group Protocol

Successful management requires immediate execution of the EMHG protocol:

                     [ SUSPECTED MALIGNANT HYPERTHERMIA ]
                                      |
    +-------------------+-------------+-------------+-------------------+
    |                   |                           |                   |
[ Stop Triggers ]  [ Hyperventilate ]         [ Dantrolene ]      [ Treat Complications ]
  - Turn off gas     - 100% O2                   - 2.5 mg/kg IV     - Treat K+ (Calcium, Insulin)
  - Alert surgeon    - Max flow (>=10-15 L/min)    rapid bolus      - Cool (stop at 38.5°C)
  - Call MH cart     - Insert charcoal filters   - Repeat q5-10min  - Diuresis >1-2 mL/kg/h

1. Cease Triggers and Call for Assistance: Discontinue all volatile anaesthetics and suxamethonium immediately. Alert the surgical team to conclude or abort the procedure. Call for the MH emergency trolley and summon additional staff.
2. Hyperventilate with 100% Oxygen: Increase fresh gas flows to maximum ($\ge 10\text{--}15\text{ L/min}$) using 100% $\text{O}_2$. Hyperventilate the patient to two to three times predicted minute ventilation to clear carbon dioxide. Insert activated charcoal vapor filters directly onto the inspiratory and expiratory limbs of the breathing circuit. Do not waste time replacing the anaesthetic machine or ventilator during active crisis.
3. Administer Dantrolene Sodium:
   • Initial Bolus: Administer $2.5\text{ mg/kg}$ IV rapidly.
   • Repeat Dosing: Repeat boluses of $1\text{--}2.5\text{ mg/kg}$ every 5 to 10 minutes until hypermetabolism, tachycardia, and rigidity subside. Total cumulative doses may exceed $10\text{ mg/kg}$.
   • Mechanism of Action: Dantrolene binds specifically to the RyR1 receptor, blocking the release of channel-mediated calcium from the sarcoplasmic reticulum without depressing cardiac excitation-contraction coupling.
   • Formulations: Dantrium (20 mg lyophilized powder with 3 g mannitol per vial, requiring reconstitution in 60 mL sterile water per vial; cumbersome and slow) versus Ryanodex (250 mg nanocrystal suspension requiring only 5 mL sterile water; reconstituted in $<1\text{ minute}$, US) and Agilus (120 mg per vial reconstituted with 20 mL water, available in Europe), which reduce the number of vials to prepare.
4. Manage Life-Threatening Hyperkalemia:
   • 10% Calcium chloride $10\text{ mg/kg}$ IV (or 10% calcium gluconate $30\text{ mg/kg}$) to stabilize myocardial membrane excitability.
   • Regular insulin 10 units with $50\text{ mL}$ of 50% glucose (or $25\text{ g}$ dextrose).
   • Sodium bicarbonate $1\text{--}2\text{ mmol/kg}$ IV for refractory acidosis.
   • Absolute Contraindication: Never administer calcium channel blockers (verapamil, diltiazem) with dantrolene. The combination precipitates fatal hyperkalemic myocardial depression and cardiovascular collapse.
5. Active Cooling Measures: Infuse cold ($4\text{°C}$) normal saline IV ($1000\text{ mL}$ boluses); apply surface ice packs to axillae, groin, and neck; perform cold cavity lavage. Stop active cooling once core temperature drops to $38.5\text{°C}$ to avoid hypothermic overshoot and coagulopathy.
6. Renal Protection: Maintain urine output $>1\text{--}2\text{ mL/kg/h}$ with IV fluids, mannitol ($0.5\text{ g/kg}$), and furosemide to prevent renal tubular precipitation of myoglobin casts and acute tubular necrosis.
7. Diagnostic Confirmation: The gold standard for definitive diagnosis is the In Vitro Contracture Test (IVCT) (in Europe, per EMHG protocol) or Caffeine-Halothane Contracture Test (CHST in North America), requiring a fresh muscle biopsy from the vastus medialis exposed to halothane and caffeine in an organ bath, supplemented by comprehensive RYR1 genetic sequencing.

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4. Severe Perioperative Anaphylaxis: Mechanisms and Culprits

Perioperative hypersensitivity reactions occur in approximately 1 in 10,000 surgical procedures. Due to patient draping and general anaesthesia, classic cutaneous signs are often concealed, presenting primarily as sudden cardiovascular collapse or catastrophic bronchospasm.

Immunological vs Non-Immunological Mechanisms

• IgE-Mediated Anaphylaxis (Type I Hypersensitivity): Requires prior immunological sensitization. Allergen-specific IgE bound to high-affinity $Fc\varepsilon RI$ receptors on tissue mast cells and basophils cross-links upon antigen re-exposure, triggering explosive release of preformed mediators (histamine, tryptase, chymase) and de novo synthesis of leukotrienes ($LTC_4, LTD_4$), prostaglandins ($PGD_2$), and platelet-activating factor (PAF).
• Non-IgE-Mediated Hypersensitivity (Anaphylactoid / Pseudoallergic): Direct, non-immune activation of mast cells and basophils. A prominent mechanism is activation of the Mas-related G protein-coupled receptor X2 (MRGPRX2) by basic compounds such as neuromuscular blockers (atracurium, mivacurium), vancomycin, fluoroquinolones, and opioids. It is clinically indistinguishable from IgE-mediated anaphylaxis during the acute crisis.

Primary Offending Agents in European Practice

The leading culprits differ between countries and over time, so local data matter.

1. Neuromuscular Blocking Agents (NMBAs): Responsible for about 50-60% of IgE-mediated perioperative anaphylaxis in French and other continental European series, but about one-third of cases in the UK NAP6 audit (2018). The allergenic epitope is the quaternary ammonium group, which is ubiquitous in cosmetics, soaps, and disinfectants (explaining anaphylaxis on first known exposure). High cross-reactivity (60-70%) exists between different NMBAs. Suxamethonium and rocuronium exhibit the highest reporting rates.
2. Antibiotics: The most common identified cause in NAP6 (about 47%, chiefly teicoplanin and co-amoxiclav) and about 15-20% in French series. Beta-lactams (penicillins and cephalosporins like cefazolin) and teicoplanin are the main culprits.
3. Chlorhexidine: About 9% of NAP6 cases; increasingly recognized as a major occult allergen present in surgical skin preps, central venous catheter coatings, urethral lubricating gels, and dressings.
4. Patent Blue V / Isosulfan Blue Dyes: About 4.5% of NAP6 cases; used for sentinel lymph node localization in breast cancer and melanoma. Reactions characteristically develop $15\text{--}45\text{ minutes}$ after intradermal injection, often presenting with blue-tinged wheals and severe hypotension. It also causes optical interference with pulse oximetry, yielding false-positive desaturation.
5. Latex: Natural rubber latex proteins; historically dominant, now reduced due to latex-free environments.
6. Colloid Plasma Expanders and Protamine: Gelatins (Gelofusine) and protamine (higher risk in patients with fish allergies or prior NPH insulin use).

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5. Clinical Grading and Resuscitation of Severe Anaphylaxis

+-------------+--------------------------------------------------------------+
| GRADE       | CLINICAL MANIFESTATIONS                                      |
+-------------+--------------------------------------------------------------+
| Grade I     | Cutaneous-mucosal signs: erythema, urticaria, angioedema     |
+-------------+--------------------------------------------------------------+
| Grade II    | Moderate multi-organ signs: hypotension, tachycardia,        |
|             | cough, mild bronchospasm, cutaneous signs                    |
+-------------+--------------------------------------------------------------+
| Grade III   | Life-threatening shock: severe hypotension, marked           |
|             | bronchospasm, elevated peak airway pressure, desaturation    |
+-------------+--------------------------------------------------------------+
| Grade IV    | Circulatory arrest: PEA or asystole                          |
+-------------+--------------------------------------------------------------+

Resuscitation Protocol

1. Discontinue Suspected Allergen: Immediately halt administration of the suspected offending infusion (antibiotic, colloid, dye, muscle relaxant). Turn off volatile anaesthetic agents.
2. Airway and Oxygenation: Deliver 100% $\text{O}_2$. Intubate early if angioedema threatens the upper airway; provide positive pressure ventilation if bronchospasm compromises gas exchange.
3. First-Line Drug: Epinephrine (Adrenaline):
   • Epinephrine is the definitive life-saving medication. Alpha-1 vasoconstriction counteracts massive systemic vasodilation and mucosal edema; beta-1 inotropy/chronotropy restores coronary perfusion; beta-2 receptor stimulation reverses bronchospasm and elevates intracellular cAMP, halting further mast cell degranulation.
   • Grade II: Titrated boluses of $10\text{--}20\text{ }\mu\text{g}$ IV ($0.1\text{--}0.2\text{ mL}$ of 1:10,000 dilution).
   • Grade III: Titrated boluses of $50\text{--}100\text{ }\mu\text{g}$ IV ($0.5\text{--}1.0\text{ mL}$ of 1:10,000 dilution), repeated every 1 to 2 minutes as required.
   • Grade IV (Cardiac Arrest): $1\text{ mg}$ IV boluses every 3 to 5 minutes per ALS algorithm.
   • Refractory Shock: Continuous infusion of epinephrine at $0.05\text{--}0.2\text{ }\mu\text{g/kg/min}$.
4. Aggressive Crystalloid Resuscitation: Up to 35% of intravascular volume extravasates into the interstitial compartment within 10 minutes due to hyperpermeability. Immediately administer $20\text{--}30\text{ mL/kg}$ of balanced crystalloid ($1\text{--}2\text{ L}$ in adults) under pressure.
5. Secondary Pharmacotherapy:
   • Second-line vasopressors: Noradrenaline infusion or vasopressin ($1\text{--}2\text{ units}$ IV) for refractory vasodilatory shock. Glucagon ($1\text{--}2\text{ mg}$ IV) is indicated for patients refractory to epinephrine due to chronic beta-blocker therapy.
   • Inhaled or IV salbutamol for persistent bronchospasm.
   • Hydrocortisone ($200\text{ mg}$ IV) to blunt delayed biphasic inflammatory reactions (onset 4-8 hours).
   • Antihistamines: Chlorpheniramine $10\text{ mg}$ IV (slow injection).

Diagnostic Immunology: Serum Tryptase Kinetics

Mast cell tryptase is a neutral protease stored in mast cell secretory granules. To substantiate acute mast cell activation, guideline-mandated serial sampling is required:

1. Sample 1: Collected as soon as feasible once resuscitation is under way (never delay treatment to take it).
2. Sample 2: Collected ideally $1\text{--}2\text{ hours}$ after the onset of the reaction, and no later than 4 hours (captures the peak).
3. Sample 3 (Baseline): Collected at $\ge 24\text{ hours}$ or at outpatient allergy follow-up.

$$\text{Significance Threshold: } \text{Peak Tryptase} \ge (1.2 \times \text{Baseline Tryptase}) + 2\text{ }\mu\text{g/L}$$

A peak tryptase exceeding this mathematical consensus confirms clinically significant mast cell degranulation. All patients must be formally referred for skin prick and intradermal testing, usually about 4 to 6 weeks after the event.