Malignant Hyperthermia

Question 1

Classify and define the signs of malignant hyperthermia

Answer 1

HYPERMETABOLISM

• ↑PaCO2
• ↓PaO2
• ↓ScvO2
• Metabolic acidosis

INCREASED SNS (PaCO2)

• Tachycardia
• Hypertension
• Arrhythmias

MUSCLE DAMAGE

• Masseter spasm
• Generalized rigidity
• Increased creatine kinase
• Hyperkalaemia
• Hypernatraemia
• Hyperphosphataemia
• Myoglobinemia
• Myoglobinuria

HYPERTHERMIA

• Fever
• Sweating

Question 2

What is the inheritance pattern of malignant hyperthermia

Answer 2

Autosomal Dominant

Question 3

What is the predominant abnormality in malignant hyperthermia sensitive individuals

Answer 3

Skeletal muscle receptor (ryanodine receptor: RYR-1)

Allows excessive accumulation of intracellular calcium in response to a triggering event –> skeletal muscle hypermetabolism

Question 4

When do the symptoms of MH usually manifest?

Answer 4

Usually within 1 hour of induction

But anytime during administration of triggering agents

Very rarely postoperatively

Question 5

What are the three early clinical indicators for the development of MH

Answer 5

1. Hypercapnoea
2. Tachycardia
3. Widening gap between FiO2 and FeO2

Question 6

Describe the common anaesthetic/surgical related problems that might mimic MH

Answer 6

1 .Insufficient anaesthesia/analgaesia (usually ↓PaCO2)

2. Insufficient FGF/Ve
3. CO2 absorption laparoscopy
4. Fever

Question 7

Apart from the common anaesthetic/surgical related problems which might mimic MH, what are other disease conditions included in the DDx

Answer 7

5. Anaphylaxis
6. Anaesthesia induced rhabdomyolysis (AIR)
7. Thyrotoxicosis
8. Transfusion reaction
9. Drugs of abuse
10. Serotonin syndrome
11. Phaeochromocytoma

Question 8

What is the immediate treatment approach for MH

Answer 8

1. Declare
   - Notify surgeon to complete/abbreviate surgery.
   - Call for help
2. Stop triggering agent
   - Change to TCI/TIVA/sedation
   - FGF > 10L/minute

Supportive
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A - site ETT
B - Hyperventilate FiO2 1
C - Large bore
D - Dantrolene mixing people
E - Cool patient

Specific
HYPERMETABOLISM
- 2.5 mg/kg IV BOLUS (180 mg in 70kg adult)
- Need to dilute 9 bottles 20 mg each with 60mL Sterile and preservative free water
= 540 milliliters
- Monitor etCO2/HR for response
- May need up to 10 mg/kg (36 bottles)

HYPERKALAEMIA

• CaCl 10 ml 10% (repeat of ECG changes persist)
• Actrapid 10U + 50 ml 50% dextrose (watch hgt)
• NaHCO3: 1 - 2 mEq/kg IV push over 5 - 10 minutes

ACIDOSIS
- NaHCO3: 1 - 2 mEq/kg IV push over 5 - 10 mins

No CCB (use amiodarone)

Question 9

What is the mortality of MH subsequent to the availability of Dantrolene

Answer 9

1 - 17%