1. Malignant Hyperthermia

2. Malignant Hyperthermia
Definition : a metabolic disease of the muscle, a hypermetabolic state caused by exposure of susceptible individuals to known trigger agents.

3. Malignant Hyperthermia
Sustained, significant hypermetabolism
Inherited component
Abnormal handling of intracellular calcium levels
“Triggered” by pharmacologic agents , possibly by heat/exercise

4. Trigger Agents for MH MH Trigger Agents
Potent Volatile Anesthetics (eg. halothane, sevoflurane, desflurane)
Succinylcholine
Not MH Triggers
Intravenous agents
Opioids
Non-depolarizing agents
Ketamine
Propofol
Anxiolytics

5. Spectrum of Presentations of Malignant Hyperthermia
The classic case
Masseter muscle rigidity
Associated with muscle disorders
MH without anesthesia

6. Signs of Malignant Hyperthermia
Specific
Muscle Rigidity
Increased CO2 Production
Rhabdomyolysis
Marked Temperature Elevation
Non Specific
Tachycardia
Tachypnea
Acidosis (Resp/Metabolic)
Hyperkalemia

7. Summary of Clinical Signs

8. Muscle Rigidity and MH
Jaw muscle rigidity may occur after succinylcholine
More common in children
Presages MH in 20-30%
Generalized rigidity not always present
When present, regularly associated with MH susceptibility
With muscle breakdown and creatine kinase above 20,00IU, the likelihood of MH is very high.

9. Masseter Muscle Rigidity
Stop Inhalation Agent
No further succinylcholine
Continue with
nontrigger agents Awaken
follow ET C patient
Observe in ICU for 24 hours
CK/electrolytes,Myoglobin
Dantrolene as needed
Recommend for biopsy

10. Disorders Associated with MH Susceptibility
Central Core Disease
Evans Myopathy
Hypokalemic Periodic Paralysis
?sodium channel myotonias

11. Mimics of Malignant Hyperthermia
Fever (without rigidity)
Thyrotoxicosis
Sepsis
Pheochromocytoma
Iatrogenic overheating
Anticholinergic syndrome
Faulty equipment
Tourniquet (children)
Fever and muscle symptoms
NMS
Hypoxic encephalopathy
Ionic contrast agents in CSF
Cocaine, amphetamine, ecstasy

12. What Tests Are Used To Diagnose MH?
Current Concepts:
Halothane, caffeine contracture test is the only gold standard
Current Investigations:
Molecular genetics
Nuclear magnetic resonance for assessing ATP and creatine phosphate with/without exercise in vivo
Calcium flux measurement in cultured muscle cells
Local increase in pC02 following IM caffeine
EMG changes in MH patients

13. What is the Incidence of MH?
Original Concepts:
Rare. One in 50,000 anesthetics
Current Concepts:
Clinically based information:
One in 20,000 to 50,000 anesthetics depending on drugs, population
Molecular Genetics based information: MH trait in 1 in 2,000-3,000 patients. Low penetrance

14. Immediate Therapy of Malignant Hyperthermia
Have a plan!
Discontinue inhalation agents, Succ
Hyperventilate with 100% 02
Bicarbonate 1-2 mg/kg as needed
Get additional help
Dantrolene 2.5mg/kg Push. Repeat PRN
Cool patient: gastric lavage, surface, wound
Treat arrhythmias-do not use calcium channel blockers
Arterial or venous blood gases
Electrolytes, coagulation studies

15. Treatment of Malignant Hyperthermia - Acute
Dantrolene-1
The only specific treatment for MH
Administer as soon as diagnosis made
20mg/bottle-dissolve with 60ml sterile water
Shake vigorously or warm bottles to dissolve
Give 2.5mg/kg STAT
Repeat as needed to control signs of MH

16. Treatment of Malignant Hyperthermia
Dantrolene-2
After crisis controlled, give dantrolene 1mg/kg every 4-6 hours for 24 hours
Continue dantrolene for 36 hours
Recrudescence rate is 25%

17. Management of Malignant Hyperthermia
Biochemical Markers
Blood gasses – esp pCO2, pH, CK
Myoglobinuria
PT, PTT, INR, fibrin split products
Liver enzymes, BUN

18. Morbidity and Mortality
RHABDOMYOLYSIS
RENAL FAILURE
DIC if temp >41.50 C
Hyperkalemia
Acidosis

19. Prevention of Malignant Hyperthermia
Preop personal/family history of anesthetic problems, neuromuscular disorders
Temperature/endtidal CO2 monitoring during general anesthesia
Recognition of masseter rigidity
Investigation of unexplained tachycardia, hypercarbia, hyperthermia
Availability of Dantrolene
Avoiding MH triggers in MH susceptibles
Using Succinylcholine in indication

20. Principles of Management of MH Susceptible
Dantrolene not necessary preoperatively (dantrolene available)
Avoid succinylcholine
Avoid potent inhalation agents
Discharge after about 2 hours in the recovery room if all signs are stable

21. Preparation for MH Susceptible
Shut/disable vaporizers
Flow 10L/min for 20 minutes (through machine and ventilator)
Change carbon dioxide absorbent
Use non-trigger agents or local anesthesia
Monitor temperature
Have dantrolene available

22. Suggested Regimen for MH Patient
Anxiolytic (ketamine permissible)
Propofol/opioid induction
Non-depolarizing relaxant
Nitrous/narcotic/propofol
Reversal of muscle relaxant
Observe 4 hours

23. Drug Safety in MH MH Trigger Agents
Potent Volatile Anesthetics (eg. halothane, sevoflurane, desflurane)
Succinylcholine
Not MH Triggers
Intravenous agents
Opioids
Non-depolarizing agents
Ketamine
Propofol
Anxiolytics

24. Credits
Website of MHAUS, Malignant Hyperthermia Association of the United States, Professional Information Center.