MH Dantrolene

Question 1

What area of the brain regulates temperature?

Answer 1

Hypothalamus
Gain center: posterior hypothalamus
Loss center: anterior hypothalamus

Question 2

For each 1 degree fahrenheit change, basal metabolic rate will change how much?

Answer 2

7%

Question 3

Routes of heat loss

Answer 3

Radiation 40%
Convection 30%
Evaporation (burn pt)
Conduction

Question 4

MH incidence?

Answer 4

1/15,000 children

1/50,000 adults

Question 5

How does someone get MH?

Answer 5

Genetic susceptibility; autosomal dominant

RYR mutations are common in MH patients

Question 6

MH pathophysiology?

Answer 6

It is a syndrome, a chain of clinical responses to muscle hypermetabolism (“decoupling”; ATP needed for Ca release)
Inc myoplasmic Ca release upon depolarization with failure of negative feedback causing hypoxemia
Aerobic metabolism replaces ATP with heat and CO2; lactic acidosis
Myoglobin released causes rhabdo, hyperkalemia
When ATP is depleted, CV collapse

Question 7

4 earliest signs of MH and other s/s?

Answer 7

4 earliest: hypercarbia, tachycardia, tachypnea, masseter spasm
Other: hyperthermia, hypertension, dysrhythmias, metabolic acidosis, hyperkalemia, myoblobinuria, hypoxemia, elevated CPK with rhabdo, coke-colored urine

Question 8

What are triggers of MH?

Answer 8

Inhalational agents (not really nitrous oxide)
SUX
Mild MH triggers: exercise in hot conditions, neuroleptic drugs, alcohol, infections

Question 9

How does someone get tested for MH?

Answer 9

1 gram of muscle is tested with the halothane-caffeine contracture test

Question 10

How does dantrolene work?

Answer 10

Reduces muscle tone and metabolism
Prevents ongoing release of Ca from muscle (SR)
Blocks external entry of Ca into sarcoplasm

Question 11

Side effects of dantrolene, E1/2t?

Answer 11

Significant muscle weakness, can last long, ICU for 36h
Phlebitis
E1/2t 10-15h

Question 12

Dantrolene interaction?

Answer 12

CCB will cause more hyperkalemia and myocardial depression

Question 13

You want the place you work to have how much dantrolene?

Answer 13

36 vials

Also lots of sterile water to mix with

Question 14

Sequence of events the second you realize your patient has MH

Answer 14

Call for help, MH cart
D/C volatile agent, sux
Change circuit and soda, hyperventilate 100% oxygen
Dantrolene
Tx acidosis with sodium bicarb
Cooling to 38C
Maintain UO with diuretics and fluids (NOT LR)
For dysrhythmias give lidocaine or procainamide (NOT CCB)
Tx hyperkalemia with 1mL/kg D50 glucose and 0.15 units/kg regular insulin, calcium chloride 5-10 mg/kg

Question 15

Dantrolene dose?

Answer 15

Bolus 2.5 mg/kg
Then maintenance dose 2 mg/kg IV q5min up to 10 mg/kg
Then 1 mg/kg q6h for 72h
Each vial of dantrole contains 20 mg dantrolene and 3g mannitol, needs to be diluted with 60 mL sterile water

Question 16

What lab tests do you want to get for someone having an MH episode?

Answer 16

ABG
CK myoglobin
Electrolytes, thyroid, LDH
PT/PTT, fibrinogen, FSP
CBC, lactic acid
Urine for myoglobin/hemoglobin

Question 17

What muscle diseases are definitely associated with MH (predispose MH reactions)

Answer 17

Central core disease
King-Denborough syndrome
Evan’s myopathy
Not directly, but somewhat associated with MD, the patient will develop rhabdo and hyperkalemia without hyper metabolic issues

Question 18

Neuroleptic malignant syndrome presentation?

Answer 18

Mimics MH

Presents with muscle rigidity, fever, autonomic instability, delirium, elevated CPK

Question 19

What is the presentation of occult myopathy in young males having surgery?

Answer 19

Mimics MH

Sudden cardiac arrest, especially soon after use of sux, muscle rigidity, hyperthermia