Malignant Hyperthermia

Front 1

Define Malignant hyperthermia.

Back 1

a sub clinical myopathy that is unmasked upon exposure to volatile anesthetics or succinylcholine.

Front 2

What is the significance of chromosomes 1,3,7,17,19?

Back 2

genetic coding site for Ca++ release channels of sarcoplasmic reticulum

Front 3

Where is the gene for MH located?

Back 3

chromosomes 1,3,7,17 & 19.

Front 4

Pathophysiology: What are some results of skeletal muscle that acutely increases its 02 consumption & lactate production?

Back 4

Heat production.
Respiratory & metabolic acidosis.
Muscle rigidity.
Sympathetic stimulation.
Increased cellular permeability.

Front 5

What are some possibilities of patients w/ normal Ry1 receptors?

Back 5

Possible abnormalities in 2º messengers & modulators of Ca++ release (Fatty acids & phosphatidylinositol).
Possible abnormal Na+ channels.

Front 6

What is MH caused by?

Back 6

a loss of control of Ca++ concentration w/n the muscle fiber. (Generalized alteration in cellular & sub cellular membrane permeability)

Front 7

What are the general mechanism of skeletal muscle contraction?

Back 7

Action potential travels along a motor nerve to its endings on muscle fibers, where the nerve secretes neurotransmitter Ach.

Front 8

How does Ach act on muscle fiber?

Back 8

acts on the area of muscle fiber membrane to open multiple Ach-gated channels through protein molecules floating in the membrane.

Front 9

What does Calcium initiate in the cell?

Back 9

initiate attractive forces b/n the actin & myosin filaments, causing them to slide alongside each other in a contractile process.

Front 10

What does opening of the Ach-gated channels in the neuromuscular junction allow?

Back 10

allows Na+ ions to flow to the interior of muscle fiber membrane initiating action potential in muscle fiber.

Front 11

What does the action potential traveling along the muscle fiber membrane do?

Back 11

causes sarcoplasmic reticulum (SR) to release Ca++ stored w/n the reticulum

Front 12

What is the genetic coding site for the Ca++ release channels of skeletal muscle sarcoplasmic reticulum?

Back 12

Rγ1 receptor

Front 13

What can having a defect in the Ry1 receptor lead to?

Back 13

A defect in this receptor affects Ca++ release channels allowing an increased flood in Ca++ & results in MH susceptibility.

Front 14

What does Dantrolene do?

Back 14

It is thought that Dantrolene interferes w/ the Ca++ release by binding at the Rγ1 receptor & Ca channel sites.

Front 15

What is the incidents of MH in children? Adults?

Back 15

1 in 12,000-15,000
1 in 40,000

Front 16

Where are higher incidents of MH seen?

Back 16

Mid-west (USA).
Children & young adults.
Operations such as Orthopedic (joint dislocation repair), Ophthalmic (ptosis & strabismus), Head & neck (cleft palate, T&A, dental).
Duchenne muscular dystrophy. (also observed in Burkitt’s lymphoma, Osteogenesis imperfecta, Myotonia congenita, Neuroleptic malignant syndrome, Myelomeningocele.

Front 17

What are some signs & symptoms of MH?

Back 17

Any characteristics of hypermetabolism. (Tachycardia, Tachypnea, Hypercarbia, Arterial hypoxemia, Metabolic or Respiratory Acidosis, Hyperkalemia, Cardiac dysrhythmias, Hypotension, Skeletal muscle rigidity after SCh, Hyperthermia, Mottled skin)

Front 18

What is the FIRST indication that an individual is susceptible when there is an absence of history?

Back 18

an exaggerated response to SCh

Front 19

What may be seen in early responses that may indicate MH?

Back 19

increased tension of masseter muscles (more pronounced in kids).
May be impossible to open mouth for intubation.

Front 20

What is Trismus-Masseter Spasm?

Back 20

Defined as jaw muscle rigidity in association w/ limb muscle flaccidity after giving SCh.
Jaw muscle tone: exaggerated, prolonged & tight, “jaws of steel”, risk increases greatly.

Front 21

What should you do once trismus appears?

Back 21

Check ETC02, urine color & arterial or venous blood for CK, acidosis, electrolytes (especially K+).
With “jaws of steel” that persist for more than a few minutes, halt procedure.

Front 22

If jaw is slightly resistant to opening, what should you do?

Back 22

Continue & observe carefully.
If jaw is modestly tight, either halt procedure or continue w/ nontriggering agents.

Front 23

What are some early signs of MH?

Back 23

Hypercarbia.
Hyperkalemia (but resolves rapidly after normothermia).

Front 24

What is the most common cause of death in MH patients?

Back 24

V-Fib.

Front 25

What are some things you may see in ABGs or venous blood work in MH patients?

Back 25

Arterial hypoxemia.
Hypercarbia (PaCO2 100-200 mmHg).
Respiratory-metabolic acidosis (pH 7.15-6.80).
Marked central venous 02 desaturation.

Front 26

What are some late signs & symptoms of MH?

Back 26

Elevated Temperature.
Rhabdomyolysis.
Elevated Transaminase enzymes & CK. (12-24hrs post)
DIC.
Pulmonary edema.
ARF.
CNS may manifest blindness, seizures, coma or paralysis.

Front 27

What are the treatment doses of Dantrolene?

Back 27

(2-3 mg/kg) IV as bolus, & repeat dose q 5-10 min until symptoms are controlled (up to or > 10 mg/kg)

Front 28

What other steps should you do if MH is identified?

Back 28

Turn off volatile gases.
Hyperventilate w/ 100% 02.
Initiate active cooling measures (stop when temp is 38ºC).
Conclude surgery ASAP.
Correct metabolic acidosis (NaHC03 1-2 mEq/kg IV).
Maintain UOP w/ hydration, mannitol 0.25 g/kg, lasix 1 mg/kg IV.
Treat cardiac dysrhythmias.
Consider treating hyperkalemia if not decreased w/ normothermia (glucose 50 ml of D50 & 10 units regular insulin).Monitor in ICU for reoccurring.

Front 29

When was Dantrolene approved for use by the FDA? What is its effectiveness? Cost?

Back 29

FDA approved in 1979.
73% show twitch depression w/ 2.5 mg/kg.
Expensive therapy ($60-100 per vial).

Front 30

What are some things that may mimic MH?

Back 30

Contrast dye.
Diabetic coma.
Drug toxicity-overdose.
Heat stroke.
Anesthesia machine malfunction w/ increased C02.
Thyroid storm.
Intracranial free blood.
Pheochromocytoma.
Sepsis.

Front 31

What are some prophylaxic Dantrolene uses & considerations?

Back 31

One protocol, 2.4 mg/kg IV over 10-30 min prior to induction.
50% of this dose repeated in 6 hrs.
Should have foley catheter in place.
May cause nausea, diarrhea, blurred vision & weakness.

Front 32

What are some triggering agents of MH?

Back 32

Volatile gases (Halothane, Enflurane, Isoflurane, Sevoflurane, Desflurane).
N20 (may be weak trigger).
Succinylcholine.

Front 33

What are some safe agents to administer in a patient w/ suspected MH?

Back 33

Barbiturates, propofol, etomidate, opioids, benzodiazepines, ketamine, nondepolarizing muscle relaxants.
N20 questionable, if in doubt, do not use.
Muscle relaxant antagonists.
Local anesthetics.
Vasopressors.

Front 34

What are some precautions, in regards to MH, you should take w/ the anesthesia machine?

Back 34

Disposable circuit & new fresh gas outlet hose.
New C02 absorbent.
No vaporizers (removed or taped off).
Continuous flow of 02 at 10L/min for 5-20 minutes.
Regional anesthesia if possible.

Front 35

Regarding MH, what are some things you can do before a surgical procedure?

Back 35

Careful evaluation of history.
Genealogy should go back several generations.
Patient can undergo muscle biopsy contracture study. (costly, false positives & only 30 centers, painful)

Front 36

What are some resources available if your patient experiences MH.

Back 36

The Malignant Hyperthermia Association of the United States (MHAUS) 1-800-644-9737.
24 hour hotline 1-800-MH-HYPER.
Web www.mhaus.org