Case of the Month

Topic:  The parturient with a suspected MH Susceptible husband

A 26 year old Gravida 1, Para 0 patient presents to the anesthesiologist for an elective consult in preparation for an uneventful delivery of her first child.  She is currently 35 weeks gestation.  There have been no pregnancy related problems.  During the interview, she informs you that she believes her husband is MH susceptible.  They believe this because her husband’s father had a clinical episode thought to be a serious or fulminant episode many years ago.  The husband has never been biopsied.

Given that the husband cannot be biopsied in the next few weeks:

1. What is the risk that the baby will inherit MH Susceptibility if the father is truly MH Susceptible?

1. 25%
2. 50%
3. 100%
4. Unable to calculate

2. What labor analgesia agent should be avoided?

1. Bupivacaine
2. Fentanyl
3. Neostigmine
4. Methoxyflurane

3. Planning for an urgent (not emergent) Caesarean Section – which should be avoided?: 

1. Labor epidural converted to epidural anesthesia
2. Spinal anesthesia with local anesthetics
3. Rapid sequence intubation with succinylcholine and vapor anesthesia
4. Propofol/Ketamine and rocuronium for facilitation of intubation

4. General anesthesia and emergent airway management is necessary unexpectedly.  If succinylcholine is used, might the infant trigger with MH if susceptible?

1. Yes
2. No

5. Do succinylcholine and vapor anesthetics cross the placenta?   

1. Yes
2. No

6. How many MH biopsy centers are still open in the United States?

1. 4
2. 6
3. 12
4. 23

7. If the father tests MH Susceptible by biopsy, how soon should the infant be biopsied?

1. Immediately in the newborn period
2. After age 2 or achieving a weight of 20 lbs.
3. After age 5 or achieving a weight of 40 lbs.
4. Wait until after the growth spurt has occurred
5. Adulthood

1. Correct answer: B.  If the biologic father is truly MH Susceptible, the infant’s risk of inheriting the trait is 50%.  This is based upon most of MH Susceptibility is due to a mutation in the RyR1 gene, and the mutations cause susceptibility if only one copy is present (autosomal dominant transmission)

2. Correct answer: D. The only anesthetic agents known to trigger an MH crisis are volatile anesthetics and succinylcholine.   Therefor, the mother should not be prescribed methoxyflurane (Penthrane) as a labor analgesic.  All local anesthetics, opioids, benzodiazepines, ketamine and neostigmine are nontriggering agents.  Local anesthetics, opioids and neostigmine have been used via the epidural and spinal routes for labor analgesia and anesthesia.

3. Correct answer: C.  For an urgent Caeserean section procedure, the patient should not receive a rapid sequence intubation with succinylcholine and vapor anesthesia.  Although succinylcholine probably crosses the placenta in minute quantities, it would probably not trigger a response in the infant.  However, volatile anesthetic agents do cross the placenta and could possibly trigger an MH episode in an infant.

4. Correct answer: A.  As above,  succinylcholine may cross the placenta in trivial quantity and is not expected to trigger the infant, however, this is not a guarantee.  If the risk of using a nondepolarizing relaxant gives the anesthesiologist concern, I do not believe there is an absolute contraindication to using succinylcholine.  Once the mother’s airway is secured, continue with nontriggering anesthesia, and monitor the infant for rigidity and/or hypermetabolism.

5. Correct answer: A.  Succinylcholine crosses the placenta in at least some animal models.  Vapor anesthetics do cross the placenta and can cause neurologic depression of the infant and could possibly trigger an MH episode in an infant (theoretically).

6. Correct answer: B.  There are 6 biopsy centers which remain open in the United States. (www.mhaus.org gives the list)

7. Correct answer:  C.  Most biopsy centers wait until a child is approximately 5 years old or weighs 40 lbs. before performing a biopsy.   The piece of muscle taken would leave an unappealing subcutaneous deformation in the skin if performed before sufficient muscle bulk is present.

Narrative:

Malignant hyperthermia susceptibility (MHS) is genetically transmitted in an autosomal dominant pattern of inheritance.  The majority of MHS is due to genetic alterations of the ryanodine-1 subtype genome and a resultant abnormal protein expressed at the sarcoplasmic reticulum.  If a gentleman is MHS, then his offspring would each be considered to have a 50% chance of inheriting the abnormal genetic sequence and be MHS.  So although the mother may not be MHS, her unborn infant may carry the MHS vulnerability.  Therefore, when planning anesthesia for labor or delivery, consideration must be given to safely anesthetize the mother, and preparing for the unlikely circumstance that the infant could trigger.

            All volatile anesthetics and succinylcholine may trigger MH.  If a parturient’s airway is precarious, then most anesthesiologists would favor succinylcholine for a rapid sequence intubation if general anesthesia was necessary.  Succinylcholine is a quarternary compound and not likely to cross the placenta, but some animal studies have detected the presence of succinylcholine in the fetus or recently delivered newborn.  It is really unknown whether this may trigger MH, and if so, how frequently.  Volatile anesthetics are known to cross the placenta and may cause neurologic depression of the infant and theoretically could trigger MH in a susceptible infant.  With the availability of ketamine, propofol, rapid acting opioids and fast onset nondepolarizing muscle relaxants, the clean technique could be followed for the parturient who required emergent general anesthesia.  The caveat here is the ability to secure the airway which may be unpredictably difficult.  Spinal or epidural labor analgesia may be accomplished with standard agents.

Joseph R. Tobin, M.D.

Professor of Anesthesiology

Director, MH Biopsy Testing Center

Wake Forest University School of Medicine