Elevated Temperature following Masseter Spasm
28 y/o female, 38 weeks gestation, without any significant previous medical history presented for stat c-section. The patient underwent one general anesthetic previously for tonsillectomy without complications. Additionally, family history is negative for MH or any other metabolic disease.
General anesthesia was performed and the patient was induced with propofol and succinycholine (rapid sequence induction). Following administering succinycholine, patient developed masseter spasm that prevented opening her mouth. However, mask ventilation was adequate for few minutes where mouth opening was possible and tracheal intubation was achieved. Maintenance of anesthesia was achieved with propofol IV infusion and nitrous oxide; inhalation agent was not used. The patient remained stable during the procedure and increased in ETCO2, temperature, HR did not occur. The patient lost 1000 of blood but did not require blood transfusion. At the end of surgery, the trachea was extubated and the patient was transferred to the PACU stable and awake and alert.
One hour later, the patient temperature increased to 38.5 C°, but the patient was still awake and alert with stable vital signs. Blood gas was normal with PCO2 of 30 mmHg and BE of -4.
1) All of the following trigger an MH episode in susceptible patients except:
A. Sevoflurane
B. Halothane
C. Succinycholine
D. Nitrous oxide
2) When faced with a masseter spasm, the anesthesia provider should do all the following except?
A. Ventilate with a face mask
B. Tracheal intubation
C. Discontinue all triggering agents
D. Monitor the patient in the recovery room for 4 hours at least
E. Check for myoglobinuria in 6-12 hours
3) What is the best action that should be taken in the recovery room now?
A. Administer dantrolene 2.5 mg/kg IV
B. Actively cool the patient
C. Continue monitoring
D. Administer antibiotics for pneumonia
4) What is currently considered to be the “gold standard” for diagnosing MH susceptibility?
A. Molecular genetic testing
B. Halothane-caffeine contracture testing
C. Masseter muscle rigidity with hypercarbia
D. 3-fold rise in CK following a rapid intraoperative temperature elevation
5) Caffeine halothane contracture testing is indicated in all the following except?
A. Clinical history suspicions for malignant hyperthermia
B. A first-degree relative of a patient with documented MH
C. Unexplained muscular rigidity with MH suspicion
D. Sudden cardiac arrest on induction of anesthesia
Answers & Narrative:
1) Halogenated agents and succinycholine are the only pharmacological triggering agents of MH episode. Nitrous oxide, propofol and narcotics are considered safe.
Answer D
2) Masseter (jaw) muscle rigidity (MMR) may occur after the administration of succinycholine, particularly in children. MMR signifies MH in approximately 15% of cases. When a patient develops MMR, triggering agents should be discontinued and ventilation should be established with a face mask as direct tracheal intubation is impossible due to a closed mouth.
Answer B
3) This is a tough question as no clear indication of MH episode is available. Although the patient had a masseter spasm following succinycholine administration (now with 15% chance of developing MH), but the temperature could not be explained by other reasons. I believe that any elevation in temperature following masseter spasm should be treated as MH episode.
Answer A
4) Currently, halothane-caffeine contracture testing is considered the best test with regard to sensitivity and specificity for diagnosing MH susceptibility. However, since only 6 centers in North American currently administer the test (for which a fresh muscle specimen is required), the test is not available to most patients with suspected MH susceptibility.
Answer B
5) Currently, the in vitro contracture test (IVCT) is the gold standard for diagnosing MH. However, the IVCT is very expensive, requires a surgical procedure that can only be performed on-site in one of approximately 10 specialized testing centers in the
Answer D
Assistant Professor, Anesthesiology
Children’s Hospital of Oklahoma
