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Topic: Generalized Rigidity
A 21-year-old woman, with no history of MH either personally or in her family and no medical problems, presents for surgery on her TM Joint. Anesthesia is induced with propofol and succinylcholine. Intubation is achieved but, shortly beginning Sevoflurane anesthesia, the surgeon complains that her jaw cannot be opened. Her ETC02 has climbed to 70 and heart rate to 110bpm from a baseline of 80. The anesthesiologist notices generalized rigidity. Her core temperature is not elevated.
1. What is the likelihood that this is a sign of MH?
A. Less than 20%
B. >20% but less than 50%
C. 50-80%
D. >80%
2. Should the anesthesiologist just stop the anesthetic and hyperventilate or should dantrolene be administered? How much?
A. Administer dantrolene 2.5mg/kg
B. Administer dantrolene 10mg/kg
C. Stop the anesthetic, hyperventilate and only administer dantrolene if the ETC02 remains elevated
D. Hyperventilate and administer a non-depolarizing relaxant to reverse the muscle rigidity
3. The anesthetic is discontinued and dantrolene given. When should the patient be extubated or remain intubated?
A. At the end of the procedure if the temperature is normal
B. When the ETC02 has normalized, the patient is awake and the patient is not tachycardic
C. When vital signs and ETC02 are normal but not until CK is obtained
D. Only when the CK is normal and the patient does not manifest myoglobinuria
E. Not for at least 12 hours
4. If the signs of hypermetabolism have subsided is it necessary to continue dantrolene? If so how much and for how long?
A. Yes, once dantrolene is administered, it must be continued for at least 36 hours
B. Dantrolene may be discontinued after 12 hours if the patient’s vital signs are normal
C. Dantrolene, 2.5mg/kg must be continued for at least 12 hours
D. No, once the patient is past the crisis stage, it is not necessary to administer dantrolene
5. How should the extent of muscle breakdown be measured?
A. By measuring myoglobin levels in the urine
B. By measuring CK levels every 8 hours
C. By assessing the patient’s muscle strength
D. By measuring BUN/Creatine and electrolytes every 12 hours
6. The following day the patient is extubated. Her CK rises to only 200 IU/L. Does the absence of a marked elevation of CK indicate that the patient is not MH susceptible?
A. Yes
B. No
7. When should the patient be discharged if all vital signs are stable?
A. Not for 24 hours following resolution of the episode and discontinuation of dantrolene
B. Only when the CK is normal
C. When the patient is asymptomatic for at least four hours
D. There is no specific guideline
8. Following discharge, the patient complains of extreme muscle weakness and can barely walk. What should the patient be told? What should be done?
A. Referred to neurologist for evaluation
B. Refer to physical therapist for muscle strengthening
C. Reassure that the symptoms are self-limited and use analgesics as needed
D. Refer to a rehabilitation center
9. When the patient recovers, what test should be performed to diagnose her susceptibility?
A. Standard muscle biopsy, since the episode is not likely to represent MH
B. Caffeine halothane contracture test
C. Genetic testing for Ryanodine gene mutations
D. Baseline CK after the patient has recovered fully.
Answers:
1. D. Over 80%. Generalized rigidity is a strong predictor of MH susceptibility.
2. A. The signs strongly suggest MH and dantrolene should be given in the recommended initial dose.
3. C. or D. are acceptable answers. One need not wait until the CK is normalized for extubation. There is no minimum time that the patient must be kept intubated following an MH episode. Because of the risk of recrudescence and in order to insure that there is no residual weakness, the vital signs must be normal, including ETC02, temperature, heart rate and acid base balance. In this case this may take several hours.
4. A. Dantrolene at a dose of 1mg/kg every 4-6 hours intravenously is recommended following a crisis.
5. B. Myoglobin in the urine generally does not appear until the CK is above 10,000 IU. Therefore, CK measurements are more representative of muscle breakdown.
6. No. CK levels do not always rise significantly after an MH episode. It is hypothesized that prompt reversal of the syndrome and dantrolene administration prevents muscle damage.
7. A. The course MH is very variable. In some cases the syndrome resolves immediately without recrudescence. In 25% recrudescence occurs within 24 hours. If the CK was elevated, as it usually is after succinylcholine-induced rigidity, then the patient must remain under observation until there is no evidence of renal damage. While there is no specific guideline for discharge from the hospital, most would recommend that the patient be free of signs of MH, muscle breakdown and weakness for 24 hours.
8. A. Although in most cases the muscle weakness is self-limited, the patient should be referred for evaluation by a neurologist and then referred for physical therapy. The neurologist should make sure that the patient’s weakness is not disabling and is improving as well as insuring that there is not residual muscle weakness.
9. B or C. The caffeine halothane muscle biopsy contracture test is the most sensitive and specific diagnostic test for MH. In most European testing centers, the contracture test is required prior to genetic testing. However, in the US in cases where the likelihood of MH susceptibility is high (such as this case), it is acceptable to have the genetic test performed first. If no known mutations are found, then the contracture test is recommended.
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Henry Rosenberg, MD, CPEDirector, Department of Medical Education and Clinical Research
Saint Barnabas Medical Center
94 Old Short Hills Road
Livingston, NJ 07039
Professor of Anesthesiology
Mount Sinai School of Medicine
