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Atypical Presentation of a Suspected Malignant Hyperthermia Episode

January 1, 2012
by Trang Nguyen, DDS, Gabriella Garisto, DDS, MSc (Dental Anaesthesia) and Christian Zaarour, MD


INTRODUCTION
There is a growing trend towards performing community-based dental treatment under deep sedation or general anaesthesia. Indications for dental treatment under anaesthesia may include patients with extensive treatment needs, acute situational anxiety, uncooperative age appropriate behaviour, immature cognitive function, disabilities or medical conditions.1 Patients known or suspected to be susceptible to malignant hyperthermia (MH) can be treated safely by avoiding known triggering agents and diligent monitoring for signs and symptoms of a reaction. Nevertheless, the possibility of an unanticipated MH crisis exists. One study demonstrated that 76% of MH susceptible patients reported an absence of a positive family history of MH and 51% had undergone a previous uneventful anaesthetic.2,3 All team members must be aware of the signs and symptoms of MH as quick recognition of an MH crisis and prompt treatment is critical.

Malignant Hyperthermia is a life-threatening, autosomal dominant, hypermetabolic disorder of skeletal muscle.2 The incidence of reactions in general anaesthetics using triggering agents is estimated at 1:15 000 in paediatrics and 1:50 000 in adults with a prevalence in Caucasians and young males.2,3 Malignant hyperthermia reactions may be triggered by depolarizing muscle relaxants or volatile anaesthetic agents (Table 1).4 Triggering agents induce an abnormally high influx of calcium into skeletal muscles producing continuous and uncontrolled muscle contraction.5 The signs and symptoms can be variable and there is no single clinical feature indicative of MH. Early characteristics of an MH crisis often include tachycardia, tachypnea, muscle rigidity (notably the masseter muscle) and hypercarbia.6,7 Late clinical manifestations can include flushing, cyanosis, hyperthermia, mixed respiratory and metabolic acidosis, ventricular tachycardia, arrhythmias, hyperkalemia, raised creatinine phosphokinase (CPK), and myoglobinuria.7 Significant morbidities associated with a MH crisis include acute renal failure, disseminated intravascular coagulation, acute lung injury, cerebral edema, seizure and death.3

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This report describes the management of an unanticipated MH crisis during general anaesthesia in a dental office, hospital emergency department care and subsequent dental treatments at The Hospital for Sick Children (SickKids).

CASE REPORT 
A 51⁄2-year-old Caucasian male, with severe caries who weighed 15.1 kg, presented for dental treatment under general anaesthetic in a community dental office. Past medical history was non-contributory. The patient had never undergone a general anaesthetic and parents stated that there were no known familial issues with anaesthesia. The patient was induced by mask using sevoflurane and subsequent IV propofol. Nasal endotracheal intubation with a 4.5 cuffed tube was established with no complications. The anaesthetic was maintained with sevoflurane and nitrous oxide uneventfully until two hours into the procedure when the anaesthesiologist noticed the patient had developed tachycardia (increasing from 80 to 130 beats per minute) and hypercarbia (increasing from an original end-tidal CO2 of 60 to 80 to >100 mmHg) despite hyperventilation. The patient was also tachypnic and his temperature rose from 36.9 to 37.8 degrees Celsius over a period of five minutes. At the time, no masseter spasm, muscle rigidity or arrhythmias were noted.

The anaesthesiologist suspected an MH crisis and immediately administered 100% oxygen through a fresh anaesthetic circuit. Dantrolene 2.0 mg/kg and mannitol were given. The nasal endotracheal tube was changed to a size five oral endotracheal tube to facilitate ventilation. Dental treatment was discontinued and teeth 64 and 65 were temporized with zinc oxide eugenol (IRM©).

The patient was transferred by emergency medical services to a community hospital and by this time an additional 40 mg of dantrolene had been administered. Vital signs taken at the hospital emergency department were: temperature 38.5°C, heart rate 110 bpm, respiratory rate 17, blood pressure 99/61 and oxygen saturation 100%. Blood gases, CPK and potassium were not elevated. The patient had good urine output and no evidence of myoglobinuria.

The patient was transferred from the community hospital to SickKids Intensive Care Unit for additional consultation with anaesthesiology and pharmacology staff. The patient was extubated and discharged the following day with no further complications. Recommendations included future anaesthetics be performed in a hospital setting, referral to the SickKids neuromuscular clinic, a dental consultation, and discussion about a possible future muscle biopsy for a definitive MH diagnosis.

Sixty days later, the patient presented to the SickKids Emergency Department with a two day history of worsening dental pain and a one day history of left facial swelling and fever. Dental examination confirmed a unilateral left facial cellulitis that involved the buccal and infraorbital spaces. The patient was placed on 30 mg/kg q8h dose of intravenous clindamycin and admitted to a paediatric ward. One day later, the swelling had decreased significantly and a draining fistula apical to 64 previously temporized with IRM was observed. Intra-oral radiographs were attempted but due to the patient’s inability to cooperate and his hypersensitive pharyngeal reflex only a panoramic radiograph was possible (Fig. 1). The patient was switched to oral clindamycin 150mg q8h for 7 days, discharged from the hospital and told to return to the dental clinic in 24 hours for extraction of the abscessed 64.

The patient was uncooperative for extraction under local anaesthetic. Due to the patient’s anxiety and safety concerns associated with treatment, the patient’s parents opted for treatment under general anaesthetic. The infection was well controlled with clindamycin and a general anaesthetic was booked to complete unfinished dental treatment with a weekly follow up to assess any signs or symptoms of infection prior to the treatment date.

Fifteen days after his initial presentation to the SickKids Emergency Department, the patient underwent a general anaesthetic following the hospital MH protocol. The patient was scheduled as the first procedure of the day. The anaesthetic machine was prepared by removal of volatile anaesthetic vaporizers, replacement of the CO2 absorber and circuit and flushing the machine for 20 minutes with high flow oxygen. The MH cart containing all necessary emergency equipment and medications, including dantrolene, was on hand. The patient had an intravenous induction with propofol and all triggering anaesthetic drugs were avoided. A 5.5 uncuffed nasal endotracheal tube was inserted and anaesthesia was maintained with 30% oxygen, 70% nitrous oxide and an infusion of propofol and remifentanil. Dental treatment consisted of two extractions and three restorations. The anaesthetic was uneventful and the patient was monitored postoperatively in the post anaesthesia recovery room for four hours according to SickKids MH protocol prior to discharge.

DISCUSSION
Sevoflurane is an anaesthetic commonly used in paediatric patients because of its nonp ungency and rapid increases in alveolar anaesthetic concentrations allowing for smooth and rapid inhalation inductions. Although the volatiles are widely used and proven to provide safe and effective anaesthetics, they have been implicated in several cases of MH2. During the initial general anaesthetic with nitrous oxide and sevoflurane, the patient unexpectedly presented with hypercarbia, tachycardia, tachypnea and hyperthermia, all characteristic of a possible MH reaction.3 There was no report of muscle rigidity, increase in CPK or potassium, consequently an atypical presentation of MH was suspected.3 The differential diagnosis included transient increase in CO2 secondary to nasal endotracheal obstruction and allergic reaction.

This patient re
covered due to the prompt recognition of the suspected MH and the initiation of the rapid administration of dantrolene. Initial intervention and emergency room management included immediate elimination of the triggering agent, administration of 100% oxygen, dantrolene 2.0 mg/kg given IV repeatedly until the patient improved followed by correction of fluid imbalance, treatment of complications and close monitoring with supportive ventilation that coincided closely with recommended treatment protocols (Table 2).7 Since the development of dantrolene, mortality rates in MH have reduced from 80% to 10% due to its ability to inhibit calcium release and prevent muscle contraction.9

The exemplary management of this suspected MH crisis in a community office underscores the unexpected onset of an episode and the need for its rapid diagnosis whether at induction or throughout anaesthesia and treatment. Preparedness includes access to dantrolene and emergency medical services.

SUMMARY
A thorough medical history is of utmost importance in screening for patients at risk of a MH reaction. It is strongly recommended that any patient with a positive history of MH requiring GA be treated in a hospital setting. However, spontaneous cases may occur wherever general anaesthetics are provided. Requirements of The Royal College of Dental Surgeons of Ontario Guidelines indicate any use of triggering agents for MH requires temperature monitoring and immediate access to dantrolene.10 If a MH reaction does occur during dental treatment, early recognition and prompt treatment is imperative to prevent life altering morbidity or fatality. OH

Dr. Trang Nguyen is a resident in the Discipline of Paediatric Dentistry at the Faculty of Dentistry, University of Toronto. trang.nguyen@sickkids.ca

Dr. Gabriella Garisto is an assistant professor in the Discipline of Anaesthesia at the Faculty of Dentistry, University of Toronto and also maintains a mobile dental anaesthesia practice.

Dr. Christian Zaarour is a staff anaesthesiologist in the Department Anaesthesia at The Hospital for Sick Children and assistant professor in the Department of Anesthesia at the University of Toronto.

Oral Health welcomes this original article.

REFERENCES
1. American Academy of Pediatric Dentistry. Guideline on use of anesthesia personnel in the administration of office-based deep sedation/general anesthesia to the pediatric dental patient. Pediatr Dent 2010;32(6):184-6.
2. Strazis KP, Fox AW. Malignant hyperthermia: a review of published cases. Anesth Analg 1993; 77: 297-304.
3. Larach MG, Gronert GA, Allen GC, Brandon BW, Lehman EB. Clinical presentation, treatment, and complications of malignant hyperthermia in North America from 1987 to 2006. Anesth Analg 2010;110:498-507.
4. Barash PG, Cullen BF, Stoelting RK (Ed.).(2001). Clinical Anesthesia 4th Eds. Philadelphia, PA: Lippincott Williams & Wilkins.
5. Haas DA, Young ER, Harper DG. Malignant hyperthermia and the general dentist: current recommendations. J Can Dent Assoc 1992;58:28-33.
6. Fortunato-Phillips N. Malignant Hyperthermia Update 2000. Crit Care Nurs Clin North Am 2000;12:199-210.
7. Hopkins PM. Malignant hyperthermia: advances in clinical management and diagnosis. Br J Anesth. 2000;85:118-28.
8. Dipchand A, Friedman J (Ed.) (2009). The Hospital for Sick Children Handbook of Pediatrics, Toronto, Canada: Saunders Elsevier.
9. Resenbaum HK, Miller JD. Malignant hyperthermia and myotonic disorders. Anesthesiol Clin N Am. 2002;20:385-426.
10. The Royal College of Dental Surgeons of Ontario. (2009). Guidelines: Use of Sedation and General Anaesthesia in Dental Practice. Dispatch. Retrieved Oct 15,2011, http://www.rcdso.org/sedationAnaesthesia_pdf/Guidelines_sedation_06_09.pdf.


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