
Every EMS provider who utilizes succinylcholine in their practice should be familiar with malignant hyperthermia.
A basic life support (BLS) crew requested advance life support (ALS) on a cold night after arriving at the site of a single major motor-vehicle collision. En route, you received a brief report of a male patient with possible head trauma and decreased level of consciousness. Dispatch told you that the closest HEMS has been activated but won’t be able to take the flight request due to the weather conditions. As you rush to the scene, you and your partner discuss the possibility of performing rapid sequence intubation (RSI).
The scene is safe upon your arrival. You found one patient involved in a single vehicle collision against a fixed object. The patient was restrained and airbags were deployed. The patient is currently being extricated by the local fire department and the BLS crew. The patient is taken out of the wreckage with spinal motion restrictions precautions, and the BLS crew reports shallow respirations with possible head trauma as they walk toward the back of your unit.
Primary survey reveals abnormal flexion upon painful stimuli, no verbal response, and closed eyes. The patient is being ventilated via BVM at 15 lpm of oxygen by a BLS crewmember. No visible hemorrhaging is noted. Initial vital signs were 140 bpm, 12 RR, 178/100 mmHg, and SpO2 of 97%.
You instruct your partner to initiate oxygenation with high-flow O2 via nasal cannula along with positive-pressure ventilation while you prepare the equipment as well as your drugs for RSI. The RSI protocol indicates the administration of succinylcholine along with a combination of etomidate as induction agent. You successfully intubate the patient on the first attempt and confirm with positive wave form capnography. Post-intubation management is initiated with benzodiazepines and opioids in order to adequately sedate the patient. The closest trauma facility is 45 to 50 minutes away.
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Your patient starts to exhibit an increased persistent heart rate along with elevated capnography waveforms indicating hypercarbia, and muscle rigidity to include the mandible, which is squeezing the endotracheal tube 20 minutes after your departure. You decide to sedate the patient more, thinking that additional sedation is required, and you increase the ventilation rate. Although mild muscle relaxation is achieved, increased heart rate and hypercarbia persist. You decide to administer a non-depolarizing agent that allows the mandible to relax and release the endotracheal tube from the squeezing. Despite the increase in ventilatory rate, the patient’s capnography refuses to go below 60 mmHg.
An abnormal elevation of the T-wave form is seen in the patient’s monitor ECG. Five minutes away from the emergency department (ED), you start noticing a sudden increase in body temperature and sweating. Your patient’s temperature is 41°C and is tympanic by the time of arrival to the emergency department. Eventually, you report the whole case to the receiving facility, along with all the new clinical manifestations presenting suddenly. Certainly, this was a strange call.
Introduction
Malignant hyperthermia (MH) is a life-threatening event that is associated with the administration of a volatile anesthetic agent with or without the administration of succinylcholine.1 It is characterized by the acceleration of skeletal muscle metabolism. Common signs and symptoms include muscle rigidity, increased heart rate, hypercarbia despite ventilatory management and high body temperature. However, increased body temperature is often a late sign.²
The use of succinylcholine in RSI protocols has been one of the most common depolarizing agents currently utilized in the prehospital setting. The use of RSI protocols is no longer a procedure unique to air medical programs or critical care ground services. In the last decade, there has been an increase in the use of succinylcholine in all EMS services across the nation. The familiarization with malignant hyperthermia is imperative for every provider who utilizes succinylcholine in their practice.
Signs and Symptoms
The most common signs and symptoms of malignant hyperthermia are as follows:
- End-tidal CO2 > 55 mmHg; PaCO2 > 60 mmHg
- Tachycardia, which may be sinus tachycardia or ventricular tachycardia
- Decreased pH < 7.25
- Generalized muscle rigidity, especially the masseter muscles
- Dark-brown urine
- Myoglobinuria
- Increased core temperature
The earliest sign of malignant hyperthermia is tachycardia, followed by an increase in end-expiratory carbon dioxide despite an increase ventilation management. Muscle rigidity is a classic symptom of MH, along with increased body temperature. Hyperthermia is often a late sign of MH.
Physiology
During a muscle contraction, the nerve endings of the pre-synaptic motor neuron release neurotransmitters such as acetylcholine. Postsynaptic acetylcholine depolarizes the muscle via T-tubules. Then, ryanodine receptors release calcium located in the sarcoplasmic reticulum within the muscle cell, which changes the confirmation of tropomyosin, allowing the myosin head attachment to cause a power stroke.
Pathophysiology
MH is associated with a mutation encoding an abnormal RYR1 or DHP receptor in most MH patients. During an MH, there is unrestrained release of calcium into the intracellular space from the sarcoplasmic reticulum, specifically from ryanodine receptors.³ The accumulation of calcium in the intracellular space leads to sustained muscle contraction. Eventually causing the accumulation of lactic acid, increased carbon dioxide, depletion of oxygen and ATP.⁴ The risk of developing rhabdomyolysis occurs later in the progression of the disease, thus leading to hyperkalemia and myoglobinuria. The prolonged muscle contraction can lead to an increase in heat production, which what generates the hyperthermia component. The mechanism of how succinylcholine triggers these events is not fully understood.
Mortality
MH, if left untreated, will lead to disseminated intravascular coagulation (DIC), kidney failure, brain injury, liver failure and cardiac arrest. Increased temperature of over 41°C is associated with increased mortality. Core temperature monitoring and management may reduce mortality. It has been seen that patients with no core temperature monitoring were at least twice as likely to die.5
Epidemiology
MH occurs more often in males than in females.1 According to the Malignant Hyperthermia Association of the United States, the exact incidence of MH in the United States is unknown. Areas with high incidence of MH in the United States include Wisconsin, Nebraska, West Virginia, and Michigan. About 1 in 2,000 patients are susceptible to MH. 6
Management and Treatment
During an acute MH event, the following actions are recommended by the Malignant Hyperthermia Association of the United States:
- Discontinuation of the triggering agent.
- Continuation of sedation with non-triggering agents such as IV sedatives, narcotics, and non-depolarizing neuromuscular agents, as needed.
- Administration of dantrolene, if available.
- Administer dantrolene IV 2.5 mg/kg as an initial bolus dose. Repeat as needed until the patient shows decreased EtCO2, decreased muscle rigidity, and/or lowered heart rate.
- Call the MHAUS Hotline (1-800-644-9737) for additional advice.
- Hyperventilation along with 100% oxygen.
- Treatment of hyperkalemia (ECG changes) with the following:
- Calcium chloride 10mg/kg (max. dose 2g), or calcium gluconate 30mg/kg (max. dose 3g) for life-threatening hyperkalemia
- Sodium bicarbonate 1–2 mEq/kg (max. dose 50 mEq)
- Initiation of core temperature cooling if < 39 °C and discontinue when temperature decreases to 38°C.
Conclusion
Due to the proliferation of RSI or drug assisted intubation protocols across the nation, the risk of encountering a patient with MH could increase. Therefore, MH recognition training must be provided in all EMS systems that use succinylcholine as one of their paralyzing agents. MH is a rare event that could lead to death if it is not recognized by the EMS personnel promptly.
For more information, please visit the Malignant Hyperthermia Association of the Unites States.
References
- Rosenberg H, Davis M, James D, Pollock N, Stowell K. Malignant hyperthermia. Orphanet J Rare Dis. 2007 Apr 24;2:21. doi: 10.1186/1750-1172-2-21. PMID: 17456235; PMCID: PMC1867813.
- https://www.uptodate.com/contents/malignant-hyperthermia-diagnosis-and-management-of-acute-crisis#references
- O’Sullivan GH, McIntosh JM, Heffron JJ. Abnormal uptake and release of Ca2+ ions from human malignant hyperthermia-susceptible sarcoplasmic reticulum. Biochem Pharmacol. 2001 Jun 15;61(12):1479-85. doi: 10.1016/s0006-2952(01)00604-9. PMID: 11377377.
- Gronert GA, Theye RA. Halothane-induced porcine malignant hyperthermia: metabolic and hemodynamic changes. Anesthesiology. 1976 Jan;44(1):36-43. doi: 10.1097/00000542-197601000-00008. PMID: 1244773.
- Larach MG, Brandom BW, Allen GC, Gronert GA, Lehman EB. Malignant hyperthermia deaths related to inadequate temperature monitoring, 2007-2012: a report from the North American malignant hyperthermia registry of the malignant hyperthermia association of the United States. Anesth Analg. 2014 Dec;119(6):1359-66. doi: 10.1213/ANE.0000000000000421. PMID: 25268394.
- https://www.mhaus.org/faw