As a critical care provider, you decide based on the clinical presentation and assessment of a patient with a traumatic head injury and altered mentation that they are going to need to be intubated for airway protection. You have established that your patient is a young healthy adult that has no medical history, allergies, or medications prior to intubation (lucky you! Getting all that helpful information prior to intubation on a scene call in the middle of BFE.) You begin setting up for RSI, including PREOXYGENATION with a nasal cannula and NRB for 3 minutes minimum. You set up your 7.5 ETT with a backup airway adjunct at the ready. You grab your BOUGIE, SUCTION, and warm your C-MAC up. You and your partner decide on induction agents of Etomidate and Succinylcholine. You prep your dosages and assess your vitals for resuscitation needs. The patient’s vitals look great with an ETCO2 of 34. You are ready in the airway seat; your partner administers etomidate. After sedation is achieved, administration of Succinylcholine is completed. You observe fasciculations and no corneal reflex. You lead with Suction, insert your C-MAC blade with a great view of the cords, pass the 7.5ETT through his cords, inflate the cuff, and verify tube placement with WAVEFORM CAPNOGRAPHY, bilateral breath sounds, and negative epigastric sounds.
After administration of post sedation medications, you notice that the patient's ETCO2 is in the 50s, the patient has marked tachycardia and they appear flush. You reach down to check the placement of leads on the patient’s chest and note they are extremely hot to the touch. You begin delivering breaths via BVETT at a faster rate to help blow off the rising ETCO2, however, the patient starts exhibiting signs of muscle rigidity. You and your partner look at each other and are puzzled as to what is going on. Then it clicks, you read about this in school and remember how rare this is. Malignant Hyperthermia! You instruct your partner to start throwing icepack in the groin and axilla, your (ambulance driver) updates you that you are 5 minutes from the nearest level 1 trauma center (hahaha, lucky). You call in your report, present your findings and the trauma team has the Dantrolene set up and ready for administration upon patient arrival.
We are taught about malignant hyperthermia (MH) going through school. Instructed on how to treat the patient. There is even a dedicated website to MH, the Malignant Hyperthermia Association of the United States, that has a dedicated 24/7 hotline to help in an active MH crisis and provide expertise. What does that mean for us as critical care providers? Because we have the capabilities to administer medications that could induce MH, we owe it to ourselves and our patients to give maximum effort in the care that we give. Hopefully, my guilt trip has encouraged you to continue reading!
The prevalence of MH during general anesthesia is estimated to be 1: 5000 to 100,000. That’s only including cases with general anesthesia. Because MH is caused by a genetic mutation, it is estimated that potentially 1 in 2,000 to 3,000 are susceptible to MH and we just don’t know it. (1,2)
Malignant Hyperthermia is a genetic abnormality of the Ry (ryanodine) receptor located on the sarcoplasmic reticulum. The MH phenotype is inherited as an autosomal- dominant trait. This genetic abnormality is dominant meaning with each pregnancy there is a 50% chance of passing this trait to the child. This risk is the same in males and females. This myopathy affects the skeletal muscle membrane by triggering an uncontrolled release of calcium from the sarcoplasmic reticulum through the ryanodine receptor. This means that the calcium continues to leave the cells and activate the skeletal muscles. This loss of calcium control and excessive muscle excitation leads to excessive metabolic demand. The onset of MH can be instantaneously or hours after exposure. Mortality is as high as 70 percent, however with early diagnosis, appropriate treatment, and the availability of Dantrolene, the mortality rate has decreased to as low as 5 percent. (3)
What induces Malignant Hyperthermia you might ask? MH can be induced with the administration of halogenated anesthetics and succinylcholine. Many might not know that MH can be induced by vigorous exercise and emotional stress, but I didn’t. Signs and symptoms include muscle rigidity, tachycardia, hypoxia, hypercapnia, hypotension, severe lactic acidosis, hyperkalemia, myoglobinuria, hyperthermia, rhabdomyolysis, acidosis and disseminated intervascular coagulation (DIC).
Specifically, I would like to discuss Succinylcholine (SCh). SCh is a neuromuscular blocking agent (NMBA) that many of us carry on our rig for RSI. This drug differs from other NMBAs that we have because it is a depolarizing neuromuscular blocking agent. This significance is how the end goal of paralysis is achieved. SCh is an agonist that works by persistently stimulating, or depolarizing nicotinic and cholinergic receptors. This can be noted by fasciculations shortly after the administration of SCh. (3) SCh induces MH because of its mechanism of action. In short, once SCh starts depolarizing, this triggers the genetic mutation of the Ryanodine receptor leading to an uncontrolled release of calcium from the sarcoplasmic reticulum.
Treatment of malignant hyperthermia can help significantly improve your survival rate as mentioned above. Once core body temperatures are over 41 Celsius, DIC is the most common cause of death. (5) Knowledge of MH inducers such as administration of succinylcholine or known family history is very important. Treatment of MH includes stopping or ceasing administration of causative agents, hyperventilation with 100 percent oxygen, rapidly cooling, aggressive fluid resuscitation, and administration of Dantrolene. Treat metabolic acidosis, and hyperkalemia according to your facility's guidelines and protocols. As always, continuously reassess your patient. Appropriate monitoring during and the post-MH incident is essential to help decrease the morbidity and permeant disability from an MH episode. Lab values such as urine myoglobin, serum myoglobin, and creatinine kinase CBC, CMP, LFTs, and coagulation panel should be trended with treatment. Monitoring should include continuous body temperature monitoring, ETCO2, cardiac monitoring, and urine output.
Dantrolene is a direct-acting skeletal muscle relaxant with a rapid onset of action. Dantrolene produces muscle relaxation by inhibiting excitation and interfering with the release of calcium from the sarcoplasmic reticulum. This helps stop and reverse the physiologic causes of MH. (4) The Dantrolene dose is 2.5mg/kg rapid IVP. Repeat doses may be required until the patient responds with a decrease in ETCO2, reduction in heart rate, and a decrease in muscle rigidity. The MHAUS recommends stocking upwards of 36 vials (20mg each) for patients requiring multiple doses. (6)
While the likely hood of you coming across this in the field is low, it is not zero. Staying current on refreshing on the little things that we tend to put on the back burner can really improve patient care and make us a well-rounded critical care provider. I hope a refresher on Malignant Hyperthermia helps set us up for success for the one-off chance that your witness MH in your career. The moral of the story is don’t use Succinylcholine. Rocuronium is superior, IMO, Have a great day!
Brittany Grandfield, Flight Nurse. 🚁✌️❤️
1. Rosenberg H, Davis M, James D, Pollock N, Stowell K. Malignant hyperthermia. Orphanet J Rare Dis. 2007;2:21.
2. Gonsalves SG, Ng D, Johnston JJ, Teer JK, Stenson PD, Cooper DN, et al. Using exome data to identify malignant hyperthermia susceptibility mutations. Anesthesiology. 2013;119(5):1043–53. 10.1097/ALN.0b013e3182a8a8e7.
3. Brown, Calvin A., et al. The Walls Manual of Emergency Airway Management. Wolters Kluwer, 2018.
4. Gahart, Betty L., et al. 2017 Intravenous Medications: A Handbook for Nurses and Health Professionals. Elsevier, 2017.
5. Gong X. Malignant hyperthermia when dantrolene is not readily available. BMC Anesthesiol. 2021;21(1):119. Published 2021 Apr 16. doi:10.1186/s12871-021-01328-3