What is malignant hyperthermia?
Malignant hyperthermia (MH) is a rare, but potentially deadly disorder of the muscles. It can be triggered with the use of
general anaesthesia during surgery. What happens to the body in patients with MH is complex. When certain individuals are exposed to anaesthetic gases and certain muscle relaxants used to put a patient to sleep during surgery, calcium levels in the muscle cells increase. This causes the muscles to have difficulty relaxing. As a result, there is a rapid increase in metabolism in the body, which leads to a rise in metabolic acids and changes to electrolytes in the patient’s bloodstream. This reaction will cause the heart to start pumping rapidly, the breathing rate to become very fast, and the core body temperature to rise very rapidly (to more than 40 degrees Celsius).
Who is affected?
Malignant hyperthermia is an inherited condition that only requires one parent to pass on the gene. Not everyone who has the defective gene will develop MH when exposed to anaesthetic gases or muscle relaxants. Malignant hyperthermia is believed to occur in one in 15,000 to 30,000 children who undergo anaesthesia. Therefore, close monitoring of patients undergoing anaesthesia is essential, for quick recognition and administration of rescue medications. Most MH reactions occur in the operating room (OR); however, in rare circumstances, a reaction may occur up to 6 hours after receiving a triggering anaesthetic.
What if I have a family history of MH and my child needs surgery?
You may not be aware that your child is at risk for MH unless a family member has had a life-threatening event resembling MH during anaesthesia or has had a test (a muscle biopsy) that confirms they have the condition. When undergoing any procedure that involves an anaesthetic, it is important to provide a detailed family history to your anesthesiologist, including incidents of high temperature, muscle stiffness, or death in family members who have had anaesthesia.
If you are aware of any family history of MH, please notify your surgeon and ask for a consultation with the pre-anaesthesia clinic. Anyone who is closely related to someone else who has experienced MH is considered susceptible (at risk) and must be managed accordingly until their status is confirmed. The consultation can be done over the phone or by appointment.
The pre-anaesthesia clinic nurses and the anaesthesiologist will review your child’s medical history. If there is a family history, a previous suspected reaction to anesthesia, or a positive muscle biopsy, then your child will be considered “malignant hyperthermia susceptible (MHS)”, meaning more at risk for developing an MH reaction. The anaesthesiologist would then use a special anaesthetic that does not contain the medications that cause the reaction.
A special type of muscle biopsy can confirm the diagnosis in suspected cases of MH. Muscle biopsy testing must be done at a hospital that is able to perform this special type of test, which is called the caffeine-halothane contracture test. Only one hospital in Canada is set up to perform this test. A significant amount of thigh muscle is required to complete the test. Due to these limitations, biopsies are rarely performed in children and a family history is usually used for an MHS diagnosis.
Day of surgery
On the day of surgery, your doctor will talk to you about your family history and the plan of care for your child. The surgery will be scheduled early in the day to allow the anaesthesiologist time to prepare the anaesthetic gas machines for your child’s procedure. Before the surgery, the anaesthesiologist will flush the machine with oxygen to ensure that there are no traces of the triggering anaesthetic gas from previous use. During the procedure, the anaesthesiologist will avoid anesthetic gases and muscle relaxants that are known to trigger MH reactions—this will almost completely remove the likelihood of an MH reaction from occurring. In the operating room, the anaesthesiologist will monitor your child closely for changes in breathing, heart rate, and heart rhythm, and will look for muscle stiffness. As well, the doctor will continuously monitor your child’s temperature and look for any other indications of an MH reaction.
After surgery
After the operation is complete, your child will be accompanied by the anaesthesiologist to the post-anaesthetic care unit (PACU) for further monitoring for signs of an MH reaction and to recover from the procedure. The anesthesiologist will inform the nurses in the recovery room of your child’s history and what kind of monitoring is required. As recommended by the Malignant Hyperthermia Association of the United States (MHAUS), your child will be closely monitored for a minimum of two hours in the recovery room, with vital signs being checked every 15 minutes. A heart rhythm monitor, temperature probe (a special thermometer), and an oxygen sensor will also be placed on your child for close observation. The anaesthesiologist will be notified by the nurse of any changes to your child’s condition. The likelihood of a reaction occurring after a trigger-free anaesthetic is very small. If no signs of a reaction develop during the first two hours of close monitoring, and your child has met the requirements for discharge, your nurse will contact the anaesthesiologist in charge of your child’s care to confirm that your child can be discharged home or be transferred to a surgical nursing unit. Transfer to a unit may be necessary for recovery from the operation or for more monitoring and nursing care. The MHAUS recommends that patients go home on the same day as surgery if they have not had problems during anaesthesia.
Staying in hospital
If your child is to be transferred to an inpatient ward, your nurse will give a report to the surgical unit nurse about your child’s stay in the recovery room and any further monitoring that is required. The MHAUS recommends that after the recovery room stay, a patient susceptible to MH should be monitored every hour for four hours, then every four hours for 24 hours. Your nurse will monitor your child for the signs listed above, in addition to any further instructions from the surgical team. If any concerns arise with your child, the nurse will contact the surgical team immediately. If your child’s stay is uneventful, the surgical team will discharge them when appropriate. Follow the physician’s instructions once the child is at home.
If you require any further information, please do not hesitate to contact your family doctor or surgeon.
Going home after surgery
If your child can be discharged and sent home, the nurse will review the discharge instructions with you. If you have any questions, please do not hesitate to ask your health care professional team. At home, we suggest that you watch your child for the signs listed below. In the unlikely event that you see any changes, you must take your child to your nearest emergency department, or return to Sick Kids (going straight to the emergency department). At the hospital your child should be assessed by a member of the anaesthesia team.
Signs to watch for:
- Core temperature (taken in the child’s ear or rectum) greater than 38.5 degrees
- Muscle stiffness (e.g., stiff legs or cramps)
- Rapid breathing
- Blue discolouration of the skin or tongue
- Dark, red-coloured urine
Further information
AboutKidsHealth.ca
- General anaesthesia
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Surgery: Getting ready for your child’s operation
- Post anaesthetic care unit: Visiting your child in the PACU
- Post operative and post anaesthesia: Caring for your child at home
- Temperature taking