Carbon dioxide
Carbon dioxide is a normal by product of respiration and metabolism. The more rapid the metabolism, the more C02 is produced in a given time. An increase of metabolism may occur from any cause of elevated body temperature, from certain medications and as a consequence of MH.
C02 levels are measured routinely during anesthesia by measuring the concentration in the exhaled gases. This is usually referred to as end-tidal C02 (i.e., occurring at the end of breath). Normal end tidal carbon dioxide level is 40mmHg, but changes of C02 may also occur from increasing or decreasing ventilation.
Contracture test
This is the test that is used to determine a patient’s susceptibility to MH. Muscle is taken from the thigh—about the size of a fingernail—and cut into strips of about one half inch long and mounted in a chamber and made to contract by electrical stimulation. When the anesthetic halothane is introduced in the chamber the muscle not only contracts but develops a contracture (a sustained contraction). This contracture is typical for MH susceptibles. The drug caffeine may also lead to an abnormal contracture, as may a variety of other anesthetics. Although the test is highly accurate, the inconvenience of the biopsy and the requirement for special technical expertise limits its use.
Creatine kinase
An enzyme found in cells, especially muscle cells. Normal levels are up to about 200iu/L. In cases of muscle membrane breakdown, the enzyme leaks out of the cell. This may occur form any type of muscle trauma, including malignant Hyperthermia. After surgery CK levels may normally rise to 1,000 to 2,000IU/L. When there is severe muscle damage the level may rise to 10,000 or more. At these levels, the muscle pigment, myoglobin, can be expected to be elevated in the blood as a result of muscle damage. In other words elevated CK is a marker for leakage of myoglobin from the cell. Elevated levels of myoglobin can lead to temporary or permanent kidney damage.
After an episode of MH the CK levels may be mildly or dramatically elevated depending in part on the promptness of treatment. In general peak levels of CK occur about 24 hours after injury and may be elevated for days.
Hence in suspected cases of MH it is important to determine CK levels.
In case of heart muscle damage, CK may be elevated, but this represents a slightly different form of CK. CK from regular muscle is termed CK MM, from heart muscle, CK-MB.
General anesthetics
Compounds that produce loss of consciousness, pain relief and amnesia. General anesthetics are either gaseous agents such as halothane, sevoflurane, desflurane (all triggers of MH). Nitrous oxide is often used as an adjunct to these agents. It is not a complete anesthetic, and also not an MH trigger.
There are a variety of agents that are given intravenously that also may produce anesthesia such as the barbiturates (e.g. thiopental), propofol, and ketamine. None are MH triggers.
A variety of other agents are often used during anesthesia such as the narcotics, benzodiazepines (e.g. Valium and Versed) which produce pain relief and sedation.
LMA –laryngeal mask airway
This device was introduced into practice only a few years ago. The device is often used when tracheal intubation is not needed, but control of the airway is desirable. It is a tube that is so constructed that it does not enter the tracheal but forms a seal around the entrance to the trachea (the glottis). Insertion of the LMA is not as traumatic as insertion of an endotracheal tube and does not require deep levels of anesthesia or muscle paralysis.
Local anesthetics
These compounds block transmission of nerve impulses involved in pain sensation. These are the “caine” drugs - novocaine, bupivicaine, lidocaine, mepivicaine. None trigger MH and are safe to use in the MH susceptibles. These drugs are commonly used by dentists, anesthesiologists, pain physicians and surgeons among others.
Molecular genetics
Genetics is the study of inheritance. Molecular genetics is the study of how changes in DNA structure, such as mutations, affect the function of the genes. Molecular, because the study of DNA entails understanding of molecular or submicroscopic changes.
Muscle relaxants
These are drugs that are more properly termed paralyzing agents. There are two classes of muscle relaxants, non-depolarizing and depolarizing agents based on their mode of action. Typical non-depolarizing agents are vecuronium, pancuronium and rocuronium. None are triggers of MH. However, the one depolarizing agent, succinylcholine is a potent trigger of MH. These agents are administered intravenously and are therefore given by anesthesiologists, emergency room physicians and intensive care physicians.
Neuroleptic malignant syndrome (NMS)
This is a constellation of signs and symptoms marked by high fever, muscle breakdown, acidosis, muscle rigidity and other signs similar to MH. However, the syndrome is induced by drugs used in the treatment of major psychiatric disorders. These drugs include thorazine, haloperidol (Haldol), olanzapine and other potent antipsychotic agents. The syndrome is not inherited and does not predispose to MH. That is, there is no greater frequency of MH in those experiencing NMS or vice versa. Interestingly, dantrolene is effective in treating NMS. There is no diagnostic test specific for NMS susceptibility.
Oxygen saturation
The main purpose of the blood is to carry Oxygen to the various parts of the body along with nutrients and to remove carbon dioxide and other byproducts of metabolism. The amount of Oxygen in a given quantity of blood is not easy to measure, however the saturation level of the hemoglobin in the blood that carries the Oxygen can easily be measured with an external probe attached to a “pulse oximeter”. Normal Oxygen saturation is above 98%. At levels below about 90% insufficient oxygen is delivered to the blood, which may lead to many problems.
Reversal agents
There are several drugs that can antagonize or “reverse” the effects of other drugs. The drug, Narcan, or naloxone reversed the effect of narcotics (including the analgesia from these agents). Some drugs, neostigmine and pyridostigmine and edrophonium, reverse the effects of the non-depolarizing muscle paralyzing drugs.
Rhabdomyolysis
When muscle is damaged and cells are disrupted, the intracellular constituents begin to leak into the blood stream. This includes creatine kinase, myoglobin and the electrolyte potassium. This is termed rhabdomyolysis. This breakdown may be manifested by muscle pain and in extreme cases dark or cola colored urine.
Tracheal intubation and mainstem intubation
In order to control gas exchange during anesthesia a plastic tube is often placed in the trachea (‘windpipe”). This is done usually when the patient is first anesthetized. One end of the tube is connected to a ventilator or respirator to control ventilation.
Since the windpipe bifurcates just below the neck line, if the tube is inserted too deeply, the end may go into one of the branches of the trachea (usually the right side) and therefore only one lung will be ventilated. This may lead to a decrease in Oxygen in the blood, and rarely an increase in carbon dioxide as well.
Triggering agents for MH
These are drugs that will lead to the onset of MH. These include all the potent gas anesthetics and succinylcholine.
MH Term Definitions
