Malignant Hyperthermia

Malignant Hyperthermia What is it? Malignant hyperthermia (MH) was the name given to a type of severe reaction under general anesthesia that was first described in 1960

Malignant Hyperthermia The ‘malignant’ part of the name MH has proved useful in emphasizing the potentially fatal nature of the reaction

Malignant Hyperthermia Monitoring during anesthesia at that time was based on clinical observation and physical signs, without the luxury of today’s advanced equipment. The apparent features of the reactions were, therefore, dominated by a progressive pyrexia that usually led to death

Malignant Hyperthermia It is a true EMERGENCY in the Operating Room.

Malignant Hyperthermia What is the incidence of developing MH during surgical operations? Over 80 genetic defects have been associated with MH. It is inherited with an autosomal dominant pattern. The incidence is 1: 15000 in pediatric patients& 1: Usually occurs between the ages of 2 and 42.

Malignant Hyperthermia Triggers: Drugs Sevoflurane Methoxyflurane Desflurane Succinylcholine Isoflurane Halothane Enflurane

What are the Clinical Manifestations of MH? Original Concepts: All patients have muscle rigidity High fever, acidosis High death rate Current Concepts: Muscle rigidity may or may not be present Temperature is a late sign End tidal CO2 is an early sign

Malignant Hyperthermia Signs of Malignant Hyperthermia Specific Muscle Rigidity Increased CO2 Production Rhabdomyolysis Marked Temperature Elevation Non Specific Tachycardia Tachypnea Acidosis (Resp/Metabolic) Hyperkalemia Some signs of MH may be more specific to the diagnosis than others. Specific signs are muscle rigidity , increased carbon dioxide production, rhabdomyolysis and marked temperature elevation. Less specific signs include tachycardia , tachypnea, acidosis and hyperkalemia. In most cases patients developing MH will demonstrate metabolic acidosis.

Malignant Hyperthermia What causes an episode of MH? MH susceptible persons have a gene mutation that results in the presence of abnormal proteins in muscle cells. When these persons are exposed to certain anesthetic agents there is an abnormal release of calcium inside the muscle cell.

Malignant Hyperthermia Causes Cont’d: This calcium release results in sustained muscle contraction and an abnormal increase in energy utilization and heat production.

Malignant Hyperthermia Causes Cont’d: This contraction will cause the muscle to run out of energy and eventually die releasing a large amount of potassium into the blood- stream. This release of potassium will lead to heart rhythm abnormalities as well as lethal rhythms such as V-fib and V- tach.

Malignant Hyperthermia Causes Cont’d: At the onset of muscle cell death, the pigment myoglobin is also released and is potentially toxic to the kidneys. If left untreated the patient will experience cardiac arrest, kidney failure, blood coagulation problems, internal hemorrhage, brain injury, and possibly death.

Emergency Treatment for An Acute MH Event Notify surgeon to halt the procedure ASAP: Discontinue volatile agents and succinylcholine If surgery must be continued maintain general anesthesia with IV non-triggering anesthetics (e.g., IV sedatives, narcotics, amnestics and non-depolarizing neuromuscular blockers as needed)

Emergency Treatment for An Acute MH Event Hyperventilate with 100% oxygen to flush volatile anesthetics and lower ETCO2 Give IV dantrolene 2.5 mg/kg rapidly through large-bore IV, if possible Dantrolene is the only specific treatment for MH Repeat as frequently as needed until the patient responds with a decrease in ETCO2, decreased muscle rigidity, and/or lowered heart rate Large doses (>10mg/kg) may be required for patients with persistent contractures or rigidity

Emergency Treatment for An Acute MH Event Obtain blood gas (venous or arterial) to determine degree of metabolic acidosis Consider administration of sodium bicarbonate, 1-2 mEq/kg dose Cool the patient if core temperature is >39°C or less if rapidly rising Stop cooling when the temperature has decreased to <38°C

Emergency Treatment for An Acute MH Event If hyperkalemia (K > 5.9 or less with ECG changes) is present, treat with: Calcium chloride 10 mg/kg or calcium gluconate 30 mg/kg for life-threatening hyperkalemia Sodium bicarbonate 1-2 mEq/kg IV

Emergency Treatment for An Acute MH Event Glucose/insulin: For pediatric patients: 0.1 units regular insulin/kg IV and 0.5 grams/kg dextrose (% in formulation not important) For adult patients: 10 units regular insulin IV and 50 ml 50% glucose& Check glucose levels hourly Furosemide 0.5-1 mg/kg once

Emergency Treatment for An Acute MH Event Institute appropriate monitoring including: core temperature, urine output with bladder catheter, and consider arterial and/or central venous monitoring Follow: HR, core temperature, ETCO2, minute ventilation, blood gases, K+, CK, urine myoglobin and coagulation studies

Emergency Treatment for An Acute MH Event When stable, transfer to ICU for at least 24 hours Key indicators of stability include: ETCO2 is declining or normal Heart rate is stable or decreasing with no signs of ominous dysrhythmias Hyperthermia is resolving If present, generalized muscular rigidity has resolved

Prevention of Malignant Hyperthermia Preoperative personal/family history of anesthetic problems, neuromuscular disorders Temperature/end tidal CO2 monitoring during general anesthesia Recognition of masseter rigidity

Prevention of Malignant Hyperthermia Investigation of unexplained tachycardia, hypercarbia, hyperthermia Availability of Dantrolene Avoiding MH triggers in MH susceptibles Using Succinylcholine in indication

A 28-year-old man presents for shoulder surgery A 28-year-old man presents for shoulder surgery. The patient had a documented episode of malignant hyperthermia in a previous surgery under general anesthesia Which of the following neuromuscular blockers is contraindicated in this patient? Vecuronium Rocuronium Pancuronium Succinylcholine

All BUT ONE of the following are true regarding malignant hyperthermia (MH). Indicate the exception: Newer volatile anesthetics such as desflurane are not believed to trigger MH Nitrous oxide is safe Dantrolene is the only therapeutic drug treatment Mortality is as high as 10% even with prompt treatment Which of the following is the first sign of a malignant hyperthemic reaction? Hyperthermia Hypercarbia Tachycardia Ventricular arrhythmias

Treatment of a malignant hyperthermia crisis includes ALL BUT ONE of the following. Indicate the exception: Turning off the volatile anesthetic Active cooling measures Dantrolene Beta blockers

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