Thursday, April 15, 2010

April 15th - MHH - NMS and Hyperthermia

What follows is a quick overview of hyperthermia (most of which comes from my intern lecture on fevers)

What is Hyperthermia?

As opposed to Fever, Hyperthermia is an increase in temperature over the body’s thermoregulatory set-point. This occurs when body metabolic heat production or environmental heat load exceeds normal heat loss capacity or when there is impaired heat loss.

 NOTE: These patients usually will have temperature elevations above 102 degrees

Causes of Hyperthermia:
Heat Stroke: Exertional vs. Non-Exertional
Heat Exhaustion
Drug Induced (i.e. malignant hypertension, neuroleptic malignant syndrome, serotonin syndrome)
Central Hyperthermia/Dysregulation (post trauma/CVA)

Some more details related to the drug-induced causes:

Neuroleptic Malignant Syndrome
Background: Seen in about 0.2 percent of patients who receive neuroleptic agents (common ones include haloperidol and chlorpromazine), usually within the first 30 days of therapy. Other drugs implicated include Phenergan and Reglan. Can be seen in patients that rapidly decrease dose of L-Dopa. 

Findings:  Over a period of 24 to 72 hours there may be symptoms of muscle rigidity, extrapyramidal abnormalities, altered consciousness, and autonomic dysfunction (labile blood pressure, diaphoresis, tachyarrhythmias, and incontinence).  Laboratory findings include hemoconcentration with leukocytosis and hypernatremia, acidosis and electrolyte disturbances, rhabdomyolysis, and abnormal renal and hepatic function.

I memember learning this for the USMLE exams to help remember some of the findings with NMS:
V—Vitals unstable
E—Elevated enzymes (elevated CPK)
R—Rigidity of muscles

Treatment:  Stop the offending medication and use cooling blankets.  Patients will likely need aggressive volume replacement.  Some studies show decreased mortality rate when bromocriptine or amantadine are administered. Dantrolene can be given, but studies show conflicting views regarding efficacy. 

Serotonin Syndrome:
Causes:  Many drugs/combination implicated: These include MAOIs, TCAS, SSRIs, opiates, cough medicines, weight-reduction agents, antiemetics, antimigraine agents, drugs of abuse.

Findings: Fever, Tachycardia, Hypertension with Mydriasis/diaphoresis. LE Myoclonus, Tremor, increased BS/diarrhea, agitation/AMS. This can be differentiated from neuroleptic maligant syndrome by a few findings: The presence of elevated CK, Leukocytosis or muscle rigidity are suggestive of NMS and NOT serotonin syndrome

Treament: Stop the offending agent and give supportive care (including benzos for agitation). More severe cases can be treated with cyproheptadine

Malignant Hyperthermia
Halogenated inhalation agents and depolarizing muscle relaxants (i.e. succinylcholine) are most often responsible for causing this.  A positive family history of similar events is common.

Findings: High Fevers and severe muscular rigidity is characteristic: other typical findings include hypotension, tacypnea, tachycardia, arrhythmias, hypoxia, hypercapnia, lactic acidosis, hyperkalemia, rhabdomyolysis, and disseminated intravascular coagulation.

Treatment: Stop the drug, give hydration and oxygen, and start cooling measures. Dantrolene should be given as well. Note that Dantrolene should be given prior to anesthetic procedures when this may occur due to prior events or family history

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