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Case Study on Heatstroke

Heat-Injury Heatstroke Case Study

This longer case study/blog post will be most helpful for the seasoned critical care provider. As we know September has arrived but don't be fooled, heat related injury is common even in the fall months. From a critical care provider point of view, how do treat heatstroke?

What is Heatstroke? 

​The definition of acute heat stroke represents a state of thermoregulatory failure with a core body temperature greater than 104F. Significant clinical findings include history of heat exposure, rectal temperature greater than 104F, and central nervous system [CNS] dysfunction. Let's take a look at scenario in which you are a crew member of a critical care transport team….

Heatstroke Scenario

As a critical care transport team member, you responded to a local Emergency Department for a 22 year-old male construction worker that collapsed on a roof during a hot fall day.

History of Present Illness 

According to the sending care team, the 22 year-old arrived to the Emergency Department unresponsive with a glasgow coma scale [GCS] of 5, a rectal temperature [Temp] of 107.6F, blood pressure [BP] of 56/32, heart rate [HR] 200 (ST), and respiratory rate [RR] of 60. His past medical history and allergies are unknown. Treatment in the Emergency Department included intubation, bilateral 18G IVs, and a triple lumen central line. The patient received dantrium, sodium bicarbonate, vitamin K, and 6 liters of crystalloid. Ice packs were placed in his axilla, behind his neck, and groin to lower his body temperature. More on treatment in a bit.

Your Clinical and Exam Findings 

Good so far? Ok. When you walk into the patient's room you find a 22 y.o. male, unresponsive with a GCS of 3T and intubated on a ventilator. His ventilator settings were AC, 16, TV 600 ml, FIO2 100% a PEEP of 5. Breath sounds were bilaterally diminished in the bases and coarse in the upper lobes. GI was soft with a nasogastric tube inserted and 700 ml output prior to arrival. Patient had a foley catheter with only 150 ml output and hematuria noted. Pupils were fixed and dilated, unfortunately motor strength were unable to assess due to neurological blockade.You find his current vital signs are BP 136/62, HR 132, RR 16, SPO2 95%, ETCO2 33, and aldrete sedation level [ASL] of 1.

Relevant Lab Work

​Pertinent lab values were a CPK of 1533, CK MB of 5.6, and CK MB index of 0.4. His troponin was elevated at 0.24 along with his lactate of 48.9. Blood gas post intubation was PH 7.12, PCO2 39.0, PO2 146, HCO3 13, and base excess of -15.9 with an O2 sat of 98. A toxicology test was negative for all substances including alcohol.

Your Initial Treatment 

Prior to transport you start fresh frozen plasma [FFP] at the request of the referring physician. During the transition to transport ventilator, the patient's SPO2 decreased to 90%. The referring physician was called to bedside. The breath sounds were reassessed and found to be equal. The ETT was suctioned and readjusted to 23 cm at the teeth. With no improvement, Furosemide 20 mg was administered along with increased PEEP +10. You suggest switching the vent to pressure control, but your Medical Control physician wanted to keep current settings and administer an additional 20 mg of Furosemide. The patient was transported the World's Best Hospital without incident. His vital signs on arrival at the World's Best Hospital were GCS of 3T, BP 134/76, HR 120, RR 18, SPO2 95%, ETCO2 33, and ASL score of 1.

Case Review Considerations 

So what does all of this mean? Remember the definition of acute heatstroke represents a state of thermoregulatory failure with a core body temperature greater than 104F. Significant clinical findings include:

  • history of heat exposure
  • rectal temperature greater than 104
  • central nervous system [CNS] dysfunction

Typically patients will exhibit hyperventilation, tachycardia, and hypotension. Depending upon the type of exposure, laboratory abnormalities include elevated or low calcium, potassium, and respiratory alkalosis. The patient may experience cardiovascular collapse as a result of dehydration, vasodilatation, and heat-induced myocardial depression. Renal failure is common due to rhabdomyolysis along with multi-organ dysfunction.

Heatstroke vs. Malignant Hyperthermia

​The definition of malignant hyperthermia is a pharmacogenetic disease that results from rare inherited abnormality of skeletal muscle membrane. Unlike heatstoke (exposure to high temperatures), malignant hyperthermia (MH) is a response to stresses or drugs. With MH, patients sustain a massive efflux of calcium from skeletal muscles resulting in contraction, rigidity, increased metabolism, elevated serum creatinine levels, heat production, and systemic hyperthermia. MH individuals generally experience acidosis, hypercapnia, tachycardia, hypoxemia, rhabdomyolysis, hyperkalemia, and renal failure.

Back to Our Case 

In this case, the exposure for this patient was the environmental and there are two very important areas the reader needs to recognize.

Thing One - Suck it up buttercup is not the answer!

As he compensated for the increase in body temperature, the patient continued to work instead of being removed from the exposing agent (a common theme in such cases). Remember the first line treatment is to remove the individual from the agent

Thing Two - Co-workers Can Save A Life

There is a good chance his co-workers may have noticed the patient's slow descent into heatstroke. By the time his co-workers said something he had a problem, this patient had already experienced cardiovascular collapse from the body's natural reaction. 

The Body's Natural Response in Heatstroke

​The skeletal muscle cells release calcium resulting in muscle contractions. As the process continues, the patient goes into an anaerobic phase of metabolism as seen in his elevated lactate level. In anaerobic metabolism, the patient will experience a rapid breakdown of skeletal muscle tissue resulting in a large release of CPK enzyme and other byproducts into the blood system to include potassium which is known as rhabdomyolysis. So one treatment goal is to account for rhabdomyolysis.

Rhabdomyolysis Treatment 

​Treatment for rhabdomyolysis is aggressive hydration to eliminate myoglobin out of the kidneys and diuretic medications to aid in flushing out the kidneys. Sodium bicarbonate may be used to maintain an alkaline urine state to prevent the dissociation of myoglobin into toxic compounds. Sodium bicarbonate also causes potassium to shift from extracellular to intracellular fluids and helps reverse hyperkalemia caused by metabolic acidosis. An elevated CPK results in injury or stress to heart, brain, or muscle tissue, in this case severe injury to skeletal muscle was significant enough to raise CK MB above normal, but such injury does not usually cause a high relative index as seen in this case.

Aggressive Hydration

​But what is aggressive hydration? Aggressive hydration means administering crystalloid fluids at 500 ml/h and titrate to maintain urine output of 2 to 3 ml/kg/h. Keep in mind as the body temperature lowers, vasoconstriction will occurred. In response, preload will increase thus increasing the patient's cardiac output. But watch out, pulmonary edema can be seen if the patient is over hydrated prior to lowering the body temperature.

Consider Administering Dantrium 

​Additionally, the patient received dantrium. But why? Dantrium induces muscle relaxation by blocking calcium release from muscle cells therefore stopping excess heat production. The recommended dosage is 3mg/kg every ten minutes for three doses until the episode resolves. Dantrium is the recommended pharmacologic agent in the treatment of malignant hyperthermia and when not available procainamide can be used instead. Calcium also has an effect on how the blood clots.

Why Fresh Frozen Plasma? 

​The liver is responsible for the modification of clotting factors, thus vitamin K and fresh frozen plasma were administered for deficiencies of coagulation proteins.

Case Take A Ways 

​Aggressive and immediate treatment of heatstroke means lowering the body temperature and hydration is important in cooling the victim. Focus on correcting hyperthermia, ABG findings, and organ dysfunction. Of course the best treatment as always, is education and prevention.

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