Heat Stroke
by Kenneth Lyen
Introduction
Global warming has caused extremely hot summers, and in July 2022 temperatures in several parts of the world have soared above 40C. This has been associated with dry weather leading to droughts, scorched fields and forest fires. Airport runways have melted and train tracks damaged. There have been a number of deaths from heat stroke.
Effects of Heat Stress on the Body
The normal body temperature is 37C, and when it is above 37.5C it is considered to be a fever. A high fever is when the body temperature exceeds 39C. Heat stroke usually occurs when the core body temperature exceeds 40C.
The body temperature rises when one is exposed to a very hot environment such as being under the sun for too long, or when one has an infectious disease. Body heat is lost through sweating and passing out hot urine. But when one is dehydrated, there is insufficient fluids to perspire and there is less urination.
With dehydration, the blood volume shrinks and the heart pumps faster to deliver more oxygen to the body. At the same time the blood pressure drops. With less blood in the blood vessels, there is a greater tendency for the blood to clot.
When less blood is sent to the brain, one might feel faint and dizzy, the mind can become confused, and the person could complain of headaches and may even have convulsions. Brain damage can cause paralysis or a stroke. Hence the term "heat stroke".
Less blood flowing to the kidneys will reduce urine production, and the kidneys can have problems regulating body electrolytes and getting rid of waste products.
The digestive system can also be affected, giving rise to the feeling of nausea and vomiting,
Muscles deprived of oxygen because of reduced blood flow may experience cramps and spasms.
Initially the skin tries to lose heat by sweating, but as one progresses into severe heat stroke, there is a paradoxical lack of sweating which can lead to overlooking the diagnosis of heat stroke.
Degrees of Severity of Heat Related Conditions
One generally categorizes heat-related illnesses into three levels:
a) Heat Cramps
b) Heat Exhaustion
c) Heat Stroke
Heat Cramps
The earliest stage that one can recognize a problem related to excessive heat is when the muscles experience painful cramps or spasms. The abdomen, arms and the leg calves can be affected. The combination of dehydration and poor blood flow to the muscles can trigger off these muscle contractions.
Immediately stop any activities, move to a cooler place, and drink more non-alcoholic fluids. If the cramps persist, seek medical attention quickly.
Heat Exhaustion
The next level of severity of the medical heat problem is heat exhaustion. The main symptoms are sweatiness, tiredness, feeling faint or dizzy, nausea and vomiting, thirst, headaches and irritability.
Once again immediately stop doing any activities and move to a cooler environment. Drink more non-alcoholic fluids, loosen clothing, use a wet cloth to wipe the body, and if the heart is beating fast or symptoms worsen, seek medical attention immediately.
Heat Stroke
Heat stroke is the most severe and serious level of heat illness. The core body temperature rises above 40C, the heart beats very fast, there is severe vomiting or diarrhoea, the skin is hot and flushed, there is loss of consciousness, and difficulty breathing. The breakdown in thermoregulation is the underlying problem causing the very high body temperatures.
Sometimes there is a paradoxical state found in extremely severe heat stroke where there is less sweating and reduced skin blood flow so when you touch the skin it feels a bit dry and does not feel excessively hot. This can lead to a misdiagnosis.
Heat stroke is an emergency, so quickly call for help. Immediately reduce body temperature by putting something cold on the skin like water or ice. Move the person out of the sun into a cooler environment. Remove unnecessary clothing. Try to get the person to drink something cold.
Prevention
What measures can one take to minimise the risk of a heat stroke? Here are some recommendations:
1. Do not go into the hot sun
2. Stay in cool indoors environment, preferaby with a fan or air-conditioning
3. Drink more non-alcoholic fluids, eat fruits and vegetables
4. Wear loose clothing with short-sleeves, short pants
5. Moisten the skin
6. Avoid intense physical activities
Final Words
The rise in environmental temperature, the drought, forest fires, affecting agriculture and travel is attributable to global warming. This is very serious, and it is something man-made. Therefore it is potentially remediable. But it needs the cooperation of everybody. Let us strive towards making the world a better place to live in.
Written by Ken Lyen
8 October 2018, updated 21 July 2022
Illustrations are from the Singapore Straits Times
Guidelines for Medical Care of Severe Heat Stroke Patients
This last section is for emergency and intensive care medical workers. Information from eMedicine MedScape and updated on 20 July 2022.
Heat stroke is a medical emergency and and carries significant morbidity and mortality. However complications and death are preventable if rapid action is taken. Fast reduction of the core body temperature is the mainstay of treatment because the duration of hyperthermia is the main factor determining outcome. Patients with heat stroke should be admitted to the hospital intensive care unit as soon as possible and monitored for at least 48 hours in case of complications.
Immediate cooling is the most important first step, and should be undertaken even if heat stroke is only suspected but not 100% confirmed. Core body temperature should be measured, and rectal thermometers are still the most accurate. Unfortunately most doctors only possess skin and ear thermometers, which are only slightly helpful. Even oral thermometers are not that accurate.
Take off restrictive clothing and spra the body with cold or ice water should be done immediately. If ice of ice packs are available, these should be placed in the armpits and the groins. If the patient looks pale or cyanosed or has difficulty breathing, supplemental oxygen is given and intubation for ventilation should be considered.
Insertion of an intravenous drip should be placed very early on because of dehydration in most cases. There is also a common occurrene of hypoglycaemia, so the recommended fluid to be given is 50% dextrose. Care must be taken not to overload the patient with excess fluids because this can lead to pulmonary oedema.
Insert a thermistor device which monitors body temperature continuously; the probe can be inserted either rectally or through a nasogastric tube. An alternative method is to insert a temperature-sensing Foley catheter which measures bladder temperature.
The Foley catheter also double functions to monitor urine output.
A nasogastric tube is inserted to monitor gastrointestinal bleeding and fluid losses
The rate of temperature redution recommended is at least 0.2°C/min, and when the core temperature drops to approximately 39°C, one should slow down the rate of cooling.
Pharmacologic Measures
Antipyretics (eg, paracetamol, aspirin, other nonsteroidal anti-inflammatory drugs) have NO role in the treatment of heat stroke because these antipyretics interrupt the change in the hypothalamic set point caused by pyrogens; they are not effective in a healthy hypothalamus in heat strokes. Indeed antipyretics may be harmful in patients who develop liver, blood, and kidney complications because they may aggravate bleeding tendencies.
Dantrolene, a muscle relaxant has recommended by some doctors, but to date, clinical trials have not proven that they are effective.
If a patient is highly agitated and shivering, the administration of benzodiazepines has been shown to be helpful. It also has a sedative effect which can be useful. Shivering is believed to further increase body temperature which is the reason why benzodiazepines are said to be helpful.
Neuroleptics (eg, chlorpromazine), were used in the past, but currently they should be avoided because they can lower the seizure threshold, interfere with thermoregulation and side effects include lowering blood pressure and hepatotoxicity.
Patients whose convulsions are not responding to benzodiazepines or barbiturate anticonvulsants should be paralyzed and mechanically ventilated. Monitoring epileptic brain activity should be done using electroencephalographic (EEG).
Fluid Resuscitation
Recommendations on the administration of intravenous fluids for circulatory support differ among patient populations and depend on the presence of hypovolemia, preexisting medical conditions, and preexisting cardiovascular disease.
Conventional monitoring of pulse rate, blood pressure, and urine output has been shown that these parameters do not provide adequate hemodynamic information. More invasive hemodynamic parameters, such as central venous pressure (CVP), pulmonary capillary wedge pressure, systemic vascular resistance index (SVRI), and cardiac index (CI) measurements are currently recommended. Patients who exhibit a hyperdynamic state (ie, high CI, low SVRI) generally respond to cooling quite well and do not necessarily need large volumes of intravenous crystalloid fluid infusions.
Isoprenoline, the beta-adrenergic receptor agonist and analog of adrenaline, used to be recommended for patients with hypotension. However its side effect of causing arrhythmias has made it less attractive. Dobutamine, which is more cardioselective and less likely to cause arrhythmias is currently recommended for the treatment of hypotension.
Alpha-adrenergic drugs are contraindicated because it causes vasoconstriction and prevent heat loss.
Rhabdomyolysis
Breakdown of skeletal muscle or rhabdomyolysis may be indicated by the development of dark, tea-colored urine and tender oedematous muscles. Large amounts of myoglobin are released, which can injure the kidneys leading to renal failure. This is compounded by hypotensive shock accompanying heat stroke. Kidney failue occurs in 25-30% of patients with heat stroke.
Treatment of rhabdomyolysis is by the infusion of quite a large quantity of intravenous fluids, which in some cases can be as high as 10 L, alkalinization of the urine, and the use of IV mannitol. Urine output should be maintained at 3 mL/kg/h to minimize the risk of renal failure.
Alkalinization of the urine (to a pH of 7.5-8.0) can help prevent myoglobin precipitation in the kidney tubules and can control acidosis and hyperkalemia in acute massive muscle necrosis. IV mannitol may also increase renal blood flow and glomerular filtration rate through its osmotic action, thereby increasing urine output, and preventing fluid accumulation in the interstitial compartment fluid. Unfortunately once renal failure occurs, dialysis is the only effective treatment for rhabdomyolysis.
Metabolic Support
Muscle necrosis may occur so quickly that hyperkalemia, hypocalcemia, and hyperphosphatemia can cause cardiac arrhythmias and require immediate therapy. In the presence of renal failure, hemodialysis is essential.
Hypertonic dextrose and sodium bicarbonate is used to shift potassium back into the intracellular environment while more definitive measures such as intestinal potassium binding dialysis is used.
Calcium should be used carefully because it can cause further muscle damage. The use of calcium is reserved for patients with ectopic ventricular arrhythmias, impending convulsions, or electrocardiographic evidence of hyperkalemia.
Several other electrolyte abnormalities have been reported in heat stroke, such as hypokalemia which is found in the early stages of heat stroke, and may accompany respiratory alkalosis, diarrhea, and sweating. Hyponatremia due to sodium losses or rehydration with salt-poor solutions (eg water) can sometimes occur, and its opposite, hypernatremia due to dehydration, have also been found. Hence the need to monitor closely and take appropriate actions.
Hepatic Injury
Heat stroke often casues severe but reversible liver damage. Hepatic injury is evidenced by raised transaminase and bilirubin levels . Accompanying liver damage are hypoglycemia, abnormal coagulation, cerebral oedema, leading to death.
Prolonged coagulation times also may due to the development of disseminated intravascular coagulation (DIC), which carries a poor prognosis. The severity can range from asymptomatic abnormal laboratory findings to generalized bleeding that usually occur around 48 hours after the initial heat stroke. DIC also may also lead to acute respiratory distress syndrome (ARDS), manifest by breathing difficulties, and which also increases mortality.
Treatment of liver failure includes:
Infusion of dextrose solutions to correct low blood glucose
In the presence of disseminated intravascular coagulation (DIC), replace clotting factors by infusing fresh frozen plasma, platelets, or whole blood transfusion
Respiratory support with oxygen and ventilation
Pulmonary Injury
Pulmonary oedema is a common complication of heat stroke and may be due to a number of factors, including fluid overload from aggressive rehydration, renal failure, congestive heart failure, and acute respiratory distress syndrome (ARDS). The latter may develop because of multiple afflictions, including heat-induced lung damage, aspiration pneumonia, and as a complication of liver failure. Acute Respiratory Distress Syndrome (ARDS) should be treated resolutely, with early mechanical ventilation and positive end-expiratory pressure (PEEP).
Renal Injury
Acute kidney injury (AKI) may occur because of direct thermal injury of the kidney, myoglobinuria, hypotension, and shock (acute tubular necrosis). Early manifestations of AKI include reduced urine output, some proteinuria, and granular casts.
AKI initially is treated with intravenous fluids, diuretics, and correction of associated acid-base and electrolyte abnormalities. If rhabdomyolysis is present, mannitol is the diuretic of choice because it does not interfere with the acid-base status of the urine, and it may have antioxidant properties. Frusemide may cause tubular acidosis and, therefore, may promote myoglobin deposition within the renal tubules, and should therefore be used with care. Once there is renal failure, hemodialysis is the treatment of choice.
References
Heat Stroke: Wikipedia: https://en.wikipedia.org/wiki/Heat_stroke
Video on heat stroke: https://www.youtube.com/watch?v=PpHM4DfPZQU&vl
Management of heat stroke: https://www.youtube.com/watch?v=iZd8-8dJIBo
Heat stroke treatment and management: https://emedicine.medscape.com/article/166320-treatment#showall