by Abdulaziz Al Mulaik
A 57-year-old male is brought to the emergency department by EMS during Hajj. The patient as stated by the paramedics was “found face down” in the street under direct sunlight, where outside temperature is 45°C. Initial vitals are BP: 91/55, HR 130 . O2Sat 95% on room air, RR 25 , Axillary temperature 39°C, and his Glucose check was 8 mmol/l. On examination, the patient is not oriented nor alert but he moans to painful stimuli, and he is maintaining his airway with no drooling. You ask a member of your team to repeat temperature measurement rectally, and he finds it to be 42.3°C. The rest of your physical examination is unremarkable. You remove all of the patient’s clothes and spray him with lukewarm tap water, you then turn on a fan and raise the head of the bed and the side rails. A continuous temperature probe is inserted rectally. A cardiac monitor with pulse oximetry is connected, and blood samples were drawn for laboratory testing. After reaching a rectal temperature of 39°C, you direct your team to dry him and cover him with a light bed sheet. On subsequent examination, the patient is conscious, alert and oriented. Vitals are HR 105, O2Sat 96% on room air, RR 20. Labs reveal multiple abnormalities including respiratory alkalosis and elevated liver enzymes. Your disposition includes appropriate medical consultation and admission to a medical ward for further management.
Basics Of Heat Transfer
Critical Bedside Actions and General Approach
Heat stroke is a devastating disease that might have permanent sequelae if lifesaving interventions are delayed. It is defined simply as a failure of thermoregulatory mechanisms to cope with either internal heat production known as exertional heat stroke (EHS) or external environmental heat, known as classic heat stroke (CHS).
To diagnose a heat a stroke, the patient has to have a Central Nervous System (CNS) impairment and core temperature of more than 40°C. The spectrum of neurological abnormalities ranges from mild confusion to full-blown coma with GCS of 3. Core temperature has to be measured and continuously monitored using rectal or esophageal probes as peripheral measures of temperature are unreliable and does not correlate with core temperature.
The essence of heat stroke management is to “Cool first, then ask questions!”, as it is a time-sensitive condition, where cooling takes precedence over everything else including confirmation of the diagnosis. ABCs are the way emergency medicine practitioners approach every patient rightfully, so, to ensure that all critical decisions are made in a timely fashion. Heat stroke is not an exception to this role, as the disturbance in consciousness could result in significant airway complications. A complete airway assessment should be immediately performed when the patient arrives in the emergency department while cooling measures being set up. Other physical examination details are important but should not delay cooling.
Two important observations are worth taking note of: the first relates to how difficult intravenous peripheral access might be during early stages of resuscitating in a dehydrated victim which is going to be compounded by cooling as this will result in peripheral vasoconstriction. The second is a phenomenon related to excessive watery diarrhea during cooling, and this mandates adequate preparation by the nursing and janitorial team. There are two possible explanations for this phenomenon; the first is the compensatory vasoconstrictive changes to the splanchnic vasculature as blood pools peripherally for cooling. The second proposed mechanism is the multisystem failure caused by heatstroke which includes the gastrointestinal system where epithelial cells shed and propagate an inflammatory diarrhea.
In a febrile illness, be it infectious or otherwise, circulating pyrogens resets the normal temperature in the thermoregulatory control center to a new set point above normal. The entire thermoregulatory pathways in the body will work to achieve the new set point; hence febrile patients will have behavioral changes where they will seek warmer environments. Cooling febrile patients by cold towels or showers has a mild effect as the body will continue warming up to the new set point. No harmful effect is exerted directly by fever alone, and clinical focus should be directed toward the cause of the fever.
Heat stroke, on the other hand, is a failure of the thermoregulatory system to cool the body. Therefore, all antipyretics are potentially harmful interventions as they work primarily on thermal set point reduction which is already normal in heat stroke patients. Reverting patients to a normal thermal level will reboot the thermoregulatory system, hence the urgency of cooling.
Minor heat illnesses are expected in the right environmental conditions. These illnesses are considered the milder side of the spectrum of heat illnesses with heat stroke on the other side. A list of these disorders with their classic presentations and recommended management strategies can be found below (Table 1).
The list of minor heat illnesses with their clinical features and treatment
|Minor Heat Illness||Most Prominent Clinical Features||Treatment|
|Prickly heat||Very pruritic vesicular rash on an erythematous base||Chlorhexidine lotion|
|Heat syncope||Standing in heat for long time with no previous acclimatization to heat||No specific treatment required|
|Heat cramps||Muscular cramps AFTER working in heat||Oral 0.1% salt solution|
|Heat edema||Swollen feet and ankles in healthy patients after standing in heat for long time||No specific treatment required|
History and Physical Examination Hints
Situational awareness is a vital skill to emergency physicians, as one should be aware of high ambient temperatures and high humidity days as they are perfect conditions for classical heat strokes. Lonely elderly community members with low socioeconomic status are particularly vulnerable to CHS as they have poor access to good air conditioning and ventilation. Usage of some medications which impairs adrenergic response to heat by sweating is another risk factor for developing heat illness. Generally speaking, CHS is not common in geographical areas where average temperature throughout the year is high, as communities living in these places will develop behavioral tactics to avoid the heat.
Intense exercise, military training, sports competitions or prolonged labor might induce another type of stroke known as exertional heat stroke (EHS), which differs from CHS in laboratory indices and long-term complications. A third less common type of heat stroke is confinement hyperpyrexia where the patient is exposed to moderately high ambient temperatures for a long time.
Measuring body core temperature is perhaps the most important physical assessment, whenever heat illnesses are considered in the differential diagnosis of a given patient. Peripheral temperature measurements correlate poorly with core temperature. The two methods of measuring core temperature are either through the esophagus or the rectum with the latter representing the majority of clinical practice. A common pitfall in using rectal temperature is inserting the probe to an insufficient depth which will render readings to be inaccurate in both directions especially if ice packs have been applied to the groin. Rectal probes, in general, have to be inserted 15 cm inside the rectum to mitigate the effects mentioned above, but manufacturers may recommend different depths.
Tachycardia and hypotension are commonly seen and represent the physiologic response to heat, as peripheral vascular resistance decreases to allow the blood to be cooled at the surface of the skin, leading to a high output status. This phenomenon might explain other heat illnesses like heat syncope and heat edema.
Heat stroke is a multisystem disease affecting almost every organ in the body. CNS effects might range from simple confusion to deep coma. Seizures, in general, are common and might be confused with shivering during cooling, but both disorders need to be treated, the former for neural protection and the latter to prevent heat generation. Heat stroke patients might have derangements in their hemostasis represented clinically as melena, hemoptysis, conjunctival hemorrhage or epistaxis. Prickly heat patients will have pruritic vesicles on an erythematous base. These vesicles are sweat glands with blocked pores by macerated stratum corneum.
Emergency Diagnostic Tests and Interpretation
EHS and CHS have different derangements in laboratory studies with some similarities. For instance, respiratory alkalosis is a physiologic response to heat stress, which is profoundly represented in CHS, whereas lactic acidosis is the prominent acid-base disturbance in EHS. Moreover, liver enzymes should be elevated in both EHS and CHS with numbers in the tens of thousands above normal cutoffs, to the degree that their elevation is a cardinal diagnostic criterion, and their absence will render the diagnosis of heat stroke unlikely. Another common difference between CHS and EHS is glucose level as it might be low in the latter but not the former.
Emergency Treatment Options
The fastest way to transfer heat and to cool patients is through conduction, which is the direct transfer of heat between molecules. Full body water immersion can do this, and although this is theoretically the best cooling method, it is clinically challenging as it poses a risk of aspiration and renders patient’s accessibility quite difficult. Convection, which is the thermal loss due to gas movement around the body, combined with evaporation can achieve the similar speed of cooling to full body immersion. This combination can be achieved by spraying the patient with lukewarm water followed by fanning with warm air. Mist fans are very convenient and have the added benefit of their ability to fan multiple patients at once. Cooling units with intermittent water sprays from all directions around the patient are costly and not available in most hospitals, and they have recently fallen out of favor, even in Hajj despite their availability, mainly due to safety concerns as they limit access to patients.
Figure 1: monitor showing the current vitals while the patient is cooled.
Invasive cooling procedures such as cool IV fluids have not been proven to change the outcomes as their evidence remains to be weak. On the other hand, thoracic, bladder, rectal and peritoneal lavage should only be used when all other measures fail. We suggest abandoning them even in the very sickest of patients, as a neurologically meaningful recovery is highly unlikely.
A protected airway should be maintained in heatstroke patients, and efforts should be taken to resist the urge to intubate them. Intubating solely for the low level of consciousness is ill-advised and will expose patients to unnecessary adverse effects of intubation. With that being said, airway protection is of utmost importance and should take priority on any other diagnostic or therapeutic procedures.
Peripheral blood pooling is in the heart of heat stroke pathology, so hypotension is common in these patients and fluid administration should be very judicious as the blood pressure usually will pick up as the core temperature drops down. Aliquots of 250 cc of crystalloids should be used when fluids are needed, and repeated dosing should take place after volume status assessments.
Special Patient Groups and Situations
Pediatric heat stroke patients are usually victims of confinement hyperpyrexia. Attention should be paid if further interventions are needed to protect a child from abuse or maltreatment. Geriatric patients, on the other hand, are usually the victims of CHS. Emergency physicians should play their role in advocating for closer community ties and socioeconomic support by appropriate authorities for those patients.
A mass casualty incident of heat stroke and heat exhaustion patients should be expected in preparing for a mass gathering event and mitigation measures should be sought in advance. Public education to seek shade, drink enough fluids, use umbrellas and installing mist pipes, venting fans, cooling stops in a path of a riot or a race are few examples.
Figure 2. The row of beds with mist fans in a sunstroke unit. A cooling unit can be seen at the far right.
Figure 3. Fiberglass grooved beds with waterproof mattresses in a sunstroke unit.
Heat stroke patients usually require higher care upon admission as their stability is not certain and further assessment of heat stroke complications should take place in the hospital. Stable, conscious heat exhaustion patients may be discharged with education and close follow up. Minor heat illnesses should be treated as a case by case scenario, but they rarely require inpatient care.
References and Further Reading
- Chris Nickson – Heat Stroke (2014) – http://lifeinthefastlane.com/ccc/heat-stroke/
- Video 1. A short further explanation of thermal transfer.
- Video 2. A short video on what happens in EHS.
- Video 3. Heat illness first aid.