As the year comes to an end, the holidays approach and, for lots of people, it means traveling to different places around the world. For those who live in the southern hemisphere, like me, the summer comes with al power, with temperatures as high as 35°C (95°F) or 40°C (104°F). For those who live in the northern hemisphere, “the winter is coming” and bring with him temperatures below 0°C (32°F) in some places. With these temperature extremes, we have some conditions to have in mind when working in the ED. How to treat a homeless patient who has slept on the streets on a freezing night? And how about an elderly person who lay on the beach sand under a blazing sun?
Hyperthermia
What is hyperthermia?
By definition, hyperthermia is a condition when there is a failure of the body’s thermoregulatory mechanisms to handle extrinsic and intrinsic heat. It’s common to see the expression “Heat-related Illness” to describe the conditions associated to the exposure to environmental heat.
Physiology
The heat-related illness (HRI) develops following a progressive pattern, divided in 3 phases [1].
- ACUTE PHASE:
- Activation of inflammatory mediators, especially in the blood vessels;
- Gastrointestinal tract hypoperfusion, leading to bacterial translocation
- Respiratory alkalosis due to hyperventilation
- ENZYMATIC PHASE:
- Coagulopathy, leading to a hypercoagulability state
- Endothelial injury and microvascular thrombosis
- All of this leading to disseminated intravascular coagulation (DIC)
- LATE PHASE:
- Liver dysfunction secondary to DIC
- Kidney failure due to dehydration and hypotension
- CNS lesions leading to cerebral edema and hemorrhage
- Cardiovascular dysfunction, worsening hypotension and causing vasoconstriction
Risk Factors
- Extremes of age
- Obesity
- Elevated humidity rate
- Lack of acclimatization and/or fitness
- Ambient temperature
- Dehydration
- Cardiovascular disease
- Drugs/medication (i.e alcohol, diuretics, amphetamines)
Categories of heat illness
- Minor Heat Illness:
- Heat cramps: Intermittent muscle cramps likely related to salt deficiency and muscular fatigue, although the exact mechanism is not well known.
- Heat Edema: Swelling of the feet and ankles typically in non-acclimatized people
- Heat Syncope: Similar to orthostatic hypotension, caused by the physiologic response to the heat: volume depletion, peripheral vasodilatation and a reduced vasomotor tonus. More common in elderly people.
- Prickly Heat: cutaneous rash caused by pores and sweat gland obstruction
- Heat Exhaustion:
- Occurs with a moderate elevation in the body core temperature (<40°C or 104°F) – RECTAL temperature is the most reliable method (even though is a level C evidence)
- Usually accompanied by symptoms related to conditions described in the Minor Heat Illness and other nonspecific symptoms like nausea/vomiting, weakness and headache
- DOES NOT PRESENT WITH ALTERED MENTAL STATUS
- Heat Stroke:
- Body temperature above 40° (104°F) WITH ALTERED MENTAL STATUS
- Target organ damage
- Usually dry and pale skin, however athletes can present with warm and wet skin
Management
- Primary, we need to proceed with the basic measures: secure airway, monitorize and place IV fluids in order to maintain a mean arterial blood pressure > 60 mmHg [2].
- The second step is to perform a rapid cooling, targeting a temperature <39°C (102°F) in the first 30 minutes. After reaching this goal, the active cooling should be stopped in order to avoid overshoot hypothermia
- Cold water immersion is the best method available (level C evidence) [3].
- Treat shivering with benzodiazepines if needed (avoiding extra heat generation)
- DO NOT USE ANTIPYRETICS, they are not effective in this scenario [4].
- Cold water immersion is the best method available (level C evidence) [3].
Disposition
- Patients with heat stroke should be admitted to a ICU to monitoring organ dysfunction, electrolytes disturbances and rebound hypothermia.
- Young and otherwise healthy patients with heat exhaustion can be discharged home
- Be aware for the risk of recurrent hyperthermia when considering discharge a patient (returning to the same ambient)
Hypothermia
What is hypothermia?
- Condition in which the body loses heat at a higher rate than its capacity in maintain the core temperature or elevate the heat production
- Clinically defined as unintentional decrease of body temperature below 35°C (95°F)
- In other settings, we can talk about “secondary hypothermia”, when the patient has an impaired thermoregulation due to a clinical condition such as hypothyroidism, ketoacidosis, malnutrition etc – In this article we will focus on accidental hypothermia, related to environmental exposure
Physiology
- Initially, the metabolic rate increases, peripheral blood flow is shunted towards vital structures, and shivering initiates to increase heat production
- If these compensations are not enough, the body temperature continues to drop, with the CNS being affected when it reaches 35°C (95°F).
- Cardiovascular: initial increase in heart rate and blood pressure; however, as core temperature declines, progressive bradycardia and hypotension occurs. In more severe hypothermia, myocardial irritability increases, leading to a high risk of arrhythmias.
- Oxygen consumption: At a temperature of 28°C (82°F), the oxygen consumption is decreased by 50%, leading to a protective effect in CNS and other vital organs – but just if it develops before asphyxia (there are several studies trying to better understand the role of hypothermia as a protective measure in cardiac arrest) [5].
Risk Factors
- Fatigue
- Sleep deprivation
- Rain, wind and water immersion
- Burn
- Extremes of age
- Trauma
- Alcohol
- Hypoglycemia
- Hypothyroidism
- Hyperthermia treatment (rapid cooling)
Classification
Stage 1: Mild Hypothermia
- Core temperature: 32 – 35°C (90 – 95°F)
- Initially presenting with tachycardia, hypertension, shivering and vasoconstriction
- Gradually develops ataxia, poor judgement, amnesia, apathy, dysarthria
Stage 2: Moderate Hypothermia
- Core temperature 28 – 32°C (82 – 90°F)
- Loss of shivering, lethargy, mydriasis, hyporeflexia, alterations in cardiac rhythm (Osborne J waves on EKG)
Stage 3: Severe Hypothermia
- Core temperature: 24 – 28°C (75 – 82°F)
- Hypoventilation, ventricular fibrillation, acid-basic disturbances, anesthesia, pulmonary edema
Stage 4: Profound Hypothermia
- Core temperature: below 24°C (75°F)
- Oliguria, fixed pupils, asystole, apnea, coma
- Curiosity: 13,7°C (56,7°F) is the lowest temperature registered at which CPR was performed with satisfactory results [6].
Management
- The first thing we need to do is to stop the cooling process
- Remove the environmental factor (take the patient out of the street, take off wet clothes etc.)
- Try stop heat loss, putting up barriers like warm clothes, blankets, sleep bags, etc
- Second step, we should identify the degree of hypothermia to guide our approach:
- For Mild hypothermia, besides the strategies described before, we need to offer calories (food and warm drinks), monitoring for at least 30 minutes and warm the trunk
- [F]or Moderate hypothermia, we also need to keep the patient laid down and still, start volume reposition with warm fluids (40 – 42°C/104 – 107°F), Avoid food and beverage.
- For Severe hypothermia: All the above and check for pulse and breathing – of pulse/breathing is absent, START CPR. – Consider transferring to a facility where ECMO is available
- ECMO is the best option for severely hypothermic patients without signs of life who do not respond to initial resuscitative efforts. It has been shown to improve neurologically intact survival (48% to 63% survival with ECMO, <37% without ECMO) [7].
- For Severe hypothermia: All the above and check for pulse and breathing – of pulse/breathing is absent, START CPR. – Consider transferring to a facility where ECMO is available
“Nobody is dead until warm and dead”
Patients with core temperatures of <28°C have decreased electroencephalographic activity and loss of brainstem and pupillary reflexes, all of which may mimic death. Because of that, the patient can not be considered “dead” until his body temperature reaches at least 32°C.
Some conditions allow us to presume death even in patients with body temperature below 32°C and no vital signs: obvious lethal injury (i.e. decapitation), frozen body, potassium > 12, avalanche victims with burial > 35min or airway packed with snow.
References and Further Reading
The primary reference for this article was the recently launched book: “Medicina em Áreas Remotas no Brasil” (Wilderness Medicine in Brazil): JULIANA R. M. SCHLAAD e SASCHA W. SCHLAAD, Medicina em Áreas Remotas no Brasil, 1ed, Barueri (SP), Manole, 2020
Other sources of information as numbered and referred in the text:
- Powers SK, Howley ET. Regulação de temperatura. In: Powers SK, Howley ET. Fisiologia do exercício: teoria e aplicação ao conhecimento e ao desempenho. 9ed. Barueri: Manole; 2017. p.261-281.
- Tran TP. Heat emergencies. In: Ma OJ, Cline DM, ed. Emergency medicine manual. 6th ed. McGraw-Hill, NY: 2004:564-565
- Becker J, Stewart L. Heat-related illness. Am Fam Physician. 2011;83(11):1325-1330
- Lipman GS, Eifling KP, Ellis MA, Gaudio FG, Otten EM, Grissom CK. Wilderness medical society practice guidelines for the prevention and treatment of heat-related illness: 2014 update. Wilderness Environ Med. 2014; 25:S55-S65
- Soar J, Perkins G, Abbas G, et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: Electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation. 2010;81(10):1400-1433.
- M. Gilbert, R. Busund, A. Skagseth, Nilsen PÅ, J.P. Solbø Resuscitation from accidental hypothermia of 13.7 degrees C with circulatory arrest Lancet, 355 (2000), pp. 375-376
- Brown DJ et al. Accidental hypothermia. NEJM 2012; 367(20): 1930-1938. PMID: 23150960
