Environmental Emergencies
An 80 year old man is brought into the Emergency Department by his concerned family. They had been sat in the garden enjoying the nice weather before noticing the patient becoming increasingly confused and complaining of a headache and dizziness. He has a past medical history of hypertension for which he takes ramipril. On examination you note his observations are:
- Heart rate: 105 beats/minute
- Blood pressure: 134/78 mmHg
- Respiratory rate: 23 breaths/minute
- Oxygen saturations: 97% on air
- Temperature: 41°C
You note normal cardiac and respiratory auscultation. You find the patient hot to touch with no sign of sweating. What is the diagnosis?
Answer:
Heat stroke is a systemic inflammatory response with a core temperature ≥ 40.6°C accompanied by a change in mental state and varying levels of organ dysfunction. Mortality from heat stroke ranges between 10 and 50%. Classic non-exertional heat stroke occurs during high environmental temperatures and often affects the elderly during heat waves.Hyperthermia and Heat Stroke
Environmental Emergencies
Last Updated: 19th September 2022
Definitions
Body temperature is usually maintained at around 36.5 - 37.5°C, in order to maintain normal enzyme and cell function. Temperature is controlled by the hypothalamus, which monitors body temperature and balances heat production with heat loss.
Hyperthermia occurs when the body’s ability to thermoregulate fails and core temperature exceeds that normally maintained by homeostatic mechanisms. Hyperthermia may be exogenous caused by environmental conditions or secondary to endogenous heat production.
Hyperthermia is not synonymous with the more common sign of fever, which is induced by cytokine activation during inflammation and regulated at the level of the hypothalamus. In hyperthermia the body's temperature set point remains unchanged; the body temperature is elevated above the thermoregulatory set point due to excessive heat production and/or insufficient heat dissipation.
Causes of hyperthermia
- Heat stroke is a systemic inflammatory response with a core temperature ≥ 40.6°C accompanied by a change in mental state and varying levels of organ dysfunction. Mortality from heat stroke ranges between 10 and 50%. There are two forms of heat stroke:
- Classic non-exertional heat stroke (occurs during high environmental temperatures and often affects the elderly during heat waves)
- Exertional heat stroke (occurs during strenuous physical exercise in high environmental temperatures and/or high humidity and usually affects healthy young adults)
- Endocrine causes
- Pheochromocytoma
- Thyroid storm
- Hypothalamic dysfunction
- Delirium tremens
- Drug induced
- Malignant hyperthermia (a rare autosomal dominant disorder of skeletal muscle calcium homeostasis characterised by muscle contracture and life-threatening hypermetabolic crisis following exposure to depolarising muscle relaxants or volatile anaesthetics; treat with oxygen, correct acidosis and electrolyte abnormalities, start active cooling and give dantrolene)
- Serotonin syndrome (a life-threatening reaction that is precipitated by the use of serotonergic drugs and overactivation of both the peripheral and central serotonin receptors)
- Neuroleptic malignant syndrome (a life-threatening reaction that can occur in response to neuroleptic or antipsychotic medication)
- Sympathomimetic or anticholinergic toxidrome
Predisposing factors for heat stroke
- Elderly
- Strenuous exercise in high ambient temperature and humidity
- Lack of acclimatisation
- Dehydration
- Obesity
- Alcohol
- Cardiovascular disease
- Skin conditions e.g. psoriasis, eczema, scleroderma, burns
- Endocrine conditions e.g. hyperthyroidism, pheochromocytoma
- Drugs e.g. anticholinergics, diamorphine, cocaine, amphetamine, phenothiazines, sympathomimetics, calcium channel blockers, beta-blockers
Clinical presentation of heat stroke
- Core temperature ≥ 40.6°C
- Hot, dry skin (sweating person in about 50% of cases of exertional heat stroke)
- Non-specific symptoms
- Extreme fatigue
- Headache
- Dizziness
- Fainting
- Facial flushing
- Vomiting
- Diarrhoea
- Cardiovascular dysfunction
- Tachycardia
- Arrhythmias
- Hypotension
- Respiratory dysfunction
- Acute respiratory distress syndrome (ARDS)
- Central nervous system dysfunction
- Confusion
- Seizures
- Coma
- Systemic dysfunction
- Liver and renal failure
- Coagulopathy
- Rhabdomyolysis
Management of heat stroke
- The mainstay of treatment is supportive therapy based on optimising the ABCDEs and rapidly cooling the patient
- The patient should be be transferred to a cool environment and laid flat
- Immediately start cooling and begin transfer to hospital
- Patients should be cooled to < 39°C (ideally 38.0 - 38.5°C) - rapid cooling is safe (cooling rates of 0.2 - 0.35°C/min are achievable)
- Measurement of core body temperature should be used to guide treatment
- Cooling techniques
- Simple techniques include cool drinks, fanning the undressed patient and spraying tepid water on the patient; ice packs over areas where there are large superficial blood vessels (e.g. axillae, groin, neck) are also useful; surface cooling may cause shivering
- In cooperative stable patients, immersion in cold water is effective; however this can cause peripheral vasoconstriction reducing heat dissipation; immersion is not appropriate for very sick patients (and is not usually available or practical)
- Use the same advanced cooling techniques as for targeted temperature management after cardiac arrest; consider the use of cold IV fluids, intravascular cooling catheters, surface cooling devices and extracorporeal circuits
- No specific drugs lower core temperature in heat stroke
- If cardiac arrest occurs, continue active cooling and follow standard procedures for basic and advanced life support and cool the patient; provide post-resuscitation care according to normal guidelines
Other heat-related illnesses
- Heat cramps
- Clinical features
- Heavy sweating during intense exercise
- Muscle pains or spasms
- Treatment
- Stop physical activity and move to cool place
- Drink water
- Wait for cramps to go before continuing physical activity
- Clinical features
- Heat exhaustion
- Clinical features
- Heavy sweating
- Cold, pale, clammy skin
- Fast, weak pulse
- Nausea or vomiting
- Muscle cramps
- Tiredness or weakness
- Dizziness
- Headache
- Fainting
- Treatment
- Move to cool place
- Loosen clothes
- Put cool, wet cloths on body or take a cool bath
- Sip water
- Clinical features
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
