The severity of a heat illness may not be apparent during the initial presentation. Morbidity and mortality are directly related to the duration of core temperature elevation.

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Abbreviations

Please consider exertional heat illness (EHI) in any patient presenting with collapse following exertion, especially during the summer months. In our experience, it is especially common in the military (including, but not exclusively, during formal military exercise), athletes and labourers; and particularly so if they are starting the exertion dehydrated.

Clinicians must be aware that the patient’s temperature may be normal on arrival in the ED as many will have (or been actively) cooled on the transfer to the hospital, so a history taken with suspicion of this is very important. Also, complications can present late and may not be present on arrival to the ED.

Complications to be aware of include rhabdomyolysis, AKI, DIC and acute liver injury and these patients may need prolonged observation to ensure these are excluded.

The diagnosis of ‘heat stroke’ is not dissimilar but is usually kept for those that have abnormal neurological findings including delirium. The treatment is essentially the same.

Ensure the patient’s condition is evaluated with an A-E assessment, as some will need airway protection, oxygenation and assisted ventilation.

A rectal thermometer should be used as other methods do NOT provide an adequate assessment of the patient’s core temperature – ideally with continuous temperature monitoring if available, or intermittent monitoring (every 10 minutes). Cooling measures should be instituted (or continued if commenced in the pre-hospital phase of their care) until their temperature is below 38.9^oC. Methods of cooling could involve use of a cold shower, or cold, wet towels / sheets reapplied every 2-5 minutes (changing them when they are no longer cold).

Vital sign monitoring should be instituted with ECG, pulse oximetry, BP measurements and if shocked a urinary catheter.

A secondary survey should include assessment of the patient’s mental status (with GCS and pupillary measurements), evaluation of their muscle compartments (looking for compartment syndrome) and rectal examination, looking for bleeding. If diffuse muscle rigidity is discovered, then it may be that the patient is developing neuroleptic malignant syndrome or malignant hyperthermia in which case, the critical care team should be involved early.

Consider past medical history of the patient, especially asking after recent infections, sickle cell trait, any relevant medications, supplements and other possible drug ingestion.

Other than the ‘usual’ bank of blood tests for a sick patient, please do not forget to request CK, LFTs and a coagulation screen.

Urinalysis should be performed looking for blood, and if found, the laboratories contacted to ask for a urine myoglobin.

ECG, CXR and a CT head should be considered.

Most of the treatment will be supportive, ensuring that the patient is cooled, have adequate fluid resuscitation and any electrolyte abnormality is corrected (hyponatraemia is common and can be significant).

Critical care should be contacted early if issues arise as these patients occasionally have complicated cardiopulmonary requirements with an ARDS-like picture.

The mainstay of cooling is with the previously mentioned steps. Antipyretics such as paracetamol and ibuprofen have little effect and may make the complications worse.

The complications of EHI are usually either directly from the heat injury itself or from the resuscitative measures that are provided.

• Electrolyte abnormalities (sodium / potassium / calcium / magnesium and phosphate can all be affected.

• Hypoglycaemia – consider especially if the patient has an altered metal state or seizures.

• ARDS / Respiratory failure

• Rhabdomyolysis

• AKI (usually due to the Rhabdomyolysis)

• Hepatic injury

• DIC

• GI bleeding / ischaemic bowel injury – may be due to a period of hypoperfusion.

• Myocardial injury / arrythmias – antiarrhythmic intervention (DCCV / drugs) is usually ineffective until the patient is cooled.

Generally, the complications are less severe the shorter the duration of hyperthermia, but usually:

• CVS issues resolve in a couple of hours

• Liver markers usually start to settle in 24-48 hours, but this can take weeks, as can renal markers.

• The CK may rise over the following 3-4 days before settling, again over the next few weeks.

• Difficulty correcting hypotension

• Seizure

• Severe encephalopathy

• Moderate encephalopathy (eg, confusion) that is not clearing rapidly

• Persistent oliguria

• Persistent myalgia suggesting evolving rhabdomyolysis

• Persistent electrolyte abnormalities

• Persistent creatinine above 180 µmol/L

• Evidence of acute kidney injury or myoglobinuria

• Evidence of disseminated intravascular coagulation

• Exertional hypoglycaemia

• Persistent substantial diarrhoea

• Significant gastrointestinal bleeding

As a rule, patients with suspected EHI will need admission, but some very well patients who had a raised temperature for a very short period of time may be well enough to be discharged following observation of 6 hours. Prior to their discharge it would be prudent to repeat their blood tests to ensure nothing has changed over that period.

Admission is usually under the medical team unless a specific surgical (e.g., compartment syndrome needing orthopaedic review) or critical care is needed.

In Frimley Park’s experience, one consideration to be made is the importance of this diagnosis in patients from the military.

If a military patient arrives with this condition, the initial treatment is as with any other patient. If there are welfare needs, critical care intervention or it is felt there is an imminent threat to the patient’s life, the hospital’s military welfare officer should be contacted to ensure appropriate family contacts are being actioned.

Once back in the barracks, they should see their Medical Officer (MO) urgently as they may need to be temporarily ‘downgraded’ and investigated further for a genetic propensity to this condition.

When discharging the patient who has had no evidence of biochemical abnormality, ask them to refrain from physical exercise before review from their MO. If they have had biochemical abnormalities, they should not undertake physical exercise until their blood tests have returned to normal.

Please ensure a discharge summary documenting all that has occurred (including any relevant test results) is given to them to let the MO know information that will inform their ongoing care.

O'Connor, F.G. and Casa, D.J. (2024) 'Exertional heat illness in adolescents and adults: Management and prevention', in T.W. Post (ed) UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/

Ministry of Defence (2021) Heat illness: Specialist investigation and rehabilitation. JSP 950. Leaflet 2-22-4 (Feb 21 v1.1). London: Ministry of Defence

This guideline has been registered with the Trust. However, clinical guidelines are guidelines only. The interpretation and application of clinical guidelines will remain the responsibility of the individual clinician. If in doubt, contact a senior colleague or expert. Caution is advised when using guidelines after the review date.

This guideline is for use in Frimley Health NHS Foundation Trust hospitals only. Any use outside this location will not be supported by the Trust and will be at the risk of the individual using it.

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