GeriQBank · Paper III · Q14
Heat Exhaustion
- Chapter
- Neurology, Neuro-ophthalmology & Environmental Emergencies
- Years asked
- Not recorded in the source
- Frequency
- Set 1× in Paper III (2009–2025)
As set in the university paper
Heat exhaustion.
Paper III · Sleep, Skin, Special Senses & Environmental · asked ×1 · 7-mark note · see in paper list
Detailed answer
Pro · free in betaAttempt it firstOutline your answer as a 7-mark note before revealing it — definition, causes, evaluation, management and the geriatric angle.Reveal answer
Heat Exhaustion Definition and place in the spectrum
Heat exhaustion is a moderate heat-related illness caused by water and/or salt depletion during heat exposure, characterised by a core temperature that is normal or only mildly elevated (usually below 40°C), with preserved sweating and an intact mental state.
It occupies the stage immediately before heat stroke on the continuum of heat-related illness: heat rash (miliaria) → heat oedema → heat cramps → heat syncope → heat exhaustion → heat stroke. Untreated, heat exhaustion progresses to heat stroke, which carries up to 80% mortality — this is why recognising it matters.
Early manifestations of heat exhaustion are non-specific; later, severe central nervous system dysfunction and anhidrosis develop, which signifies progression to heat stroke.
Pathophysiology
Prolonged heat exposure causes sustained cutaneous vasodilatation and profuse sweating, producing loss of water and sodium, hypovolaemia and reduced cardiac output, and hence inadequate tissue perfusion. Crucially, thermoregulation remains intact — which is why sweating continues and consciousness is preserved.
Two overlapping types: water-depletion heat exhaustion (inadequate fluid intake; hypernatraemia; rapid onset — the dominant form in the elderly, in whom thirst is blunted) and salt-depletion heat exhaustion (losses replaced with water alone; hyponatraemia; prominent cramps; more insidious onset).
Why older adults are vulnerable: impaired temperature perception, diminished sweating from reduced sweat gland numbers and dermal vascularisation, blunted thirst sensation, reduced renal concentrating ability, lower total body water, diuretic and anticholinergic use, immobility and dependence on carers for fluids, and dementia limiting self-protective behaviour.
Clinical features
Early/non-specific symptoms (Table 12-14): dizziness, weakness, sensation of warmth, anorexia, nausea, vomiting, headache and dyspnoea.
Additional features: profuse sweating with cool clammy skin, intense thirst, fatigue, myalgia and muscle cramps, irritability, tachycardia, postural hypotension and near-syncope, and oliguria with concentrated urine.
The cardinal distinction from heat stroke: in heat exhaustion the core temperature is below 40°C, the skin is moist because sweating is preserved, and there is no severe CNS dysfunction — no psychosis, delirium, coma or seizures. Mild irritability or feeling faint is acceptable; any frank alteration of sensorium means heat stroke until proved otherwise.
In older people the picture is easily mistaken for gastroenteritis, urinary sepsis, drug adverse effects or delirium — a high index of suspicion during a heatwave is essential, exactly as for heat stroke.
Investigations
Rectal core temperature (essential to separate exhaustion from stroke), capillary glucose, serum electrolytes (sodium may be high or low depending on the type), urea and creatinine (pre-renal pattern), creatine kinase (to exclude rhabdomyolysis), urine specific gravity and ECG.
Investigate to exclude infection or another acute illness whenever the diagnosis is not clear-cut, since heat illness and sepsis coexist and mimic each other in the elderly.
Management
Move the patient immediately to a cool, shaded or air-conditioned environment and lay them supine with the legs elevated; remove excess clothing.
Active external cooling — cool water spray with fanning, cool wet cloths, and ice packs to the neck, axillae and groin. Cooling is less aggressive than for heat stroke but should still be prompt.
Oral rehydration with cool electrolyte-containing fluid (ORS) if the patient is alert and not vomiting. Intravenous isotonic saline if there is vomiting, marked postural hypotension or failure to improve; in older patients infuse cautiously with monitoring for fluid overload and heart failure.
Correct electrolyte abnormalities; correct hyponatraemia slowly to avoid osmotic demyelination. Rest and avoid further heat exposure for 24–48 hours.
Do not give antipyretics — the hypothalamic set point is normal, so they are ineffective.
Monitor core temperature, blood pressure, urine output and mental status. Any deterioration in mental status, or a core temperature reaching 40°C, means the patient has progressed to heat stroke — begin aggressive cooling immediately.
Indications for admission in older adults: advanced age with comorbidity, persistent symptoms after 30–60 minutes of cooling and rehydration, significant electrolyte derangement, renal impairment, rhabdomyolysis, inability to take oral fluids, and an unsafe or unairconditioned home environment.
Prognosis is excellent with prompt treatment — heat exhaustion resolves fully without sequelae. Its clinical importance lies entirely in being the recognisable and completely reversible stage before the very high mortality of heat stroke.
Prevention
Identical to heat stroke prevention: education of older adults about their susceptibility and about appropriate behaviour in extremes of environmental temperature, and close monitoring of the most vulnerable.
Practical measures: pre-summer medication review (diuretics, anticholinergics, antipsychotics, β-blockers); scheduled fluid intake rather than thirst-driven drinking; avoid outdoor activity between noon and 3 pm; light loose clothing; cool showers; use of cooling centres; buddy check-in systems; and temporary relocation of very high-risk older people to a protected environment.
Latest Updates (2023–Present)
SCCM Heat Stroke Guidelines (Critical Care Medicine, 2025) emphasise that the distinction between heat exhaustion and heat stroke rests on core temperature and CNS dysfunction, and that where there is any doubt the patient should be treated as heat stroke and cooled — the risk of over-treating exhaustion is trivial compared with the risk of under-treating stroke.
India — NCDC/NPCCHH "National Action Plan on Heat Related Illnesses" provides standard case definitions, symptoms and first aid for heat rash, heat cramps, heat syncope, heat exhaustion and heat stroke (Annexure 2), and mandates daily reporting of heat-related illness and deaths on the IHIP portal. The March 2024 "Emergency Cooling for Severe Heat-Related Illnesses" document supplements this for severe cases, and the NPCCHH Programme Implementation Plan funds procurement of emergency cooling equipment. MoHFW 2025 heatwave advisory requires facility preparedness — a designated cooling area, ice packs and a written heat illness protocol at every health facility.
Oral rehydration solution is superior to plain water in salt-depletion heat exhaustion (2024–2025 occupational and sports medicine literature); ice-slurry or "slushy" ingestion provides useful internal cooling and is being adopted for outdoor workers.
WHO–WMO heat and health guidance (2024) and India's state and city Heat Action Plans (with the Ahmedabad Heat Action Plan as the internationally cited model) identify older adults as a priority vulnerable group, with early warning systems, cooling shelters and targeted outreach.
Lancet Countdown (2025): heat exposure days and heat-attributable mortality in adults over 65 continue to rise in India. ICMR-NIN guidance advises older adults to take roughly 2–2.5 litres of fluid daily in summer unless fluid-restricted for heart failure or chronic kidney disease.
Current Practice Update
Textbook Position (Essentials 7th ed.) Current Evidence-Based Practice (2023–2026) Heat exhaustion described only as the "early Now a distinct entity with its own case definition and first-aid protocol under manifestations of hyperthermia", without a India's NPCCHH National Action Plan on Heat Related Illnesses separate management protocol Distinction from heat stroke implied by the Explicit criteria: core temperature <40°C, preserved sweating, intact sensorium. early/late signs table When in doubt, treat as heat stroke and cool (SCCM 2025)
Rehydration not specified in detail Oral rehydration solution preferred over plain water in salt depletion; IV isotonic saline with cautious monitoring for fluid overload in older adults Prevention through education and relocation of the Operationalised through state and city Heat Action Plans, early warning systems, high-risk cooling shelters and mandatory IHIP reporting Examiner's Tip — say these lines verbatim:
"Heat exhaustion is water and/or salt depletion during heat exposure, with a core temperature below 40°C, preserved sweating and an intact sensorium."
"The early manifestations of heat exhaustion are non-specific — dizziness, weakness, a sensation of warmth, anorexia, nausea, vomiting, headache and dyspnoea."
"The single discriminator from heat stroke is CNS dysfunction with anhidrosis — if the sensorium is altered and the skin is hot and dry, it is heat stroke."
"Two types: water-depletion (hypernatraemic, rapid, commoner in the elderly because thirst is blunted) and salt-depletion (hyponatraemic, insidious, prominent cramps)."
"Treatment is cool environment, supine with legs elevated, active external cooling, and oral rehydration solution or cautious isotonic saline."
"Do not give antipyretics — the hypothalamic set point is normal."
"Heat exhaustion is the completely reversible stage before heat stroke, which carries up to 80% mortality — recognising it is the whole point."
"Prevention is the most appropriate approach to management of temperature dysregulation in older adults." Rapid Revision Grid — Night Before the Examination Topic One-line textbook anchor Single most examinable 2023–2026 update Epilepsy in the elderly 3rd commonest neurological disorder; stroke causes Choose ASM by tolerability, not efficacy; no 40–53%; treat after first unprovoked seizure prophylaxis after stroke; lacosamide/lamotrigine/levetiracetam Coma Arousal (ARAS) + awareness (cortex); GCS ≤8; Cognitive motor dissociation in ~25% (NEJM preserved pupils = metabolic 2024); FOUR score; cEEG for NCSE Subdural haematoma Acute = mass effect; chronic = inflammation from MMA embolisation — EMBOLISE and STEM blood degradation products; subdural drain lowers positive, MAGIC-MT neutral; dexamethasone recurrence harmful (DEX-CSDH)
Lacunar infarct <15 mm deep infarct; microatheroma or LACI-2 (2023): isosorbide mononitrate reduces lipohyalinosis; no cortical signs, no field defect recurrence and cognitive impairment; cilostazol reduces dependence SACD Posterior columns + lateral corticospinal tracts; NICE NG239 (2024): IM hydroxocobalamin brisk knees, absent ankles, extensor plantars immediately in neurological disease; nitrous oxide SACD Motor neuron disease Mixed UMN + LMN in one region; eyes, sphincters Tofersen approved for SOD1-ALS; AMX0035 and sensation spared; riluzole + NIV prolong withdrawn (2024); Gold Coast criteria survival Peripheral neuropathy 11% over 55; diabetes 44%; NCS/EMG is the initial Test for hATTR in progressive "idiopathic" study in unexplained cases neuropathy; screen for DPN at diagnosis of T2DM Neuritic pain Lesion or disease of the somatosensory nervous Suzetrigine (Nav1.8 inhibitor), FDA-approved system; NNT 3.6 TCA, 7.7 pregabalin January 2025; OPTION-DM supports combination Carotid stenosis NASCET method; image within 24 h; CEA within 7 CREST-2 (NEJM 2025): in asymptomatic ≥70%, days for symptomatic 50–99% stenting helped, CEA did not Bedside swallow 78% dysphagic after stroke; gag reflex unreliable; Screen within 4 hours, before any oral intake; use water → purée → solids; watch for wet gurgly voice GUSS or Yale; oral care not antibiotics Visual impairment 75% unreported; cataract, glaucoma, AMD, diabetic Lancet Commission 2024: vision loss is a retinopathy; cataract surgery lowers hip fracture modifiable dementia risk factor; LiGHT — SLT risk first-line for glaucoma Macular degeneration Macula depends on choriocapillaris; CFH + Pegcetacoplan and avacincaptad approved 2023 LOC387715 give 50-fold risk; metamorphopsia; refer for GA — but no functional benefit and rejected for rehabilitation by EMA Heat stroke >40.6°C + CNS dysfunction + anhidrosis; mortality SCCM 2025: cool to <39°C within 30 minutes; up to 80%; cool to 38.9°C within 1 hour "cool first, transport second"; India NPCCHH/IHIP reporting Heat exhaustion <40°C, sweating preserved, sensorium intact; the Distinct case definition and first aid under India's reversible stage before heat stroke National Action Plan on Heat Related Illnesses Prepared from Pathy's Principles and Practice of Geriatric Medicine (6th edition) and Essentials of Clinical Geriatrics (7th edition) as primary sources, supplemented with peer-reviewed literature and guidelines published between 2023 and 2026. Where the textbook position and current evidence differ, the difference is set out explicitly in the Current Practice Update table for that question.
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References
- PAPERS-2-3-4_COMBINED.pdf — page 611
- GeriQBank source PDF — p. 611
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