About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Drowning: primary problem is HYPOXIA — give rescue breaths early (5 initial breaths before compressions)
- Hypothermia classification: mild (32–35°C), moderate (28–32°C), severe (<28°C). Below 30°C: risk of VF
- "Not dead until warm and dead" — continue CPR in hypothermic arrest until core temp ≥32°C or rewarming fails
- Rewarming: mild → passive (warm blankets, warm environment). Moderate/severe → active external (forced warm air, e.g. Bair Hugger) and/or active internal (warm IV fluids 40°C, peritoneal/pleural lavage, ECMO)
- Hypothermic VF: defibrillate up to 3 times. If VF persists at <30°C, withhold further shocks and adrenaline until core temp >30°C
- Measure core temperature: oesophageal probe (most accurate) or rectal. Tympanic and axillary are unreliable in severe hypothermia
Overview
Drowning is defined as the process of experiencing respiratory impairment from submersion or immersion in liquid. It is a leading cause of accidental death worldwide, particularly in children under 5 and young males. The primary pathophysiology is hypoxia from aspiration and laryngospasm, leading to pulmonary oedema, surfactant washout, and ARDS. Hypothermia is defined as a core body temperature below 35°C and is classified as mild (32–35°C), moderate (28–32°C), or severe (<28°C). Causes include environmental exposure (cold water immersion, outdoor exposure), trauma, sepsis, hypothyroidism, and drug/alcohol intoxication. Below approximately 30°C, the myocardium becomes increasingly irritable and vulnerable to VF. However, hypothermia also provides some neuroprotective effect by reducing cerebral metabolic demand — hence prolonged CPR may achieve good outcomes.
Epidemiology
There are approximately 400 deaths from drowning per year in the UK. It is the third leading cause of unintentional injury death globally. Males are at 2–4× higher risk. Cold water shock (sudden immersion in cold water causing gasp reflex, tachycardia, and incapacitation) contributes to many drowning deaths in the UK. Accidental hypothermia affects approximately 1,000 patients presenting to UK hospitals annually, though mild hypothermia is likely significantly underreported. Elderly, homeless, and intoxicated individuals are at highest risk. Hypothermic cardiac arrest has survival rates of 50% or higher with appropriate prolonged resuscitation and rewarming.
Clinical Features
Symptoms
Drowning: witnessed or reported submersion/immersion. Coughing, choking, respiratory distress
Hypothermia mild (32–35°C): shivering, confusion, tachycardia, hyperventilation
Hypothermia moderate (28–32°C): decreased consciousness, shivering stops, bradycardia, hypotension
Hypothermia severe (<28°C): coma, absent reflexes, VF or asystole, appears dead
Signs
Drowning: cyanosis, tachypnoea/apnoea, pulmonary crackles (aspiration/oedema), reduced GCS, cardiac arrest
Hypothermia: core temperature <35°C on reliable thermometer
Cold, pale skin. Paradoxical undressing in moderate hypothermia
Bradycardia (progressive with temperature drop). Atrial fibrillation common at 28–32°C. VF below 28°C
Osborn (J) waves on ECG — positive deflection at J point, pathognomonic but not always present
Muscle rigidity (may mimic rigor mortis in severe hypothermia)
Investigations
First-line
Core temperatureOesophageal probe (gold standard in intubated patients) or low-reading rectal thermometer. Standard tympanic/oral thermometers are unreliable <32°C
ECGBradycardia, prolonged intervals, Osborn J waves, AF, VF, asystole
ABGHypoxia, acidosis, lactate. In hypothermia: temperature-corrected values vs uncorrected — use alpha-stat (uncorrected) for management
Second-line
FBC, U&Es, clotting, glucoseHypothermia causes coagulopathy, electrolyte derangements (hyperkalaemia), hypoglycaemia
CXRDrowning: pulmonary oedema, aspiration. May be initially normal — delayed ARDS
Serum potassiumK⁺ >12 mmol/L in hypothermic arrest = non-survivable (indicates prolonged cellular death before cooling)
Specialist
CT head/C-spineIf traumatic mechanism (diving injury, fall into water) or prolonged submersion with potential anoxic brain injury
1
Drowning rescue and resuscitation
- Ensure rescuer safety — do not enter water unless trained. Call 999. Reach/throw/wade before swimming
- Remove from water as soon as safely possible. Assume cervical spine injury if diving/fall mechanism
- Give 5 initial RESCUE BREATHS (hypoxia is the primary problem — ventilation is priority)
- Then standard 30:2 CPR. Deliver breaths even in water if trained (before extraction)
- Expect vomiting (aspiration of water) — turn to side to drain, suction if available
- All submersion victims should be assessed in hospital (risk of delayed pulmonary oedema/ARDS)
2
Hypothermia management
- Mild (32–35°C): passive rewarming — remove wet clothing, warm blankets, warm environment. Target rewarming rate 0.5–1°C/h
- Moderate (28–32°C): active external rewarming — forced warm air blanket (Bair Hugger), warm IV fluids (40°C). Handle gently (rough handling can trigger VF)
- Severe (<28°C): active internal rewarming — warm IV fluids, warm humidified oxygen, peritoneal/pleural lavage with warm fluid. Consider ECMO if available and in cardiac arrest
- Avoid rough handling, IV insertion to central veins (risk of triggering VF)
- Warmed fluids: all IV fluids warmed to 38–40°C
3
Hypothermic cardiac arrest
- "Not dead until warm and dead" — continue CPR
- Attempt defibrillation up to 3 times. If VF persists at core temp <30°C: withhold further shocks until temp >30°C
- Withhold adrenaline below 30°C (ineffective and accumulates). Give at double the normal interval (6–10 min) between 30–35°C
- Rewarm towards 32°C — if VF persists after rewarming, follow standard ALS algorithm
- Consider ECMO/cardiopulmonary bypass for refractory hypothermic arrest (best outcomes)
- Continue CPR for prolonged period — good neurological outcomes reported after hours of CPR in hypothermia
Complications
- ARDS: Pulmonary oedema and surfactant washout from aspiration — may develop hours after submersion ("secondary drowning")
- Hypoxic brain injury: Leading determinant of outcome in drowning survivors
- Cardiac arrhythmias: VF (especially <28°C), bradycardia, asystole. Afterdrop phenomenon: continued core cooling after rescue → VF
- Coagulopathy: Hypothermia impairs clotting cascade — clinically significant below 35°C
- Rhabdomyolysis: From prolonged immobility and cold exposure
- Rewarming complications: Afterdrop (paradoxical core temperature fall during rewarming), rewarming shock (peripheral vasodilation → hypotension)
UKMLA Exam Tips
- 1Drowning CPR: 5 initial BREATHS (not compressions) — hypoxia is the primary mechanism. Different from standard BLS
- 2"Not dead until warm and dead" — do not declare death in hypothermic arrest until rewarmed to ≥32°C
- 3Osborn (J) waves on ECG: positive deflection at J point — classic hypothermia finding. Not always present
- 4Below 30°C: limit to 3 shocks, withhold adrenaline. These drugs are ineffective in cold myocardium
- 5Serum K⁺ >12 mmol/L in hypothermic arrest suggests cellular death occurred before cooling — non-survivable
- 6Afterdrop: core temperature continues to fall after removal from cold (cold peripheral blood returns to core). Handle gently
- 7All near-drowning survivors need hospital observation — risk of delayed pulmonary oedema (secondary drowning) for 24 h
practicetest your knowledge on drowning & hypothermiaApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — emergency medicine and beyond.
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