Drowning — SAQ

Stem

A 19-year-old man is pulled from a river after a witnessed submersion of approximately 8 minutes. Bystanders began basic life support at the scene. On arrival in the emergency department he is unconscious (GCS 3), apnoeic, with pink frothy secretions in his mouth and around the endotracheal tube the paramedics have just inserted. He has no palpable central pulse. Cardiac monitoring shows a slow, wide complex rhythm at 25 per minute with no associated pulse (pulseless electrical activity). Core temperature (low-reading probe) is 29.2 degrees C. He smells of alcohol. There is no obvious external injury, but the mechanism is uncertain. His companion reports that he had been drinking heavily and dived into the river from a bridge. Blood gas (post-intubation, on 100 percent oxygen): pH 7.02, PaO2 52 mmHg, PaCO2 62 mmHg, bicarbonate 12 mmol/L, lactate 9.4 mmol/L. Chest X-ray shows bilateral diffuse alveolar infiltrates.

Questions

a) Give the current WHO definition of drowning and state the four words in it that examiners test. (2 marks)

Drowning is the process of experiencing respiratory impairment from submersion or immersion in liquid (the 2002 World Congress on Drowning definition, published by van Beeck et al. 2005 and now adopted by the WHO, ILCOR, AHA, and ERC). The four tested words are process (it is a continuum, not an event), respiratory impairment (the lung is the organ first injured — the primary problem is hypoxia, not circulation), submersion or immersion (submersion = the whole airway is under liquid; immersion = the face/airway is under liquid while the body may be supported), and liquid (usually water, but the definition covers any liquid). The outcome is recorded as fatal drowning, non-fatal drowning with morbidity, or non-fatal drowning without morbidity (a rescue). The terms 'near-drowning', 'dry drowning', 'wet drowning', and 'secondary drowning' are obsolete and must not be used.

b) Explain the mechanism by which drowning produces this clinical picture — the cardiac arrest rhythm, the lung infiltrates, and the acidosis. (3 marks)

This is a hypoxic (asphyxial) arrest. The submersion caused either laryngospasm (about 10 to 20 percent) or aspiration of water into the alveoli (about 80 to 90 percent); both converge on hypoxia. Aspirated water washes out and inactivates pulmonary surfactant, collapses alveoli (atelectasis), increases capillary permeability, and produces non-cardiogenic pulmonary oedema and ventilation-perfusion mismatch/shunt — the bilateral alveolar infiltrates and the refractory hypoxaemia on the blood gas. The resulting hypoxia progressively injures the myocardium: the heart first slows (bradycardia from the diving reflex and hypoxia) and finally arrests in asystole or pulseless electrical activity (PEA) — exactly the rhythm seen here. Ventricular fibrillation is uncommon as the presenting rhythm in drowning because the arrest is asphyxial, not primary cardiac; this is why ventilation must come before compressions. The combined respiratory and metabolic acidosis reflects CO2 retention from hypoventilation/apnoea plus a marked lactic acidosis from tissue hypoxia and shock — the base deficit and lactate are markers of the severity of the hypoxic insult and predict poor outcome.

c) Outline the immediate resuscitation, naming the drowning-specific modification to BLS and justifying it. (3 marks)

The defining drowning-specific modification is that ventilation comes before circulation. In a drowning cardiac arrest the standard sequence is:

1. 5 initial rescue breaths (each about 1 second, enough to produce chest rise) to oxygenate the flooded, collapsed, hypoxic alveoli — then 30 chest compressions to 2 breaths. This is the deliberate departure from the standard primary-cardiac-arrest sequence that begins with compressions, and it exists because the arrest is hypoxic: oxygenating the lung and blood must precede circulating it. (In this intubated patient, give continuous compressions with asynchronous ventilation at 10 breaths per minute.)
2. Continue high-quality CPR with minimal interruption; attach the defibrillator and shock only if a shockable rhythm (VF/pVT) appears — uncommon in drowning. Do NOT give adrenaline or further shocks if the core temperature is under 30 degrees C — the cold myocardium is unresponsive; rewarm first.
3. Oxygenate maximally — 100 percent oxygen via the endotracheal tube; this patient already has pulmonary oedema and ARDS, so he will need lung-protective mechanical ventilation (tidal volume 6 mL/kg ideal body weight, PEEP titrated, plateau pressure under 30 cmH2O) once ROSC is achieved.
4. Rewarm actively — he is at 29.2 degrees C (moderate-to-severe hypothermia). Use warmed IV fluids (39 degrees C), forced-air warming blanket, warmed humidified gases. "Not dead until warm and dead" — continue resuscitation until the core temperature is at least 32 degrees C and asystole persists. For hypothermic cardiac arrest under 28 degrees C with circulatory arrest, extracorporeal membrane oxygenation with extracorporeal rewarming is the method of choice if available.
5. Treat reversible causes — exclude and immobilise the cervical spine (he dived into a river — a concerning mechanism, so immobilise until cleared); check glucose; send bloods.

Why not start with compressions? Because in drowning the blood leaving the heart is desaturated; circulating desaturated blood through the brain and coronaries does more harm than good. Oxygenate first.

d) Name TWO manoeuvres that must NOT be performed, and ONE management decision that requires special caution because of his temperature. (2 marks)

Must NOT perform:

1. The Heimlich manoeuvre / abdominal thrusts — they do not remove significant water (water is in the alveoli, not the upper airway), they delay CPR, and they cause regurgitation, aspiration, and intra-abdominal injury. Water in the upper airway drains with the airway open and the patient on their side; do not delay CPR to "drain" the lungs.
2. Premature termination of resuscitation — in a hypothermic victim the rule "stop after 20 minutes of asystolic arrest" does NOT apply. He must be resuscitated and rewarmed to at least 32 degrees C before any decision to stop is made.

The management decision requiring special caution: defibrillation and drug dosing in hypothermia. At a core temperature under 30 degrees C the cold myocardium is electrically irritable and unresponsive — if a shockable rhythm appears, deliver up to 3 shocks, but if it does not convert, withhold further shocks and IV adrenaline until the core temperature is over 30 degrees C (interval between doses doubled between 30 and 35 degrees C). Continue CPR throughout rewarming; consider extracorporeal rewarming given he is in PEA arrest at 29.2 degrees C.

(Bonus mark-worthy point: given the uncertain mechanism and the alcohol, screen the cervical spine with CT once ROSC is achieved, and — because he is young and the drowning is partly unexplained — perform a 12-lead ECG once stable to check the QTc and screen for a channelopathy.)