Drowning and immersion injury

Abstract

Drowning is a frequent cause of accidental deaths and injuries, resulting in a significant but preventable global health problem. It is characterized by respiratory impairment due to submersion of the airway, or immersion of the body including the airway, leading to global hypoxic injury. Risk factors for drowning include inadequate supervision of children, recreational or occupational access to water, risk-taking behaviour and underlying medical conditions. Management priorities include rescue and basic life support, with an emphasis on rescue breaths and reversal of hypoxia. Supportive critical care is directed towards optimizing oxygenation and circulation, and preventing complications. Temperature control is important, as hypothermia complicates drowning and may limit the efficacy of resuscitative attempts when severe. Survival rates after cardiac arrest due to drowning are poor, and patients who are unconscious on admission to hospital have a guarded prognosis. Public health initiatives are important to prevent drowning.

Learning objectives

After reading this article, you should be able to:

•

describe the epidemiology and pathophysiology of drowning
•

state the management priorities of drowning
•

identify the complications and prognostic factors after drowning

Definition

‘Drowning is a process resulting in primary respiratory impairment from submersion/immersion in a liquid medium. The victim may live or die after this process, but whatever the outcome, he or she has been involved in a drowning incident’. The terms near-drowning, wet and dry drowning and secondary drowning are no longer recommended.

Epidemiology ^,

According to the World Health Organization (WHO), drowning is the third leading cause of unintentional injury deaths worldwide, with an estimated annual incidence of over 372,000 deaths. Over 90% of these deaths occur in low-and middle-income countries, while in developed countries, it is responsible for 1.0–1.8 deaths per 100,000 per year.

Young people and in particular children under the age of 5 years are at the greatest risk of drowning, although children may also have a higher rate of rescue. Males have a two to four times higher rate of drowning than females, and tourists have a higher risk than locals. Intoxication with drugs and alcohol contributes to 10–30% of drownings. Individuals over the age of 65 years are at increased risk of fatal drowning due to the occurrence of falls and the prevalence of medical comorbidities.

Natural waterways, such as lakes, rivers and beaches are frequent locations of fatal drownings. Entrapment in submerging vehicles is another mechanism, with escape becoming more difficult as the vehicle becomes submerged.

Medical conditions associated with an increased risk of drowning include arrhythmias, long QT syndrome, cardiomyopathies, coronary artery disease, cerebrovascular disease, diabetes mellitus and depression. Epilepsy increases the risk of drowning, possibly up to ten times.

Factors affecting survival include water temperature, submersion duration, whether the drowning was witnessed, adequacy of cardiopulmonary resuscitation (CPR), time to arrival of the emergency medical services (EMS), and the initial cardiac rhythm upon EMS arrival. Strategies to prevent drowning are listed in Box 1 .

Box 1

Preventative measures proposed by the World Health Organization

1.

Install barriers controlling access to water
2.

Provide safe places (eg. a creche) away from water for preschool children, with capable child care
3.

Teach school-age children basic swimming, water safety and safe rescue skills
4.

Train bystanders in safe rescue and resuscitation
5.

Strengthen public awareness and highlight the vulnerability of children
6.

Set and enforce safe boating, shipping and ferry regulations
7.

Build resilience and manage flood risks and other hazards locally and nationally
8.

Coordinate drowning prevention efforts with those of other sectors and agendas
9.

Develop a national water safety plan
10.

Address priority research questions with well-designed studies

Pathophysiology

Following submersion or immersion there is respiratory impairment leading to panic and voluntary and involuntary efforts to shout, swim, restore ventilation and prevent aspiration. This causes increased metabolic demand, lactic acidosis and water swallowing.

After submersion there is breath-holding, until the hypercapnic respiratory drive becomes impossible to voluntarily overcome. This leads to respiratory muscular movement, with or without opening the airway. Eventually hypoxia leads to loss of consciousness and release of laryngospasm, followed by cardiac arrest. Cardiac arrest and hypoxic brain injury are the major causes of death and disability following drowning.

Airway

Liquid entering the mouth, pharynx and larynx triggers voluntary and involuntary responses including swallowing, coughing, and the pharyngo-glottal closure reflex, as well as laryngospasm and bronchospasm. These protective responses cease upon either loss of consciousness or laryngeal muscle hypoxia.

Breathing

Hypoxia is the mechanism of morbidity and mortality following drowning.

The duration of breath-holding is highly variable, and the ability to breath-hold is adversely affected by factors such as the increased metabolic demand from struggling, alcohol intoxication and cold-water immersion. Near the limit of breath-holding there is involuntary contraction of the respiratory musculature which, against a closed glottis, can lead to barotrauma, pulmonary oedema or swallowing of liquid. Not all drowning victims aspirate liquid.

Aspirated saltwater may draw fluid into the alveoli, whereas fresh water is largely absorbed into the circulation. The volumes of water aspirated are believed to be small (3–4 ml/kg), and are unlikely to cause clinically significant cardiovascular fluid shifts. Both fresh and saltwater can cause surfactant washout, leading to atelectasis and alveolar damage similar to acute respiratory distress syndrome (ARDS). This results in increased pulmonary shunt.

Cardiovascular and autonomic nervous systems

The initial response to drowning is panic, leading to increased sympathetic tone, with increased heart rate, peripheral vasoconstriction and increased metabolic demand.

With onset of breath-holding, parasympathetic drive overtakes the sympathetic response, especially in cold water. The concept of ‘autonomic conflict’, where there are competing positive and negative chronotropic signals to the heart, has been linked to arrythmias but these are predominantly supraventricular and rarely fatal. Observed fatal arrythmias are usually pulseless electrical activity (PEA) or asystole. An initial ‘shockable’ rhythm (ventricular fibrillation or ventricular tachycardia) is present in only about 5% of cases, although ventricular fibrillation may be precipitated by movement of the victim.

The interaction between the diving response and drowning physiology is incompletely understood. Immersion of the head, especially in cold water, causes bradycardia, peripheral vasoconstriction, decreased oxygen demand and increased cerebral perfusion pressure. This response has been hypothesized to lead to vagally mediated cardiac arrest.

Swallowing and emesis

There is little data regarding water swallowing and its physiological implications. Between 25% and 86% of drowning victims will vomit, and around 24% who die will have aspirated gastric contents. It should be noted that emesis occurs in 30–35% of cardiac arrests of all causes and is not specific to drowning.

Electrolytes

The small amounts of either fresh or salt water aspirated or ingested during drowning do not generally cause clinically significant electrolyte changes although prolonged salt-water immersion may cause hypernatraemia. Acute kidney injury may develop as a consequence of the hypoxic and hypoperfusion injuries.

Temperature

The majority of drownings occur in water below the thermoneutral temperature of 35°C, leading to various degrees of hypothermia.

The cold shock response occurs in water below 25°C and can override voluntary attempts at swimming to safety or breath-holding. Sub-epidermal temperature sensors cause gasping and hyperventilation, increased cardiac output and peripheral vasoconstriction.

Deep tissue hypothermia is neuroprotective; however, there are significant differences between medically induced hypothermia and accidental hypothermia in drowning. In submersion, superficial cooling occurs first and the resultant muscle weakness and slowed nerve conduction can cause physical incapacitation long before core temperature falls below 35°C.

As the core temperature drops, there is a predictable progression of symptoms: shivering, confusion, amnesia, cardiac arrythmia, loss of consciousness, ventricular fibrillation and death. Below a core temperature of 28°C spontaneous cardiac arrest is possible and decreased cerebral metabolism will render the patient deeply unconscious, possibly with absent deep tendon reflexes and fixed dilated pupils mimicking death.

Conversely, hot water drowning can occur, for example in the tropics or in hot springs. Typically, there is significant peripheral vasodilation and tachycardia. Drowning in hot water most often occurs when trying to stand up out of the water. Loss of the external hydrostatic pressure leads to hypotension and can cause loss of consciousness.

Infective complications

Pneumonia may complicate up to 50% of drownings. The source of respiratory infections may be oropharyngeal secretions, vomitus or contamination in the water itself. Less commonly, fungal infections or delayed central nervous system infections may occur in immunocompromised patients. Empiric antibiotics may be considered in patients at high risk of pneumonia. Common infective organisms are summarized in Box 2 .

Box 2

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