Drowning

Introduction

Australia, the driest inhabited continent, has one of the highest reported incidences of drowning in the developed world. It is a major cause of death and disability in youths with peaks in young children and young adult males. Nomenclature and definitions are now generally agreed with all respiratory distress (of any level, e.g. cough, wheeze, rales) from immersion or submersion defined as drowning (fatal or non-fatal).

Good outcomes are mainly determined by pre-hospital factors, particularly witnessed drowning, short immersion times, early cardiopulmonary resuscitation (CPR), prehospital signs of life, and early access to emergency medical services (EMS). An accurate history, well-run resuscitation and informed judgement on prognosis will optimize outcomes, resource use and aid patient management and family interactions. Patients with spontaneous respiration and/or neurological responsiveness on arrival in the emergency department (ED) are expected to recover unless acute respiratory distress syndrome (ARDS) supervenes. Treatment after a non-fatal drowning is mainly supportive, although extracorporeal membrane oxygenation (ECMO) and direct lung therapy may improve future outcomes.

In many areas, preventative and educative measures (e.g. pool fencing, life vests, life guards, boat licensing) have reduced fatality rates dramatically. Emergency physicians should be strong advocates for these initiatives.

Epidemiology

Rates of drowning have significantly declined worldwide over the last 2 to 3 decades but it is still a major cause of death and disability in young populations. Overall, males drown more frequently, in most age groups with ratios up to 9:1. This seems to have declined recently with ratios around 2 to 4:1. Groups with highest rates of drowning include infants 0 to 4, (up to 10× higher than 5 to 15, particularly males), young adult males (15 to 30 years), epileptics (up to 20× higher), overseas visitors, the mentally disabled and those from deprived/under-resourced communities with poor public health initiatives. More recently, richer populations are over-represented in countries with high rates of home pools. In young adult males, bravado, inexperience and alcohol lead to many deaths. Alcohol is found in 14% to 60% of adult drownings. The majority of male adult drownings are related to recreational activities. In the elderly, underlying medical illnesses and suicide attempts are more frequently seen. Most of these factors (except age) are associated with worse outcomes. Cold water has been associated with worse outcomes overall (shorter time to submersion in icy waters), although very occasionally younger patients may survive prolonged immersions potentially by rapid brain cooling.

The ratio of those who initially survive (but require medical attention) to fatal drownings is not accurately known because of differences in nomenclature, definitions and the inability to collect all attendances related to drowning, but is estimated at between 2 and 20:1. In a well-conducted observational study from the Netherlands, the ratio of patients admitted to the intensive care unit (ICU) following drowning compared with those who died before admission was 2:1.

Prevention

Prevention of drowning is a major area for ongoing research and an area emergency physicians should strongly advocate for preventative strategies of proven benefit. Marked reductions in drowning rates in developed countries are suggestive prevention works.

Patrolled beaches with shorter submersion times, early, good quality CPR with assisted breathing and early EMS activation are associated with better outcomes. Important educational initiatives include early swimming/survival lessons, CPR training, parental supervision of children, using supervised swimming areas, avoiding mixing alcohol and water activities and appropriate water safety equipment. Protective pool fencing, enforcement of water vehicle alcohol laws, and water and safety regulations enforcement for water activity are also important.

Definitions and terminology

Much confusion has been caused in research and management by imprecise definitions. Phrases commonly used have been near-drowning, dry, wet, active, passive or silent, late or secondary drowning, immersion, submersion, suffocation and asphyxia. Most of these were ill defined and confusing.

In 2015, ILCOR concurred on the Utstein style definition: drowning is a process resulting in primary respiratory impairment from submersion/immersion in a liquid medium. Implicit in this definition is that a liquid/air interface is present at the entrance of the victim's airway, preventing the victim from breathing air. The victim may live or die after this process, but whatever the outcome, he or she has been involved in a drowning incident.

‘Near-drowning’ is redundant as drownings are either fatal or non-fatal. Similarly, ‘wet’ and ‘dry’ drownings are redundant as all drowning is wet with differing amounts of aspiration. Descriptions by bystanders for activity in drowning are now only described as ‘witnessed’ and ‘unwitnessed’ drowning, according to whether or not entry to the water was observed. The term ‘secondary drowning’ was used to describe both causative problems drowning (e.g. intoxication, illness) or death due to secondary problems (e.g. ARDS, encephalopathy) and was inherently confusing. Therefore precipitating factors or sequelae should be specifically described. Immersion describes any is the inability to maintain a fluid-free airway interface, whereas submersion implies the whole airway is underwater. They are rarely important distinctions for management or epidemiology.

Pathophysiology

The sequential pathophysiology of drowning is well described:

• Initial submersion/immersion leads to voluntary apnoea if drowning is due to initial loss of consciousness (e.g. cardiac arrhythmia or other catastrophic illness). Unless voluntary, most adult victims panic and struggle, with spitting or expulsion of fluid from nasal and oral cavities with associated increases in blood pressure (BP) and pulse rate (PR). Slow PR may occur secondary to primitive dive reflexes or cold-induced reflex brady arrhythmias, particularly in children or intoxicated adults, in cold water and late on in drownings.

• After an interval dependent on presubmersion oxygenation, intoxication, injuries, illness, fitness and the degree of panic and struggle, synergistic hypercapnia and hypoxia lead to an involuntary breath known as the ‘breaking point’, normally reached in under a minute. During this stage, large quantities of water are often swallowed/aspirated. If an individual hyperventilates before diving (a highly dangerous activity), plasma CO ₂ concentrations may remain so low that hypoxic unconsciousness occurs before the breaking point is reached. This is known as ‘shallow water blackout’.

• Fluid inhalation causes sudden increases in airway pressures, bronchoconstriction, pulmonary hypertension and shunting. In 10% to 20%, laryngospasm reduces further aspiration, with a mucus and foam plug forming (previously called ‘dry drowning’).

• Secondary apnoea occurs, closely followed by unconsciousness.

• Involuntary gasping respirations lead to lungs flooding and alveolar injury, surfactant loss, increased ventilation/perfusion (V/Q) mismatch, shunting and hypoxia. Vomiting of swallowed fluid is common, potentially causing pulmonary aspiration.

• Hypoxia causes marked bradycardia, hypotension and irreversible brain injury within 3 to 10 min (except occasionally in icy water induced rapid hypothermia), culminating in respiratory or cardiorespiratory arrests. In fatal drownings, the average lung fluid retrieved is 3 to 4 mL/kg, less than 10% of lung volume. However, the effect on the lungs is dramatic. Experimentally, fresh water and sea water cause alveolar injury by different mechanisms. Fresh water denatures surfactant and damages the alveolar cells. Sea water tends to draw in fluid, wash out surfactant and cause foam formation. Aspirated vomitus and/or chemicals may further complicate the clinical picture. Soap and chlorine in water do not appear to affect outcome. Clinically, the type of water inhaled rarely makes a difference, unless grossly polluted. Electrolyte disturbances are normally minimal and transient except in prolonged arrests, owing to the small volumes aspirated (more than 20 mL/kg are required for major disturbances).

Clinical features and organ-specific effects