eMedicine Specialties > Emergency Medicine > Environmental

Drowning

Author: Suzanne Moore Shepherd, MD, MS, DTM&H, FACEP, FAAEM, Associate Professor, Department of Emergency Medicine, Hospital of the University of Pennsylvania; Director of Education and Research, PENN Travel Medicine
Coauthor(s): William H Shoff, MD, DTM&H, Director, PENN Travel Medicine, Associate Professor, Department of Emergency Medicine, Hospital of the University of Pennsylvania
Contributor Information and Disclosures

Updated: Jun 9, 2009

Introduction

Background

Drowning is a significant cause of disability and death. Drowning has been previously defined as death secondary to asphyxia while immersed in a liquid, usually water, or within 24 hours of submersion. At the 2002 World Congress on Drowning, held in Amsterdam, a group of experts suggested a new consensus definition for drowning in order to decrease the confusion over the number of terms and definitions (>20) referring to this process that have appeared in the literature.¹ The group believed that a uniform definition would allow more accurate analysis and comparison of studies, allow researchers to draw more meaningful conclusions from pooled data, and improve the ease of surveillance and prevention activities.

The new definition states that drowning is a process resulting in primary respiratory impairment from submersion in a liquid medium. Implicit to this definition, is that a liquid-air interface is present at the victim's airway. Outcome may include delayed morbidity or death, death, or life without morbidity. The terms wet drowning, dry drowning, active or passive drowning, near-drowning, secondary drowning, and silent drowning would be discarded.

The classic image of a victim helplessly gasping and thrashing in the water rarely is reported. A more ominous scenario of a motionless individual floating in the water or quietly disappearing beneath the surface is more typical.

Pathophysiology

The principal physiologic consequences of drowning are prolonged hypoxemia and acidosis and the multiorgan effects of these processes.

After initial gasping and possible aspiration, immersion stimulates hyperventilation, followed by voluntary apnea and a variable degree and duration of laryngospasm. This leads to hypoxemia.

Depending upon the degree of hypoxemia and resultant acidosis, the person may develop myocardial dysfunction and electrical instability, cardiac arrest, and central nervous system (CNS) ischemia. Asphyxia leads to relaxation of the airway, which permits the lungs to take in water in many individuals (previously referred to as "wet drowning"), although most patients aspirate less than 4 mL/kg of fluid. Approximately 10-20% of individuals maintain tight laryngospasm until cardiac arrest occurs and inspiratory efforts have ceased. These victims do not aspirate any appreciable fluid (previously referred to as "dry drowning"). Most individuals are found after having been submerged in liquid for an unobserved period of time. Ingestion of large volumes of freshwater, rather than aspiration, is the likely cause of clinically significant electrolyte disturbances, such as hyponatremia, in children after drowning.

In young children suddenly immersed in cold water (<20°C), the mammalian diving reflex may occur and produce apnea, bradycardia, and vasoconstriction of nonessential vascular beds with shunting of blood to the coronary and cerebral circulation.

The target organ of submersion injury is the lung. Aspiration of 1-3 mL/kg fluid leads to significantly impaired gas exchange. Injury to other systems is largely secondary to hypoxia and ischemic acidosis. Additional CNS insult may result from concomitant head or spinal cord injury. Fluid aspirated into the lungs produces vagally mediated pulmonary vasoconstriction and hypertension. Fresh water moves rapidly across the alveolar-capillary membrane into the microcirculation. Surfactant is destroyed, producing alveolar instability, atelectasis, and decreased compliance with marked ventilation/perfusion (V/Q) mismatching. As much as 75% of blood flow may circulate through hypoventilated lungs.

In salt water drowning, surfactant washout occurs, and protein-rich fluid exudates rapidly into the alveoli and pulmonary interstitium. Compliance is reduced, alveolar-capillary basement membrane is damaged directly, and shunting occurs. This results in rapid induction of serious hypoxia. Fluid-induced bronchospasm also may contribute to hypoxia. The distinction between fluid type is somewhat academic, as other than epidemiologic importance, the initial treatment is similar.

Frequency

United States

More than 8,000 deaths are due to drowning annually in the United States, with 1,500 of these deaths occurring in children. In 2005, the Centers for Disease Control and Prevention reported that 3,582 unintentional fatal drownings occurred in the United States.⁶ This averages to 10 deaths per day. Approximately one quarter of these deaths occur in children 14 years or younger. Four times as many children receive emergency department care for nonfatal injuries for every child that dies. In fact, a bimodal distribution of deaths is observed, with an initial peak in the toddler age group and a second peak in adolescent to young adult males.

In the toddler group, most incidents occur in bathtubs and swimming pools. In the adolescent and young adult groups (aged 15-24 y), most incidents occur in natural bodies of water. For every death from drowning, an estimated 4 individuals are hospitalized and 14 individuals visit the ED.

In 2005, of all children aged 1-4 years who died, almost 30% died from drowning. Despite preventative measures, the 2006 NationalCenter for Injury Prevention and Control statistics noted drowning to be second only to motor vehicle collisions as the most common cause of death in children aged 1-14 years.⁷ Morbidity from submersion occurs in 12-27% of survivors in this age group. Preschool-aged boys are at greatest risk of submersion injury. A survey of 9420 primary school children in South Carolina estimated that approximately 10% of children younger than 5 years had an experience judged a "serious threat" of near drowning. Residential swimming pools are the most common submersion site in this age group.^8,9

An additional 1,200 reported immersion deaths are boating related (90% of boating deaths), 500 are motor vehicle associated, and 1,000 reported drownings are of undetermined etiology. Studies in a number of countries with active fishing industries have targeted drowning for injury control and prevention. 

Scuba diving accounts for an estimated 700-800 deaths per year (etiologies include inadequate experience/training, exhaustion, panic, carelessness, and barotrauma). Denoble et al studied 947 recreational diving accidents from 1992-2003, during which 70% of the victims drowned. Drowning was usually secondary to a disabling injury, equipment problems, problems with air supply, and cardiac events in these individuals.¹⁰

Submersion-related injuries are the fifth leading cause of accidental death in the United States in all age groups; incidence is approximately 2.5-3.5 per 100,000 population. California reports approximately 25,000 ocean rescues on its beaches each year. However, true incidence of near drowning has yet to be defined accurately, since many cases are not reported.

International

Annually, approximately 150,000 deaths are reported worldwide from drowning, with an annual incidence probably closer to 500,000. Several of the most densely populated nations in the world fail to report near-drowning incidents. This, along with the fact that many cases are never brought to medical attention, renders accurate worldwide incidence approximation virtually impossible.

The incidence of near drowning has an estimated range of 20-500 times the rate of drowning.

A Danish occupational medical study of 114 drowning fatalities in the period 1989-2005 among fishing industry seamen, found that approximately one half of the deaths occurred during vessel disasters in rough weather, with capsizing and foundering, or collisions. One third occurred during other occupational accidents that caused the victim to go overboard. One third occurred when the victim underwent difficult disembarkation during nighttime hours in foreign ports or was intoxicated.¹¹

A recent Canadian study of drowning during work-related and recreational helicopter crashes over water also focused on factors that increased the likelihood of death, especially in settings with limited warning time. The authors found that educational strategies to increase survival likelihood included wearing survival gear during the trip, prior escape training, ensuring that crew and passengers possessed appropriate knowledge of escape routes, and assuming appropriate crash positioning. They suggested that companies using helicopter transport over water should focus on regular and repeated safety training and improvement in safety measures on helicopters.¹²

Mortality/Morbidity

Morbidity and death in immersion injuries are due primarily to laryngospasm and pulmonary injury, resulting hypoxemia and acidosis, and their effects on the brain and other organ systems.

Prevention is as important as any measures that can be taken after the fact.

• A high risk of death exists secondary to the development of adult respiratory distress syndrome (ARDS), which has been termed postimmersion syndrome or secondary drowning. Morbidity is due to neurologic insult as well as to multiple organ system failure.
• The adult mortality rate is difficult to quantify because of poor reporting and inconsistent record keeping.
• Thirty-five percent of immersion episodes in children are fatal; 33% result in some degree of neurologic impairment and 11% in severe neurologic sequelae.

In 2002, per CDC data, approximately 2,822 individuals are treated for drowning in US Emergency Departments.

Race

The overall rate of drowning for African American children is 1.7 times higher than that for white children; however, the relative rates vary with age.

• African American children aged 0-4 years exhibit a lower rate of drowning (2.32 per 100,000), probably secondary to less pool access.
• In older pediatric age groups, the incidence is 2-5 times higher.

Sex

• Male-to-female ratios are approximately 12:1 for boat-related drownings and 4:1 for non–boat-related drownings.
• Only in bathtub incidents do girls predominate in incidence.

Age

Peak incidences of submersion injury occur in the following 2 age groups:

• Children younger than 4 years
• Young adults aged 15-24 years

Clinical

History

• Typical incidents involve a toddler left unattended temporarily or under the supervision of an older sibling, an adolescent found floating in the water, or a victim diving and not resurfacing. Less typically, submersion injury may be a deliberate form of child abuse, including Munchhausen syndrome by proxy.
• The age of the victim, submersion time, water temperature, water tonicity, degree of water contamination, symptoms, associated injuries (especially cervical spine and head), presence of co-ingestants, underlying medical conditions, type and timing of rescue and resuscitation efforts, and response to initial resuscitation are all relevant factors.
  • Thermal conduction of water is 25-30 times that of air. The temperature of thermally neutral water, in which a nude individual's heat production balances heat loss, is 33°C.
  • Physical exertion increases heat loss secondary to convection/conduction up to 35-50% faster.
  • A significant risk of hypothermia usually develops in water temperatures less than 25°C, which is the temperature found in most US natural waters during the majority of the year.
  • During immersion in ice water, a subject will become hypothermic in approximately 30 minutes. Cooling at this temperature becomes life-threatening in approximately 60 minutes.¹³
• Other important historical factors include the following:
  • Shortness of breath, difficulty breathing, apnea
  • Persistent cough, wheezing
  • In stream, lake, or salt water immersion, possible aspiration of foreign material, or exposure to fungi, bacteria, and other microorganisms
  • Level of consciousness at presentation, history of loss of consciousness, anxiety
  • Vomiting, diarrhea
  • Coincident alcohol or drug use
  • Pertinent past medical history, particularly seizure disorder, diabetes mellitus, psychiatric history, severe arthritis, or neuromuscular disorder - A United Kingdom study examined the risk of drowning in individuals with epilepsy and found the risk increased 15 to 19 fold.¹⁴
• Bradycardia or tachycardia, dysrhythmia

Physical

A victim of a submersion incident may be classified initially into 1 of the following 4 groups:

• Asymptomatic
• Symptomatic
  • Altered vital signs (eg, hypothermia, tachycardia, bradycardia)
  • Anxious appearance
  • Tachypnea, dyspnea, or hypoxia: If dyspnea occurs, no matter how slight, the patient is considered symptomatic.
  • Metabolic acidosis (may exist in asymptomatic patients as well)
  • Altered level of consciousness, neurologic deficit
• Cardiopulmonary arrest
  • Apnea
  • Asystole (55%), ventricular tachycardia/fibrillation (29%), bradycardia (16%)
  • Immersion syndrome
• Obviously dead
  • Normothermic with asystole
  • Apnea
  • Rigor mortis
  • Dependent lividity
  • No apparent CNS function

Causes

• Bathtub drowning is most common in children younger than 1 year.
  • Most of these victims drown during a brief (<5 min) lapse in adult supervision.
  • Bathtub and pail drownings may represent child abuse; carefully examine the child for other evidence of injury, review the child's history for previous events, and review the details of the incident very carefully with the child's parent or guardian.
• In preschool-aged children, drownings occur most commonly in residential swimming pools.
  • Many residential pools have no physical barrier between the pool and the home.
  • Open gates are involved in up to 70% of drownings in cases involving fenced-in pools. Pools may also be accessed through unlocked windows when the pool area abuts the house.
  • As recently pointed out in 2 studies from Australia (water tank drowning)¹⁵ and Bangladesh (ditches, canals, and ponds)¹⁶ , water exposure is both culturally and geographically related. Limiting access to these areas was again cited as an important target for prevention strategies.
• Young adults typically drown in ponds, lakes, rivers, and oceans. Approximately 90% of drownings occur within 10 yards of safety.
  • Cervical spine injuries and head trauma, which result from diving into water that may be shallow or contain rocks and other hazards, have been implicated.
  • Alcohol and, to a lesser extent, other recreational drugs are implicated in many cases. Australian, Scottish, and Canadian data showed that 30-50% of older adolescents and adults who drowned in boating incidents were inebriated, as determined by blood alcohol concentrations.
• Consider underlying disease/illness in all age groups.
  • Seizure disorder
  • Myocardial infarction (MI) or syncopal episode
  • Poor neuromuscular control, such as that seen with significant arthritis, Parkinson disease, or other neurologic disorders
  • Major depression/suicide - A recent study by the European Alliance Against Depression reviewed gender-specific suicide methods in 16 European countries.¹⁷ They found that women were more likely to choose drowning as a suicide method. They suggested that gender-specific prevention strategies should be developed.
  • Anxiety/panic disorder
  • Diabetes, hypoglycemia
• Water sports hazards, especially with personal watercraft
  • Poor judgment and substance abuse (alcohol or other recreational drugs) in conjunction with boat operation
  • Cervical spine injury and head trauma associated with surfing, water skiing, and jet skiing
  • Scuba diving accidents and other injuries (eg, bites, stings, lacerations)

• Search for CME/CE on This Topic »

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