Age

Young people have the highest likelihood of drowning. A bimodal age distribution characterizes drowning in children, with children less than 4 years old and adolescent males accounting for the peaks. There is an additional smaller peak later in life among persons who are more than 65 years old.¹⁸¹ In 2005, of all children between the ages of 1 and 4 years who died in the United States, 30% died from drowning.⁴⁰ High risk of drowning among children occurs as a result of poor swimming ability, large head-to-body ratio (increasing risk of head submersion), lack of barriers around pools and bathtubs, and poor supervision (especially of toddlers). Children in this age group are developmentally able to move independently, but lack the ability to recognize water hazards or effect self-rescue. Despite the American Academy of Pediatrics recommendation never to leave a child unsupervised in the bathtub, one study reported that nearly 33% of parents leave their children unattended in this setting.²⁰⁵ Children bathing with a sibling who was less than 2 years old with brief unsupervised time were reported to account for 22% to 58% of bathtub drowning deaths.³⁴ Drowning among adolescents and teenagers is often seen with risk-taking behaviors, lack of supervision, and drug and alcohol intake. The scene of drowning in this age group is most commonly a natural body of water, such as a lake, pond, or river. Incidents often occur far from medical assistance and may take place where rescue is challenging; however, these events are often witnessed.^{4,7,31,181,185} Among people who are more than 65 years old, deaths are evenly divided between open-water drowning and bathtub-related drowning, often from falls or exacerbations of concomitant illnesses (e.g., cardiac arrhythmias), which may not be recognized at autopsy.¹⁸¹

Gender

In 2005, males were four times more likely than females in all age groups to die from unintentional drowning in the United States.³⁸ Drowning among females peaks at 1 year of age and declines throughout the rest of life. It is speculated that this trend is the result of increased risk-taking behavior and greater alcohol consumption among adolescent males as compared with females. Worldwide, males have a higher mortality rate from drowning as compared with females in all age groups and regions.¹⁷⁵

Race

In the United States between 2000 and 2005, the rate of fatal drowning for blacks was 1.3 times higher than that of whites.⁴¹ The rate was 1.8 times higher than that of whites for Alaska natives and Native Americans.⁴⁰ In Alaska, drowning rates are twice as high among Native American children as compared with white and black children.⁶ In the 10- to 14-year-old age group, the fatal drowning rate for blacks is 3.2 times that of white children of the same age, and is 2.8 times higher for Alaska native and Native American children.³⁸ This pattern is reflected in the military, where black soldiers drown with a frequency of 62% greater than that of white soldiers.¹⁵ The reasons behind the racial differences in drowning rates are unclear, but factors such as decreased routine access to swimming pools, lower emphasis on swimming lessons, and less participation in recreational water-related activities are suspected.¹⁵² If, overall, minorities participate in fewer water-related activities, their drowning rates per exposure may be even higher than reported.²⁶

Location

Any body of water, no matter how shallow or small, can be the site of drowning. Oceans, seas, and rivers account for fewer submersion events than do backyard pools, recreational lakes, bathtubs, and buckets of water. In the United States, submersion events involving young children occur primarily in fresh water; children who are less than 1 year old most often drown in bathtubs, buckets, or toilets, whereas those between the ages of 1 and 4 years most often drown in residential pools.* Despite these statistics, only a small proportion of home pools are properly protected, and most are easily accessible by ambulatory toddlers and curious children.^195,209 One study found that most young children who drowned in residential pools had been out of sight of adults for less than 5 minutes, and were in the care of one or both parents at the time.¹⁷⁹ Among individuals between the ages of 5 and 64 years, drowning typically occurs in open-water recreational settings such as lakes, rivers, and oceans.^31,176 Persons who are more than 65 years old have the highest rates of bathtub drowning per age group.¹⁸¹

Visitors to domestic and international locations are at a higher risk for drowning as compared with natives in the same region. After motor vehicle accidents and homicide, drowning is the leading cause of injury death among U.S. citizens traveling abroad.²²⁰ In island locations, it is the leading cause of injury death; it accounts for 63% of traveler deaths by injury as compared with 3.5% for native citizens of the respective countries.^84,220 Lack of familiarity with the environment,¹²³ lack of understanding of local hydrology, overestimation of abilities, and presence of alcohol use while vacationing are likely contributors to drowning rates among travelers.

Submersion in vehicles is a cause of death by drowning that is not routinely classified as a drowning death, although the incidence of drowning in a submerged vehicle was as high as 5% to 10% of all motor vehicle accident deaths in one series.^207,244 A more recent study²¹⁰ demonstrated that, of 83 drowning deaths in vehicles, more than 92% of victims had insignificant traumatic injuries, suggesting that the primary source of death in submerged vehicles is drowning rather than trauma.

The Divers Alert Network reported 138 deaths internationally in 2006 from scuba diving accidents:⁵⁶ 51 of these were in the United States, with Florida having the highest incidence, followed by California. The cause of death was reported in 58 cases (77% of the total); of those, 86% were attributed to drowning, which is by far the most common cause of death in this series. Several patients had known preexisting medical conditions, including cardiovascular disease, which may have contributed to drowning. Death from scuba diving remains relatively infrequent, and 50-year data show an overall decrease in the diving-related mortality rate per diver.

Water birth (i.e., labor and delivery while immersed in water) is a risk factor for both submersion injury and drowning. Documented adverse neonatal outcomes from underwater birth include unexplained death, drowning, asphyxiation, water intoxication, hyponatremia with seizures, water aspiration leading to respiratory distress and failure, pulmonary edema, hypoxic–ischemic encephalopathy, and pneumonia and other infections, including Pseudomonas and Legionella infection.^{67,74,160,171} Other observational series have shown similar Apgar scores, rates of neonatal resuscitation, and complications for both regular births and water births.^75,160 There has been a vigorous debate in the pediatrics community regarding the safety of this birth modality, but what is undisputed is that there are few reliable data demonstrating the safety of water birthing.¹⁹⁸

Ability to Swim

Although they are very popular, swimming programs for young children do not fully protect against drowning; children should always be supervised while swimming. The American Academy of Pediatrics has long recommended that children should not receive swimming lessons if they are less than 4 years old. This policy was recently revised—amidst controversy in the pediatrics community—to reflect a study demonstrating that drowning victims between the ages of 1 and 4 years were less likely than matched controls (3% versus 26%, respectively) to have had formal swimming instruction.³⁰ The latest recommendation is that children as young as 1 year old can be enrolled in formal survival swimming courses. This is part of a multipronged approach, and does not replace the need for direct supervision and use of pool barriers. Swimming lessons are recommended for nearly all children after the age of 4 years. Prevention focuses on supervision, restricting access to home pools, and reducing use of drugs and alcohol among teenagers around water.^4–6

Highly experienced swimmers are not immune from drowning; competitive swimmers and breath-hold divers sometimes engage in intentional hyperventilation and die as a result of shallow water syncope or blackout. Breath-hold diving is defined as in-water activity without self-contained or surface-supplied breathing gas. Breath-hold activities include snorkeling, spear fishing, and free diving, from which there were 34 fatal drowning cases reported worldwide by the Divers Alert Network in 2006.⁵⁶ More than one-half occurred in the United States, primarily in Florida, Hawaii, California, and Texas; this may be the result of higher rates of reporting in the United States as compared with worldwide rates, and suggests that safety and prevention strategies should be focused on specific geographic regions. Twelve cases were associated with blackout due to hypoxic loss of consciousness, likely as a result of intentional hyperventilation to prolong breath-holding time.

According to the International Swimming Federation, open-water swimming is defined as any competition that takes place in a lake, river, or ocean. Marathon open-water swimming was approved as an Olympic event for the 2008 Olympic Games in Beijing, China. Several studies have demonstrated a risk for hypothermia during open-water swimming competitions, but the extent of risk varied depending on the modality of temperature measurement used and remains unclear.^27,36

Alcohol and Drugs

Alcohol has been implicated as a contributing factor in 25% to 50% of recreational water-related deaths and in 20% of boating-related fatalities.^{33,58,121,123,150} Studies have demonstrated blood alcohol levels of 100 mg/dL or more as a factor in 25% of boating-related fatalities,³³ in 25% of teen drowning deaths,¹⁸⁵ and in 33% of drowning deaths of young adults between the ages of 20 and 34 years. In Australia, 21% of people who drowned during a 5-year period had measurable levels of alcohol in their blood.⁶⁶ Despite federal laws that prohibit alcohol use during recreation on the open water, a survey of adults in the United States showed that 31% of 597 respondents reported operating a motorboat while under the influence of alcohol; these operators were overwhelmingly males between the ages of 25 and 34 years.¹²⁴ Impaired judgment caused by intoxicants can lead to accidents as well as loss of body heat, decreased laryngeal reflexes, higher risk of aspiration, decreased supervision of children, and decreased use of safety devices such as personal flotation devices (PFDs).^181,248 Illicit recreational drug use with and without alcohol has been reported as a factor in water-related deaths.³³ All types of drugs that affect judgment can result in watercraft overcrowding, speeding, failure to wear PFDs, and inattentive or reckless handling of watercraft.

Preexisting Disease

Risk of submersion injury or death in water increases significantly when medical conditions compromise the chance for self-rescue and survival. Situations are particularly dangerous for unpredictable medical conditions such as cardiac and neurologic conditions. Individuals with relevant preexisting conditions must take special care to never be alone and to optimize treatment for the underlying condition before engaging in water-related activities.

Seizure disorders have been shown to increase the risk of drowning among adults and children in both natural bodies of water and in homes.^14,17,28 Drowning is the most common cause of unintentional death injury among patients with seizure disorders.¹⁸³ One study found the risk of drowning among people with epilepsy to be 15 to 19 times greater than that of the general population.¹⁴ It is when patients are alone that the risk of death increases drastically. Other neurologic conditions (e.g., cerebrovascular accident, arteriovenous malformation) that manifest as seizure have been associated with drowning.⁷⁷

Cardiac disorders associated with arrhythmias may manifest while a person is submerged in water; however, the exact mechanism for rhythm disturbance as a result of submersion remains to be determined.^1,24 Long QT syndrome, a conduction disorder associated with sudden death, has been linked by forensic molecular screening to some drowning deaths, indicating a possible gene-specific arrhythmogenic presentation of long QT syndrome triggered by swimming; however, this remains a theoretic possibility.^2,128 Adverse events, such as unstable tachycardia or loss of consciousness from myocardial infarction, may also lead to drowning deaths.

Child Abuse, Homicide, And Suicide

Abuse or neglect should be investigated in any suspicious pediatric submersion incident, which must undergo a thorough social service and legal investigation. One series found abuse or neglect to account for 19% of bathtub submersion deaths among patients less than 5 years old.¹⁸⁵ In the adult population, homicide by drowning is relatively uncommon. The postmortem determination of death by drowning (as opposed to body disposal in water after another mechanism of homicide) is very difficult to make. Drowning by suicide is relatively uncommon.^166,229,239 An Australian study of 123 suicides by drowning found women to more commonly choose bathtubs or the ocean for drowning, whereas men chose rivers, ditches, and lakes.³⁵

Boating-Related Drowning

Recreational and commercial boating accidents are among the leading causes of unintentional drowning. Deaths result from capsized vessels or falls overboard. Risk is determined by water depth, temperature, distance from shore, and currents, including hydraulics at the bases of dams or spillways. Alcohol use, lack of personal protective equipment, and unsafe boating practices are involved in many boat-related drowning incidents.^33,121 In 2008, the U.S. Coast Guard reported 3331 injuries and 710 deaths as a result of recreational boating accidents;²²⁴ 519 of these deaths were the result of drowning and of these, 459 patients (90%) were not wearing PFDs or lifejackets. Studies suggest there is significant underuse of PFDs among recreational boaters.^105,184 In the United States in 2008, alcohol was the leading contributing factor in fatal boating accidents, followed by operator inexperience and careless or reckless operation. The majority of fatal accidents occurred in open motorboats, followed by canoes and kayaks. States with the highest death rates (i.e., >10 per 100,000 registered boats) were Alaska, Hawaii, Montana, Idaho, Utah, Texas, Louisiana, and Vermont.²²⁴

The commercial fishing industry also contributes to boating-related drowning deaths internationally. The International Labor Organization estimated that 36 million people worldwide were employed in aquaculture industries in 1998; most are located in Asia and Africa. Death rates among commercially employed fisherman are among the highest of any occupation.^122,190 In the United States, death rates of fishermen are 16 times higher than those of police and firefighters and 8 times higher than those of persons who drive motor vehicles for a living.²²³ Another population affected by water transport and drowning is that of refugees seeking asylum, who are often in rough weather and poorly equipped, overcrowded boats without lifejackets. A 2004 study reported that 4000 asylum seekers are estimated to drown annually at sea.^59,180

The Human Body and Water

The degree to which the body floats (i.e., its buoyancy) depends on the amount of air in the lungs, body fat, and clothing. When the lungs are maximally filled with air (close to total lung capacity), the body has about 2.5 kg (5.5 lb) of flotation. It has greater buoyancy during inspiration as the lungs fill with air and lesser buoyancy during expiration. Clothing can affect both heat conservation and buoyancy, and can be integral to survival in the wilderness water environment. PFDs are specifically designed to increase buoyancy (Figure 75-2).¹⁵⁹ Percentage of body fat is a factor in the ability to conserve body heat during prolonged immersion.

FIGURE 75-2 Types of personal flotation devices.

(Courtesy Justin Sempsrott, MD; adapted from Personal Flotation Device Manufacturers Association. http://www.pfdma.org/choosing/types.aspx.)

The Initial Event

Submersion begins when the patient’s airway lies below the surface of a liquid medium, usually water. There is typically an initial period of struggle with attempted breath holding. This may not occur during trauma-associated submersion, when the patient may have been unconscious before or upon entry into the water.^117,169 After gasping occurs, the initial struggle is sometimes followed by laryngospasm to protect the lower airways from liquid in the upper airways (i.e., nares, oropharynx, larynx). Laryngospasm may limit the amount of water aspirated, and occurs in an estimated 7% to 10% of drowning cases.^139,145 The relevance of this distinction to the ultimate pathophysiology is controversial.^117,167,196 It is now felt that all submersion patients likely aspirate at least a small amount of liquid. Particularly during cold-water submersion, the initial event is accompanied by a drive to hyperventilate caused by stimulation of thermal skin receptors, in addition to increasing hypoxemia. During this initial time, patients will often swallow large amounts of water to avoid aspiration.¹⁴⁵ Eventually, the outcomes of breath holding are hypoventilation, hypercapnea, respiratory acidosis, and hypoxemia. At a certain break point, breath-holding attempts are overwhelmed, and no further voluntary efforts can prevent respiration. Loss of consciousness ensues and cardiopulmonary arrest follows (Figure 75-3).

FIGURE 75-3 Pathophysiologic events of the drowning process.

(Courtesy Andrew Schmidt, DD.)

The duration of tissue hypoxemia, timing of rescue, and institution of effective cardiopulmonary resuscitation (CPR) and field resuscitation are significant factors that affect whether the initial submersion injury is survivable. Duration of submersion, water temperature, and tissue susceptibility to hypoxemia determine the effects of submersion on different organ systems and the likelihood of ultimate survival.

Pulmonary system

During submersion events, the lung is the first major interface between the environment and the body. Aspiration of water of any type and volume immediately affects alveolar ventilation, gas exchange, and the mechanical characteristics of the lung.^54,71,169 Hypoxemia is the hallmark of pulmonary pathophysiology during submersion. Breath holding and apnea lead to a rise in partial pressure of carbon dioxide and a fall in partial pressure of oxygen in both the alveolus and arterial blood. In addition, inhalation of any liquid causes surfactant disruption and alveolar collapse, resulting in areas of ventilation/perfusion () mismatch, shunting, and further worsening of hypoxemia. Pulmonary sequelae may range from asymptomatic to acute respiratory distress syndrome (ARDS), depending on the amount of water aspirated and the duration of submersion. Usually symptoms of pulmonary involvement are present immediately; however, there are reports of delayed ARDS after an initially normal chest radiograph.⁵⁴

Volumes of aspirated liquid of as little as 1 to 3 mL/kg are sufficient to cause disruptions in alveolar gas exchange and hypoxemia. Diminished pulmonary gas exchange occurs in part due to surfactant disruption as a result of aspiration. Surfactant is produced by type 2 pneumocytes, pulmonary epithelial cells responsible for maintaining alveolar surface tension, increasing pulmonary compliance, and preventing atelectasis. Disruption of surfactant leads to malfunctioning of the alveolar epithelial lining and increased mismatch. Hyperosmolar saltwater draws fluid into the alveolar spaces, resulting in surfactant “washout” or dilution, and ultimately causing pulmonary edema; hypo-osmolar freshwater disrupts surfactant functioning and is directly cytotoxic to type 2 pneumocytes, resulting in mismatch and loss of alveolar compliance.^71,117 Interstitial and microvascular damage ensue in response to alveolar–capillary basement membrane disruption, releasing an inflammatory cascade that results in pulmonary edema caused by extravasation of fluid into the alveolar space, bronchospasm, worsening mismatch, and hypoxemia.¹¹⁷ Areas of hypoxic pulmonary vasoconstriction further worsen shunting and increase pulmonary hypertension, leading to increased pressure across the alveolar–capillary basement membrane and further extravasation of fluid into the alveoli. In severe cases of submersion, patients present with ARDS, profound hypoxemia, noncardiogenic pulmonary edema, and a significant alveolar–arterial oxygen gradient. In profoundly ill patients, intubation and artificial ventilation may be required, increasing the risk of subsequent ventilator-associated lung injury and ventilator-associated pneumonia. With adequate resuscitation and treatment of patients without significant neurologic compromise, pulmonary dysfunction may initially be severe, but ultimate recovery of baseline lung function after submersion is the rule rather than the exception.^83,145

Contamination by debris from petroleum products, sewage, sand, and organic matter is more common in saltwater and brackish water. Such debris accentuates the possibility of further inflammation and lung injury, which increase mortality rates. Inhalation of mud, sand, and other particulates may require fiber-optic bronchoalveolar lavage to cleanse the airways. Aspiration of microbes and related potential infections are discussed later. Figures 75-4 to 75-6 show examples of foreign-body and contaminant aspiration after drowning.

FIGURE 75-4 Chest radiograph taken in the emergency department, showing sand bronchograms in the right lower lobe (solid arrow). Note sand within the gastric fundus (open arrow).

(From Dunagan DP, Cox JE, Chang MC, et al: Sand aspiration with near-drowning: Radiographic and bronchoscopic findings, Am J Respir Crit Care Med 156:292, 1997.)

FIGURE 75-5 Chest CT scan showing bilateral sand bronchograms within the lower lobes (solid arrows) as well as significant air space opacification.

(From Dunagan DP, Cox JE, Chang MC, Haponik EF: Sand aspiration with near-drowning: Radiographic and bronchoscopic findings, Am J Respir Crit Care Med 156:292, 1997.)

FIGURE 75-6 Fiberoptic bronchoscopy, demonstrating pieces of sand (black arrows), significant airway erythema, and inflammation following drowning and sand aspiration.

(From Dunagan DP, Cox JE, Chang MC, et al: Sand aspiration with near-drowning: Radiographic and bronchoscopic findings, Am J Respir Crit Care Med 156:292, 1997.)

Swimming-induced pulmonary edema has been described in several case reports as affecting scuba divers, Navy SEALS, and individuals who engage in strenuous surface swimming (e.g., triathletes). The pathophysiology of this disorder is unclear, but proposed mechanisms include central blood pooling related to immersion and strenuous swimming resulting in elevated pulmonary artery pressure and diastolic dysfunction. Experimental equine data demonstrate increases in right ventricular and pulmonary arterial pressures with varying degrees of submersion in water, presumably resulting in capillary fracture. The case definition of swimming-induced pulmonary edema consists of acute hypoxemia during or immediately after a swimming event, a demonstrable chest radiograph abnormality with resolution within 48 hours in the absence of evidence of underlying pulmonary infection, and aspiration of water or attempted breathing against a closed glottis. The significance of this clinical entity is unclear, and it appears to be relatively uncommon.^138,200

Central Nervous System

The central nervous system (CNS) is highly sensitive to even brief periods of hypoxemia and is the most susceptible organ system to the negative effects of submersion. The major determinant of survival and long-term morbidity from a submersion injury is the extent of CNS injury. Most submersion patients suffer a brief period of unconsciousness that is caused by cerebral hypoxemia. Full neurologic recovery rarely occurs after 5 to 7 minutes of anoxia in normothermic conditions; hypothermia under controlled circumstances can prolong this to more than 40 minutes.²⁴² In most cases, prolonged submersion leads to death from neurologic asphyxia. Even with aggressive CPR and return of spontaneous circulation, submersion is associated with significant neurologic morbidity. Patients who present either awake or with blunted mental status have a better prognosis than those who present in a coma; mortality rate in one study was as high as 34% among patients who were comatose on arrival to the hospital.^52,142 Of the surviving patients, 10% to 23% demonstrated severe and persistent neurologic sequelae.^52,142 Prolonged hypoxemia and acidosis lead to neuronal cell death and demyelination.^25,100,134 Thus, the longer the submersion, the more CNS damage suffered. Areas of high metabolic activity in the brain are most prone to damage from hypoxemia: gray matter (more than white), vascular end zones, cerebral cortex, thalamus, basal ganglia, and hippocampus. Initial computed tomography scanning of the brain after submersion that shows any abnormalities of edema, loss of differentiation between gray and white matter, or focal infarct is highly predictive of poor outcome.^186,192

After the initial hypoxic event, subsequent reperfusion of damaged neurons can result in cell lysis as well as interstitial and cerebral edema that are further worsened by systemic acidosis, hypotension, hyperglycemia, and, if present, seizure activity.¹⁷² Hypothermia can increase cerebral tolerance of ischemia and hypoxemia, and prolonged submersion in cold water may ultimately be neuroprotective. There are multiple case reports of survival with good neurologic outcomes after prolonged submersion, particularly among children, and this is thought to be the result of decreased cerebral oxygen demand in the setting of hypothermia.* This requires rapidly induced hypothermia before the onset of anoxic damage, which occurs with sudden submersion in very cold water. Therapeutic hypothermia (TH) in cases of cardiac arrest have resulted in improved neurologic outcome, and there are several case reports of complete neurologic recovery after IH in drowning patients.^12a,234,238a Drowning patients often arrive hypothermic at temperatures below the 32° to 34° C [90° to 93° F] of TH. This is an area of active research, and in the absence of randomized control trials of IH in non-ventricular fibrillation arrest, the decision to initiate TH is based on expert consensus and theoretical benefit. This is discussed further in Hypothermia, later.

Cardiovascular system

Cardiac rhythm, output, and function are affected by hypoxemia and acidosis, with more severe manifestations in prolonged submersion.¹⁵³ Dysrhythmias may occur as a result of acidosis and hypoxemia. Decreased cardiac output may result from direct effects of hypoxemia on myocardium. Pulmonary hypertension caused by aspirated fluid can result in right ventricular overload and further decreased cardiac output. Patients with underlying cardiac disease may be more susceptible to the effects of hypoxemia on myocardial function. A sudden cardiac dysrhythmia may precipitate submersion and drowning in patients with preexisting cardiac disease, although this can be difficult to discern from submersion-related injury during a postmortem analysis. One small study showed a significant correlation between a personal or family history of drowning in subjects with autosomal dominant long QT syndrome, suggesting a gene-specific arrhythmogenic trigger for drowning.^1,2 However, subsequent pathologic postmortem screening of drowning subjects has failed to show mutations in genes associated with long QT syndrome,¹²⁸ so it remains a theoretic correlation.

Hematologic and Electrolyte Disturbances

Prior data indicating systemic electrolyte disturbances from aspiration of saltwater are of little practicality for human drowning patients, because such derangements are rarely seen. Although the massive instillation of saltwater in animal models has resulted in disturbances in sodium, chloride, magnesium, and calcium^46,243,248 (presumably as a result of osmotic gradients across the alveolar epithelium), these results require a large volume of fluid aspiration (i.e., >22 mL/kg). With submersion, such volumes are rare.^141,143,144 Similarly, canine models have demonstrated gross hemolysis, resulting in hyperkalemia and disseminated intravascular coagulation after large-volume aspiration; however, clinically relevant changes in hematocrit and hemoglobin levels are rarely seen in human submersion patients.¹⁴⁵ Routine observation and laboratory analysis with treatment for gross abnormalities are all that are indicated in the hospital setting.

Hypothermia

For submersion patients who do not drown immediately, subsequent drowning may result from hypothermia.^50,94 Water at 91.4° F (33° C) is thermally neutral, where heat loss equals heat production for a swimmer without clothes; water any colder than this leads to ongoing heat loss. The thermal conductivity of cold water is 25 to 30 times that of air.^94,120 Even in only moderately cold water, hypothermia may ensue rapidly and lead to a loss of consciousness and subsequent drowning. This is particularly true among children, who have less subcutaneous fat and relatively greater body surface area as compared with adults.^20,49,80,90 Survival is unlikely after 60 minutes in water that is cooler than 32° F (0° C); however, people can survive for up to 6 hours at a water temperature of 59° F (15° C)⁴⁷ (Table 75-1).

TABLE 75-1 Estimated Survival Times in Cold Water

(Courtesy U.S. Search and Rescue Task Force. http://www.ussartf.org/cold_water_survival.htm)

There are many factors that affect an individual’s response to cold-water submersion. In some cases, hypothermia appears to be protective if it coincides with the submersion event. Dramatic recoveries after prolonged hypothermia have been documented in children and adults.^{177,202,216,247} This is an area of active research in cardiac arrest, where therapeutic hypothermia (TH) has been shown to decrease cerebral metabolic demand and improve neurologic outcomes.⁹⁹ Protocols for TH were adopted by the American Heart Association in 2002 and by the European Resuscitation Council in 2003 for out-of-hospital cardiac arrest patients. Case reports of survival after submersion in cold water with profound hypothermia have provoked questions as to whether this would provide the same physiologic effect of neuroprotection for submersion patients who become rapidly hypothermic, and might warrant maintenance of low core temperature in comatose submersion patients.^117,230 A panel of experts during the World Congress on Drowning in 2002 concluded that “drowning victims with restoration of adequate spontaneous circulation who remain comatose should not be actively re-warmed to temperature values above 32° to 34° C (90° to 93° F). If core temperature exceeds 34° C (93.2° F), hypothermia at 32° to 34° C (90° to 93° F) should be achieved as soon as possible and sustained for 12 to 24 hours.”²³⁴ There are several cases of full neurologic recovery after submersion with subsequent TH^148,231; however, optimal temperature management for submersion patients remains an area of active discussion.

The pathophysiologic response to hypothermia ranges from shivering with an increased metabolic rate to coma, massive metabolic acidosis, and spontaneous ventricular fibrillation. Patients progress from mild hypothermia, characterized by shivering, increased metabolic rate, and tachycardia, to profound hypothermia at varying rates, depending on the surrounding water temperature, protection and clothing, duration of exposure, and position in the water (Figure 75-7).

FIGURE 75-7 Survival times in cool (10° C [50° F]) water using various techniques in several situations. HELP, heat escape lessening posture.

(Data from Collis ML: Survival behaviour in cold water immersion. In Proceedings of the Cold Water Symposium, Toronto, Royal Life-Saving Society of Canada, 1976.)

In some cases, patients suffer from immersion syndrome, which involves sudden death from bradycardia, tachycardia, or ventricular fibrillation and cardiac arrest from cold water exposure before onset of systemic hypothermia.¹⁶⁹ Immersion in cold water (i.e., <5° C [<41° F]) produces a rapid fall in core body temperature. Heat loss through convection and conduction is further compounded by increased muscle activity during swimming and struggling.

The “diving reflex” in diving mammals is a vestigial but inducible reflex in humans that may contribute to survival in cases of prolonged submersion and subsequent hypothermia.^49,80,91,132 The reflex is activated by vagal stimulation from cutaneous receptors that respond to cold by shunting blood to the brain and cardiac muscles and away from the skin, extremities, and splanchnic vascular beds, along with bradycardia and decreased metabolic rate. Bradycardia and vasoconstriction in all vascular beds (except those serving the heart and brain) results in preserved mean arterial pressure for those organs and overall decreased cardiac output. The reflex may be inducible in only 15% to 30% of humans,²¹ but may be a contributing factor for persons who survive submersion.^62,80,111 However, some discount its role.

Immersion hypothermia occurs as the core temperature falls. It can be divided into three distinct phases. Times given are for immersion in 10° C (50° F) water.

Cold-Shock Response Time: 0 to 3 Minutes

Cold-shock response is the most common cause of drowning in cold water. Upon exposure to cold water, subjects may experience uncontrollable gasping that lasts approximately 1 to 3 minutes.^32,61 This phenomenon may result in aspiration of water unless the head is kept above the surface. Sudden skin cooling results in increased peripheral vascular resistance of superficial blood vessels. Heart rate and cardiac output increase, and an outpouring of catecholamines may predispose these individuals to fatal dysrhythmias. Cooling of the periphery decreases nerve conduction, and muscle control becomes difficult, making any attempt at self-rescue virtually impossible. The priority for self-rescue during this phase is only to maintain the head above water. Patients should assume the heat escape lessening position (HELP) (Figure 75-8), if possible. If two or more persons are in the water, the huddle position (Figure 75-9) is recommended to lessen total body heat loss. Because children become hypothermic much more quickly than do adults, they should be placed in the middle of the huddle.

FIGURE 75-8 Heat escape lessening posture (HELP).

(Courtesy Alan Steinman, MD.)

FIGURE 75-9 Huddle technique.

(Courtesy Alan Steinman, MD.)