Drowning

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Chapter 145

Drowning

David B. Richards and Gabrielle A. Jacquet

Perspective

Unintentional drowning is the sixth most common cause of accidental death, accounting for 4086 deaths (1.4 per 100,000) in the United States in 2007.¹ Among children 1 to 4 years of age, drowning is the leading cause of injury mortality; for 10- to 14-year-olds, it is second only to motor vehicle crashes.^1–3

Each year an estimated 500,000 people die worldwide after drowning, which exceeds mortality due to war.⁴ Low- and middle-income countries account for 97% of all drowning deaths.⁵ A study of drowning deaths in South Africa indicated a death rate of 12 per 100,000 for all ages in 2004.⁶

The incidence of drowning with nonfatal outcomes is unknown. The Centers for Disease Control and Prevention estimates that for every child who dies by drowning in the United States, another four receive emergency department (ED) care for a submersion event, and half of these children require hospitalization.⁷ Among all age groups, an estimated one to four hospitalizations secondary to nonfatal submersions occur for every drowning death.^8–10 The economic implications of drowning injuries are profound. In Australia, drowning has the highest average lifetime cost (US $40,071) of any injury type.¹¹

Submersion injuries occur in domestic settings such as swimming pools, hot tubs, bathtubs, large buckets, and rainwater tanks and in all forms of natural bodies of water. A review of all drowning deaths among individuals younger than 20 years in the United States during a 1-year period revealed that 55% of infants younger than 1 year drown in bathtubs, and nearly 16% drown in large household buckets.¹² Most (56%) children 1 to 4 years old drown in artificial pools, whereas most (63%) deaths among older children occur in natural bodies of fresh water.¹²

Because of the recent natural disasters, the incidence of drowning injuries and fatalities is rising. In disasters such as floods and tsunamis, older populations are disproportionately affected. A study from hurricane Katrina found that 49% of fatalities were in people 75 years of age or older.¹³

Principles of Disease

Definitions

Traditionally, the terminology describing submersion injuries has been confusing and impractical. In the past, drowning referred to death within 24 hours of suffocation from submersion in a liquid, whereas near-drowning described victims who survived at least 24 hours past the initial event regardless of the outcome. In 2005 the World Health Organization (WHO) published a new policy defining drowning to clarify documentation and to better track submersion injuries worldwide. Drowning was defined as “the process of experiencing respiratory impairment from submersion/immersion in liquid.” Furthermore, the WHO policy stated, “Drowning outcomes should be classified as: death, morbidity, and no morbidity. … the terms wet, dry, active, passive, silent, and secondary drowning should no longer be used.”⁴ The term near-drowning should not be used, and the association of the term drowning with a fatal outcome should be abandoned.

Immersion syndrome refers specifically to syncope resulting from cardiac dysrhythmias on sudden contact with water that is at least 5° C lower than body temperature. The risk is proportional to the difference between body temperature and water temperature. Wetting of the face and head before entrance into the water may prevent the inciting sequence of events. Putative mechanisms for the syndrome are vagal stimulation leading to asystole and ventricular fibrillation secondary to QT prolongation after a massive release of catecholamines on contact with cold water. The resultant loss of consciousness leads to secondary drowning.²

Age, gender, and race affect incidence of drowning. Toddlers and older teenagers are at greatest risk of death by drowning, with annual incidences of 2.46 and 1.47 per 100,000, respectively.¹ Boys account for almost 80% of victims older than 1 year.¹ Black males between 15 and 19 years of age have the highest annual incidence of drowning mortality (3.92 per 100,000), and black children between the ages of 5 and 14 years drown at nearly three times the rate of white children of the same age.^1,7,12 The risk of death by drowning within the American Indian population is twice as high as it is for the white population.¹

Ethanol consumption in proximity with water is a major risk factor for submersion injury or death. Acute ethanol intoxication may be a contributing factor in 30 to 50% of drownings among adults and adolescents.⁸ In one study of boating fatalities, most of which were due to drowning, an association was established between blood ethanol concentration (BEC) and risk of death from drowning while using watercraft. Odds ratios of fatality from drowning followed a trend from 2.8 for a BEC of 1 to 49 mg/dL to 37.4 for a BEC of 150 mg/dL or greater compared with sober case controls.¹⁴

Drowning in the United States follows clear temporal patterns. Two thirds of pediatric deaths occur between May and August, and most submersion injuries occur on weekends between noon and 8 PM.⁸ Submersion victims older than 20 years are most often participating in water sports or using watercraft.

The relationship between swimming ability and the risk of drowning is unclear. No direct evidence exists to suggest that inexperienced swimmers are more likely to drown. On the contrary, skilled swimmers have greater exposure to water and may be more prone to submersion incidents.¹⁵

Numerous medical conditions confer an increased likelihood of drowning or submersion injury. Seizure disorders increase the chance of drowning among children and adolescents nearly 20 times.¹⁶ Autism and other developmental and behavioral disorders increase risk in children as well.^17–19 Prolonged QT syndrome is also a risk factor for drowning. Laboratory studies show that immersion in cold water extends the QT interval. Interrogation of the automated internal cardiac defibrillator of a 12-year-old girl with prolonged QT syndrome who had a cardiac arrest on diving into the ocean revealed immediate further prolongation of the QT interval, followed by a premature ventricular complex and subsequent ventricular tachycardia within 5 seconds.^20,21 This phenomenon may account for a significant proportion of immersion syndrome events and otherwise unexplained submersion injuries.

Pathophysiology

Unexpected submersion triggers breath-holding, panic, and a struggle to surface. Air hunger and hypoxia develop, and the victim begins to swallow water. As breath-holding is overcome, involuntary gasps result in aspiration. The quantity of fluid aspirated, rather than the composition, determines subsequent pulmonary derangement.

The historical emphasis on pathophysiologic differences between freshwater and saltwater aspiration with respect to resultant electrolyte imbalance, hemolysis, and fluid compartment shifting was based on animal studies conducted in the early 20th century. Subsequent investigations revealed that significant intravascular abnormalities do not occur until the amount of aspirated water exceeds 11 mL/kg of body weight; autopsy studies show that most drowning victims aspirate less than 4 mL/kg.²² In one review of the hospital treatment of 91 submersion victims, no patient required emergent intervention for a significant electrolyte abnormality.²³ Aspiration of 1 to 3 mL/kg of either fresh water or salt water destroys the integrity of pulmonary surfactant, leading to alveolar collapse, atelectasis, noncardiogenic pulmonary edema, intrapulmonary shunting, and ventilation-perfusion mismatch.² Profound hypoxia and metabolic and respiratory acidoses ensue, leading to cardiovascular collapse, neuronal injury, and ultimately death.

The classic hypothesis was that 10 to 15% of drowning victims die without aspiration of a significant amount of water. Death from such dry drowning putatively results from severe laryngospasm causing hypoxia, convulsion, and death without entry of fluid into the lungs. An exhaustive review of the literature failed to corroborate this hypothesis.²⁴ Dry drownings more appropriately reflect deaths from causes other than simple submersion.

Many factors may influence the pathophysiologic sequence of events in submersion injury and affect the chance of survival, including age, water temperature, duration and degree of hypothermia, diving reflex, and effectiveness of resuscitative efforts. Because of a lower ratio of body mass to surface area, children have hypothermia more quickly and to a greater degree after immersion in cold water than adults do. Hypothermia lowers cerebral metabolic rate and is neuroprotective to some extent for victims of submersion injury.²⁵ Despite dramatic case reports of patients surviving prolonged submersion in cold water with full neurologic recovery, hypothermia is generally a poor prognostic finding. Cold-water immersion speeds the development of exhaustion, altered consciousness, and cardiac dysrhythmia. The diving reflex may also play a protective role in infant and child submersions. Activation of the diving reflex by fear or immersion of the face in cold water shunts blood centrally to the heart and brain. Apnea and bradycardia ensue, prolonging the duration of submersion tolerated without central nervous system damage.²⁶

Clinical Features

Symptoms and Signs

Many submersion injuries are witnessed. Toddler drownings are an important exception, however, often occurring because of a lapse in supervision. On occasion, the history of coughing, choking, or vomiting in a patient found near a body of water suggests the diagnosis. Signs of pulmonary injury may be obvious in a submersion victim who is hypoxic, cyanotic, and in obvious respiratory distress or arrest. More subtle clues, such as increased respiratory rate and audible rhonchi, rales, or wheezes, should alert the clinician to evolving respiratory compromise. Submersion victims swallow a significantly greater volume of water than is aspirated, and gastric distention from positive-pressure ventilation during rescue is common. As a result, 60% of patients vomit after a submersion event.² Aspiration of gastric contents greatly compounds the degree of pulmonary injury and increases the likelihood that acute respiratory distress syndrome will ensue. In addition, aspiration of particulate contaminants such as mud, sewage, and bacteria may obstruct the smaller bronchi and bronchioles and greatly increase the risk of infection (both bacterial and fungal in nature).²⁷

Victims with central nervous system injury may present with symptoms ranging from mild lethargy to coma with fixed and dilated pupils. Central nervous system injury results from the initial hypoxic or ischemic insult and from the cascade of reperfusion injury that follows reestablishment of cerebral blood flow after an arrest. The release of inflammatory mediators and the generation of oxygen free radicals in the postresuscitative period contribute to cytotoxic cerebral edema, compromise of the blood-brain barrier, and increased intracranial pressure. Cerebral arteriolar vasospasm and enhanced platelet aggregation impede cerebral perfusion at the macrocirculatory and microcirculatory levels.²⁶

Cardiac dysrhythmias may incite a submersion injury or develop as its consequence. Hypoxemia, acidosis, and, potentially, hypothermia are the primary factors responsible for dysrhythmias ranging from ventricular tachycardia and fibrillation to bradycardia-asystole. Electrolyte disturbances are rarely significant enough to be dysrhythmogenic.²³

Other clinical sequelae of submersion injury may include acute renal impairment, present in approximately 50% of patients as the result of lactic acidosis; prolonged hypoperfusion; and, in some instances, rhabdomyolysis.²⁸ Coagulopathy as a consequence of associated hypothermia or disseminated intravascular coagulation may also occur.

Prognostic Factors

Many factors help predict patients who will survive a submersion injury neurologically intact. Hypoxia, which is usually dependent on submersion time, is the most important factor related to outcome and subsequent quality of life in drowning victims.²⁹ Submersion victims who arrive in the ED alert with normal hemodynamics are unlikely to experience neurologic impairment. Circumstantial variables that portend a poor outcome include victim age younger than 3 years, submersion for longer than 5 to 10 minutes, and initiation of cardiopulmonary resuscitation (CPR) more than 10 minutes after rescue.^2,30 Adverse neurologic findings on initial presentation do not preclude full neurologic recovery, although in general, patients whose duration of submersion or resuscitation exceeds 25 minutes have an unfavorable outcome.³¹ With the exception of victim age, however, such measurements are generally either unknown or inaccurately estimated at the time of a patient’s arrival in the ED. On arrival, objective findings associated with an unfavorable prognosis include hypothermia, severe acidosis, unreactive pupils, a Glasgow Coma Scale score of 3, and asystole or the need for ongoing CPR.^2,32–35 Neurologically intact survival is reported for individual patients even with several of these factors present; none of several proposed scoring systems using combinations of these variables has 100% predictive power.^30,33,36,37

A retrospective study of submersion injury in children noted that all patients who present with an abnormal head computed tomography (CT) scan within the first 24 hours eventually die. Furthermore, an abnormal head CT scan at any time is associated with poor outcome (death or persistent vegetative state).³⁸

Differential Considerations

The precipitants of a submersion injury, such as drug or ethanol intoxication, cardiac arrest, hypoglycemia, seizure, and attempted suicide or homicide, should be considered in patients found unresponsive in the water. For pediatric victims, child abuse or neglect should also be considered a potential cause.

Potential head or cervical spine injury is an important consideration in submersion associated with trauma. A review of 2244 cases of submersion injury in Washington State identified only 11 (0.5%) patients with a cervical spine injury. Each patient had either clinical signs of serious trauma or a history of motor vehicle crash, fall from height, or diving into the water.³⁹ Unless such factors are present, routine cervical spine immobilization for submersion victims is not warranted.

Diagnostic Studies

Cardiac monitoring and an electrocardiogram should be obtained to determine the presence of significant dysrhythmias, QT prolongation, or ischemia. Hypothermia resulting from drowning may cause vasoconstriction and coronary vessel spasm and may be responsible for cardiac ischemia and myocardial injury.⁴⁰ Pulse oximetry, capnography, and arterial blood gases should be monitored closely in all submersion victims for signs of hypoxemia, hypercarbia, and acidosis. Blood glucose, serum creatinine, and electrolyte values should be obtained, although serum creatinine concentration and electrolyte levels are usually normal on initial presentation. Similarly, complete blood count is often normal with the exception of leukocytosis. Toxicologic screening may be appropriate, depending on the circumstances of the submersion. Subsequently, evidence of renal failure, hepatic dysfunction, and disseminated intravascular coagulation may be noted on laboratory testing.

The initial chest radiograph may underestimate the severity of pulmonary injury, although infiltrates or pulmonary edema may be evident within hours. Cranial CT is rarely initially contributory unless significant trauma or other pertinent injury is suspected. Magnetic resonance imaging of the brain may predict neurologic outcome after submersion injury, but its prognostic value is not optimal until 3 or 4 days elapse.37,41

Management

Salient details of the events surrounding the accident should be ascertained rapidly. Resuscitation of pulseless and apneic patients should be attempted initially in most cases because bystander estimates of total submersion time are often inaccurate. The clinical presentation of severe hypothermia often mimics death, and case reports exist of functional recovery for individuals submerged for 66 minutes.42,43

For a victim without vital signs, outcome depends on the interval preceding CPR. Mouth-to-mouth assisted ventilation should begin immediately, even before the victim is extricated from the water. Chest compressions are impractical before extrication but should be initiated as soon as the individual is placed on a solid surface. Maneuvers such as those proposed by Heimlich and Patrick to remove fluid from the lungs are ineffective and dangerous in a victim at risk for aspiration and may delay ventilation. Use of such maneuvers is not recommended unless there is reason to suspect airway occlusion by a foreign body.⁴⁴

On arrival in the ED, cardiac monitoring and continuous pulse oximetry should be established. A core temperature obtained with a low-reading probe is indicated for any unstable or lethargic patient. Values obtained by use of infrared ear thermometry are unreliable.⁴⁵ Rewarming of a hypothermic patient may suffice for hemodynamic stabilization and improvement in mental status. Bedside blood glucose measurement and empirical naloxone administration are warranted. A spontaneously breathing patient should be monitored for signs of developing pulmonary injury. Initial chest radiographs are often unremarkable even in the setting of serious and evolving pathologic processes. Frequent arterial blood gas measurements are indicated to monitor rapidly changing respiratory function.

Clinical impression and objective determination of the adequacy of oxygenation and ventilation should determine the decision for tracheal intubation. Apparent or developing respiratory distress, absence of protective airway reflexes, and significant associated head or chest injuries are indications. A PaCO₂ greater than 50 mm Hg should prompt strong consideration of intubation and mechanical ventilation. Patients unable to maintain oxygen saturation greater than 90% or with a PaO₂ greater than 60 mm Hg on high-flow oxygen require positive airway pressure to increase functional residual capacity, to decrease intrapulmonary shunting, and to reduce ventilation-perfusion mismatch. In awake patients, this may be accomplished by face or nasal mask (continuous positive airway pressure), but the risk of potential gastric distention, vomiting, and aspiration should be considered. Otherwise, tracheal intubation and mechanical ventilation with positive end-expiratory pressure are necessary. The hemodynamic consequences of positive end-expiratory pressure should be monitored carefully because increased intrathoracic pressure may compromise venous return and cardiac output. Decreased cranial venous return may impede cerebral perfusion.

No consensus exists with regard to the appropriate length of resuscitative effort for hypothermic submersion victims in the ED. The safest parameter is to continue until the core temperature reaches at least 32 to 35° C because cerebral death cannot be diagnosed accurately in hypothermic patients with temperatures below this level. This parameter may not always be practical, however, because brain-dead patients are often poikilothermic.

The administration of corticosteroids in the setting of submersion injury and potential acute respiratory distress syndrome does not improve outcome.2,37 Barbiturate-induced coma, aggressive diuresis, neuromuscular blockade, and hyperventilation do not improve neurologic outcome and, particularly in the case of hyperventilation, may be harmful.²⁶ Similarly, empirical antibiotics do not increase survival and should be administered only to the rare patient who was submerged in grossly contaminated water or who shows signs of infection or sepsis.²

Interventions such as induced or permissive hypothermia aimed at attenuation of reperfusion injury after anoxic brain insult are the focus of intense investigative effort. A case report of twin toddlers with identical submersion injury and subsequent prolonged cardiac arrest indicated that therapeutic hypothermia may be a factor in influencing a good neurologic outcome. One twin was treated with therapeutic hypothermia for 72 hours and had a return to normal neurologic status. The other twin was not cooled and survived, but with significant neurologic impairment.⁴⁶ Drowning victims in cardiac arrest are usually colder than 30° C and require warming. Comatose patients who have been resuscitated after reasonable submersion time regardless of rhythm should not be rewarmed above 34° C. Case reports suggest that rewarming only up to 34° C followed by a 24-hour mild hypothermic treatment before normothermia is reached may be advantageous because of decreased pulmonary reperfusion injury and reduced secondary brain injury.^47,48 Reports such as these and studies in the resuscitation literature indicate an emerging role for therapeutic hypothermia in drowning victims.

Disposition

Symptomatic patients should be admitted for treatment. Patients with a history of apnea, unconsciousness, or hypoxia and any patients who manifest dysrhythmia or an abnormal chest radiograph also require admission. Patients who are asymptomatic on presentation to the ED, maintain a normal room air oxygen saturation, and have no chest radiograph or arterial blood gas abnormalities can be discharged safely after an observation period of 6 hours.37,49 Careful instructions about symptoms or signs of delayed pulmonary complications are necessary, and the patient should be discharged in the care of a competent adult.

Preventive Efforts

The mortality rate from drowning is decreasing since the 1990s in the United States.1,3,37 A similar downward trend in submersion injuries is reported in Great Britain.⁵⁰ Although the exact causes of this decline are unknown, an increased public awareness of preventive measures and an emphasis on public education with regard to CPR and the dangers of ethanol use in conjunction with water-related activities are contributing significantly to the reduction in fatalities. A longitudinal study of drownings during a 21-year period in Washington State noted that the incidence of death attributable to ethanol use has decreased by 81%.²

Parental education about the danger of pediatric drowning is an important focus of preventive effort. Inadequate supervision of children playing in or near water is one of the most common causes of pediatric submersion death, underscoring the importance of increasing awareness of the need for constant oversight of children in this setting.10,51 Most pediatric submersion injuries in swimming pools occur at the victim’s home.¹⁰ In most cases, the child is last seen in the house, is left unattended for a moment, and enters the pool on an unfenced side closest to the home with no audible splash or screaming.¹² Adequate and fully circumferential fencing of residential pools is a current recommendation of the American Academy of Pediatrics. A meta-analysis of the literature regarding the efficacy of this preventive step reported an odds ratio of 0.27 for drowning or submersion in a properly fenced compared with a nonfenced pool.^51,52 In Australia, safety legislation is associated with a 30% reduction in drowning rates in young children.⁵³ Some areas require fencing of pools and other artificial bodies of water. Unfortunately, legislation requiring appropriate fencing is poorly adhered to, and one study revealed that only 40% of households are compliant.⁵⁴ Even though bodies of water can be fenced in high-income countries, the fencing of all waterways, ponds, and ditches would be unrealistic in low- and middle-income countries. In these countries, swimming education programs are an attractive alternative.

Pool covers are inadequate and potentially dangerous as barriers. Solar blankets do not support the weight of a child and can enmesh and obscure a struggling victim from view. A rigid pool cover may convey a false sense of stability to a child tempted to walk across its surface and is considered an insufficient substitute for effective four-sided fencing.⁵¹

Medical care providers are a vital resource for enhancement of public awareness of the importance of these measures. The literature supports the concept that education in the ED about drowning prevention can have a positive impact on patient and family awareness of steps to lessen the likelihood of catastrophic drowning or submersion injury.55,56

Key Concepts

The fluid medium in which a submersion injury occurs (fresh water versus salt water) is usually of little clinical relevance; all significant submersions induce pulmonary injury and hypoxia by the amount of water aspirated and the duration of submersion, not the water content.