Pathophysiology:

In young children suddenly immersed in cold water, the mammalian diving reflex may occur and produce immediate involuntary apnea, bradycardia, and vasoconstriction of nonessential vascular beds with shunting of blood to the coronary and cerebral circulation to increase the chance of survival.

In salt water near drowning, surfactant washout occurs, and protein-rich fluid exudates rapidly fill 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. In fresh water drowning surfactant is also destroyed, producing alveolar instability, atelectasis, and decreased compliance with marked ventilation/blood perfusion mismatching.

Frequency:

Despite preventive measures, the 1997 National Center for Health Statistics found drowning second only to motor vehicle accidents (MVAs) as the most common cause of injury and death in children aged 1 month to 14 years. In 3 states, Arizona, Florida, and California, drowning actually exceeded MVAs. 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 9,420 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, with pools estimated to be 14 times more likely to be the cause of death in children younger than 5 years than motor vehicles.

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. Scuba diving accounts for an estimated 700-800 deaths per year (etiologies include inadequate experience/ training, exhaustion, panic, carelessness, and barotrauma).

Submersion-related injuries are the fifth leading cause of accidental death in the US 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. True incidence of near drowning has yet to be defined accurately, however, since many cases are not reported.

History:

The 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 of rescue, and response to initial resuscitation are all relevant factors in the injury and outcome.

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.

Other important historical factors include the following: Shortness of breath, difficulty breathing, apnea, persistent cough, wheezing, and vomiting. Coincident alcohol or drug use must be ascertained. Pertinent past medical history, particularly seizure disorder, diabetes mellitus, psychiatric history, severe arthritis, or neuromuscular disorder must be elicited.

Physical:

Causes:

In the preschool-aged children, drownings occur most commonly to 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.

Young adults typically drown in ponds, lakes, rivers, and oceans. 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. Studies show that 30-50% of older adolescents and adults who drowned in boating incidents were inebriated, as determined by blood alcohol concentrations.

It is important to consider underlying disease/illness in all age groups. Those would include: Seizure disorder, Myocardial infarction (MI) or syncopal episode, Poor neuromuscular control, such as that seen with significant arthritis, Parkinson, or other neurologic disorders, Major depression/suicide, Anxiety/panic disorder, Diabetes, and hypoglycemia.

Other causes include: 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, and scuba diving accidents and other injuries (e.g.: bites, stings, and lacerations).

Lab Studies:

If initial tests show elevated serum creatinine, marked metabolic acidosis, abnormal urinalysis, or significant lymphocytosis, serial estimations of serum creatinine should be performed. Acute renal impairment is known to occur frequently in near drowning, and while usually mild (serum creatinine <0.3 mmol/L or 3.4 mg/dL), severe renal impairment requiring dialysis may occur. A blood alcohol level and urine toxicology screen for use of drugs should be performed in age appropriate cases.>

Imaging Studies:

Procedures:

Extracorporeal membrane oxygenation (ECMO) has been shown to be beneficial in individuals with respiratory compromise despite intubation and aggressive mechanical ventilation and persistent hypothermia unresponsive to other warming methods.

Bronchoscopy may be necessary for removal of significant inhaled sediment.

Aggressive warming, with method dependent on the degree of hypothermia and the patient's response, may be warranted. Central venous pressure monitoring may be warranted. Urinary catheterization for ongoing urine output measurement may be warranted.

Prehospital Care:

Optimal prehospital care is a significant determinant of outcome in the management of immersion victims. The victim should be removed from the water at the earliest opportunity. Rescue breathing may be performed in water, but chest compressions are inadequate because of buoyancy issues. The patient should be removed from the water with attention to cervical spine precautions. If possible, the individual should be lifted out in a prone/supine position. Theoretically, hypotension may follow lifting the individual out in an upright manner because of the relative change in pressure surrounding the body from water to air. Management of the ABCs (airway, breathing, circulation) is the priority, with particular attention to securing the earliest possible airway and providing adequate oxygenation and ventilation. In the patient with an altered mental status, the airway should be checked for foreign material and vomitus.

Immediately place the patient on 100% oxygen by mask. If available, continuous noninvasive pulse oximetry is optimal. If the patient remains dyspneic on 100% oxygen, or manifests a low oxygen saturation, use CPAP if available. If it is not available, consider early intubation, with appropriate use of positive end-expiratory pressure (PEEP). The neck should be immobilized if the patient has facial or head injury, is unable to give an adequate history, or may have been involved in a diving accident or MVA. The patient should be carefully stripped of wet clothing and wrapped in warming blankets.

Emergency Department Care:

Intubated victims of submersion injury may require PEEP with mechanical ventilation to maintain adequate oxygenation. PEEP has been shown to improve ventilation patterns in the noncompliant lung in several ways, including (1) shifting interstitial pulmonary water into the capillaries, (2) increasing lung volume via prevention of expiratory airway collapse, (3) providing better alveolar ventilation and decreasing capillary blood flow, and (4) increasing the diameter of both small and large airways to improve distribution of ventilation. ECMO has been shown to be helpful in individuals who remain hypoxic despite aggressive mechanical ventilation.

Hypothermic patients with core temperatures less than 86°F, who have undergone sudden, rapid immersion, may display slowing of metabolism and preferential shunting of blood to the heart, brain, and lungs, which may exert a protective effect during submersion. This is not, however, the case with most immersion victims, who have become hypothermic gradually and are at risk for ventricular fibrillation and neurologic injury. As such, vigorously rewarm hypothermic patients to normothermia.

Many authors have postulated that a primitive mammalian diving reflex may be responsible for survival after extended immersion in cold water. The mechanism for this reflex has been postulated to be reflex inhibition of the respiratory center (apnea), bradycardia, and vasoconstriction of nonessential capillary beds triggered by the sensory stimulus of cold water touching the face; these responses preserve the circulation to the heart and brain and conserve oxygen, thereby prolonging survival. The sudden temperature drop may depress cellular metabolism significantly, limiting the harmful effects of hypoxia and metabolic acidosis.

Additional important maneuvers in the emergency department include placing a nasogastric tube to assist in rewarming efforts and urinary catheter to assess urine output. Core rewarming with warmed oxygen, continuous bladder lavage with fluid at 40°C, and intravenous (IV) infusion of isotonic fluids at 40°C should be initiated during resuscitation. Warm peritoneal lavage may be required for core rewarming in severely hypothermic patients. A surgeon's assistance in necessary in this regard. A cascade unit on the ventilator provides warm inspired air.

Thoracotomy with open heart massage and warm mediastinal lavage has been shown to sometimes be effective. The hypothermic heart is typically unresponsive to pharmacotherapy and countershock. Extracorporeal blood rewarming may be used in severely hypothermic patients who do not respond to lavage/thoracotomy or who are in arrest. When a central line is placed, it must be done cautiously in order to avoid stimulation of the hypothermic atrium and resultant dysrhythmias. Most importantly, resuscitation of a submersion victim should not be abandoned until the patient has been warmed to a minimum of 30°C. The heart becomes more responsive to resuscitation at normal body temperatures.

Patients able to relay a good history of minor immersion injury, without evidence of significant injury and without evidence of bronchospasm, tachypnea/dyspnea, or inadequate oxygenation (by ABG analysis and pulse oximetry) can be safely discharged from the hospital after 6-8 hours of observation. However, older individuals or those with underlying medical conditions that might place them at increased risk of hypoxic injury and acidosis should be observed for longer periods. Victims of mild to moderately severe submersion, who only have mild symptoms that improve during observation and have no abnormalities on ABG or pulse oximetry and chest radiograph, should be observed for a more prolonged period of time in the hospital because of post-immersion syndrome. Certain patients may display mild to moderately severe hypoxemia that is corrected easily with oxygen. These patients should be admitted for a few days of observation. All patients who are intubated and on mechanical ventilation should be admitted to the ICU. Varying degrees of neurologic as well as pulmonary insults typically complicate their courses.

Deterrence/Prevention:

All individuals involved in boating should be able to swim, should use personal flotation devices when on the boat or in the water, and should avoid the use of alcohol or other recreational drugs. Boaters should be taught to anticipate wind, waves, and water temperature, and to use protective suits and other insulating garments in cold weather.

All children should be taught to check the water carefully for depth and possible injurious objects before diving in. Children also should be taught their swimming limitations and to not play dangerously in pools or on the decks surrounding pools.

People should not drink alcohol or use other recreational drugs when swimming.

Individuals with underlying medical illnesses that may place them at risk when swimming, such as seizure disorders, diabetes mellitus, significant coronary artery disease, severe arthritis, and disorders of neuromuscular function, should swim under the observation of another adult who can rescue them should they get into trouble.

Complications:

Prognosis:

Medical/Legal Concerns:

Cervical spine trauma may be present in any victim of shallow- or rocky-water immersion injury. If the victim is unable to give a clear history of the events, has evidence of head or facial injury, or is found unresponsive in a pool or other shallow body of water, the cervical spine must be protected until injury is excluded.

Early rewarming is essential. Delays are associated with a poor outcome. Also, patients who look well can decompensate later. This is called post-immersion syndrome. That is why patients should undergo a liberal period of observation. Finally, child abuse in young children who are the victims of submersion injury in bath tubs, buckets, or other shallow water receptacles should be ruled out.