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Update on Drowning
By Saadia R. Akhtar, MD, MSc, St. Luke's Idaho Pulmonary Associates, Boise, is Associate Editor for Critical Care Alert.
Dr. Akhtar reports no financial relationship to this field of study.
INTRODUCTION AND EPIDEMIOLOGY
Drowning is defined as asphyxia or suffocation from submersion/immersion in a liquid medium. Tissue oxygen deprivation is what leads to organ injury and death. Drowning also has been defined as death by asphyxia within 24 hours of submersion with terms such as near-drowning, secondary drowning, submersion injury, and immersion syndrome used for longer survival after submersion or other clinical circumstances; current guidelines recommend simply using the term drowning.1
Drowning is a common and usually preventable cause of considerable morbidity and mortality in pediatric and adult populations. It is the sixth leading cause of accidental death in persons of all ages in the United States (and the second leading cause of death for those aged 1-14 years), resulting in 3939 deaths in 2007. It is the fourth leading cause of death worldwide with more than 300,000 deaths yearly.2,3
The incidence of near-drowning (i.e., survival after drowning) is not as well known (since many cases are never reported) but is estimated to be several-fold greater than that of drowning with some authors estimating as many as 70,000 persons affected yearly in the United States. Of these, it has been observed that about 10%-25% die; of the survivors, 10% are left with neurological deficits and the remainder survive intact.4
Drowning is most common in children (usually in the home environment) and young adults (age 15-25 years, usually in lakes or rivers). The bulk (> 90%) of drownings occur in fresh water. The majority of episodes of drowning involve males; African American and Native American persons are at higher risk than Caucasians. Alcohol is a factor in about 50% of cases.2,5
Risk factors for drowning include alcohol or drug use, poor swimming skills and, for children, lack of adult supervision. Presence of an underlying seizure disorder (increases risk of drowning in children by > 10-fold), hyperventilation prior to swimming or occurrence of concomitant trauma, acute myocardial infarction, acute stroke, or arrhythmia may lead to drowning (15% of syncopal events related to long QT syndrome occur during swimming).6-8
PATHOPHYSIOLOGY AND PRESENTATION
Hypoxia is the common denominator of the pathophysiology of drowning. The initial response to submersion is breath holding and panic/struggle to rise to the surface, for up to a few minutes. Ultimately the victim takes an involuntary breath and water enters the hypopharynx, leading to laryngospasm. Sustained laryngospasm occurs in < 10%-15% of victims (formerly termed "dry drowning"), while glottic relaxation occurs in the majority of persons ("wet drowning") and results in more significant lung injury. There may be vomiting and aspiration of gastric contents as well. Ongoing hypoxemia then leads to brain and myocardial injury, circulatory collapse, other end-organ ischemia, and ultimately, death.6,9
More specifically, from a pulmonary standpoint, aspiration of water results in disruption of surfactant, alveolar collapse, and atelectasis. Alveolar-capillary damage from aspiration causes capillary leak and pulmonary edema; there also may be a component of cardiogenic or neurogenic pulmonary edema. Small airways may be obstructed by aspirated water, debris, or gastric material and there may be bronchospasm. Risk of acute lung injury in the setting of drowning is estimated to be as high as 40%.4,6,10
Historically, it was believed that due to osmotic shifts, salt water drownings were associated with greater pulmonary edema and perhaps relative hypovolemia while fresh water drownings carried a higher risk of hypervolemia and electrolyte abnormalities such as hyponatremia. Experience has shown that although there may be some theoretical differences between salt water and fresh water aspiration, these are rarely clinically significant.11
From a cardiac standpoint, victims of drowning may have evidence of shock with reduced cardiac function. Hypoxemia and hypothermia predispose to arrhythmias (most commonly bradycardia). Cold diuresis may also lead to relative hypovolemia and hemodynamic instability.4,6
Neurologically, diffuse neuronal damage and loss of blood-brain barrier occur resulting in cerebral edema. In the normothermic patient, full and normal neurologic recovery may be possible at 5-7 minutes of anoxia but is unlikely with greater periods of anoxia; this interval can be several-fold higher in the hypothermic patient. Finally, unless the drowning was known to have been high-impact or in a high-risk setting, the likelihood of cervical spine injury is quite low at < 1% in one large study of more than 1000 patients.12
Metabolic acidosis (lactic acidosis from initial muscle overuse and fatigue while struggling and then hypoxia/hypoperfusion of tissues), respiratory acidosis (related to apnea), acute tubular necrosis, and small transient changes/abnormalities in electrolytes may occur. Rarely, hemolysis and diffuse intravascular coagulation are also seen.
The clinical presentation of drowning varies widely with victims being asymptomatic to obtunded. Cough, dyspnea, and tachypnea are common presenting symptoms and signs. Chest x-ray is normal in about a fifth of patients; pulmonary edema and atelectasis are the usual findings in the rest.
Historically, there have been some unusual approaches to resuscitation and treatment of victims of near-drowning, including "insufflation of smoke of tobacco into the rectum," slinging persons in prone position on a horse, or placing victims on a tilting board to move the diaphragm.4 These are no longer practiced.
The first steps in managing a drowning victim are to remove him or her from the water and, if indicated, initiate CPR and ACLS protocol; obtaining a history of events also is essential. Rescue breathing should begin even while in the water. Caution should be used with manipulating the neck in case of cervical spine/cord injuries but, as discussed above, unless a high-risk/high-impact event clearly took place, the risk of spinal cord injury in most drownings is small and routine stabilization of the C-spine after drowning is not necessary.1
Once the victim is out of the water, wet clothing should be removed and the person covered/warmed with dry blankets. Rewarming is recommended for those with core body temperature < 34°C. CPR and resuscitation should not be stopped until body temperature is at least > 32°C; good neurological outcomes have been reported for resuscitation after prolonged cold-water submersion. Although reported in small studies with variable outcomes, maintenance or induction of hypothermia is not recommended at this time for victims of drowning. Neither are corticosteroids or barbiturates (considered in the past for prevention or limitation of cerebral edema in drowning).6,13
Application of the Heimlich maneuver or any attempted postural drainage of water is not recommended; these measures do not aid in removal of lung water, may precipitate aspiration, and can delay initiation of effective therapies.4
In the emergency room and hospital, full evaluation for trauma/other injury is indicated. Airway protection with intubation and provision of ventilatory support must be considered. IV fluid support should be provided, typically without glucose. (The recommendation to avoid hyperglycemia in victims of drowning is based on data from outcomes in patients with ischemic stroke, animal models of drowning, and some retrospective studies of pediatric drowning that suggest worse outcome with hyperglycemia.)
Routine antibiotic prophylaxis is not recommended; antibiotics should only be considered for persons who are submersed in grossly contaminated water. There are multiple case reports of pneumonia after drowning with Aeromonas, Pseudomonas, Aspergillus, Pseudallescheria, and others.14
Finally, although there are case reports of use of exogenous surfactant for victims of drowning, surfactant is not recommended as standard therapy for lung injury or hypoxia from drowning.15
Overall survival after drowning is 75%-90% with the majority of patients having normal neurological outcome (75%-80%). Although several predictive scoring systems have been proposed and tested in limited trials (Orlowski, Conn-Modell, Graf and others), none have performed consistently or been incorporated into standard clinical practice. Not surprisingly, clinical course and neurological exam over the first 24-72 hours are the best predictors of outcome. Submersion time < 10 minutes, younger age, and mild hypothermia at presentation are predictors of improved survival. Time to initiation of CPR, duration of resuscitation, initial GSC < 5, fixed dilated pupils, asystole on arrival to hospital, and initial arterial pH < 7.1 are associated with poor survival.8,16
Drowning is an avoidable injury that causes significant morbidity and mortality. Hypoxia leads to end-organ injury with the lungs and brain most commonly and severely impacted. The treatment is standard aggressive resuscitation including effective CPR, correction of hypothermia, volume support, appropriate low tidal volume ventilation for acute lung injury, and other usual supportive care.
Prevention is key. Some effective measures are: public education on water safety and CPR, good swimming skills, avoidance of alcohol/drugs when engaged in water activities, supervision for children or poor swimmers, and swimming with another person particularly if there is a history of seizures or syncope.