Drowning

Published on 06/06/2015 by admin

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6 Drowning

Drowning is defined as a process of respiratory impairment from submersion or immersion in a liquid. Although complicated terminology to define drowning has been used in the past, the 2002 World Congress on Drowning established this universal definition, and recommends against the use of other terms, including “near drowning” and “dry drowning.”

Pediatric drowning is the second leading cause of accidental childhood death in the United States, surpassed only by motor vehicle collisions. It is most common in young toddlers and adolescents, and boys are more likely to drown in all age groups. Toddlers are most likely to drown in small, household water sources such as bathtubs and buckets. Inadequate adult supervision is often responsible, although children have usually been out of sight for less than 5 minutes. Toddlers have large heads relative to their bodies, making them more likely to fall forward into buckets or tubs and less able to right themselves (Figure 6-1). Adolescents are more likely to drown during recreational activities such as boating and in natural bodies of water. Alcohol use contributes to up to 50% of teenage drownings. Pediatric drownings carry high morbidity and mortality; 30% to 50% of drowning victims die, and 10% survive with severe neurologic impairment.

Figure 6-1 Toddlers have high centers of gravity.

Etiology and Pathogenesis

Hypoxemia is the driving force of the process of drowning, initially caused by apnea and then caused by aspiration. After submersion, drowning victims typically hold their breath and struggle. Small amounts of water are aspirated, and involuntary laryngospasm and hypoxia ensue. With continued hypoxia, the vocal cords relax, and larger amounts of water are aspirated. Even greater amounts of water are swallowed than aspirated, and vomiting is common. The cascade of pulmonary damage from drowning can occur with aspiration of as little as 1 to 3 mL/kg of water.

The effects of aspiration and continued submersion are many (Figure 6-2). Within the alveoli, water prevents diffusion of oxygen across the capillary/alveolar membrane. The capillary endothelium becomes increasingly permeable, resulting in pulmonary edema. Aspiration of gastric contents contributes to lung injury. As pulmonary edema and intrapulmonary shunt progress, hypoxia, hypercarbia, and acidosis ensue. These metabolic disturbances decrease myocardial contractility, increase systemic vascular resistance, and contribute to arrhythmias. If submersion continues long enough, drowning will progress to cardiac arrest. Clinically, there is little difference between fresh and salt-water drownings; however, there are some putative pathophysiologic differences. Whereas fresh water is particularly destructive to surfactant, salt water causes osmotic forces to draw additional fluid into the alveoli. Electrolyte disturbances are rare; however, ingestion of large amounts of fresh water can cause hyponatremia, and salt water ingestion can cause hypernatremia. Ingestion of large quantities of fresh water in the setting of hypoxemia may lead to hemolysis, although this is also a rare event.

Figure 6-2 Pathophysiology of drowning.

Hypothermia is often present and causes peripheral vasoconstriction, which preserves blood flow to the central organs. Increased core blood flow triggers central volume receptors to perceive greater blood volume and thus produce less antidiuretic hormone, resulting in diuresis and volume depletion.

Clinical Presentation

The duration of submersion and hypoxia will determine the clinical presentation and outcome in drowning victims. Submersions less than 5 minutes are associated with intact survival, but submersions more than 25 minutes have almost universally poor outcomes. Many victims are rescued from the water in cardiac arrest, and immediate, effective cardiopulmonary resuscitation (CPR) can improve survival rates and neurologic outcome. After pulses are restored, signs of shock may be present, including hypotension, diminished peripheral pulses, altered level of consciousness, acidosis, and decreased urine output. Patients may appear cold, cyanotic, and unresponsive. More mildly affected patients may have isolated pulmonary findings such as wheezes, crackles, cough, or hypoxia. Neurologic findings range from an alert child to any amount of central nervous system compromise, including coma with flexor or extensor posturing.

Many studies have evaluated factors associated with good outcomes, and better prediction is possible with parameters measured later in the hospital course than at initial presentation or in the field. There have been reports of pediatric survivors with good outcomes despite ominous predictors such as submersion over 1 hour. Thus, all patients should receive aggressive initial resuscitation in the field and emergency department (ED), regardless of circumstances surrounding the drowning. After initial resuscitation, failure to exhibit reflexes or response to external stimuli within the first 24 hours of care predicts a poor neurologic outcome.

Unusually good outcomes have occurred in cold-water drownings in children. It is believed that sudden exposure of the face to icy water triggers a protective “diving reflex” that causes apnea, bradycardia, and vasoconstriction. The resultant decreased metabolic demands seem to improve the chances of neurologic recovery compared with warm-water drownings of similar duration. An alternative theory is that rapid cerebral cooling leads to decreased cerebral metabolic demand and is responsible for these outcomes. Ultimately, these good outcomes are relatively rare, and the reasons for them remain unclear.

It is important to consider potential coexistent injuries and risk factors for drowning. Drowning may be associated with other trauma, including head injury, blunt abdominal trauma, and spinal injury (Figure 6-3). Seizures, cardiac arrhythmias, hypoglycemia, and intoxication can all contribute to a drowning event.

Figure 6-3 Injury to the cervical spine during drowning.

Evaluation and Management

Unresponsive patients should be evaluated according to Basic Life Support guidelines and receive CPR as indicated at the scene (see Chapter 1). The Heimlich maneuver and attempts to drain water from the lungs should be avoided. Further cooling of the patient should be prevented by removing wet clothing and insulating the patient with dry blankets. Prehospital care and ED providers should evaluate the patient’s airway and ventilatory efforts, provide oxygen, and consider intubation. Unresponsive and hypoxic patients most likely require intubation because vomiting is common, and lung injury will probably continue to worsen. If cervical spine (c-spine) injury is a possibility, resuscitation should occur with c-spine immobilization throughout. Gastric decompression is an important step in early resuscitation. Use of a nasogastric or orogastric tube to remove stomach contents decreases vomiting and aids in ventilation by allowing easier distension of the lungs.

Initial laboratory studies should include an arterial blood gas analysis, chest radiograph, complete blood count, electrolytes, and urinalysis. Attention should be paid to reversing hypoxemia and metabolic acidosis. Shock is common after initial resuscitation of drowning victims. Myocardial dysfunction caused by hypoxia, acidosis, hypothermia, and volume loss contribute to decreased perfusion. Both volume resuscitation and inotropic support may be required. Dobutamine is an inotrope recommended for drowning patients if cardiovascular support is required.

Hypothermia was once universally treated with active rewarming; however, emerging evidence suggests that maintaining cooler temperatures may be protective. Ice water drownings have better outcomes than expected, and hypothermia after cardiac arrest in adults may improve neurologic outcome. Thus, the decision to aggressively rewarm should be made carefully. All patients with a core temperature below 28°C with coagulopathy, hypotension, or arrhythmia should be actively rewarmed. A target temperature of 32° to 34°C is recommended for comatose drowning patients. Active rewarming may use external heating blankets and lamps, and internal rewarming may include warm intravenous fluids, warm bladder irrigation, and even cardiac bypass or extracorporeal membranous oxygenation (ECMO) for the most unstable patients. Passive rewarming should be used to keep all patients from becoming cooler. Hyperthermia is detrimental for all patients and should be avoided in patients who are being actively rewarmed. Continuous temperature monitoring with special hypothermia thermometers (which can read lower temperatures than routine thermometers) is recommended.

Lung injury rapidly evolves in the initial hours after drowning, and the patient may require prolonged mechanical ventilation and possibly nonconventional ventilatory modalities or ECMO. Decreased lung compliance, edema, surfactant deficiency, and alveolar damage can progress to acute respiratory distress syndrome (ARDS). Although ARDS is commonly managed with permissive hypercapnia, in a drowning patient with suspected brain injury, normocapnia preserves cerebral perfusion, making ventilatory strategies more challenging. Diuretics have not been shown to be helpful in treating pulmonary edema from drowning and may even be harmful in patients who are volume depleted. Fluid status and renal function should be carefully monitored. Pneumonia can occur and should be treated if clinically apparent; however, prophylactic antibiotics are not recommended except for drowning in grossly contaminated water such as sewage. Aeromonas is an organism that has been associated with severe pneumonia after drowning.

Although primary hypoxic injury to the brain cannot be reversed, prevention of secondary neurologic injury is a goal of acute postresuscitative care. This involves careful monitoring of all body systems to maintain normotension, normoglycemia, and normocapnia and to prevent hypoxia. Seizures are common and should be promptly controlled with anticonvulsants. Monitoring of intracranial pressure or placement of a ventriculostomy drain has not been shown to improve outcomes in drowning victims. Long-term sequelae of hypoxic-ischemic brain injury from drowning may range from mild cognitive difficulties to seizures to persistent vegetative states. Some children may develop reactive airway disease as well.

After acute resuscitation and management of airway, breathing, and circulation, evaluation for concomitant injury and the underlying cause of drowning should occur. Circumstances surrounding the event help guide this workup, and evaluation of a patient with a suspected traumatic mechanism should follow the approach to the trauma patient (see Chapter 8). A history of high-impact trauma such as diving, striking an object, or being in a motorized boat increases the likelihood of requiring computed tomography scans to evaluate for c-spine, intraabdominal, or head injuries. The serum glucose level should be checked both to detect causative hypoglycemia and to preserve normoglycemia. Hypoxic-ischemic injury to the liver and kidneys may present as coagulation abnormalities and acute tubular necrosis.

Seizures are the most common underlying medical cause of drowning. Arrhythmias should also be considered. An electrocardiogram should be evaluated in an otherwise healthy person who drowns without a traumatic mechanism or apparent cause. A congenitally prolonged QT interval can lead to arrhythmia and loss of consciousness with subsequent drowning in the water. Cold-water exposure, exercise, and breath holding appear to trigger arrhythmia in patients with congenital long QT syndrome. If it is suspected, family members should also be evaluated. Urine and blood testing for drugs of abuse may be considered in adolescents. Child abuse sometimes leads to drowning, and a careful history and physical examination should be performed to evaluate for other signs that this might be a possibility.

Many drowning victims have no symptoms. Patients with Glasgow Coma Scale scores greater than 13 who remain asymptomatic for 6 to 8 hours may be considered for discharge. Some advocate routine chest radiography in such patients before discharge. Even mild symptoms during the first 6 hours should prompt hospitalization because lung disease can continue to progress. Any patient with a submersion lasting more than 1 minute with apnea or cyanosis should be admitted for observation.