Drowning: 2012 Review (More PulmCCM Topic Updates)
There are a thousand ways to die (it's even a TV show), but few seem as horrible and inspire such primal fear as death by drowning. Drowning is uncommon but by no means rare in the U.S.: it's the second leading cause of death by injury in the U.S. among toddlers (3 per 100,000 among children aged 1 to 4), and you are 200 times more likely to die by drowning during a boat ride as to die from trauma during a trip by automobile. Drowning kills about 500,000 people a year worldwide, according to the WHO. David Szpillman, Joost Bierens, Anthony Handley, and James Orlowski provide an update on drowning in the May 31 2012 New England Journal of Medicine.
How People Drown: Pathophysiology
We can only hold our breath for about a minute. Eventually, a person submerged in water gasps for air, aspirates water, and starts coughing as a reflex response; continued aspiration follows. Hypoxemia leads to unconsciousness, apnea, and cardiac decompensation: tachycardia, then bradycardia, pulseless electrical activity (PEA), then asystole. From the last breath of air to final cardiac arrest, drowning may take less than a minute, to several minutes. Colder water (hypothermia) slows the entire process.
An alternative (but no less macabre) method of drowning involves hypoxemia by involuntary laryngospasm after water enters the throat and trachea. A few people may prevent water from entering their lungs this way (complicating medical examiners' autopsies in some cases), but hypoxemia results nevertheless, followed by relaxation of the larynx with unconsciousness progressing to cardiac arrest.
Treating Drowning Victims in the Emergency Department
Recognize that only 6% of people rescued by lifeguards require hospital-level medical care. For those that do require care in the emergency department, authors advise standard measures of supportive care: Restore oxygenation and secure an airway if needed; restore circulation with crystalloid and vasopressors if necessary; insert a gastric tube. Also, they say:
Thermally insulate the patient.
Expect a metabolic acidosis that will correct itself in most patients as they (or you) increase their minute ventilation;
Patients on mechanical ventilation may require high delivered minute ventilations, and may benefit from high peak inspiratory pressures (authors mention 35 cm H2O).
Routine sodium bicarbonate for metabolic acidosis is not advised by the authors.
Consider ingestions or intoxications, or cervical spine or head injuries, especially for patients who remain unresponsive despite the above measures. Other lab abnormalities (e.g., electrolytes, creatinine, hematocrit) are rarely contributory, authors say.
Many patients will improve to baseline with normal oxygen saturation on ambient air within 6 to 8 hours, and in the absence of complicated comorbidities may be safely discharged (authors say); others should be admitted to an intermediate care or ICU setting.
Treating Drowning Victims in the ICU
Authors advise the following:
Mechanical Ventilation for Drowning Victims
Treat drowning victims as ARDS patients, with low tidal-volume lung-protective mechanical ventilation.
Not weaning mechanical ventilation for at least 24 hours, even if a drowning victim appears ready to extubate: the underlying pulmonary injury may result in recurrence of pulmonary edema, reintubation and increased risk of complications.
Pneumonia is usually not present initially (12% in one series) and authors believe antibiotics may be over-prescribed and sometimes harmful; instead, use clinical evidence of infection or bronchoscopic / mini-BAL sampling to identify pneumonia and need for antibiotics. Swimming pool water in particular is unlikely to cause pneumonia.
On the other hand, late-onset nosocomial pneumonias (i.e., ventilator-associated pneumonia) may be equally common among mechanically ventilated drowning victims as those with other causes of respiratory failure.
Systemic inflammatory response syndrome (SIRS) can occur after drowning -- authors advise not to "misinterpret [it] as infection," but also say that sepsis is possible, too (not helpful).
Expect a faster respiratory recovery than in typical ARDS patients, with full recovery of pulmonary function in most cases.
Shock and Cardiac Dysfunction in Drowning Victims
Resuscitation with crystalloid infusion and re-warming hypothermic patients restores normal circulation, cardiac output and blood pressure in most drowning victims. Severe drowning victims may have cardiac dysfunction and/or circulatory collapse despite adequate fluid resuscitation and rewarming; authors advise echocardiography in to guide the use of vasopressors and/or inotropes, in these patients.
Induced Hypothermia For Drowning Victims: Warm, Then Cool?
Case reports have described better-than-expected outcomes by using induced hypothermia for drowning victims (two were young men, aged 12 and 19, another was a 29 year old woman). Induced hypothermia / targeted temperature management is not the standard of care for all drowning victims, according to the American Heart Association's 2010 guidelines.
Patients who present with hypothermia and shock may require initial re-warming in order to restore circulatory system function and blood pressure. The cases described presented in shock with hypothermia and were warmed to ~34 degrees Celsius as part of a hypothermia protocol combined with ECMO. All regained near-normal neurologic function after being submerged for at least 10-15 minutes each; the 29-year old woman was submerged in ice water for as long as 40 minutes and had a core temperature of 13 degrees Celsius.
First, Do Not Drown: Prevention
Most drownings are preventable. Safety guidelines advise everyone to:
Learn how to swim, and don't overestimate your own swimming ability.
Swim safe: never swim alone, obey warning signs, don't drink alcohol and swim, and swim where lifeguards are present.
Know how and when to use a life jacket.
Avoid rip currents, which cause most deaths at the beach.
Always enter shallow or unknown depth water feet first.
You may notice that "not eating 30 minutes before swimming" isn't on here -- that's just a myth your mom told you.
Szpillman D et al. Current Concepts: Drowning. NEJM 2012;366:2102-2110.
Bierens JJ et al. Drowning. Curr Opin Crit Care. 2002 Dec;8(6):578-86.
Salomez F et al. Drowning: a review of epidemiology, pathophysiology, treatment and prevention. Resuscitation. 2004 Dec;63(3):261-8.
American Heart Association guidelines on resuscitation after drowning. Circulation 2010.