Drowning

Even though drowning is considered a form of asphyxia with death resulting from anoxia, the mechanism incorporated in drowning can have factors other than asphyxia and the physical characteristics differ from those found in other forms of asphyxia (Sinclair et al., 2006). The diagnosis of drowning is made from information dissimilar from typical asphyxia deaths (Sinclair et al., 2006). For these reasons, drowning is considered separately from other forms of asphyxia in this chapter.

A definition of drowning is death secondary to hypoxemia from asphyxia when immersed in a liquid (Merck & Miller, 2013). Submersion may be the whole body or enough to immerse just the external airway openings (Merck & Miller, 2013). A primary pathophysiologic abnormality observed in drowning is hypoxic tissue damage due to the inability to maintain adequate pulmonary gas exchange (Powell, 2015). Drowning appears to be an uncommon reason for the veterinary evaluation of companion animals (Heffner et al., 2008). This fact alone should raise suspicions about events and circumstances if drowning is suspected as a cause of injury or death. According to Pet-Abuse.com U.S. Animal Abuse Classifications as of September 2017, drowning encompassed less than 1% of animal abuse cases nationally (PetAbuse.com).

Intentional drowning as a form of animal abuse consists of several forms (Sinclair et al., 2006). A primary form of drowning is "nuisance animals": wildlife or unwanted offspring are drowned in a misdirected attempt at euthanasia or “disposal drowning” (Sinclair et al., 2006). A secondary form is an act of punishment or attack, meant to frighten, intimidate or abuse an animal victim or a human victim associated with an animal. This is known as “furious drowning" (Sinclair et al., 2006). A third form is "faux drowning” in which an animal is killed by some noninvasive means, for example strangulation or blunt force trauma to the head, and then the animal’s body is saturated with water or immersed it in a container or body of water to simulate drowning. This type of drowning may be used as a means of intimidation of another person (as in domestic violence) or an attempt to cover up another form of animal abuse (Sinclair et al., 2006). According to the AVMA report on euthanasia, drowning is not an acceptable means of euthanasia and is inhumane. Investigation of a drowning case may demonstrate the cause of death may have been slow, stressful, and painful, consistent with the legal definition of torture, which can result in a felony charge (Sinclair et al., 2006).

In 2002, the World Health Organization (WHO) defined drowning and its possible outcomes by an international expert committee: "Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid” and “outcomes are death, morbidity, or no morbidity” (McEwen & Gerdin, 2016). The findings were that adoption of these new terms should be considered by veterinary pathologists and forensic veterinarians (McEwen & Gerdin, 2016). Submersion occurs when the entire body is under water, and immersion signifies the body being partially covered with water; it is necessary for the airway to be immersed as well for drowning to occur.

Establishing drowning as a cause of death in animals is challenging. When an animal is found in a body of water or completely wet, drowning must be a differential. A key question is whether the animal was alive at the time it entered the water or was exposed to water (McEwen & Gerdin, 2016). A diagnosis of drowning is often one of exclusion, requiring additional information from the crime scene, the medical history (if available), or witness statements (McEwen & Gerdin, 2016).

Mechanism of Drowning

The primary mechanism of drowning is the rapid and persistent onset of hypoxemia after the entrance of liquids into the airways (McEwen & Gerdin, 2016). The drowning process is multifaceted, involving cardiorespiratory reflexes and electrolyte and blood gas abnormalities. It results in the aspiration and swallowing of liquid (water) and vomit. Struggling ensues with involuntary movement, physical exertion/exhaustion, and breathlessness resulting in death (McEwen & Gerdin, 2016).

The overall effect is an immediate decrease in arterial oxygenation with concurrent acidosis and hypercarbia. The arterial levels of carbon dioxide are usually below the 95 mm of mercury for carbon dioxide—induced necrosis that was thought to cause unconsciousness in drowning animal victims (McEwen & Gerdin, 2016). This is a primary reason drowning is considered inhumane (McEwen & Gerdin, 2016).

Phases of Drowning

In the past, the drowning process was reviewed in the literature through experimentation on dogs, demonstrating behavioral and biological drowning responses (McEwen & Gerdin, 2016). These have been generalized in the five phases of drowning (McEwen & Gerdin, 2016). In phases 1 and 2 escape attempts, violent struggling, and breath holding are observed. The third phase has deep respiratory movements of the chest, swallowing, and convulsions. Phase 4 results in diminished corneal reflexes and dilated pupils. The final fifth phase has diminished respiratory movements, head and jaw muscle fasciculations, and death (McEwen & Gerdin, 2016).

A dog can struggle violently for up to 1.5 minutes; the glottis is usually closed and thoracic inspiratory movements continue to be attempted, resulting in liquid being swallowed (McEwen & Gerdin, 2016). If unconsciousness results due to hypoxemia, the larynx can relax, and liquid is aspirated, or if the animal does remain conscious water is aspirated and swallowed from inspiratory gasping (McEwen & Gerdin, 2016). After 3 minutes, spasmodic convulsions and seizures can occur, and resulting overinflation of the stomach with liquid causes vomiting (McEwen & Gerdin, 2016). Cardiac asystole or death can occur in 5 minutes but may take up to 10 minutes after submersion (McEwen & Gerdin, 2016). Initial hypoxemia is complicated by pulmonary edema, catecholamine release, vasoconstriction, cardiac arrhythmias, pulmonary hypertension, and right-to-left intrapulmonary shunting (McEwen & Gerdin, 2016).

Electrolyte and intravascular changes from drowning are due to the salinity and/or volume of water aspirated into the lungs. These biochemical effects of water are osmotic (McEwen & Gerdin, 2016). Differentiating saltwater and freshwater drowning is forensically important. In fresh water, animals may demonstrate hemodilution, hypervolemia, decreased serum chloride, sodium, osmolality, hematocrit, and hyperkalemia. These changes may be temporary via redistribution of fluids in the animal’s body but can persist with larger volumes of water aspirated 22 mL/kg or above. In dogs, aspirated fresh water infiltrates the circulation within 3 minutes and approximately 10% of body weight can be absorbed in the lungs during a fresh-water drowning (McEwen & Gerdin, 2016).

Saltwater aspiration may be more deadly than freshwater, only requiring half the aspirated volume of fresh water to cause drowning. Drowning in saltwater causes hemoconcentration with increased serum sodium, osmolality, and potassium. The hypertonicity of saltwater pulls fluid from the circulation into the alveoli, altering the basement membrane, causing washout of surfactant and diminished lung capacity resulting in pulmonary edema (McEwen & Gerdin, 2016).

Drowning causes progressive cerebral hypoxia and death. Injury occurs in selective regions of the brain within 4-10 minutes and maybe irreversible. In addition, persistent coma may develop within minutes after this time period (McEwen & Gerdin, 2016).