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Canine Drowning O T S R E T T U H S CE Article #2 m o c . k c Canine Drowning o t s r e t t u h S / Carrie E. Goldkamp, VMD a d z a Michael Schaer, DVM, DACVIM, DACVECC a G y l r e University of Florida b m i K 8 0 0 2 © ABSTRACT: Drowning is potentially fatal. Physiologic responses to aspiration of water differ according to whether the water is salt or fresh; whether these responses are significant depends on the volume of fluid aspirated. Resuscitation efforts should be started at the scene of the accident. Oxygen therapy is essential . Many patients require continuous positive airway pressure or positive end-expiratory pressure to reverse hypoxemia. Physiologic responses induced by ice-water submersion can be protective during the initial insult. The prognosis for submersion injuries is guarded and is influenced by several variables. rowning is defined as “the process of presumed that in these cases, death occurred experiencing respiratory impairment before the person entered the water or was due from submersion or immersion in liq - to a sudden cessation of circulation without D1 uid.” The terms near-drowning and drowning aspiration of water. Active aspiration is required were previously used to classify outcomes with for water to enter the lungs. 6 A conscious, sub - regard to survival. 2 However, these terms have merged person usually aspirates water as he or been replaced with death , morbidity , and no mor - she struggles in panic, which is associated with bidity following a drowning episode. 1 In 2004, massive catecholamine release. 7 Conversely, drowning was the second most common cause when a person loses consciousness before sub - of accidental death in children younger than 14 mersion/immersion (e.g., as a result of seizure), years in the United States, with approximately he or she quickly sinks, and there may be no five times as many children of this age sustain - catecholamine release. 7 The terms dry drowning ing morbidity from drowning. 3 and wet drowning are no longer used. 1 It was previously believed that 85% to 90% of Most of the initial studies on the pathophysi - humans who drown experience wet drowning , ology of submersion/immersion injuries and the in which a large volume of water is aspirated, treatments for morbidity were conducted in and that 10% to 15% experience dry drowning , dogs. Although the prevalence of drowning in in which little or no water is aspirated but dogs does not reach that in children, there are severe laryngospasm causes severe hypoxemia numerous unpublished reports of submersion/ and eventual death. 4 A more recent study, 5 immersion injuries in dogs. Canine drowning however, found that less than has been associated with falling into water, 2% of human deaths from swimming accidents, intentional immersion, drowning were “dry.” It is now seizures near water, and falling through ice. 8 This •Take CE tests article reviews the human literature based on the aDr. Schaer discloses that he has re- canine model, describes the pathophysiology of • See full-text articles ceived financial support from VCA Antech and from Novartis Animal drowning, and presents the treatment and prog - CompendiumVet.com Health. nosis for the associated morbidity. COMPENDIUM 340 June 2008 342 CE Canine Drowning PATHOPHYSIOLOGY hydrophilic material produced by type II pneumocytes Initial Injury (specialized cells in the alveoli). Normally, the alveoli are The earliest studies in dogs investigated the pathophys - lined with surfactant, which, by decreasing the surface iology of freshwater versus saltwater drowning. Although tension of water, prevents their collapse during lung drowning in either type of water can cause severe, poten - deflation and promotes lung compliance, or ease of lung tially fatal hypoxemia, differences in the volume and com - inflation or expansion. Freshwater interferes with the position of the fluid aspirated induce distinct physiologic ionic composition of surfactant, thereby altering its sur - responses. There is no evidence that chlorinated water has face tension properties. 12 The alveoli readily collapse, and any effect on the pathophysiology or outcome. 9–12 right-to-left intrapulmonary shunting, in which blood The presence of liquid in the oropharynx or larynx flows from the right side of the circulation to the left side usually triggers a vagally mediated laryngospasm, 1,13,14 without ever coming into contact with a functional gas followed by reflex vasoconstriction in the lungs and exchange unit, occurs. 10 The lungs also become less com - immediate pulmonary hypertension. 13 Freshwater, pliant. Conversely, salt water washes out some surfactant because its tonicity is lower than that of the body’s extra - but leaves the remaining surfactant intact without chang - cellular fluid, is rapidly absorbed from the alveoli ing its surface tension properties. 12 Because hypertonic through the alveolar –capillary basement membrane into salt water pulls fluid into the alveoli, an intrapulmonary the intravascular space. 15 Blood volume and extracellular shunt again results. The alveoli are perfused but, because electrolyte concentrations immediately change secondary they are filled with fluid, ventilation does not occur. 10 Cardiopulmonary efforts, including external cardiac massage and mouth-to-nose ventilation, should be started at the scene of the accident. to a dilutional effect; hyponatremia and hypervolemia Lung Damage have consistently been observed moments after aspira - Both types of fluid directly damage the type I and type II tion of a significant quantity of freshwater. 9,13,15–18 The pneumocytes of the alveolar epithelium and the pulmonary hypotonicity of freshwater can also cause intravascular capillary endothelial cells, causing inflammation, transuda - hemolysis with resultant hyperkalemia, hemoglobinemia, tion of protein-rich fluid into the alveolar space, and inter - and hemoglobinuria. 4,19 The hematocrit can increase, stitial and alveolar edema. 22 The mechanical barrier between presumably from swelling of erythrocytes. 9,15,19 However, the environment and the patient is disrupted, increasing unless the volume of freshwater aspirated is large (>22 susceptibility to infection through bacterial translocation. 23 ml/kg), these hematologic changes are rarely clinically Normal epithelial fluid and ion transport cannot occur, and significant. 9,15 In fact, by the time patients that have aspi - the production of surfactant is altered. 24 The alveo - rated freshwater present to a hospital, hypervolemia has lar–capillary basement membrane is exposed, leading to fur - often given way to hypovolemia due to redistribution of ther migration and activation of neutrophils and fluids and pulmonary edema, 20 and electrolyte concentra - macrophages and increased inflammatory cytokine produc - tions are within normal ranges. 9,15 tion. 24 Perfusion of the alveoli continues without ventilation, In contrast to freshwater, salt water has a higher increasing the shunt fraction. The resultant hypoxemia is tonicity than the body’s extracellular fluid and thus has unresponsive to increased oxygen content of inspired air due opposite effects. Salt water draws fluid from the to the totally obstructed alveoli or to shunting. The alveoli intravascular space through the alveolar–capillary base - collapse because of the loss of surfactant, and lung compli - ment membrane into the alveolar space. 21 Hypo- ance is decreased. This cascade of events is referred to as volemia, 21 a transient increase in plasma concentration acute respiratory distress syndrome (ARDS ). 24 of extracellular electrolytes, 13,21 and increased pulmonary fluid volumes result. 13,16,21 Hypoxemia and Acidosis In addition to their differences in tonicity, freshwater Right-to-left intrapulmonary shunting, decreased pul - and salt water have different effects on the chemical monary compliance, and ARDS cause a rapid decrease in properties of pulmonary surfactant, 12 a hydrophobic– arterial oxygen tension 10 ; the patient may also be unable to COMPENDIUM June 2008 Canine Drowning CE 343 expire carbon dioxide, causing hypercapnia. 4,25 Retrospective bacteria. If the material is an appropriate size, it may studies found that humans who drowned in freshwater or obstruct the smaller bronchi and bronchioles. 2 Severe salt water were consistently hypoxemic and acidotic. 4,9,10,15 pulmonary infection may also develop in dogs. In Metabolic acidosis in these patients is secondary to hypox - humans, airway obstruction has generally not been emia and lactic acidosis. 24 By the time the patient arrives at found to interfere with artificial ventilation, and severe the hospital, resuscitation efforts have usually been started infection rarely develops. 26 and ventilation has been improved. Therefore, hypercapnia and respiratory acidosis are not usually evident on blood gas ON-SITE RESUSCITATION measurements, but persistent hypoxemia is documented and Cardiopulmonary resuscitation efforts should be requires additional therapy. 9,13,23 started at the scene of the accident. Mouth-to-nose resuscitation should be commenced if the animal is Hemodynamic Effects apneic. 7 External cardiac massage should be performed The hemodynamic effects of drowning include if a heartbeat is not detected. 7 The drowned animal can decreased cardiac output, increased pulmonary capillary quickly be positioned to promote gravitational drainage wedge pressure (a reflection of left atrial pressure), and of fluid from the lungs; however, the rescuer should not increased pulmonary vascular resistance, all
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