Drowning is a rare but often fatal condition that most veterinary professionals will encounter at some point in their career. Evidence regarding animal drowning is sparse and much of what we know is extrapolated from human medical literature.
Drowning may occur due to fatigue, seizure or accidents while swimming, falling into or being trapped in a body of water, and in cases of animal abuse. The term drowning refers to all cases regardless of survival, and the terms near-drowning or non-fatal drowning are no longer used. If a patient presents collapsed or dyspnoeic after being in water, drowning should always be considered as a differential diagnosis.
Pathophysiology of drowning
Drowning is defined as an immersion (liquid splashing on the face) or submersion (the airways are submerged below the surface of a liquid) causing respiratory impairment. As a result, the respiratory drive leads to aspiration of liquid and airway flooding, causing hypoxaemia, brain hypoxia, apnoea and death. Usually, this occurs in a matter of minutes, but hypothermia may delay drowning as it can have a neuro-protectant effect.
Secondary drowning
Aspiration of water affects lung surfactant composition, leading to alveolar collapse and ventilation-perfusion mismatch. Direct damage to alveolar pneumocytes and pulmonary vasculature endothelial cells initiates an inflammatory cascade and leakage of protein-rich fluid into the lungs. The subsequent non-cardiogenic pulmonary oedema (NCPO) or ‘secondary drowning’ can occur hours to days after the initial incident. Laryngeal spasm can cause negative pressure pulmonary oedema (NPPO) and may lead to secondary drowning even when minimal water is aspirated. Consequently, owners should be advised that deterioration may occur suddenly and pets must be monitored carefully for several days following a drowning incident.
If water reaches the larynx but not the lungs, it can trigger severe laryngospasm and physical airway obstruction. This was previously known as ‘dry drowning’ and can be differentiated from NCPO and NPPO as it occurs immediately and without delay.
Drowning first aid
Efforts can be made at the site of a drowning to revive an affected pet. Immediate head-down tipping of the patient may drain excessive pulmonary fluid but is often poorly effective. The Heimlich manoeuvre can cause further fluid aspiration from gastric contents and should be avoided. Mouth-to-nose rescue breaths may be effective in apnoeic patients, whereas efforts should focus on cardiac compressions in patients experiencing cardiac arrest. Resuscitation efforts should be instigated while travelling to a veterinary clinic whenever possible.
Preparing the veterinary team
Prior to patient arrival, emergency room set-up should include: oxygen therapy, crash cart, endotracheal tubes, laryngoscope, intravenous access, imaging modalities (radiography and ultrasound) and monitoring equipment (doppler blood pressure, multiparameter monitor, capnography, blood gas machine etc.). Remember, drowning patients are at high risk of respiratory failure.
Treatment for drowning patients is time-critical, and preparing your team in advance with education can impact your patient’s chances of survival. Enrolling your veterinary and nursing teams on emergency and critical care (ECC) CPD courses and running crash drills can be invaluable in improving team confidence and providing rapid and effective treatment in ‘real-life’ crash scenarios. Further training in focused assessment with sonography in trauma can also prove crucial in assessing drowning patients.
When the patient arrives, appoint a team member to get a thorough clinical history. When staff numbers are low, patient treatment should be prioritised and a brief history obtained once the patient is more stable.
Patient stabilisation
Oxygen therapy should start immediately. Masked oxygen can be used as a temporary measure until the patient can be transferred to an oxygen kennel, nasal prongs or nasal catheters. The method selected should aim to minimise patient stress.
Intravenous (i/v) access and oxygen saturation (SPO2) readings should be gained promptly without compromising patient safety. Anxiolytic sedation with butorphanol may be required prior to full clinical assessment.
If supplemental oxygen is insufficient, continuous positive airway pressure (CPAP) oxygen may be required; however, this relies on spontaneous respiration and specialist equipment, which may not be available in all veterinary settings. In severe respiratory distress, anaesthesia may be required in order to start mechanical ventilation.
Where cardiac arrest occurs, cardiopulmonary resuscitation and administration of adrenaline should be performed in line with the current RECOVER guidelines.
Investigations
A full clinical examination and baseline blood panel are crucial as other underlying conditions might predispose a pet to drowning.
Blood changes are often non-specific, e.g. stress leukogram or hyperglycaemia. Electrolyte disturbances may occur in patients who have swallowed large volumes of water – hyponatraemia in freshwater consumption, hypernatraemia in salt water and drowning. Further complications resulting from hypoxaemia and hypotension include acute kidney injury, neurological dysfunction and hepatopathies.
Metabolic acidosis secondary to hypoxaemia is common and arterial blood gas samples can be used to monitor oxygenation.
Drowning patients are at risk of haemostatic disorders, including disseminated intravascular coagulopathy. Thrombocytopenia may occur and clotting profiles may show increases in PT and APTT.
‘B lines’ on lung ultrasound indicate interstitial-alveolar oedema and are a practical alternative to thoracic radiography, particularly for sequential monitoring of intensive care patients with pulmonary oedema.
Radiography changes include severe pulmonary oedema and air bronchograms. Mixed bronchial and interstitial lung patterns may also be seen. However, restraint for radiography may carry increased risk to dyspnoeic patients. Transtracheal washes or bronchoalveolar lavage for culture samples may also be precluded by patient risk in some cases.
Treatment
Oxygen therapy is the cornerstone of treatment for drowning, alongside supportive treatment for hypothermia and shock. Judicious use of intravenous fluids (lactated ringers solution) is recommended to address hypovolaemia and maintain hydration and organ perfusion.
Prophylactic antibiotic use is controversial and can select for resistant bacterial infections. In humans, drowning-associated pneumonia is common and increases the risk of death; however, bacterial isolates are often resistant to amoxicillin-clavulanate. Ideally, veterinary patients should be carefully monitored for signs of pneumonia and treatment initiated while awaiting culture and sensitivity results.
If the stomach is dilated with fluid, nasogastric tube placement will allow gastric emptying to prevent vomiting and aspiration. It can also provide nutrition to the critically ill patient.
Bronchodilators may be useful in some patients. However, there is poor evidence to support diuretic use in human and veterinary cases of drowning and NCPO. There is no evidence for the use of glucocorticoids in these patients.
Monitoring
Patients should be monitored for signs of bacterial pneumonia: deterioration in respiration, cough, increased white cell count, pyrexia, increased C-reactive protein, changes on lung ultrasound (shred sign) and/or xrays if tolerated. Mechanical ventilation may also predispose patients to airway infections.
General ongoing monitoring should include oxygen saturation, creatinine, urea, glucose, electrolytes and urine output.
Prognosis
In animals, prognosis is uncertain, with one study reporting that 0/3 cats and 18/25 dogs survived. The median time to hospital discharge was 2 days (range 2 hours – 17 days). In humans, several factors have been associated with worse outcomes, including prolonged submersion, severe metabolic acidosis, fixed mydriasis on presentation and delayed resuscitation.
In conclusion, a successful outcome in drowning cases relies on several factors and management of these patients is often a team effort. Undertaking advanced ECC CPD can benefit the entire clinical team and provide knowledge and confidence to treat these patients as effectively as possible, thus increasing their chances of survival.
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Written by By Rosalind Wright BVSc BSc GPCert(EMS) MRCVS
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References
Heffner, G.G., Rozanski, E.A., Beal, M.W.,et al. (2008) Evaluation of freshwater submersion in small animals: 28 cases (1996-2006). Journal of the American Veterinary Medical Association 232(2), 244-8
https://www.who.int/news-room/fact-sheets/detail/drowning
Szpilman, D., Bierens, J.J., Handley, A.J.,et al. (2012) Drowning. The New England Journal of Medicine. 366(22), 2102-10
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