Summertime fun 3 – Not drowning, waving…

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Who doesn’t love a romp on the beach?

I used to enjoy seeing the band of this name back in the 80’s (showing my age) so couldn’t resist the title for my next post on near drowning episodes (hope they don’t mind?).  Oh, the beach is such a wonderful place to spend the summer here in Australia, and who can pass on a cool dip on a hot summer’s day?  Dogs sometimes love the challenge of rushing out through the whitewash to chase a stick or rubber ball (though hopefully after one of my earlier posts, my readers will not be throwing sticks for their dogs!).  But the turbulence can be too much for some of them and while a belly full of water is not a fun way to end the day, lungs full of water is even worse!

Near drowning, or submersion injury, may be seen at the beach or in the backyard.  There have been a few older patients we have seen who have mistakenly stepped off the edge of the pool, not realising exactly where they were. Death from submersion falls into two categories – drowning deaths and near drowning deaths.  The drowned patient is one who succumbs to the event and dies within the first 24 hours.  The patient suffering from near drowning experiences a period of suffocation during the submersion but survives for at least 24 hours or more.  This all sounds a bit depressing so I will insert here that animals can survive near drowning episodes (as can humans), so it is not all bad, but it can be difficult.

The events in near drowning involve the initial submersion and panic with aspiration of a small amount of water which causes the larynx (or voice box) to spasm with a resulting apnoea (discontinuation of breathing for a period).  If the struggling continues, more water may be taken on board, both into the lungs and belly, which may lead to vomiting, aspiration of stomach contents on top of the water, and loss of consciousness.  The most significant effect of near drowning is the disturbed oxygen supply to vital organs which, aside from the lung injury that occurs, leads to secondary organ injury.  This may contribute to death at a later stage as a result of organ failure.  So, near drowning can be a true global disorder.

The take home message at this stage – if your pet survives the initial near drowning insult, it may still die, so try to maintain a positive outlook and let the vets do their job to the best of their abilities.  There could be a long road ahead.

It does not require a lot of water to cause significant impairment of gas exchange in the lungs.  As little as 1-3ml per kg of body weight can interfere with lung function.  I remember a time when we discussed whether it was better to have a salt water vs a fresh water near drowning, but at the end of the day both are very damaging to the lungs.  Fresh water tends to disrupt the surfactant lining the lung.  This is a type of fluid which allows the lung pockets (alveoli) to open and close during ventilation without friction, and so loss of surfactant results in further trauma to the alveoli and collapse (atalectasis), essentially shutting down parts of the lungs.  Salt water tends to draw fluid into the air spaces diluting the surfactant and obstructing the passage of gas exchange through the air pockets.

Other factors which can impact on the severity of lung injury include contaminants in the water.  Chlorine is irritating to lung tissue, and freshwater bodies may be contaminated by bacteria and other organisms.  Salt water/sea water may also contain bacteria and algae, sand and other particulate matter that can irritate and damage the airways.  Pneumonia is, thus, a common consequence of both types of near drowning.

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Lateral chest x-ray of a dog after a near drowning episode at the beach. There is some aeration of the top (dorsal) of the chest field but the ventral (lower) field is moderately consolidated

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Front on view of the chest of the same patient. The lungs are much “whiter” than they should be as a result of fluid being drawn into the air spaces. This interferes with adequate ventilation and essentially blocks the passage of oxygen across the pulmonary surface.  This patient actually did really well and was discharged two days later.

Aside from lung injury, the resulting hypoxaemia (or, lack of oxygen in the blood) affects normal tissue metabolism and can lead to secondary heart and brain injury.  In fact the most common cause of death in these cases is acute, severe cerebral hypoxia (brain damage due to lack of oxygen).  In some cases, the pressure around the brain can rise as a result of hypoxia, and this requires careful monitoring to detect and control, to help reduce further brain injury.

A lack of oxygen makes the blood more acidic (metabolic acidosis) which can have profound effects on the heart.  Cardiac function is impacted on by direct damage to the heart muscle and the electrical circuitry from hypoxaemia, which will affect the amount of blood the heart is able to pump (cardiac output).  Reduced cardiac output leads to reduced organ perfusion thus promoting a vicious cycle of cardiovascular dysfunction and contributing to death.

Patients who survive the initial episode may be awake and responsive but showing signs of abnormal and rapid breathing, potentially seizures or “syncope” (a sudden loss of consciousness not associated with a seizure), and lethargy with minimal exertion.  They may have cyanotic (purplish/blue) gums and may be coughing.  They may be responsive but in an obtunded or semi-comatose condition.  They should be evaluated by a veterinarian immediately.

At the veterinary hospital, they will be provided with oxygen support and an intravenous catheter will be placed to draw bloods and allow fluids to be provided for support of blood pressure and perfusion (blood flow).  Several parameters will need to be evaluated including general ABC’s if the pet is poorly responsive, body temperature, oxygenation of blood and blood gas analysis, and a neurological assessment.  A chest x-ray will be taken but may not be overly informative initially.  Changes in lung disease can take time to reach their full potential so serial radiographs are most informative.  If severe lung pattern alterations are evident on initial x-rays, the patient may not survive without aggressive respiratory support.

Initial diagnostic tests will likely need to be repeated at points throughout the patient’s stay in hospital (yes, it will be recommended that your pet stays in hospital!).  Things can change dramatically during the first 12-24 hours following a submersion, and often for the worse.  Monitoring of oxygenating ability may indicate that a patient needs support to breathe more effectively.  Some patients will require induction of general anaesthesia for mechanical/assisted ventilation, since this may be the only means of adequately oxygenating the lower airways and aiding gas transportation into the blood stream.  Unfortunately, there is no way of removing fluid from the tiny airways and alveoli of the lungs, so ventilation support is the only means by which some of the collapsed airways can be opened for breathing.  Ventilation may also be required for support of brain injury by ensuring that the body’s carbon dioxide levels do not build up too high if the patient becomes tired of working hard to breathe.

Other therapies may include antibiotics if an infectious pneumonia is proven or suspected, and other medications to help reduce pressure around the brain and support cardiac function, if indicated.  Outcomes in near drowning cases depend on the extent of lung damage (which may not be obvious initially and may progress with time), the neurologic status (severe changes are unlikely to correlate well with survival) and whether the patient requires mechanical ventilation.  The need for ventilation in itself is not a good sign for survival where lung disease is a factor (note that with tick paralysis, the lungs are often healthy, the patient is just tired, so a better outlook can be expected).  If looking for a number that allows us to say what the chances of survival are, a paper written in 2008 by Heffner, et al (JAVMA) suggests a survival rate of 64%.  Not bad but not great either.  Not a great way to end a lovely relaxing day on Australia’s beautiful coastline!

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