Treating smoke inhalation in pets

Karen M. Roach, RVT, VTS (ECC), began her critical care lecture at the 2022 Atlantic Coast Veterinary Conference in Atlantic City, New Jersey, recounting a personal experience that left a lasting impression.

“At the beginning of my career in emergency veterinary medicine, I was working in an emergency clinic and standing in the treatment room. The front door to the hospital opened to reveal a firefighter in full gear, carrying a cat wearing an oxygen mask. This was well before the days where if you had a cellphone in your pocket, you could take a photo, but that image stuck in my head,” she said.

“There had been a fire at an apartment building, and for the rest of the day he kept going back to look for pets. He was very much an animal person and knew the types of places animals would hide. By the end of the day, I think he had brought us 4 more animals,” she added.

First responders do as much as they can after rescuing an animal from a fire, but then it is up to us, Roach continued. “What do we do? What do we have to monitor for? What are the concerns for smoke inhalation patients?”

Treating a fire-rescued patient

Expect anything when treating a patient rescued from a fire, warned Roach, an emergency and critical care technician specialist at Mount Laurel Animal Hospital in Mount Laurel, New Jersey. The patient could have severe burns, could be severely dysthymic, or even have died. “You need to be prepared to move fast and most importantly: oxygen, oxygen, oxygen,” she said.

Once oxygen is delivered, veterinary professionals can proceed with an initial assessment, Roach added. Special attention should be spent on deciphering any signs of respiratory despair. Primary concerns include hypoxemia, pulmonary damage, and thermal injury to the lungs and extremities.

5 common clinical consequences of smoke inhalation are as follows:

1. Bronchospasm
2. Upper airway obstruction
3. Small airway occlusion
4. Pulmonary infection
5. Respiratory failure

Roach recommended checking pulse oximetry, co-oximetry, and the patient’s hemodynamic stability. In the ideal situation, obtaining an arterial blood gas will provide further information on how well the patient is ventilating. Additionally, co-oximetry allows for more detailed insight into a patient’s severity. Because pulse oximetry cannot differentiate between oxyhemoglobin and carboxyhemoglobin, oxygenation saturation can appear normal even when it is not, she explained.

A co-oximeter, on the other hand, measures the specific hemoglobin species and oxygenation status in patients with both pulmonary injury and carbon monoxide and/or cyanide toxicity. Patients with these conditions can also experience metabolic acidosis (hyperlactatemia secondary to systemic hypoxia) or respiratory acidosis due to hypoventilation.

“These patients need to be very closely monitored,” Roach said. “We want to watch their breathing at all times and, as often as we can, checking the upper airway for signs of swelling. Things progress quickly.”

As with any emergency patient, history-taking is crucial for animals suffering from smoke inhalation. However, as Roach pointed out, because of the circumstances, the owner might be receiving treatment elsewhere and unable to provide a medical history. Therefore, a thorough and focused physical exam will become even more imperative before you can treat the patient. At the very least, try to ascertain how long the patient was in the smoke-filled environment, she encouraged.

“We have to assume that every smoke inhalation patient has carboxyhemoglobin,” Roach explained, reiterating the importance of immediate oxygen administration.

A patient might initially present mildly, but as the soot and heat settle in the airways, swelling and edema can advance. “Things can go downhill pretty quickly,” she advised.

For instance, direct heat injury and inflammation in the upper airway can lead to edema and, subsequently, airway obstruction. At a minimum, patients should continue to receive oxygen for 4 hours. Extended care may be necessary depending on the case.

When patients present with noticeable respiratory signs, they must be closely monitored for the next 48 hours. If the patient presents as stable with no signs of respiratory distress, they can usually be observed for 6 to 8 hours and then discharged. However, these patients should be rechecked at 72 hours to ensure that any potential injuries to the pulmonary tissues are not progressing, Roach outlined.

In more serious cases, mechanical ventilation may be necessary if the patient cannot maintain their blood gasses within a normal range or if they become fatigued. It could take up to 4 days of ventilation before the patient’s edema resolves, she explained.

Navigating toxicities

Notably, there is an increased risk of toxic chemicals being inhaled when synthetic materials–such as plastic, wool, silk, or nylon–have been burned, Roach said. The subsequent fumes in the air are going to become carbon monoxide and cyanide.

Inhalation of carbon monoxide leads to the production of carboxyhemoglobin and causes the oxyhemoglobin curve to shift to the left. This then impairs oxygen release to the tissues, which leads to cellular hypoxia, reduced myocardial function, central nervous system demyelination, and predisposes the patient to reperfusion injury. This, as well as cyanide toxicity, is going to add to respiratory distress, Roach explained.

Prolonged breathing of fumes may also lead to chemical tracheal bronchitis that could cause incredible damage. “One of my coworkers had a [dog with] smoke inhalation that coughed up the lining of its trachea, all in one piece. You can imagine how raw the lining of that poor dog’s trachea was after that,” Roach said.

Remember, because the animal is inhaling incredibly hot fumes and smoke, the damage to the inside of the patient is likely much worse than what is observed externally.

Beyond the breath

A thorough external examination must be performed. Roach advised looking for indications of burn injuries, soot on fur, and singed whiskers or fur. Be sure to examine the oral cavity and the nose for signs of soot, burns, or edema.

Assess the severity of burns using a system similar to human medicine. “If more than 20% of the body is burned, that is considered a severe burn. You have to expect these patients will have extreme electrolyte challenges and even multiorgan dysfunction,” she said.

Inspect the mucus membrane for signs of discoloration, which relates back to the possibility that the patient is cyanotic. A cherry red mucous membrane is an indication of carbon monoxide exposure.

Once respiratory emergencies and external burns are addressed, an optical examination is needed to pinpoint signs of additional thermal damage. “Look for any swelling, discharge, corneal ulcers, and corneal edema. Then treat the eyes as necessary,” Roach said.

She suggested lubricating the eyes upon a patient’s arrival before quickly moving on to more pressing matters and returning for a complete examination. Although an animal’s sight is important and should be saved, it is unlikely that an ocular injury would cause death.

“We also need to worry about the cardiovascular system,” Roach added. Pain, hypercapnia, and hypoxia–especially if the animal presents in shock–could all lead to an increased heart rate and the chance of arrhythmias.

Roach further advised that all smoke inhalation patients receive X-rays before discharge, but not at the detriment of the animal’s overall health. What is discovered on an X-ray will not change the situation very much at the beginning, she pointed out. “Sometimes changes will not appear on thoracic radiographs until a few hours later,” she said.

Determining a prognosis

Prognosis depends on how long the patient was exposed to the smoke-filled environment, how severe their clinical signs are, and if they also have burn injuries, Roach concluded. Most dogs and cats will be discharged if they recover from carbon monoxide and cyanide toxicity quickly and have minimal respiratory and/or neurological signs in the initial 24 to 72 hours.

Mortality from smoke inhalation is significantly higher in animals that have thermal burns. Dogs and cats with smoke inhalation alone are reported to have a survival rate of up to 90%, Roach noted.

Long-term, Roach explained, patients that have experienced smoke inhalation are more likely to suffer from chronic bronchitis, bronchial stenosis, and pulmonary fibrosis. In addition to the diagnostic tests that will become part of the patient's medical history, X-rays are a wonderful tool to provide a baseline for future appointments and care.

Reference

Roach K. You’re my hero! Smoke Inhalation. Presented at: Atlantic Coast Veterinary Conference; October 10-12, 2022: Atlantic City, New Jersey. www.dvm360.com/2022-acvc-proceedings