Endotracheal intubation was one of the first advanced veterinary medical skills I learned in tech school. Of course it doesn’t seem very advanced now, but it was the first technique I learned that could actually save a life. In the ABC’s of an emergency, “A” stands for Airway. I could barely draw blood from the jugular of a Labrador, and I could palpate a cat’s bladder only about half the time, but I could do the “A”. I could establish an airway. And it made me feel pretty useful.
I came to rely on an endotracheal tube to do more than just establish an airway. An anesthetist not only uses it to deliver oxygen, anesthetics, and other drugs, an ET tube also protects the airway from contamination during and after anesthesia. As a matter of fact, that’s why we leave the tube in place during recovery until the patient can swallow. The swallow reflex naturally protects the airway, so the ET tube needs to remain in the trachea until that returns in order to prevent aspiration of stomach contents. There were many times over the years that I was glad to have a tube in place, as a patient regurgitated during a procedure or vomited during recovery.
But when it comes to regurgitation and vomiting during anesthesia, having the airway protected is not the end of the story. Which brings us to the topic of this blog post. Passive reflux and regurgitation can happen in up to 50% of anesthetized dogs – especially those undergoing orthopedic procedures. We’ll use an informative article written by Kiko Bracker, DVM, DACVECC, to help us navigate through Peri-anesthetic Gastroesophageal Reflux and Regurgitation in the anesthetized dog.
Gastric reflux usually goes undiagnosed except in a research setting because a pH probe is needed to identify it. If the pH of the gastric reflux contents is acidic, which is common, the risk of damage to the mucosal layer in the esophagus is high. Of course, contact time of acidic contents plays a role in the amount of damage that occurs. Mild reflux usually doesn’t cause significant problems to the patient, but if it’s severe and goes untreated, it could cause an esophageal stricture, weight loss, aspiration pneumonia, and even death. So it’s worth being aware of.
The pictures above illustrate how reflux is released into the esophagus. Gastric reflux is when the contents of the stomach passively move from the stomach, up through the lower esophageal sphincter and back into the esophagus. A sphincter is actually a ring of muscle surrounding a tube like the esophagus, and serving to guard or close its opening. The diagram on the left of the picture shows the lower esophageal sphincter closed, preventing the stomach contents from moving back into the esophagus. On the right, the sphincter is open allowing the contents to migrate into the esophagus.
One of the reasons animals are fasted before anesthesia is to reduce the stomach contents, and hopefully minimize the incidence of gastric reflux. Studies have generally been inconclusive about the efficacy of prolonged fasting prior to anesthesia, with one study suggesting that a longer fasting time (18 hours) results in less esophageal sphincter tone, and may actually increase the likelihood of reflux during anesthesia.
The type of procedure seems to also influence the incidence of gastric reflux and regurgitation. In a paper that looked at regurgitation in 4271 anesthetized dogs, they identified a 25 times greater incidence of regurgitation in dogs having orthopedic procedures performed. This may be due to the opioid analgesics used for orthopedic procedures. Many medications used during anesthesia are shown to reduce lower esophageal sphincter tone including morphine, atropine, acepromazine, and even isoflurane.
Also orthopedic patients are often repositioned multiple times under anesthesia during the clip and surgical prep prior to surgery. This may trigger reflux events. However, another study reported patient position and even the tilt of the surgical table had no influence on reflux frequency. So it’s hard to draw a straight line from cause to effect.
This is all very interesting, but we’re left with a problem that may be happening to half of our patients, is difficult to detect conclusively, and we don’t know what causes it, so we can’t really predict when it’s going to happen. I brought this up why?
I remember the flash of understanding that came when I learned that even with my patient’s airway protected by an endotracheal tube, a little trickle of fluid coming out of its mouth may be significant. Aspiration may not be a worry, but acid erosion of the esophageal mucosa was. When I see it, I need to respond to it.
Inform the doctor of your concerns and then these simple tools – a dose syringe and a red rubber feeding tube – go a long way in treating suspected gastric reflux and regurgitation. Delivering warm water on the way down the esophagus, and aspirating it on the way out helps to dilute and remove whatever reflux may be resting in the esophagus. Repeat this procedure several times until your aspirate is clear and clean. Logic dictates that diluting the reflux like this would lower its acidity and therefore protect the esophageal mucosa. However Dr Bracker’s article shines new light on this logic. He writes Interestingly, neither suctioning of the esophagus nor water lavage alone were shown to reduce the acidity of the esophagus post-reflux, but if the esophagus was lavaged with dilute sodium bicarbonate after suctioning and water lavage – the esophageal pH predictably rose to 7.0 for the duration of the procedure. His statement is referenced and I have no doubt it’s true, and if I was in practice today I would add dilute sodium bicarbonate as a final step to my treatment.
Dr Kiko Bracker’s article Peri-anesthetic Gastroesophageal Reflux and Regurgitation is an excellent review of the issue of reflux and regurgitation in the anesthetized dog, and its prevention and treatment. It’s also well referenced. I encourage you to take a look at it to learn more.
Author’s note: I am sad to say that this is my last post to this blog. I am leaving Advanced Anesthesia Specialists. I have enjoyed sharing my passion, knowledge, and experience in veterinary anesthesia. I hope you’ve found this blog useful. To me, it’s been a labor of love. Warm regards, Ken.
Ken Crump AAS, AHT is a writer and animal anesthetist, and writes Making Anesthesia Easier for DarvallVet, a division of Advanced Anesthesia Specialists. He makes dozens of Continuing Education presentations on veterinary anesthesia and oncology across the United States and in Canada. Ken retired from the Veterinary Teaching Hospital at Colorado State University in 2008.