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The incidence of pneumonia in post-operative IVDD dogs | VETgirl Veterinary Continuing Education Podcasts

Have you treated cases of postoperative pneumonia or aspiration pneumonia in your practice? Have you wondered what factors might predispose your canine patients to developing postoperative respiratory complications? In people, there are a number of risk factors for aspiration pneumonia in the peri- and postoperative period that include: increased age, co-morbidities, preexisting pulmonary disease, immobility, decreased consciousness, analgesia and gastrointestinal problems like motility disorders, increased gastric acid, esophageal disease, among others.

In our veterinary patients, we don’t know as much about these risk factors since only a handful of studies exist. So Java et al out of University of Pennsylvania wanted to look at the incidence of and risk factors for postoperative pneumonia in dogs anesthetized for the diagnosis or treatment of intervertebral disc disease (what we’ll call IVDD from now on). They retrospectively evaluated a total of 707 dogs in this study from two different time periods (1992-1996 and 2002-2006). Of the 707 dogs included in this study, 338 dogs were from between 1992 and 1996 and 369 dogs were from between 2002 and 2006.

This study then compared results between the early and later study periods. Overall, they found that 0.6% (2/338) of dogs anesthetized between 1992 and 1996 developed postoperative pneumonia, while 4.6% (17/369) of dogs anesthetized between 2002 and 2006 developed postoperative pneumonia. The incidence of postoperative pneumonia was significantly higher during the later study period. They also found that the use of MRI and CT were used significantly more, and hemilaminectomy was performed significantly more, in the later study period. The number of anesthetic periods was also significantly higher and duration of hospitalization was significantly longer in the later study period.

In this study, there was a significantly higher incidence of pneumonia in dogs that were anesthetized more than once compared to those that were anesthetized just one time [2/24(8%) compared to 0/314 (0%) in earlier study period] vs [8/44 (18%) compared to 9/325 (3%) in later study period]. Dogs that were anesthetized more than once were 7.8X more likely to develop postoperative pneumonia. This study also found that dogs that had cervical lesions had a significantly higher incidence of postoperative pneumonia at 9% (11/129) compared to 1% dogs with thoracolumbar lesion (6/494, 1%) or 2% with lumbosacral lesions (2/84). Dogs with cervical lesions were 6.6X more likely to develop postoperative pneumonia, and were significantly more likely to be anesthetized more than once.

Dogs with cervical lesions were significantly more likely to develop postoperative pneumonia if they had undergone anesthesia more than once (8/34, 24%) than if they had undergone general anesthesia only once (3/95, 3%). Dogs with cervical lesions in the later study period were 6.8X more likely to develop postoperative pneumonia (9/56, 16%) compared to dogs in the early study period (2/73, 3%). Dogs that underwent MRI were significantly more likely to develop postoperative pneumonia (7/54, 13%) compared to dogs undergoing myelography or CT (12/652, 2%). Dogs that underwent MRI were 7.9X more likely to develop postoperative pneumonia.

Among dogs that were anesthetized only once, dogs that underwent MRI were significantly more likely to develop postoperative pneumonia (2/16, 12.5% compared to 7/623, 1%). Dogs that had anesthesia only once for MRI were 12.6X more likely to develop postoperative pneumonia. For dogs that had general anesthesia more than once, there was no significant difference in dogs that underwent MRI compared to other diagnostic modalities (5/38, 13% compared to 5/29, 17%). In other words, it’s not the MRI itself that’s making dogs aspirate!

Overall, this study found that there was no significant differences in age, sex, body weight, ASA, physical status score, or postoperative body temperature between affected and control dogs. Dogs that vomited or regurgitated after general anesthesia were significantly more likely to develop postoperative pneumonia compared to those that didn’t. Makes sense.

This study also found that dogs with tetraparesis prior to anesthesia were 17.85X more likely to develop postoperative pneumonia. Dogs with postoperative pneumonia were significantly more likely to have undergone more than one general anesthesia episode, and more likely to have cervical lesions compared to other lesions.

For those of you guys wanting to blame it on the pre-medications, there was no significant differences between groups regarding drugs administered during the first general anesthesia. That said, when it came to a second general anesthesia, dogs that developed postoperative pneumonia were significantly more likely to have received hydromorphone than control dogs. Dogs that received fentanyl were significantly less likely to develop postoperative pneumonia.

The incidence of postoperative pneumonia in dogs anesthetized for IVDD diagnosis or treatment increased between the two time periods. Risk factors for postoperative pneumonia included more than one general anesthesia, longer duration of the first anesthetic procedure, MRI, cervical lesions, tetraparesis prior to general anesthesia, and vomiting or regurgitation after general anesthesia.

What about the pros and cons of this study?
Overall, this was a pretty large study (by veterinary standards) with good methods and a nice comparison of two time points. However, it was a retrospective study, which makes it difficult to make conclusions about some of the risk factors, since it may have been difficult to glean all of this information from all of the medical records.

That said, what can we take from this VETgirl podcast?
The incidence of postoperative pneumonia may be increasing, partially due to longer anesthesia times (due to time of advanced diagnostics) or multiple anesthesias in dogs with IVDD. Clinically, what do we do differently? If you are anesthetizing a dog for diagnosis or treatment of IVDD (or for any other procedure) be aware of the risk factors for postoperative aspiration pneumonia and make sure to monitor your patient carefully in the postoperative period!

VETgirl’s hints? If you’re giving hydromorphone as a pre-medication, know it’s a cervical lesion, know your patient is going to have a long anesthesia, I’d recommend giving a dose of a potent anti-emetic like Cerenia (maropitant), ondasetron, or dolasetron as part of your “pre-med!”

References:
Java MA, Drobatz KJ, Gilley RS et al. Incidence of and risk factors for postoperative pneumonia in dogs anesthetized for diagnosis or treatment of intervertebral disk disease. J Am Vet Med AssocT 2009;235:281-287.

Abbreviations:
IVDD: intervertebral disk disease

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