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Outcome in dogs with uroabdomen | VETgirl Veterinary Continuing Education Blog

In this VETgirl online veterinary continuing education blog, we review uroabdomen in dogs. We've also talked about how to diagnose uroabdomen in a previous VETgirl blog here.

What kind of prognosis do you give clients after you have diagnosed their pet with a uroabdomen? Do you recommend medical management or surgical intervention? The ability to utilize common diagnostic tools in the veterinary facility for obtaining prognostic information is crucial to the veterinarian’s day-to-day practice. Sadly, veterinary medicine is still lacking for prognostic information for many of our encountered pet diseases. Common causes for a uroabdomen in pets include traumatic injuries to the pelvis, urethral tearing during manual deobstruction (e.g., unblocking), and surgery for urinary calculi.

So, Grimes et al out of UGA and LSU wanted to evaluate the prognosis of dogs suffering from spontaneous uroabdomen obtained by various causes such as trauma, obstruction, iatrogenic (ex. cystocentesis) and from unknown causes in a recent study called "Outcomes in dogs with uroabdomen: 43 cases (2006-2015)."

Let’s refresh our understanding of the pathophysiology behind uroabdomens and the biochemical abnormalities produced. When urine leaks from the urinary system into the abdomen, both potassium and creatinine from the leaked urine will accumulate in the abdominal effusion. The peritoneal lining can reabsorb potassium more efficiently than creatinine, resulting in a peripheral hyperkalemia. In order to remove some of the circulating potassium, the kidneys respond by concentrating it in the urine. However, due to the urinary disruption, this potassium-laden urine leaks into the abdomen and creates a higher potassium concentration in the abdominal effusion than the peripheral blood. The creatinine concentration of the abdominal effusion will be higher than the peripheral creatinine concentration because creatinine cannot be readily absorbed across the peritoneal membrane and remains stuck in the abdominal effusion. A shift in body water occurs, favoring movement of water down a concentration gradient created by the abdominal effusion creatinine into the abdomen. The resultant fluid shift causes hypovolemia and dehydration.

The ratios created by the difference between accumulation of potassium and creatinine within the abdominal effusion and the peripheral circulating concentrations can aid the veterinarian in diagnosing uroabdomen. Schmiedt et. al describe in a 2001 JVECC article, “Evaluation of abdominal fluid: peripheral blood creatinine and potassium ratios for diagnosis of uroperitoneum in dogs” how to compare and evaluate these diagnostic comparisons for diagnosing a uroperitoneum as follows: Effusion creatinine > 4X that of the serum creatinine’s upper reference limit, an effusion creatinine that is 2X or > 2X that of the serum creatinine, and an effusion potassium that is greater than 1.4X that of the serum potassium are all supportive of a uroperitoneum. If 2 or more of these tests are identified in your patient, Schmiedt et. al say that these combined tests offer 100% sensitivity and specificity for diagnosing a uroperitoneum.

So after you have identified that your patient has a uroperitoneum, what can you say about the prognosis with treatment for this patient?

Grimes et al. retroactively evaluated the records of 43 dogs between 2006 and 2015. Inclusion criteria for this study included at least one of the following: ESCr > 2, identifiable extravasation of contrast material from the urinary tract, or surgical identification of a urinary leakage from the urinary tract. When evaluating the biochemical diagnostic tests described above for the identification of an abdominal urine leakage, the ESCR > 2 was successful 90% of the time, the ESKr > 1.4 was successful 57% of the time, and contrast imaging was successful 87% of the time. An important tidbit to take from these findings is that when working up a patient for abdominal effusion, these described diagnostics are not going to catch 100% of all uroperitoneums. Subjectively, I have found that smaller urinary leakages caught early will fail to produce these pathognomonic biochemical changes described above, but will hover somewhere close to the cut-off values.

Within the 9-year time span of this study’s medical record review, the urinary disruptions were mostly caused by trauma (47%), obstruction (21%), and iatrogenic causes (16%), with 16% left from unknown causes. The urinary bladder was the most common (56%) location for urinary leakage followed by the urethra (26%), undetermined (9%), the kidney (5%), a ureter (2%), and a combination of both kidney and bladder (2%).

Most of the canines [37(86%)] in this study were treated with surgical management for their uroperitoneum. For 92% of the surgical cases, the urinary defect was identified at the time of surgery and corrected. For the remaining 8% where a defect was not found during surgery, they either received an indwelling urinary catheter, or were euthanized or died. This study found that although most of the surgical candidates received pre-operative contrast studies to attempt localization of the urinary disruption, this modality did not increase the likelihood of finding the urinary disruption during surgery. However, the authors still recommend performing contrast studies prior to surgical intervention. Intraoperative complications for the surgically treated canines included hypotension, bradycardia, hemorrhage, regurgitation, and death. Post-operative complications included death, regurgitation, continued urinary leakage, aspiration pneumonia, DIC, incisional infection, septic peritonitis resulting from incisional infection, urinary incontinence, and anemia. Cystotomy tubes were only placed in patients suffering from obstructions that could not be resolved. Urinary catheters were placed post operatively in a little over half (58%) of the surgically treated patients. At one of the two hospitals in this study, it was commonplace to place a peritoneal drain prior to surgical intervention when a uroabdomen was diagnosed. There was a trend toward decreased mortality in these patients, but this failed to reach statistical significance. Based on this favorable trend, the authors do recommend placing peritoneal drains for the purpose of helping to stabilize the biochemical abnormalities in these patients prior to anesthesia for surgical intervention (However, again, this is not statistically significant!). Subjectively, I recommend that if a peritoneal drain cannot be placed, clinicians should attempt to drain as much of the urine out of the abdomen as possible and may need to repeat drainage to help stabilize the patient (e.g., the good old abdominocentesis trick + urinary catheterization).

Only 6 (14%) of the dogs were treated with medical management which involved a urinary catheter placement and/or a urethral stent for obstructive neoplasia. The most common sites of urinary disruption in these patients was the urinary bladder or the urethra. Most of these cases resolved with 3 days after urinary catheter placement. One of the dogs with the urinary catheter pulled on day 4 had a recurrence of uroabdomen that then resolved after 8 additional days of urinary catheter diversion.

Overall, 79% of dogs survived to discharge (21% mortality rate). This study failed to show a significant difference in survival rate between dogs with rupture of the urinary bladder and those with rupture of the urethra, and cause of the rupture did not correlate with survival. Also important to note was that serum creatinine and BUN concentrations were not correlated to survival to discharge, so don't give up on these patients regardless of how azotemic they are! Not surprisingly, the surgically managed dogs that developed intra- or post-operative complications were the ones more likely not to survive to discharge. The most common site of urinary leakage was the bladder, followed by the urethra, and the most common cause of urinary disruption was blunt force trauma. Although the placement of a peritoneal drain prior to surgery did not produce statistically significant improvement in mortality rates, the authors recommend peritoneal drain placement in cases of uroabdomen to improve patient stabilization.

When in doubt, don't give up on these uroabdomens - while their blood work may look terrible, with rapid diagnosis, treatment and therapy, these patients can do well!

Abbreviations:
ESCr = Effusion-to-serum creatinine ratio
ESKr = Effusion-to-serum potassium ratio

References:
1. Grimes JA, Fletcher JM, Schmiedt CW. Outcomes in dogs with uroabdomen: 43 cases (2006–2015). J Am Vet Med Assoc 2018;252(1):92-97.

2. Schmiedt C, Tobias, KM, Otto CM. Evaluation of Abdominal Fluid: Peripheral Blood Creatinine and Potassium Ratios for Diagnosis of Uroperitoneum in Dogs. J Vet Emerg Crit Care 2007;11(4):275–280.

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