Questions and answers with veterinary internist Barrak Pressler of Purdue University.
His experience with the diagnosis and treatment of acute renal failure is very broad given his position as assistant professor of internal medicine of small animals at Purdue University and his special interest in the areas of kidney disease. Can you describe some of the most common presentations in dogs and cats?
Pressler: In general, patients with acute renal failure are much sicker than patients with chronic kidney disease with azotemia (ie, chronic kidney failure). Both dogs and cats are usually moderately and severely dehydrated at the time of diagnosis, and owners can comment on a recent increase in thirst and urination. Dogs tend to have many more severe gastrointestinal (GI) signs (intense vomiting, in particular) than cats, which more often stop eating and become less sociable, according to their owners. Anuria or oliguria is the most feared presentation for patients with acute renal failure in both species, with cats being more prone to have a decrease in urine production than dogs.
Discarding causes: According to Dr. Pressler, a thorough history can help rule out possible toxins and other causes of acute kidney failure.
Do these patients often have recurrent conditions of the pathology?
Pressler: Many patients with acute renal failure have other diseases or conditions diagnosed at the time of presentation. These concurrent conditions may be the cause of their acute renal failure – for example, pancreatitis, heart failure or hypoadrenocorticism – or they may be consequences of the same conditions that led to kidney damage as in the case of disseminated intravascular coagulopathy (DIC). Concurrent conditions may also have developed after renal failure itself, as in the case of pulmonary edema, pancreatitis, hypovolemic or hypotensive shock or pancreatitis. In general, cats seem less likely to have most of these concurrent diseases, but, on the contrary, are more likely to have kidney disease by infiltration such as lymphoma or feline infectious peritonitis (FIP) or ureteral obstruction as the cause of their kidney failure.
How does the diagnosis approach in cases of suspected acute renal failure?
Pressler: Acute renal failure, by definition, is at least partially reversible with aggressive therapy. Therefore, diagnosing the underlying cause of kidney disease offers the best chance to prevent the damage from progressing through targeted aggressive general support therapy. Naturally, I always start with a clinical history and a thorough physical examination. I never ask the owners if their pets could have ingested any toxin because many people do not know that some common plants and medicines in the home can cause kidney disease. Instead, I make a list of possible toxins with the owners and ask individually about lilies, NSAIDs, grapes, etc. I treat all dogs with acute renal failure due to leptospirosis while waiting for the results of the blood titers, both for its prevalence and for the zoonotic risk. I also perform a urine culture, regardless of the results of urine sediment, in case renal failure is due to pyelonephritis. Finally, I always include abdominal images in my diagnostic evaluation of patients with acute renal failure in order to diagnose infiltration diseases such as lymphoma or FIP or to detect ureteral obstructions.
What are the most important concerns when treating a dog with acute kidney failure?
Pressler: The importance of constantly correcting and monitoring the state of hydration in any patient with acute renal failure can not be overemphasized. Many patients are dehydrated at the time of the first presentation. Aggressive replacement of any fluid deficit (usually within a few hours) is needed to normalize renal blood flow; this allows the production of urine, which will unblock nephrons clogged by damaged and flaked cells, provide oxygen to injured and healing tubules, and maintain blood flow to the renal medulla, which is very sensitive to hypoxemic damage. Patients with acute renal failure should be carefully monitored to ensure that the intravenous fluid rate is sufficient to maintain hydration