Managing the common comorbidities of feline urethral obstruction
Comorbidities of urethral obstruction in male cats can be divided into two categories: those that exist at the time of presentation and those that develop during the course of treatment. In this article, I will review the causes of and treatment approach for seven of the most common concurrent morbidities in blocked male cats.
PROBLEMS THAT EXIST AT PRESENTATIONAzotemia
Azotemia in blocked cats is classically attributed to prerenal and postrenal causes. Because the cat is unable to urinate (postrenal component), the pressure in the bladder, ureters, and kidneys increases.2 When the intratubular pressure in the kidney increases, the kidney's glomerular filtration rate (GFR) and therefore its ability to filter toxins (including blood urea nitrogen [BUN] and creatinine) decreases.2 This leads to an increase in blood concentrations of these toxins. Additionally, cats that are azotemic may feel nauseated and inappetent, leading to fluid loss from vomiting and decreased intake of water and food. The resulting dehydration causes prerenal azotemia.
Treating azotemia. Treatment for azotemia involves relieving the obstruction to allow urine flow out of the bladder and administering crystalloid fluids. When a urinary catheter is placed, urine can flow and reestablish GFR. This leads to filtration and elimination of the BUN, creatinine, and other waste products from the bloodstream. Additionally, fluid administration dilutes the BUN and creatinine concentrations, as well as improves GFR to increase the filtration rate of toxins. The most efficient route of fluid administration is intravenous. Subcutaneous fluids are less effective than intravenous fluids because they are usually given in smaller quantities and at a slower rate.