Methods for quantifying urine output:
Urinary Catheter:
Perhaps the most reliable method, it is also the most invasive. Female urinary catheterization in both cats and dogs is a simple process once you get the hang of it. We will discuss that more in the RTS. Male dogs and cats are generally very simple to catheterize.
Figure 2: Urinary Catheter in male dog.
Figure 3: Example of a closed collection system.
There are inherent problems of course with catheterization, the most important of which is the development of urinary catheter associated urinary tract infection (CAUTI). CAUTI can arise via either intraluminal (through the inside of the catheter) or extraluminal (along the outside of the atheter) means. Most often in veterinary patients, contamination comes from feces on the urinary line, or through self-grooming behavior.
The use of urinary catheters in ARF patients can be relatively long-term; therefore asepsis upon placement and routine maintenance to avoid contamination is of the utmost importance. It has been suggested where possible to use intermittent catheterization in preference to indwelling catheterization. This may be an option for many male dogs depending on their temperament, but not for most cats or female dogs. The frequency of catheterization must also be considered, as an indwelling catheter may be less traumatic and more practical. Standard urinary catheter maintenance including q 8hr swabbing with 0.05 % chlorhexidine tincture along the length of catheter and collection line, changing collection bags and culturing urine q 72hrs should be adhered to.
In anuric or oliguric patients, placing an indwelling urinary catheter, but capping the end with an injection port will allow periodic removal with a needle and syringe to determine urine volume. This method may allow easier quantification than a collection system due to the low volume of urine, as the urine will often only fill the line, not the bag.
In this case, a urinary catheter is often avoided if the animal is not recumbent and urine can be collected by one of the other methods we will discuss.
Other Collection Methods:
Dogs can be walked outdoors and the urine collected and measured. This is particularly useful for polyuric animals, although it can become quite labour intensive when they have to urinate every half an hour. Cats can use a non-absorbent litter or the litter pan can be weighed before and after to get an approximate volume (assumption that 1 g = 1 ml). A metabolic cage can also be used, where the urine is directed to a central drain for collection. Providing that the patient can be kept clean and dry, these types of cages work very well. For recumbent patients, diaper pads are a good option, as long as they can be changed frequently to avoid the patient becoming wet. The pads are weighed prior to and after use to assess urine volume.
Figure 4: A metabolic cage that will direct urine to a central drain. Works well for very polyuric animals.
Body Weight:
Assessing body weight on a frequent basis (ideally 2-4 times per day) will also assist in quantifying hydration. Having an accurate scale is very important. If there is more than one scale available, the scale used should be noted on the patient's flow sheet to maintain consistency.