To Pee or Not to Pee....AAAaaahhhhhh.....
Sections covered: Kidney Basics, Kidney Failure, (Acute Renal Failure, ChronicRenal Failure), Diagnostic Approach, Treatment Plan
The kidney is really a multifunctional organ, controlling not only the conservation of fluid and the removal of bodily wastes, but also the regulation of bone and calcium (including vitamin D) metabolism, bone marrow (red blood cell ) activity, and electrolyte concentrations.
Conservation of Fluid & Removal of Waste Products:
Think about the kidney as a container holding thousands of individual filtering units (each called a "nephron") with tiny pores. Blood passes through the kidney, and in the process is routed through each of these filters; toxins and other wastes are removed, most of the fluid (about 95%) is reabsorbed back to the bloodstream (water is conserved), electrolyte concentrations (primarily sodium, potassium, calcium, phosphorus, chloride) are delicately adjusted, and urine is produced. This urine is stored in the urinary bladder until it is voided. Inadequate filtration and removal of waste products can result in excessive circulation of toxins that damage other tissues, such as the mucosal layers of the gastrointestinal tract ("uremic ulcers"), including the tissues of the mouth, stomach, small and large intestines. Additionally, some toxins may affect the central nervous system, resulting in neurologic signs, such as seizures.
Bone & Calcium metabolism:
The kidney is responsible for providing the precursor for the synthesis of Vitamin D3; Vitamin D3 is necessary for the absorption of calcium from the gastrointestinal tract. In addition, the regulation of concentrations of calcium and phosphorus is also determined by the action of parathyroid hormone, produced, by the parathyroid glands, in large part due to the kidneys' response to excess circulating phosphorus, and to some extent a response to a decrease in circulating calcium (the ionized form) which can occur because with renal failure, there is a relative decrease in Vitamin D3.Normally, this hormone is responsible for adjusting serum calcium and phosphorus levels, primarily by activating removal of calcium from bone and promoting phosphorus excretion in the urine. However, chronically elevated levels of parathyroid hormone have been shown to, ultimately, be harmful to kidney health and function.
Red Blood Cell Synthesis
The production of red blood cells by the bone marrow is stimulated by the presence of a erythropoietin, which is produced by the kidney when red blood cell are in short supply and/or the delivery of oxygen to the tissues throughout the body is inadequate.
Blood Pressure Regulation
When blood pressure is low, there is a consequent decrease in filtered urine The kidney, detecting this, then triggers a cascade of biochemical events which result in sodium and fluid retention, an average decrease in the diameter of blood vessels (though with an unchanged blood volume), an increased heart rate and force of heart muscle contraction, together, increasing the blood pressure (force) throughout the circulatory system. Under normal circumstances, this process insures adequate blood pressure such that all important organs and tissues receive appropriate oxygen and nutrition, and the kidneys are able to process waste.
The causes of kidney (renal) disease and failure are numerous and in some instances, not understood.. Acute renal failure occurs at any age and if diagnosed and treated early, damage can in many instances, be arrested. In the majority of cases of acute renal failure where treatment is instituted early, the prognosis for full recovery is excellent. Chronic renal failure appears to be more common in geriatric cats than dogs; occasionally, it is documented in exotic species such as rabbits, birds, ferrets, and reptiles, though the causes of renal failure in these species is more poorly appreciated. Damage is usually irreversible, but progression and severity of disease and the quality of life can be temporarily modulated with careful medical and dietary controls.
Acute Renal Failure (ARF):
In veterinary medicine, the most common causes of ARF are:
Chronic Renal Failure (CRF):
Chronic renal failure occurs as an insidious, irreversible progression of damage to essential kidney structure which results in reduced function. Causes include:
- persistent dental disease
- chronic skin infection (bacterial, fungal, viral)
- chronic allergic dermatitis
- inflammatory bowel disease, gastroenteritis, pancreatitis (chronic or recurring)
- hyperadrenocorticism and diabetes
Additional factors which may contribute to the progression of disease and failure are:
- High or Low blood pressure (many causes possible)
- Abnormal electrolyte concentrations (sodium, potassium, chloride, calcium, phosphorus, magnesium)
- Improper diet:
- acidifying diet
- too much phosphorus, sodium, protein
- too little potassium
Physical examination may reveal the presence of abnormalities that guide your veterinarinan to consider whether there is kidney disease. Examples of findings might include abnormal kidney shape or size, oral ulcers, signs suggesting the presence of hypertension.....and others.
Routine Lab work.:
Bloodwork and urinalysis frequently will reveal if there is a renal problem. Keep in mind, though, that abnormalities on routine labwork may not become apparent until there is a loss of 65%-75% of kidney function . Thus is early stages of degeneration, routine laboratory results can be non-diagnostic.
Plain x-rays and ultrasound are the most common modes for "visualizing" aberrations in the number, size and texture and position of the kidneys and related structures., as well as the presence of mineralized densities ("stones"). To assess integrity and functionality, your veterinarian may choose special contrast media (i.e.dyes) coupled with additional x-rays.
Once renal disease is diagnosed your veterinarian may need to determine the cause and the extent of damage via a tissue biopsy or cytology. Biopsy can be accomplished relatively safely during the ultrasound procedure ("ultrasound-guided biopsy) or via surgery. Cytology entails aspiration of a tiny amount of kidney tissue via a needle and syringe .a quick procedure (anesthesia is usually not needed).
Treatment Plan: 1
As you now realize, renal failure is complex. A patient's clinical signs, including secondary abnormalities to other organ systems, are uniquely variable (does that make sense?) from one individual to the other. For this reason, medical management must be tailored to the specific requirements of the victim. Thus, the multitude of direct and indirect effects to various body systems, the extent and magnitude of each problem, as well as the possible quality of life attainable in the short and long terms are variables which require careful consideration when configuring and beginning the treatment plan.. Ultimately.....the treatment must be determined by you and your veterinarian. Here is just an oversimplified "algorithm" for managing renal failure:
In the case of Chronic Renal Failure, there will likely be a requirement for long term, sometimes labor-intensive, medical care to keep your pet comfortable and to maintain some abatement of disease progression. This may involve dietary restrictions, appetite stimulants, drugs to manage blood pressure and to decrease anemia, fluid administration for periodic dehydration, other medications to control calcium and parathyroid hormone levels (including Vitamin D3-calcitriol), phosphorus and other electrolyte abnormalities,vomiting and/or diarrhea...and any other unforeseeable complications which may develop. The key...take-home word here is COMMITMENT.
1. There is presently an option for kidney transplantation which is being performed only at a handful of veterinary hospitals.
2. Additional information may be obtained at the Feline CRF Home Page
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