Chronic kidney disease, or CKD, is the most common renal disease we see in our dogs and cats.

These patients require intensive nursing care throughout hospitalisation, and beyond, as they return regularly for blood pressure measurement, blood tests and urine analysis. As veterinary nurses, we have the potential to make an enormous difference in their care, both in and out of the hospital.

To allow you to do just that, in this post I’m talking you through what CKD is, how it affects our patients, the signs we see, staging and diagnosis, and sharing my top tips on nursing the CKD patient.

I’m also giving you a sneak peek into something really exciting coming up this spring, which will really help you plan long-term care for these patients - more on that at the end of this post!

Pathophysiology

We can define CKD as renal damage or reduced renal function, which has persisted for over 3 months. The loss of function seen in CKD is permanent, irreversible, and progressive, unlike other renal disorders such as acute kidney injury.

Initially, the kidneys are able to compensate for a reduction in function for short periods, through methods such as renal hypertrophy. However, in CKD, these compensatory mechanisms become overwhelmed and permanent damage occurs. This damage continues, leading to a slow decline in renal function over a period of months to years.

Causes

There are several specific causes of CKD, including:

• Renal dysplasia, a congenital condition where the kidneys do not form properly

• Following pyelonephritis (renal infection)

• Following urolithiasis (e.g. following a ureteral obstruction)

• Neoplasia (e.g. renal lymphoma)

• Glomerulonephritis or amyloidosis (leading to protein-losing nephropathy - more on this in a future post in this series!)

However, in many cases the underlying cause of the renal dysfunction is unknown.

Though the disease cannot be reversed, long-term management of CKD can slow the progression of the disease, increasing survival time and improving quality of life.

Clinical Signs

The clinical signs of CKD are varied, and most commonly include:

• Polyuria (as the kidneys lose their ability to concentrate urine, more water is lost, causing polyuria)

• Polydipsia (as patients drink more to compensate for their increased losses)

• Lethargy

• Weakness

• Anorexia

• Weight loss

• Poor coat quality

• Dehydration

If the patient is also hypertensive (common in CKD), we may also see signs of target organ damage, including blindness (retinal detachment), hyphema (blood in the eye), cardiac and neurological effects. 

If uremia is present (in severe, advanced CKD) vomiting, marked weight loss, anorexia and halitosis may also be seen. 

In some cases, alterations to calcium and phosphorus balance can lead to secondary renal hyperparathyroidism may also be seen; this is particularly associated with younger animals. Signs of this condition include impaired muscle function and bone resorption in the skull and mandible, leading to softening of these areas.

Diagnosis

Many diagnostic tests are used to diagnose and stage CKD, including biochemistry testing, urine analysis, and blood pressure analysis. Ideally, abdominal ultrasound should also be performed, to assess the structure of the kidneys, measure their size, and identify abnormalities such as uroliths.

Common abnormalities on diagnostic tests include:

• Azotaemia (increased BUN/creatinine) - this is not seen until around 75% of renal function is lost

• Increased SDMA

• Metabolic acidosis

• Hypokalaemia

• Reduced urine SG - this is seen at around 60-66% loss of renal function

• Proteinuria - as the nephrons become ‘leaky’ allowing larger molecules such as proteins to pass through into the urine

• Possible urinary tract infection - this is seen more commonly in patients with CKD due to their dilute urine.

Staging

We can also use our diagnostic results to ‘stage’ our patient’s CKD. When we talk about ‘staging’, we are classifying the severity of the disease into one of four stages set by the International Renal Interest Society (IRIS). These stages are:

• Stage 1: Nonazotaemic (creatinine of <125umol/L in dogs, and <140umol/L in cats)

• Stage 2: Mild renal azotaemia (creatinine of 125-180 in dogs, and 140-250 in cats)

• Stage 3: Moderate renal azotaemia (creatinine of 181-440 in dogs and 251-440 in cats)

• Stage 4: Increasing risk of systemic signs and uremia (creatinine of >440 in both dogs and cats)

Staging is performed based on serum creatinine levels, to assess the degree of azotaemia. We also sub-stage CKD with urine analysis (assessing the degree of proteinuria) and systolic arterial pressure measurement (assessing for systemic hypertension/risk of target organ damage).

Blood Pressure Substage:

• Normotensive: Systolic arterial pressure <140mmHg

• Prehypertensive: Systolic arterial pressure 140-159mmHg

• Hypertensive: Systolic arterial pressure 160-179mmHg

• Severely hypertensive: Systolic arterial pressure >180mmHg

Urine Protein:Creatinine Substage:

• Non-proteinuric: UPCR <0.2

• Borderline proteinuric: UPCR 0.2-0.5 in dogs, 0.2-0.4 in cats

• Proteinuric: UCPR >0.5 in dogs and >0.4 in cats

A patient may have stage 2 or 3 CKD but not be proteinuric or hypertensive. Because a patient’s status can change over time, staging should be repeated regularly in order to detect and treat any changes rapidly.

Treatment and Nursing Care

Inpatient Care

Care of the CKD patient in the clinic includes intravenous fluid therapy to correct any hydration deficits and reduce the degree of azotaemia and supportive medications such as anti-emetics (where nausea is suspected) and appetite stimulants (where inappetence or anorexia is present). 

The fluid deficit should be carefully calculated based on the patient’s clinical signs, and this should be used to determine their % dehydration:

• <5%: No detectable clinical signs

• 5-6%: Subtle loss of skin elasticity

• 6-8%: Skin tent with tacky mucous membranes

• 8-10% Marked skin tent, dry mucous membranes, slightly sunken eyes

• 10-12%: Dry mucous membranes, skin tent stays in place, sunken eyes, progressive signs of shock

We can then use this figure to calculate the patient’s fluid deficit using the following formula: 

% dehydration x weight in kg x 10 = fluid deficit (in ml). 

On top of this, any ongoing losses, as well as daily maintenance fluid requirements should be accounted for. The patient’s fluid balance should be assessed regularly and their rate adjusted as required.

Additional agents such as electrolyte supplementation may be required in addition to plain crystalloid IVFT. Potassium supplementation in particular is commonly required in these patients. As potassium is a heavier compound than IV fluids, the bag should be regularly rotated to prevent accidental administration of more concentrated potassium solutions to the patient. Care should also be taken when flushing the line/catheter, and medications should not be given through the drip line, to prevent administering potassium-containing solutions too quickly.

CKD patients are often anorexic and enteral feeding support may be required. Supportive medications may be indicated, and any underlying causes of inappetence such as nausea or pain should be addressed. Care should be taken not to overwhelm the patient with multiple food choices at any one time, which could cause food aversion. In patients with inappetence lasting >3 days, a feeding tube should be placed to allow appropriate nutrition to be administered. Naso-oesophageal tubes are ideal in these patients as these avoid anaesthesia in a patient with renal compromise; however, if the patient is vomiting, these tubes should be avoided.

In addition to supportive care, if an underlying cause for the CKD is identified, this should be managed appropriately. This includes relief of any urinary tract obstructions and antibiotic treatment for pyelonephritis. In many cases (e.g. following upper urinary tract obstruction) some degree of CKD will remain.

Outpatient Care & Ongoing Management

Long-term care of the CKD patient includes dietary modification and supportive medications for hypertension or proteinuria, as required. 

Diets should have a restricted phosphorus content, controlled protein restriction, fatty acid and antioxidant supplementation, and be neutral-to-slightly-alkalinising in nature, due to the metabolic acidosis often seen with kidney disease. 

These requirements are typically met with a prescription diet designed for renal disease; however, if a patient will not eat this, phosphate binders may be added to food to reduce dietary phosphorus content.

Treatment of proteinuria (UPCR >0.4 in cats, or 0.5 in dogs) may be required, e.g. with angiotensin receptor blockers such as telmisartan or angiotensin-converting enzyme inhibitors such as benazepril. These medications suppress the renin-angiotensin-aldosterone system (the pathway that regulates fluid balance and blood pressure, which begins in the kidney, with the release of renin).

If systemic hypertension is present, treatment with antihypertensive agents such as calcium channel blockers (e.g. amlodipine) is indicated.

In addition to the above medications/dietary modifications, steps should be taken to increase the patient’s water intake at home. This includes:

• Providing multiple water receptacles in different locations

• Using water flavourings such as fish/meat cooking liquids (avoid high salt concentrations)

• Providing moving water sources such as water fountains.

In addition, administration of subcutaneous fluids at home may be required especially in more advanced stages of CKD. Clients can be easily taught to perform the skill at home, and it is generally well tolerated. 

Regular follow-up care and support should be provided; in between consultations with the veterinary surgeon, nurse consultations can be a really useful tool to ensure our patients and clients have ongoing support from both the vet and nurse teams.

During these nurse consultations, the RVN should:

• Collect an updated clinical history from the client

• Perform a full physical examination

• Weigh the patient

• Perform body and muscle condition scoring

• Measure blood pressure

• Collect blood samples as needed

• Perform urine analysis as needed

• Provide advice on things like medication, nutrition, fluid balance and monitoring.

So that’s an overview of chronic kidney disease, and our considerations as nurses when treating and caring for these patients!

Do you perform renal clinics in your practice? Would you like to start?

Very soon I will be making spots available on a brand new course aimed at RVNs wanting to offer clinics to their medical patients. One of the modules in this is all about our renal patients - giving you the tools you need to plan and deliver amazing renal clinics.

If you want to get notified when the course goes live, you can sign up to the waiting list here.

References:

1. Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.

2. International Renal Interest Society, 2022. IRIS Staging of CKD. Available from: http://iris-kidney.com/guidelines/staging.html