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==Introduction==

==Introduction==

Acute Renal Failure is a syndrome caused by the '''acute failure of haemodynamic, filtration and excetory functions in the [[Kidney - Anatomy & Physiology|kidney''']]. This results in the '''accumulation of [[Uraemia|uraemic toxins]]''' and the '''dysregulation of acid-base, fluid and electrolyte balances'''.

Acute Renal Failure is a syndrome caused by the '''acute failure of haemodynamic, filtration and excretory functions in the [[Kidney - Anatomy & Physiology|kidney''']]. This results in the '''accumulation of [[Uraemia|uraemic toxins]]''' and the '''dysregulation of acid-base, fluid and electrolyte balances'''.

It is rapidly progressive but may be reversible. It can result from pre-renal, intra-renal or post-renal factors.

It is rapidly progressive but may be reversible. It can result from pre-renal, intra-renal or post-renal factors.

This section only covers the intrinsic causes or ARF, as pre- and post-renal failure are very different disease processes.  

This section only covers the intrinsic causes or ARF, as pre- and post-renal failure are very different disease processes.  

'''[[Toxicology|Toxic injury]]''' is the most common cause. [[Toxicology|Toxins]] such as '''aminoglycosides, [[Ethylene Glycol Toxicity|ethylene glycol]], [[NSAIDs|NSAIDs]], [[House Plant Toxicity|easter lillies]] and ACE-inhibitors''' can all cause renal failure. Some toxic agents act directly on tubular cells, some act on the haemodynamics of the [[Kidney - Anatomy & Physiology|kidney]], whilst others cause damage by precipitating within the tubules.  

'''[[Toxicology|Toxic injury]]''' is the most common cause. Toxins such as '''aminoglycosides, [[Ethylene Glycol Toxicity|ethylene glycol]], [[NSAIDs|NSAIDs]], [[House Plant Toxicity|easter lillies]] and ACE-inhibitors''' can all cause renal failure. Some toxic agents act directly on tubular cells, some act on the haemodynamics of the kidney, whilst others cause damage by precipitating within the tubules.  

'''[[Ischaemia|Ischaemic injury]]''' is also common, especially following hospitalisation. It is therefore essential to monitor the fluid therapy requirements of hospital patients, especially peri- and post-operatively to prevent pre-renal [[Azotaemia|azotaemia]] and subsequent ischaemia.  

'''[[Ischaemia|Ischaemic injury]]''' is also common, especially following hospitalisation. It is therefore essential to monitor the fluid therapy requirements of hospital patients, especially peri- and post-operatively to prevent pre-renal [[Azotaemia|azotaemia]] and subsequent ischaemia.  

==Pathogenesis==

==Pathogenesis==

 

A reduction in [[GFR|GFR]] is caused by the decrease in surface area or conductivity of glomerular capillaries (resulting in a drop in the ultra-filtration coefficient). Epithelial cells and debris obstruct the tubules. Toxin precipitates may contribute to this. Tubular fluid leaks out of the tubules and across the epithelium, back into the interstitium - causing a drop in GFR. Ischaemic injury to the peripheral medulla occurs due to intra-renal vasoconstriction.

* A reduction in [[GFR|GFR]] is caused by the decreased in surface area or conductivity of glomerular capillaries (resulting in a drop in the ultra-filtration coefficient)

 

* Epithelial cells and debris obstruct the tubules. Toxin precipitates may contribute to this

 

* Tubular fluid leaks out of the tubules and across the epithelium, back into the interstitium - causing a drop in GFR

 

* Ischaemic injury to the peripheral medulla occurs due to intra-renal vasoconstriction

==Clinical Signs==

==Clinical Signs==

The most significant information can be gleaned from the history. It is important to ask the owners about [[Toxicology|toxin]] ingestion and urine production.   

The most significant information can be gleaned from the history. It is important to ask the owners about [[Toxicology|toxin]] ingestion and urine production.   

Clinical exams normally reveals fairly non-specific signs such as:

Clinical exam normally reveals fairly non-specific signs such as:

 

* '''[[Dehydration|Dehydration]]'''

* '''[[Dehydration|Dehydration]]'''

* '''Lethargy'''

* '''Lethargy'''

* '''Malaise'''

* '''Malaise'''

* '''[[Vomiting|Vomiting]]'''

* '''[[Vomiting|Vomiting]]'''

There may also be evidence of swollen or painful kidneys abdominal palpation, an increased or decreased heart rate, hypothermia and [[Uraemia|oral ulceration]] or signs of a concurrent disease.  

There may also be evidence of swollen or painful kidneys on abdominal palpation, an increased or decreased heart rate, hypothermia and oral ulceration or signs of a concurrent disease.  

The most suggestive sign of severe acute renal failure is '''oliguria or anuria'''. It does not occur in all cases so should not be completely relied on for diagnosis. Bloodwork should show azotaemia.  

The most suggestive sign of severe acute renal failure is '''oliguria or anuria'''. It does not occur in all cases so should not be completely relied on for diagnosis. Bloodwork should show [[azotaemia]].  

==Diagnosis==

==Diagnosis==

On presentation is it important to establish two things:

On presentation is it important to establish two things:

As mentioned it is important to differentiate ARF from decompensated [[Chronic Renal Failure|CRF]], as '''ARF''' is potentially '''reversible with aggressive therapy'''. The only diagnostic test that can achieve this is [[Renal Biopsy|'''biopsy''']], but due to the high level of risk involved in an already sick animal this is normally not performed. Instead the following factors can be used by the clinician to guide diagnosis:

 

 

As mentioned it is important to differentiate ARF from decomensated [[Chronic Renal Failure|CRF]], as '''ARF''' is potentially '''reversible with aggressive therapy'''. The only diagnostic test that can achieve this is '''biopsy''', but due to the high level of risk involved in an already sick animal this is normally not performed. Instead the following factors can be used by the clinician to guide diagnosis:

'''(1) History'''

'''(1) History'''

 

:With ARF there may be a history of ingestion of or access to toxins/nephrotoxic drugs, and oliguria. Cats with CRF normally have a history of chronic weight loss, anorexia and polyuria/polydypsia (PU/PD).

With ARF there may be a history of ingestion of or access to toxins/nephrotoxic drugs, and oliguria. Cats with CRF normally have a history of chronic weight loss, anorexia and PU/PD.

'''(2) Clinical Exam'''

'''(2) Clinical Exam'''

 

:ARF cats tend to have a good body condition score, and healthy skin and coat. CRF cases have a poor body condition score and a dull/scruffy coat.

ARF cats tend to have a good body condition score, and healthy skin and coat. CRF cases have a poor body condition score and a dull/scruffy coat.

'''(3) Renal Parameters - palpation, ultrasound, radiography'''

'''(3) Renal Parameters - palpation, ultrasound, radiography'''

 

:The kidneys in ARF cats are normal sized or enlarged, and normally painful. In CRF, the kidneys are shrunken, firm and non-painful.

The kidneys in ARF cats are normal sized or enlarged, and normally painful. In CRF, the kidneys are shrunken, firm and non-painful

'''(4) Other'''

'''(4) Other'''

 

:The presence of secondary renal [[hyperparathyroidism]] and non regenerative [[:Category:Anaemia|anaemia]] is suggestive of CRF

The presence of secondary renal hyperparathyroidism and non regenerative anaemia is suggestive of CRF

'''(1) Pre-renal'''

'''(1) Pre-renal'''

 

:Caused by severe '''dehydration''', shock or any other pathology that results in '''poor renal perfusion'''. In these cases USG is >1.035 in the cat and >1.030 in the dog before [[:Category:Fluid Therapy|fluid therapy]]. There should be no evidence of inflammation and urine sodium concentrations are low. Diagnosis is confirmed by a '''rapid and dramatic response to fluid therapy'''.  

Caused by severe '''dehydration''', shock or any other pathology that results in '''poor renal perfusion'''. In these cases USG is >1.035 in the cat and >1.030 in the dog before fluid therapy. There should be no evidence of inflammation and urine sodium concentrations are low. Diagnosis is confirmed by a '''rapid and dramatic response to fluid therapy'''.  

'''(2) Renal'''

'''(2) Renal'''

 

:This is caused by a '''direct insult to the kidney''', with intrinsic damage. In these cases azotaemia is present, and urine specific gravity is between 1.007 and 1.025. There may be evidence of inflammation in the urine sediment and a high sodium content. There is only a '''minimal response to fluid therapy'''. The hallmark of primary renal failure is '''azotaemia''' in the presence of '''poorly concentrated urine'''.

This is caused by a '''direct insult to the kidney''', with intrinsic damage. In these cases azotaemia is present, and urine specific gravity is between 1.007 and 1.025. There may be evident of inflammation in the urine sediment and a high sodium content. There is only a '''minimal response to fluid therapy'''. The hallmark of primary renal failure is '''azotaemia''' in the presence of '''poorly concentrated urine'''.

'''(3) Post-renal'''

'''(3) Post-renal'''

 

:Post-renal failure is caused by an '''obstruction''' or '''rupture''' within the urinary system. This is normally identifiable following a thorough '''history and physical exam'''.

Post-renal failure is caused by an '''obstruction''' or '''rupture''' with in the urinary system. This is normally identifiable following a thorough '''history and physical exam'''.

==Treatment==

==Treatment==

The aim of treatment is to '''support the patient whilst the tubules repair'''. If the ingestion of a specific toxin is known then further exposure should be prevented and  an '''antidote''' may be given if available (for example ethanol in [[Ethylene Glycol Toxicity|ethylene glycol toxicity]]). More commonly, by the time of presentation the damage to the kidneys has already occurred and it is no longer appropriate to administer the antidote. If any other underlying cause has been identified (such as [[Pyelonephritis|pyelonephritis]]), this should be treated appropriately.

The aim of treatment is to '''support the patient whilst the tubules repair'''. If the ingestion of a specific toxin is known then further exposure should be prevented and  an '''antidote''' may be given if available (for example ethanol in [[Ethylene Glycol Toxicity|ethylene glycol toxicity]]). More commonly, by the time of presentation the damage to the kidneys has already occurred and it is no longer appropriate to administer the antidote. If any other underlying cause has been identified (such as [[Pyelonephritis|pyelonephritis]]), this should be treated appropriately.

'''Aggressive [[Fluid therapy|fluid therapy]] is the mainstay of treatment in ARF cases'''. A mild level of volume overload is ideal as it promotes urine production, however as animals are often oliguric, care should be taken not to overload the body with too much fluid. In addition [[Diuretics Effects on Kidneys - Anatomy & Physiology|'''diuretics''']] such '''frusemide and mannitol''' can be administered to stimulate urine production. A '''closed collection system''' should be used to '''monitor urine output'''.  

'''Aggressive [[Fluid therapy|fluid therapy]] is the mainstay of treatment in ARF cases'''. A mild level of volume overload is ideal as it promotes urine production, however as animals are often oliguric, care should be taken not to overload the body with too much fluid. In addition [[Diuretics Effects on Kidneys - Anatomy & Physiology|'''diuretics''']] such '''frusemide and mannitol''' can be administered to stimulate urine production. A '''closed collection system''' should be used to '''monitor urine output'''.  

Severe '''metabolic disturbances''' occur secondary to ARF. '''Hyperkalaemia''' is a common occurrence and is also treated with '''fluid therapy''' using a product such as saline. If it is severe and compromising the cardiac function of the animal then '''calcium gluconate''' can be administered to stabilise the heart (whilst levels are reduced by fluid therapy). '''Metabolic acidosis''' [[File:Hemodialysismachine.jpg|thumb|100px|right|'''Hemodialysis machine''' (Wikimedia Commons)]] also occurs, and again can be treated with '''fluid therapy'''. A fluid such as '''Hartmanns''' which contains '''bicarbonate''' should be used. If this is insufficient to resolve the acidosis then bicarbonate can be administered directly. The use of dopamine in dogs to cause renal vasodilation can be used but its currently not recommended.  

Severe '''metabolic disturbances''' occur secondary to ARF. '''Hyperkalaemia''' is a common occurrence and is also treated with '''fluid therapy''' using a product such as saline. If it is severe and compromising the cardiac function of the animal then '''calcium gluconate''' can be administered to stabilise the heart (whilst levels are reduced by fluid therapy).  

[[File:Hemodialysismachine.jpg|thumb|100px|right|'''Hemodialysis machine''' (Wikimedia Commons)]]

'''Metabolic acidosis''' also occurs, and again can be treated with '''fluid therapy'''. A fluid such as '''Hartmanns''' which contains '''bicarbonate''' should be used. If this is insufficient to resolve the acidosis then bicarbonate can be administered directly. The use of dopamine in dogs to cause renal vasodilation is currently not recommended.  

Additional supportive treatment includes '''anti-emetic drugs''' and [[Gastroprotective Drugs|'''gastro-protectants''']] such as sucralfate and ranitidine. A low protein diet can be fed to reduce the levels of uraemic toxins and an oesophageal tube should be placed in any anorexic animals.  

Additional supportive treatment includes '''anti-emetic drugs''' and [[Gastroprotective Drugs|'''gastro-protectants''']] such as sucralfate and ranitidine. A low protein diet can be fed to reduce the levels of uraemic toxins and an oesophageal tube should be placed in any anorexic animals.  

It this treatment is not sufficient to maintain the animal then a method of '''dialysis''' may be considered.

If this treatment is not sufficient to maintain the animal then a method of '''dialysis''' may be considered.

 

:'''Peritoneal Dialysis:''' This technique uses the omentum within the peritoneum as a filter to remove uraemic toxins. It is used in specialist referral centres when it is considered likely that the cat may recover from ARF. The technique is labour intensive but well tolerated by the animal.  

'''Peritoneal Dialysis:''' This technique uses the omentum within the peritoneum as a filter to remove uraemic toxins. It is used in specialist referral centres when it is considered likely that the cat may recover from ARF. The technique is labour intensive but well tolerated by the animal.  

:'''Hemodialysis:''' This is rarely performed due to the high cost of equipment and ethical questions surrounding longterm treatment. It is only available at a limited number of specialist hospitals.   

 

'''Hemodialysis:''' This is rarely performed due to the high cost of equipment and ethical questions surrounding longterm treatment. It is only available at a limited number of specialist hospitals.   

   

   

==Prognosis==

==Prognosis==

RVC staff (2009) '''Urogenital system''' RVC Intergrated BVetMed Course, ''Royal Veterinary College''

RVC staff (2009) '''Urogenital system''' RVC Intergrated BVetMed Course, ''Royal Veterinary College''

Sparks, AH & Caney, SMA (2005) '''Self-Assessment Colour Review Feline Medicine''' ''Manson''

Sparks, AH & Caney, SMA (2005) '''Self-Assessment Colour Review Feline Medicine''' ''Manson Publishing''

{{Learning

{{Learning

|flashcards = [[Feline Medicine Q&A 23]]

|flashcards = [[Feline Medicine Q&A 23]]<br>[[Feline Medicine Q&A 24]]

}}

}}

[[Category:Renal Failure]]

[[Category:Renal Failure]]

[[Category:To Do - Urinary]]

[[Category:Expert Review - Small Animal]]

[[Category:To Do - Manson review]]