Reviewing the chemistry panel: Kidney cases (Proceedings)


Causes of acute renal failure: 1. Hemodynamic causes; 2. Toxic causes; 3. Inflammatory causes.

Renal Components of the Chemistry Panel

     1. Creatinine

     2. BUN

     3. Electrolytes

               • Sodium: N to ↓

               • Chloride: N to ↓

               • Potassium: ↑

               • Calcium: acute= ↓ Ca: chronic=↑

               • Phosphorus: acute= ↑

               • Acid – base parameters: TCO2: ↓

               • Anion Gap:↑

Creatinine/BUN: Increase means that GFR has decreased (prerenal,renal) or post-renal disease is present

Renal Disease

          • Hyponatremia, hypochloremia

          • Hyperkalemia (normal to high)

          • Metabolic acidemia (Low TCO2)

                o Anion Gap often increases

          • Acute Renal Failure

                o Hypocalcemia

                o Hyperphosphatemia

          • Chronic Renal Failure

                o Hypercalcemia

                o Hypophosphatemia

Causes of acute renal failure: 1. Hemodynamic causes; 2. Toxic causes; 3. Inflammatory causes

          1 Hemodynamic causes

          • Prolonged hypovolemia

          • Coagulopathy Endotoxemia/SIRS

          2 Toxic causes

          • Phenylbutazone

          • Aminoglycosides

          • Tetracycline*

          • Pigments- hgb, mgb

          • Heavy metals

          • Blister Beetle

          3 Inflammatory causes

          • Pyelonephritis

          • Leptospirosis

          • Neoplasia

          • Immune-mediated causes

Glomerulonephritis – Proteinuria

Secondary to Strep equi equi

Prerenal vs Renal Azotemia

          • Horses with prerenal azotemia are dehydrated

                o Urine is concentrated

                o USG > 1.020

          • Horses with renal azotemia are isosthenuric regardless of hydration status

                o USG: 1.008 – 1.020


A rapid decrease in creatinine is expected with fluid therapy. It should be markedly decreased and close to normal within 24 h if prerenal. Persistent elevation of creatinine in the face of fluids indicates renal disease

Prolonged prerenal azotemia will lead to renal failure if not corrected

Prerenal vs Renal Azotemia

          • Fractional Excretion of Sodium

                o < 1 % in prerenal cases (Normal FENa is < 1 %)

                o 1 % indicates renal dysfunction

          • FE reflects tubular reabsorptive capacity

          • FENa+ = SerumCr X UrineNa

          • UrineCr SerumNa

Case 1: 10-month Paint filly

History: Severe bilateral forelimb contracture

          • Unable to fix distal limb

          • Upright digit and fetlock joint

          • Painful, lies down often, partial anorexia

Historical Treatment

          • 0.5 g phenylbutazone PO BID

          • Full limb wraps

          • Oxytetracycline (44 mg/kg; total 15 g IV twice)

Risk Factors

          • Partial anorexia = likely not drinking well > dehydration

          • Phenylbutazone: NSAIDS: renal ischemia through inhibition of PGE and PGI

          • Oxytetracycline: toxic to tubule epithelium

On day 3 the filly was depressed and Anorexic:

Key Questions:

1. Is it prerenal, renal, post-renal?

Urine Specific Gravity: 1.012

Observed to urinate normal stream

          • ANSWER>>>Renal

2. Is it chronic or acute?

Body condition is good

Calcium is normal

Phosphorus is high

No anemia, no dental tartar

          • ANSWER>>>Acute

US is helpful – shows enlarged kidneys with perirenal edema

Treatment: Discontinue bute and tetracycline; Opioids for analgesia if pain medication needed


Isotonic crystalloids: Initial bolus 30 mL/kg, then 3 mL/kg/h

Maintained on fluids for approximately 5 days

Case 2: 3-Yr old Paint Mare

Key Questions

1. Prerenal, renal, post-renal ?

          • Urinary catheter passes easily, normal bladder palpated

USG: 1.010

FE: Scr x UNa

Ucr SNa

FE: 5.1 x 50 = 0.03 = 3 % HIGH ==== ANSWER = RENAL 65 131

Key Questions

Acute or Chronic ?

Weight loss

Mild anemia


Suggest chronic

US is confirmatory

Histopathology is definitive

Biopsy Results

• Severe, Multifocal Chronic Lymphoplasmacytic Interstitial Nephritis With Severe Interstitial Fibrosis And Glomerulosclerosis

Mare euthanized due to biopsy results, marked US changes, and poor clinical response

Case 3: 5 Yr Old QH Gelding

Acute colic: began this morning; nonresponsive to analgesics; HR: 70

          • PE: HR: 70

                o 8 % dehydrated/hypovolemic

                o Moderately painful

                o Large colonic distention with tight bands across abdomen on rectal

                o US reveals distended colon obscuring liver on right

Right Dorsal Displacement Suspected

Key Findings

          • Azotemia

          • Mild acidemia

          • Increased liver enzymes and BR-Functional indicators are ok

Key Questions

1. Prerenal, renal, or post-renal?

USG: 1.039 – very concentrated

Observed to urinate normally by owners; no ascites

.>>PRERENAL due to hemodynamic causes

Response to fluid therapy confirms this

With fluid diuresis the next day:

          • Creatinine has decreased from 3.1 to 2.0

          • BUN has decreased from 45 to 27

Liver Enzymes

Liver appeared normal on US and at time of surgery

Enzymes decreased to normal over several days in the post-operative period

Example of transient liver disease secondary to GI causes (endotoxemia or biliary obstruction)

General Guidelines: Therapy of Acute Renal Failure

I. Polyuric Renal Failure

1. IV fluid therapy:

Replace deficits

Then 1.5-2 X maintenance rate

          • 4-5 mL/kg/h initially

          • As improvement occurs, the rate can be decreased to 2-3 mL/kg/h

          • Diuresis should continue until creatinine normalizes or plateaus for 48-72 h

          • Avoid nephrotoxic agents such as NSAIDS, Aminoglycosides

2. Nutrition

          • If anorexic, add dextrose 1.5-5 %

          • Feed low calcium diets in longer term

          • Feed lower quantity, but higher quality protein

          • Omega 3 fatty acids (flaxseed)

Treatment of Anuria/Oliguria

          • Replace fluid deficits

          • Diuretics: Furosemide (Lasix): One or two doses of 1 mg/kg boluses IV

If no response, try continuous rate infusion (CRI) at 0.12 mg/kg/h

Mannitol – 0.5 g/kg bolus, do not repeat if no urine is produced; OR 1 mg/kg/min concerned about volume overload

3. Low dose dopamine to make urine flow: - 2 ?g/kg/min for renal afferent arteriolar dilation

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