AZOTEMIA & ACUTE KIDNEY INJURY Gregory F. Grauer, DVM, MS, DACVIM (SAIM) Sarah Guess, DVM, MS Kansas State University FIRST-TIME DIAGNOSIS OF AZOTEMIA OR ACUTE-ONSET AZOTEMIA INVESTIGATION Assess USG HYPERSTHENURIA PRESENT NO Rule out postrenal azotemia (dogs, ≥1.030; cats, ≥1.035)? (from obstruction or leakage) with ultrasonography and positive contrast imaging, if necessary YES TREATMENT Probable renal azotemia TREATMENT Reassess adequacy of If prerenal dehydration/azotemia confirmed volume replacement (eg, skin tenting, tacky mucous membranes, after 24 and 48 hours; elevated serum albumin concentration), initiate continue fluid therapy fluid therapy to rehydrate patient (Table 2) INVESTIGATION Rule out CKD and acute-on-chronic kidney disease (Table 1) Azotemia resolves? NO YES TREATMENT Initiate fluid therapy (if not already started) to rehydrate patient Volume-responsive azotemia (Table 2) DIAGNOSIS Prerenal azotemia superimposed on YES Azotemia resolves? inability to concentrate urine (eg, diabetes mellitus, hypoadrenocorticism, hypercalcemia, pyometra) NO Suspect AKI and pursue AKI = acute kidney injury therapy (page 30) CKD = chronic kidney disease USG = urine specific gravity 28 cliniciansbrief.com October 2016 MANAGEMENT TREE h NEPHROLOGY h PEER REVIEWED TABLE 1 TABLE 2 HISTORY, EXAMINATION, EXAMPLE OF FLUID VOLUME & LABORATORY FINDINGS REQUIREMENTS FOR A 20-KG DOG OF CKD & AKI* WITH 8% DEHYDRATION & AKI Findings CKD AKI Deficit needs (8% × 20 kg) = 1600 mL over 6 hours (replace over 4-6 hours) Weight loss, poor coat, poor body + - condition Maintenance (60 mL/kg/day) = 1200 mL/day Small, irregular kidneys (on radiography + - Continuing losses (dog vomits = 400 mL/day or palpation) 4 times at 100 mL/episode) Nonregenerative anemia + - Total = 3200 mL/day (deficit replaced over 4-6 hours Acidosis/hyperkalemia - + if possible) Oliguria/anuria - + TABLE 3 Small, irregular kidneys with + - hyperechoic cortices with or without HYPOTHETICAL COMPARISON loss of corticomedullary junction (on OF TOTAL FLUID NEEDS IN NORMAL, ultrasonography) OLIGURIC, & POLYURIC DOGS Chronic history of polyuria/polydipsia or + - stage 1 CKD Normal Oliguric Polyuric Urine sediment changes compatible with - + tubular cell damage (eg, granular casts, Insensible 20 mL/kg/day 20 mL/kg/day 20 mL/kg/day renal tubular epithelial cells) fluid needs Relatively severe signs for magnitude of - + Sensible fluid 40 mL/kg/day 6 mL/kg/day 165 mL/kg/day azotemia needs (urine *+ = presence more likely; - = presence less likely output) Total 60 mL/kg/day 26 mL/kg/day 185 mL/kg/day Suggested Reading Cowgill LD, Langston C. Acute kidney insufficiency. In: Bartges J, Polzin Langston C. Acute uremia. In: Ettinger SJ, Feldman EC, eds. D, eds. Nephrology and Urology of Small Animals. West Sussex, United Textbook of Veterinary Internal Medicine. 7th ed. St. Louis, MO: Kingdom: Wiley-Blackwell; 2011:472-523. Saunders Elsevier; 2010:1969-1985. Harison E, Langston C, Palma D, Lamb K. Acute azotemia as a predictor Ross L. Acute renal failure. In: Bonagura JD, Twedt DC, eds. of mortality in dogs and cats. J Vet Intern Med. 2012;26(5):1093-1098. Kirk’s Current Veterinary Therapy XIV. St. Louis, MO: Saunders Elsevier; 2009:879-882. October 2016 cliniciansbrief.com 29 MANAGEMENT TREE h NEPHROLOGY h PEER REVIEWED AKI SUSPECTED INVESTIGATION Perform complete minimum database (ie, CBC, serum chemistry profile with electrolytes, urinalysis with sediment examination, BP) DIAGNOSTICS INVESTIGATION h Leptospirosis serum titers and urine leptospirosis PCR Rule out CKD via imaging, history, and physical examination (Table 1, page 29) h Urine culture, UP:C h Abdominal ultrasonography to find obstruction caused by nephrolithiasis, evidence AKI confirmed of pyelonephritis, or h Acutely elevated serum creatinine with isosthenuria (USG 1.008-1.012) abdominal effusion or minimally concentrated urine (USG 1.013-1.030/1.035) CAUSE KNOWN? YES TREATMENT Treat underlying TREATMENT condition (eg, toxicity, Initiate fluid therapy and diagnostics for thromboembolism) nonspecific AKI. Other therapy may be considered: NO h Antihypertensive therapy (eg, amlodipine) h Antibiotics if pyelonephritis or leptospirosis is suspected; avoid aminoglycosides and other nephrotoxic antibiotics TREATMENT Fluid therapy h Pain medications; avoid NSAIDs h Nutritional therapy (eg, nasoesophageal tube, esophagostomy tube, total parenteral nutrition) if patient not vomiting h Treatment for uremic ulcers, if present STEP 1 STEP 6 h Antiemetics (eg, ondansetron, dolasetron) Choose replacement fluids (eg, h Monitor for signs of lactated Ringer solution, 0.9% overhydration (eg, increased NaCl [if hyperkalemic]) bronchovesicular sounds, tachycardia, serous nasal Anuria discharge, chemosis, weight h Urine output 0 mL/kg/hr, despite adequate gain, increased central venous rehydration pressure) STEP 2 h h Cautious use of volume expansion and/or Estimate dehydration % (eg, Recheck creatinine and diuretics because of no proven benefit skin tenting, capillary refill time, electrolytes every 6-24 hours h Reassess central venous pressure); h Prognosis poor, especially if no response to determine timeline for correction therapy and worsening azotemia (eg, 4-6 hours; Table 2, page 29) STEP 5 Reassess Oliguria h If weight loss occurs, calculate h Urine output <0.5 mL/kg/hr after rehydration STEP 3 kg lost × 1000 and add to h Cautious use of volume expansion and/or Determine if electrolyte current fluid rate; recheck diuretics because of no proven benefit supplementation needed (eg, weight in 4-6 hours h Reassess KCl ≤0.5 mEq/kg/hr) h Base fluid therapy volume on h Prognosis guarded, unless converted to polyuria, urine output for which prognosis improves with response to rehydration STEP 4 Initiate fluid therapy AKI = acute kidney injury Polyuria h Measure body weight every h Urine output >1 mL/kg/hr 4-6 hours BP = blood pressure h h Quantify urine output Base fluid rate on output and body weight gain CKD = chronic kidney disease or loss if possible (Table 3, page 29) h Prognosis is fair-to-good, especially with PCR = polymerase chain reaction resolving azotemia UP:C = urine protein:creatinine USG = urine specific gravity 30 cliniciansbrief.com October 2016.