POST OPERATIVE OLIGURIA and its management

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1. Post operative oliguria

2. INTRODUCTION Decreased urine output and acute kidney injury (AKI) are among the most important complications that may develop in the post-operative period Acute kidney injury is associated with > 25% increase in overall mortality rate, thus preventing the development of AKI by maintaining adequate urine output is of paramount importance

3. Oliguria Urine output < 400/day (<1ml/kg/hr) Definition according to RIFLE and AKIN classification

4. ETIOLOGY Can be broadly classified into Pre-renal Renal Post-renal

5. Pre-renal causes Most Common cause of oliguria (70%) Main pathophysiology  Hypotension and Kidney Hypoperfusion  Secondary to decrease in blood volume Absolute decrease  Dehydration, Hemorrhage, GI loss Relative decrease  Sepsis, Vasodilator drugs, Renal artery stenosis, Intraabdominal Hypertension

6. Compensatory mechanism includes Myogenic autoregulation + prostaglandins release  Affarent dilatation Angiotensin II release  Efferent constriction Net effect  Increased GFR Significance: Cyclosporine, Tacrolimus  Inhibitors of Myogenic autoregulation NSAIDs  Inhibitors of prostaglandins ACE inhibitors  Angiotension II release inhibitors Leads to decrease GFR  can precipitate AKI

7. Patient presenting with hypotension and tachycardia Hypovolemia Adrenal insufficiency Anaphylaxis Patient presenting with hypotension and bradycardia Beta-blockage Heart block Prolonged hypoxemia

8. Mean arterial pressure of 60-65 mmHg is usually sufficient to maintain renal perfusion In patient with pre-existing hypertension, MAP should be maintained within 20% of baseline value for adequate renal perfusion

9. Renal causes Main pathophysiology  Parenchymal injury Secondary to Acute glomerulonephritis Interstitial Nephritits Acute tubular necrosis (ischemia, drugs or toxins)

10. Post-renal causes Main pathophysiology  Obstruction Secondary to Calculi Tumor Obstructed Foley’s catheter

11. SYSTEMIC COMPLICATIONS OF OLIGURIA Urinary tract infection  Most common cause of morbidity and mortality Anemia  due to decreased EPO Pulmonary edema, pleural effusion and ascites Hypocalcemia  Decreased excretion of phosphate  Decreased absorption of calcium from GI tract Hyperkalemia  Decreased GFR  Decreased tubular secretion

12. MANAGEMENT Need of Urgent Resuscitation? Any pre-existing condition or symptoms exacerbating the hypovolemia Any H/O vomiting, Diarrhea, Fever, low intake (Oral and IV) Any active bleeding, wound infection  Septicemia Any symptoms suggestive of bladder outlet obstruction from prostatic hypertrophy Hesitancy, difficult voiding, dribbling

13. Any history suggestive of Acute renal failure Previous history, Renal diseases H/O nephrotoxic drug use ( Aminoglycosides , NSAID) H/O exposure to nephrotoxic agents (contrast, chemotherapy) Any pre-existing condition that may result in oliguria Cardiac failure Cirrhosis of liver

14. On examination , Patient may present with Hypertension (decreased urine output) Tachycardia Decreased skin turgor , dry mucous membranes Flat neck veins Rales on chest auscultation (CHF) Ascites (Cirrhosis of liver) Distended bladder (outlet obstruction) Per Rectal examination (enlarged prostate) Per Vaginal examination (mass)

15. On investigation Urine analysis High specific gravity  volume depletion Protein or red cell cast  glomerular diseases WBC cast  infection or severe inflammation Granular cast  Acute tubular necrosis Significant hematuria  Renal stones

16. Renal Function test Blood urea : Creatinine  > 10 : 1  Most likely Pre-renal cause (can be post-renal as well such as obstruction) Blood Urea : Creatinine  < 10:1  Most likely Renal cause Urine sodium levels < 15mmol/L  Pre-renal cause > 20mmol/L  Rena cause

17. Ultrasound abdomen and pelvis Voiding Cystourethrography Suspected bladder outlet obstruction Chest radiography  Pulmonary edema Echocardiography  Congestive cardiac failure

18. treatment Minimal acceptable urine output  1 mL /kg/hr Maintain strict input output chart Stop all nephrotoxic drugs Aminoglycosides , NSAIDS, COX-2 inhibitors Look for foci of sepsis Surgical drainage site, UTI

19. Initial therapy for fluid management Isotonic Saline/Ringer Lactate @ 20mL/Kg over 30 min Can be repeated twice if needed Time frame for response to occur  4-6 hours Potassium supplements are contraindicated If volume overload is seen, IV loop diuretics like furosmide is given No response to furosemide  Acute tubular necrosis  Dialysis

20. DAILY FLUID AND ELECTROLYTE REQUIREMENT Daily maintenance fluid required 4-2-1 ml/kg/hr or 100-50-20 ml/kg/day Daily maintenance electrolytes required 1 mmol /kg/day of Na+,K+,Cl - Daily requirement of glucose 100-150 g/day

21. Calculation of Nil per Oral deficit NPO = No of hours * Maintenance fluid required Calculation of third space loss Superficial surgical trauma  1-2 ml/kg/hr Minimal Surgical trauma(hernia)  3-4 ml/kg/hr Moderate Surgical trauma (Hysterectomy)  5-6 ml/kg/hr Severe Surgical trauma(Nephrectomy)  8-10 ml/kg/hr

22. Calculation of fluid required for blood loss 3 cc of crystalloid solution per cc of blood loss Calculation of intraoperative fluid requirement Fluid deficit  1.5 ml/kg/hr * No of hrs NPO If bowel preparation done  + 1 ltr Maintenance  1.5 ml/kg/hr * No of hrs in OT Third Space loss  According to Surgery * No of hrs Blood loss  Amount of blood * 3

23. Management of Pre-Renal causes Volume Challenge  500 ml NS over 24 hours Follow hourly urine output Frusemide (if volume overload is suspected) Management of Renal causes Loop Diuretics such as Frusemide Emergency dialysis Management of Post Renal causes Foley’s catheterization If already placed, irrigation/replacement

24. INDICATIONS FOR DIALYSIS

25. Prevention of Acute Kidney Injury in Post-operative patient with Oliguria Monitoring  Prevention of perioperative renal perfusion and ischemic injury  Prevent hypovolemia and hypotension Fluid therapy  Mainstay of therapy in prevention of AKI Vasopressor therapy  Secondary line of management after adequate fluid therapy Avoid contrast induced Nephropathy  IV fluid infusion after the IV contrast administration