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  1. 1. Urine Output Assessment Definitions, terminology and approach
  2. 2. What is “GFR”? <ul><li>Glomerular filtration rate ( GFR ) is the volume of fluid filtered from the kidney glomerular capillaries into Bowman’s capsule per unit time. </li></ul><ul><li>Normal GFR for men is 165-180 liters per day (115-125 ml/min) </li></ul><ul><li>Normal GFR for women is 130-145 liters per day (90-100 ml/min) </li></ul>
  3. 3. How to Estimate GFR <ul><li>Creatinine clearance is used to measure GFR </li></ul><ul><li>Creatinine is derived from the metabolism of creatine in skeletal muscle and from dietary meat intake; it is released into the circulation at a relatively constant rate and has a stable plasma concentration. </li></ul><ul><li>Creatinine is freely filtered across the glomerulus and is neither reabsorbed nor metabolized by the kidney. </li></ul><ul><li>The creatinine clearance is usually determined by a 24 hour urine collection or by using estimation equations based on serum creatinine [Cr] </li></ul>
  4. 4. Creatinine Clearance <ul><li>Two equations are used to estimate GFR from serum [Cr]: MDRD (modification of diet in renal disease) and Cockcroft-Gault (C-G) </li></ul><ul><li>The MDRD study population was mostly white and had non-diabetic kidney disease </li></ul><ul><li>Both MDRD and C-G lose accuracy in obese patients and in patient’s with normal kidneys </li></ul><ul><li>MDRD works better for kidney transplant patients </li></ul><ul><li>C-G tends to underestimate GFR in elderly patients compared to MDRD </li></ul><ul><li>Both equations may be of limited use for non-white ethnicities because of dietary differences. </li></ul><ul><li>Our Laboratory Medicine department uses MDRD to calculate GFR </li></ul>
  5. 5. GFR and Urine output reconciled? <ul><li>Urine volume is variable in patients with renal disease and can be difficult to interpret </li></ul><ul><li>Although GFR may be reduced, urine output is determine by GFR and Kidney reabsorbtion. </li></ul><ul><li>Example A: normal male GFR is about 180 liters a day. If 179 liters per day are reabsorbed, daily urine output would be 1 liter. </li></ul><ul><li>Example B: patient with chronic kidney failure may have GFR of 10 liters a day and only be able to reabsorb 9 liters resulting in daily urine output of……… 1 liter. </li></ul>
  6. 6. Urine Output Definitions <ul><li>Oliguria: less than 400 cc urine output per day </li></ul><ul><ul><li>Roughly correlates with < 17 cc per hour </li></ul></ul><ul><li>Anuria: less than 50 cc urine output a day </li></ul><ul><li>Polyuria: more than 3 liters of urine output a day (adult definition) </li></ul>
  7. 7. Case 1: <ul><li>76 year old female s/p total right hip replacement yesterday </li></ul><ul><li>Past medical history significant for hypertension and arthritis </li></ul><ul><li>Serum [Cr] up to 1.2 from 0.8 on admission </li></ul><ul><li>Medications: toradol, lisinopril, lasix, bowel program </li></ul><ul><li>Urine output of 100 cc in the last 12 hours </li></ul><ul><li>What are some possible explanations for this patient’s oliguria? </li></ul>
  8. 8. Simplified approach <ul><li>3 categories for cause of acute oliguria </li></ul><ul><li>Prerenal: hypovolemia or heart failure </li></ul><ul><li>Renal: usually acute tubular necrosis (ATN) caused by renal hypoperfusion and ischemia or nephrotoxins </li></ul><ul><li>Postrenal: urinary tract obstruction </li></ul>
  9. 9. Oliguria <ul><li>When acute oliguria develops as an outpatient, there’s usually only one renal cause and prognosis is good </li></ul><ul><li>Patients who develop acute oliguria in the hospital usually have multiple renal injuries, frequently have severe renal insufficiency, and have a worse prognosis than outpatients </li></ul><ul><li>In the ICU, acute oliguria usually develops late in the course of severe illness with multi-organ system failure </li></ul>
  10. 10. Inpatient oliguria <ul><li>Most common etiologies of inpatient oliguria: </li></ul><ul><ul><li>Hypovolemia </li></ul></ul><ul><ul><li>Decreased cardiac output </li></ul></ul><ul><ul><li>Use of diuretics </li></ul></ul><ul><ul><li>Use of nephrotoxic drugs </li></ul></ul><ul><ul><li>Use of radiographic contrast agents </li></ul></ul><ul><ul><li>Effect of anesthesia or surgery </li></ul></ul>
  11. 12. Effect of ACE-inhibitor
  12. 13. Case 1 continued: <ul><li>What interventions could you suggest that may help treat this patient’s oliguria? </li></ul><ul><li>What complications, symptoms, etc. are sometimes associated with oliguria? </li></ul><ul><li>When do we start using Lasix? </li></ul>
  13. 14. Complications of Acute Oliguria <ul><li>Infections develop in 30-70% of patients with acute renal failure: usually respiratory, urinary tract, or catheter related </li></ul><ul><li>Neurologic complications: confusion, somnolence, even seizures </li></ul><ul><li>GI complications: anorexia, nausea, ileus, bleeding </li></ul><ul><li>GI bleeding occurs in 10-30% of patients with acute renal failure </li></ul>
  14. 15. Lasix in acute renal failure <ul><li>High-dose furosemide for established ARF: a prospective, randomized, double-blind, placebo-controlled, multicenter trial. American Journal of Kidney Disease September 2004 </li></ul><ul><li>Three hundred thirty-eight patients with ARF requiring dialysis therapy were randomly assigned to the administration of either furosemide (25 mg/kg/d intravenously or 35 mg/kg/d orally) or matched placebo. </li></ul><ul><li>The primary end point was survival. </li></ul><ul><li>The secondary end point was number of dialysis sessions. </li></ul><ul><li>Tertiary end points included time on dialysis therapy, time to achieve a serum creatinine level less than 2.26 mg/dl, and time to reach a 2-L/d diuresis. </li></ul><ul><li>RESULTS: There were no differences in survival and renal recovery rates between the 2 groups. Time to achieve a 2-L/d diuresis was shorter with furosemide. There were no significant differences in number of dialysis sessions and time on dialysis therapy between the furosemide and placebo groups, even in the subgroup of patients reaching a 2-L/d diuresis. </li></ul><ul><li>CONCLUSION: High-dose furosemide helps maintain urinary output, but does not have an impact on the survival and renal recovery rate of patients with established ARF. </li></ul>
  15. 16. Case #2: <ul><li>45 yo male with foreign body related infection in left foot admitted by podiatry. No history of kidney disease. You are consulted regarding oliguria on day 3 of hospitalization. </li></ul><ul><li>Diagnostic approach? </li></ul><ul><li>Therapies? </li></ul>
  16. 17. Case #3: <ul><li>55 year old female admitted with abscess at right forearm by a Plastic Surgeon. She had her I&D earlier that day. You are consulted because of urine output of 100cc in a 8 hour shift. </li></ul><ul><li>Diagnostic approach? </li></ul><ul><li>Therapy? </li></ul>
  17. 18. Questions? <ul><li>Thanks for coming! </li></ul>