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  1. Approach To Medicine
  2. Nephrology

Nephrology

Modified 01:37, 23 Apr 2017 by apavel | Page History
    Table of Contents
    1. 1. Physiology Overview
    2. 2. Approach to Hematuria
      1. 2.1. Maintenance
    3. 3. Urine Lytes
    4. 4. Chronic Kidney Disease
      1. 4.1. Hypertension
    5. 5. GFR Estimation
    6. 6. Nephrotic Syndrome

     

    Physiology Overview

    NephronPhysiology.gif

    Approach to Hematuria

    • Determine if cause is glomerular or non-glomerular by looking at urinalysis, urine microscopy (dysmorphic cells, RBC casts, etc.)
      • Glomerular --> continue workup, labs, consider renal biopsy
      • Non-Glomerular --> Needs upper & lower tract assessment
        • Cystoscopy --> upper tract
        • CT urogram --> lower tract

     

     

     

    Maintenance

    • How much to give?
      • 4-2-1 Rule
        • 4 mL/kg/h for first 10kg or less
        • 2 mL/kg/h for next 10kg
        • 1 mL/kg/h for remainting kg
        • Example.  3kg infant (12mL/h), 25kg child: 4x10+2x10+1x5=65 mL/hr
      • Ask Ins/Outs. 
    • Which Fluid to give?
      • Before starting IV fluids, check electrolytes (Na, K, glucose, urea, creat).
      • Monitor lytes daily if >50% maintenance fluid via IV.
      • Start with NS or RL.  Then depends on Na
        • [Na+] <138 mmol/L, continue RL or NS
        • [Na+] 138-144 mmol/L, use 1/2 NS, NS, or RL (IV solution with [Na+] 77-135
        • [Na+] 145-154 mmol/L, use 1/2 NS ([Na+] ~77)
        • [Na+] >154 mmol/L (Hypernatremia)
          • Risk of cerebral edema with rapid rehydration.
          • Correct slowly. Use formulas to determine Na deficit and rate of correction. (TODO)

    Urine Lytes

    • Urine Osmolality
      • If <200 --> ADH is OFF (dilute urine)
      • If >200 --> ADH is ON (urine concentrated)
    • Urine Sodium
      • if < 20 --> Aldosterone effective (absorbing Na and water)
      • If > 40 --> Aldosterone NOT effective (losiing Na in kideys)  Renal failure, etc..
    • Urine Chloride
      • If High --> Hyperaldosteronism
      • If Low --> Vomiting, Diarrhea

     

    Chronic Kidney Disease

    Hypertension

    • Managing hypertension is indicated for all patients with kidney disease. (regardless of etiology)
    • Controlling blood pressure helps to decrease cardiovascular risk and may help to prevent progression to end-stage kidney disease.
    • ACEi/ARB are preferred Anti-HTN agents in CKD, especially in those with proteinuria.
    • Mechanism:
      • ACEi/ARB lower efferent arteriolar resistance and lower intraglomerular pressure.
      • The lower intraglomerular pressure is thought to be protective for the kidney but may be associated with a slight increase in the serum creatinine level (30% increase is acceptable).
      • CAUTION: Use of these agents also may cause hyperkalemia.  Use diuretics to manage hyperkalemia, further HTN, and edema.
      • Higher doses of diuretics are often required.

     

    GFR Estimation

    • Ways to estimate:
      • Modification of Diet in Renal Disease (MDRD) study
        • Underestimates GFR at higher (normal) values.
        • If calculated eGFR is >60 mL/min/1.73m^2 then report as 60.
        • Study included patients with CKD with lower muscle mass than general population.
          • Underestimates GFR in healthy, low-risk persons with normal/increased muscle mass.
      • Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)
        • Reduced bias associated with MDRD, shown in NHANES study.
          • NHANES: median eGFR was 94.5 mL/min/1.73m^2 using CKD-EPI and 85 using MDRD.
        • Some patients Stage 3 CKD via MDRD and no CKD by CKD-EPI.
      • Cockcroft-Gault
        • Underestimates GFR at higher values.
        • Less accurate than MDRD and CKD-EPI?
      • 24-hour urine collection - for Creat Clearance.
        • Good but inaccurate due to difficulty in collecting 24-hr urine sample.
        • Undercollection = inaccurate GFR.
      • Radionucleotide kidney clearance scanning
        • Very accurate, but more invasive and expensive than eGFR.
        • Often used in evaluating live kidney donors.
    • CKD Stage GFR level (mL/min/1.73 m2)
      Stage 1 ≥ 90
      Stage 2 60 - 89
      Stage 3 30 - 59
      Stage 4 15 - 29
      Stage 5 < 15

     

    Nephrotic Syndrome

    • 24-hr urine proteinuria
      • Normal < 150 mg/day
      • Nephrotic Range >3.5g/day
    • Workup (causes)
      • Serology: ANA, C3/4, SPEP, UPEP, syphilis, HepB, cryoglobulins
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