Nephrology

     

    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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