The Clinical Kidney

what is glomerular filtration rate (GFR)?

-sum of filtration rate in all nephrons

-not precisely correlated to nephron loss

-measured using ideal filtration markers that are not reabsorbed, secreted, or metabolized

-estimated using creatinine with or without cystatin C

what is creatinine and its function?

-endogenous marker that undergoes filtration and secretion

-non GFR determinants include muscle mass, diet, etc

-measured with IDMS assay

what is cystatin C and its function?

-endogenous marker that undergoes filtration and metabolism

-non GFR determinants include adiposity, smoking, etc

-increase more quickly than creatinine in acute disease

what are the 5 steps of GFR assessment?

-determine creatinine

-consider sources of error and clinical need for accuracy

-if doubt, determine creatinine-cystatin-c

-consider sources of error and clinical need for accuracy

-if doubt, measure GFR with an exogenous marker or measure CrCl with urine collection

what is the cockcroft-gault equation?

[(140 - age) x weight] / [72 x SCr] [x 0.85 if female], resulting in mL/min

when should total body weight and adjusted body weight be used?

-TBW: if TBW 1.3 x IBW

what is the average amount of urine output per day?

0.5-2 mL/kg/hr

what are the urine output levels for oliguria and anuria?

-oliguria: < 500 mL/day

-anuria: < 50 mL/day

what are the 3 classifications of kidney issues?

-prerenal: decreased perfusion pressure

-intrinsic: direct pathology

-postrenal: obstruction of urine flow

what are 5 indications for renal replacement therapy?

-acidemia

-electrolytes

-intoxicants

-overload

-uremia

what are the 3 main modalities for RRT?

-hemodialysis (HD, iHD)

-peritoneal dialysis (PD)

-continuous renal replacement therapy (CRRT)

what is hemodialysis?

-blood and dialysate fluid pumped through dialyzer in countercurrent fashion

-typically 3-5 hrs, 2-3 times per week

what is peritoneal dialysis?

-dialysate fluid instilled into peritoneal space, allowed to dwell, and drained

-4-6 hrs

what are the 3 advantages of PD vs HD?

-less physiologically stressful

-does not require vascular access or anticoagulation

-flexible

what are the 4 disadvantages of PD vs HD?

-slower solute removal

-cannot adjust diffusion vs convection

-complicated by peritonitis and abdominal involvement

-greater patient involvement

what is the main difference between convection and diffusion?

diffusion moves small mlcs using the concentration gradient while convection moves medium/large mlcs using the hydrostatic pressure gradient

what are the 4 advantages of CRT vs HD?

-less physiologically stressful

-greater fluid and solute removal

-greater clearance of inflammatory mediators, like cytokines

-consistent

what are the 2 disadvantages of CRT vs HD?

-slower fluid and solute removal

-continuous

what are 4 potential pharmacokinetic changes in kidney dysfunction?

-BA may increase

-protein binding may decrease

-Vd may increase

-CL may decrease

what are the 3 dosing recommendations without RRT?

-evaluate drug information recommendations when available

-use CKD-EPI, MDRD, or cockgroft gault

-adjust to body surface are when needed

what are the 3 dosing recommendations with RRT?

-evaluate drug information recommendations when available

-administer doses post HD unless otherwise specified

-determine effluent flow rate for CRRT

what medication type is most likely to require a dose decrease in the setting of kidney dysfunction?

a medication with a high degree of first pass metabolism

what are the 3 classes of albuminuria and proteinuria?

-normal to mildly increased: ACR <30

-moderately increased: ACR between 30-300

-severely increased: ACR >300

what are 3 types of CRRT and their differences?

-CVVH: convection, useful when fluid overload is the main issue

-CVVHD: diffusion

-CVVHDF: convection and diffusion, may help with cytokine removal