Pathophysiology and Management of Kidney Disease
Core concepts
CKD is staged by GFR (G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15 mL/min/1.73 m²) combined with an albuminuria category (A1 <30, A2 30–300, A3 >300 mg/g). Staging requires kidney damage or reduced GFR persisting more than three months; a single abnormal creatinine is not CKD.
AKI uses KDIGO criteria: creatinine rise ≥0.3 mg/dL within 48 hours, ≥1.5× baseline within 7 days, or urine output <0.5 mL/kg/h for 6 hours. Separate prerenal, intrinsic (ATN, glomerular, interstitial) and postrenal (obstruction) causes, because the nursing priority differs - a fluid challenge versus a bladder scan.
Know the indications that force dialysis initiation: refractory hyperkalemia, severe acidosis, volume overload with pulmonary edema, uremic pericarditis or encephalopathy, and uremic bleeding. Hyperkalemia is the immediate emergency; uremic pericarditis means dialyze now, not next week.
Anemia reflects erythropoietin deficiency. CKD–mineral bone disease reflects phosphate retention, low calcitriol, hypocalcemia and secondary hyperparathyroidism. Phosphate binders are taken with meals - a frequent distractor is "take on an empty stomach."
Trap: equating a low BUN with good clearance. BUN also falls with poor protein intake or liver disease; adequacy is judged by Kt/V and urea reduction ratio.
Worked example: creatinine 4.0 mg/dL a year ago and 4.2 today, no proteinuria, normal ultrasound. Do not label stage 5 CKD from one value - document the trend and markers of kidney damage over time before assigning a stage.