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The Kidneys Kidneys: primary organs for regulating fluid balance, electrolyte composition and acid-base
balance
Secrete renin, which helps regulate BP
Release erythropoietin, a hormone that stimulates RBC production
Produce calcitriol, the active form of vitamin D, which helps maintain bone homeostasis
Each kidney contains ~ 1 million nephrons
Blood is filtered through the glomerulus
Water and other small molecules readily pass through the glomerulus and enter Bowman’s capsule (the first section of the nephron) and then the proximal tubule
Once in the nephron, the fluid is called filtrate
After leaving the proximal tubule, the filtrate passes through the Loop of Henle and subsequently, the distal tubule
Nephrons empty their infiltrate into collecting ducts and then, into larger structures in the kidney
Fluid leaving the collecting ducts and entering subsequent parts of the kidney is called urine
Comments: Primary use: HTNLess efficacious than loop diureticsNot effective in severe renal impairmentIn certain situations may combine with loop diuretic to provide synergistic diuresisChlorothiazide: only parenteral thiazide available
Comments: Least effective diureticsMost commonly used in combination with other diuretics to reduce potassium lossCaution use in renal impairment or pre-existing hyperkalemiaOveruse: hyperchloremic metabolic acidosis
Comments: Determine and treat underlying causeAssess osmolalityAssess fluid statusCalculate total Na deficitMaximum rate of correction: 8-12 mEq/24 hoursMonitor Na levels q2h during correctionMany medications implicated as the cause
KCl, Kphosphate, Kacetatesodium polystyrene sulfonate (Kayexalate), HD
Comments: Determine and treat underlying causePrimary concern: life threatening arrhythmiasCheck for ECG changesCheck serum Mg level; replete if necessaryHypomagnesemia can cause refractory hypokalemiaMax rate: 10 mEq/hour**Max Conc: 10 mEq/50 mL**Oral repletion: no more than 40 mEq at onceMonitor potassium level q2-4 hours or after each 80 mEq
Comments: Regulated by parathyroid hormone, vitamin D, and calcitonin99% of total body Ca found in bones, less than 1% in the serum40-50% of Ca in the blood is bound to albuminMust correct for hypoalbuminemiaFree or ionized Ca level may be more reliableMax rate: 1 gram (4.65 mEq)/hour**Max Conc: 1 gram/50-100 mL**Preferred agent: Ca gluconateCa chloride used for emergent situations
Na phosphate, K phosphatehydration, oral phosphate binders, HD
Comments: Majority of Phos found in bonesMax rate: 15 mmol over 5 hours**Max Conc: 15 mmol/100 mL**Infused slowly to reduce/avoid the risk of thrombophlebitis and calcium-phosphate precipitationWatch the salt (Na vs. K) content:30 mmol Phos = 44 mEq K or 40 mEq NaWeight based dosing guidelines available