Hemodialysis: Core Curriculum 2014 Am J Kidney Dis. 2014;63(1): 위지완

Principles of Dialysis and How Modalities Differ  Ultrafiltration’s solvent drag effects led to an appreciation of the importance of convective transport and its advantage in enhancing the removal of species of larger molecular size  Extraction ratio = (Cin – Cout)/Cin  Blood flow rates (Qb)  Dialysate flow rates (Qd)  Dialyzer membrane  Solute property  ER : thrice-weekly hemodialysis > short daily HD

Principles of Dialysis and How Modalities Differ  Blood clearance in HD = extraction ratio x Qb

Principles of Dialysis and How Modalities Differ  Comparison of weekly standardized Kt/Vurea over different modalities

Components of the Hemodialysis Prescription

Dialyzer Performance and Selection  The major clinical factors  Membrane material  Sterilization method  Surface area  Preferred flux  Anaphylactic reactions  ACEi predispose patients when exposed to polyacrylnitrile membranes  Rare reactions to polysulfone  Sterilized by ethylene oxide, steam, radiation, or chemical reprocessing

Assessing Inadequate Urea Clearance  Failure to deliver thrice-weekly spKt/V > 1.2 deserves attention 1.The access is adequate to deliver Qb > 300 mL/min 2.If this does not occur while Qb and dialyzer size are maximized, it is necessary to increase dialysis time

Anticoagulation  Weight-based unfractionated heparin  Inexpensive & short half-life  Bleeding, heparin-induced thrombocytopenia  Alternatives  Low-molecular-weight heparins  Direct thrombin inhibitors  Regional anticoagulation with citrate or prostacyclin  Anticoagulation-free treatment

Sodium  Primary determinant of plasma and extracellular osmolality  Reduction in sodium intake  Blood pressure, cardiovascular morbidity, mortality ↓  Dietary sodium restriction  Interdialytic weight gain, antihypertensive medications, mortality ↓

Sodium  Modern nonexpanding dialyzers  Greater hydrostatic pressure  Smaller extracorporeal blood volume commitment  Greater ultrafiltration in a shorter time  S/E: muscle cramps, hypotension, dialysis disequilibrium↑  Dialysate sodium concentration ↑ or sodium modeling

Sodium modeling  Goal  To shift water from intracellular to extracellular compartments, where this added water supports circulation  Benefit  Reduced incidences of dialysis disequilibrium, vascular instability, muscle cramps  Example  First period of dialysis : sodium concentration of 160 mEq/L  Second equal period : 120 mEq/L  S/E : greater thirst, interdialytic weight gain, hypertension

Potassium  Depends on the gradient created between extracellular fluid and dialysate  Intracellular potassium effluxes extracellularly to re-establish equilibrium as extracellular potassium is removed by dialysis  Liver and skeletal muscles are rich in potassium  Atrophy → post-HD extracellular potassium replenishment↓

Potassium  Decrease potassium removal  Absorption of dialysate glucose decreases potassium removal by stimulating insulin  Increase potassium removal  Extracellular acidosis leads to cellular potassium efflux, which increases extracellular potassium concentration  “rule of 7s”  Patient’s K + + dialysate K + concentration ≒ 7

Potassium  K + < 3 mEq/L  Weakness, muscle pain  Rhabdomyolysis, paralysis, cardiac arrhythmias, cardiopulmonary arrest  Immediate postdialysis hypokalemia → rebound increase in serum potassium level will occur within 1-2 hours  Better survival : predialysis serum K + levels of mEq/L

Bicarbonate  Correction of metabolic acidosis : adding base + removing acid

Bicarbonate  Lower base concentration (susceptible to alkalosis)  Poor protein intake, small muscle mass, persistent vomiting, receiving total parenteral nutrition  Usual dialysate bicarbonate concentration : 35 mEq/L  KDOQI guideline : predialysis plasma bicarbonate 22 mEq/L  Low mortality : mEq/L

Calcium  Protein bound 40%, ionized 50%, anion complexed 10%  Ionized calcium gradient is the driving force of calcium transfer during dialysis - equilibration occurs by diffusion  Dialysate calcium concentration influence hemodynamics  Lower dialysate calcium → intradialytic hypotension, acute arrhythmias, sudden cardiac death  Higher dialysate calcium → risk of calcification

Complications of Hemodialysis  Hypotension  Cramps  Arrhythmias and Angina  Hypoxia  Hypoglycemia  Hemorrhage

Hypotension  Most common acute complication (15-30%)  Ultrafiltration rate  Rate of intravascular volume removal > rate of refilling  >1.5 L/h  Dialysate composition  Sodium, calcium, bicarbonate, acetate  Dialysate Na + ↑→ pNa & pOsm↑ ⇒ supporting plasma volume during HD  Medication, autonomic dysfunction(DM)

Hypotension  Without edema or heart failure : patient’s dry weight underestimated  Reduce ultrafiltration volume or rate  Increasing postdialysis dry weight  Excessive interdialytic weight gain  Increased dialysis time or frequency  Dialysate cooled to 35 ℃  Sodium modeling  Oral α1-adrenergic agonist (midodrine) : 5-10 mg, min before HD

Cramps  Frequent : ultrafiltration rates↑, low sodium dialysate  Effective therapies  Reducing ultrafiltration rate  200mL bolus of 0.9% sodium chloride solution  5mL increments of 23% hypertonic saline solution  D50W solution  Diazepam : pain resulting from very severe cramps  Quinine sulfate  Increases the refractory period and excitability of skeletal muscle  Effective in preventing cramping if administered 1-2 hours before dialysis