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RRB Dialysis Technician practice questions

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Question 1Renal Anatomy, Physiology and Pathophysiology

Which structure in the nephron is primarily responsible for the reabsorption of the majority of filtered water, sodium, and glucose?

  1. Proximal convoluted tubule Correct answer.
  2. Descending limb of the loop of Henle
  3. Collecting duct
  4. Distal convoluted tubule

Explanation

The proximal convoluted tubule reabsorbs roughly 65 percent of filtered sodium and water along with nearly all filtered glucose and amino acids. Its brush border and dense mitochondria support this high-capacity active transport. Later segments fine-tune rather than perform bulk reabsorption.

Question 2Renal Anatomy, Physiology and Pathophysiology

A dialysis technician notes that a patient's kidneys have lost the ability to produce erythropoietin. Which clinical finding is most directly explained by this loss?

  1. Normocytic normochromic anemia Correct answer.
  2. Hypocalcemia
  3. Metabolic alkalosis
  4. Hyperkalemia

Explanation

Erythropoietin stimulates red blood cell production in the bone marrow, so its deficiency in chronic kidney disease causes a normocytic normochromic anemia. This anemia is a direct consequence of lost endocrine renal function. Electrolyte and acid-base disturbances arise from lost excretory function instead.

Question 3Renal Anatomy, Physiology and Pathophysiology

Which hormone is released by the posterior pituitary and increases water permeability of the collecting duct?

  1. Aldosterone
  2. Parathyroid hormone
  3. Antidiuretic hormone Correct answer.
  4. Atrial natriuretic peptide

Explanation

Antidiuretic hormone, also called vasopressin, inserts aquaporin-2 channels into collecting duct cells to increase water reabsorption. This concentrates the urine and reduces urine volume. Aldosterone acts on sodium and potassium, not primarily on water permeability.

Question 4Renal Anatomy, Physiology and Pathophysiology

The glomerular filtration rate in a healthy adult is best described as approximately which value?

  1. 25 mL/min
  2. 125 mL/min Correct answer.
  3. 50 mL/min
  4. 600 mL/min

Explanation

Normal glomerular filtration rate in a healthy adult is about 125 mL per minute, which totals roughly 180 liters per day. This high filtration rate reflects the large surface area and permeability of the glomerular capillaries. Values far below this indicate impaired kidney function.

Question 5Renal Anatomy, Physiology and Pathophysiology

Which part of the kidney contains the glomeruli and is the site where filtration begins?

  1. Renal papilla
  2. Renal pelvis
  3. Renal medulla
  4. Renal cortex Correct answer.

Explanation

The renal cortex is the outer region of the kidney and contains all the glomeruli along with the proximal and distal convoluted tubules. Filtration begins in the glomerular capillaries located in the cortex. The medulla and pelvis contain tubules and collecting structures instead.

Question 6Renal Anatomy, Physiology and Pathophysiology

A patient with end-stage renal disease has a serum potassium of 6.8 mEq/L. Which pathophysiologic mechanism best explains this finding?

  1. Reduced renal potassium excretion Correct answer.
  2. Excessive potassium loss through dialysis
  3. Increased urinary dilution
  4. Increased renal potassium excretion

Explanation

The kidneys normally excrete most of the daily potassium load, so failing kidneys retain potassium and produce hyperkalemia. Reduced glomerular filtration and diminished tubular secretion both contribute. This makes potassium control a central concern in dialysis care.

Question 7Renal Anatomy, Physiology and Pathophysiology

In chronic kidney disease, metabolic acidosis develops primarily because the kidneys fail to perform which function?

  1. Reabsorb bicarbonate and excrete hydrogen ions Correct answer.
  2. Excrete calcium
  3. Reabsorb hydrogen ions
  4. Excrete bicarbonate

Explanation

Healthy kidneys regenerate and reabsorb bicarbonate while excreting hydrogen ions to maintain acid-base balance. When this capacity declines, hydrogen ions accumulate and bicarbonate is depleted, producing metabolic acidosis. Excreting bicarbonate would worsen rather than correct acidosis.

Question 8Renal Anatomy, Physiology and Pathophysiology

Which structure carries urine from the kidney to the urinary bladder?

  1. Renal calyx
  2. Urethra
  3. Collecting duct
  4. Ureter Correct answer.

Explanation

The ureter is the muscular tube that transports urine from the renal pelvis to the bladder through peristaltic contractions. The urethra carries urine from the bladder to the outside of the body. Calyces and collecting ducts are internal kidney structures.

Question 9Renal Anatomy, Physiology and Pathophysiology

The countercurrent multiplier system of the loop of Henle is most important for which renal function?

  1. Secreting erythropoietin
  2. Concentrating urine Correct answer.
  3. Filtering plasma proteins
  4. Regulating blood pressure acutely

Explanation

The countercurrent multiplier establishes an osmotic gradient in the medulla that allows the collecting duct to reabsorb water and concentrate urine under ADH influence. This mechanism is central to water conservation. It does not filter proteins or secrete hormones.

Question 10Renal Anatomy, Physiology and Pathophysiology

Which component of the nephron is the primary site of action for aldosterone on sodium reabsorption?

  1. Loop of Henle
  2. Proximal convoluted tubule
  3. Distal convoluted tubule and collecting duct Correct answer.
  4. Glomerulus

Explanation

Aldosterone acts on the distal convoluted tubule and collecting duct to increase sodium reabsorption and potassium secretion. This fine-tuning of sodium balance helps regulate blood volume and pressure. The proximal tubule and loop of Henle handle bulk reabsorption not primarily driven by aldosterone.

Question 11Renal Anatomy, Physiology and Pathophysiology

A patient on hemodialysis has persistent hyperphosphatemia. Which physiologic relationship best explains this finding?

  1. Phosphate is retained as filtration fails Correct answer.
  2. Phosphate is excessively excreted by failing kidneys
  3. Phosphate is bound to albumin and not filtered
  4. Phosphate absorption is reduced in renal failure

Explanation

As glomerular filtration declines, the kidneys cannot excrete phosphate adequately, so serum phosphate rises. This retention also contributes to secondary hyperparathyroidism and renal bone disease. Reduced absorption or excessive excretion would lower phosphate rather than raise it.

Question 12Renal Anatomy, Physiology and Pathophysiology

Which statement best describes the role of the juxtaglomerular apparatus in renal physiology?

  1. It filters blood to form urine
  2. It produces antidiuretic hormone
  3. It senses sodium and pressure to regulate renin release Correct answer.
  4. It reabsorbs glucose from filtrate

Explanation

The juxtaglomerular apparatus includes the macula densa, which senses sodium chloride concentration, and granular cells that release renin in response to reduced pressure or sodium. Renin initiates the renin-angiotensin-aldosterone system to support blood pressure. It does not filter blood or produce ADH.

Question 13Renal Anatomy, Physiology and Pathophysiology

A patient presents with oliguria and a rising creatinine. Which term best describes the reduced urine output?

  1. Nocturia
  2. Dysuria
  3. Polyuria
  4. Oliguria Correct answer.

Explanation

Oliguria refers to abnormally reduced urine output, typically defined as less than 400 to 500 mL per day in adults. It is a common sign of impaired renal function. Polyuria is excessive output, nocturia is nighttime urination, and dysuria is painful urination.

Question 14Renal Anatomy, Physiology and Pathophysiology

Which mechanism explains why loop diuretics are effective in patients with reduced renal function?

  1. They block ADH release
  2. They inhibit sodium reabsorption in the thick ascending limb Correct answer.
  3. They increase proximal glucose reabsorption
  4. They increase glomerular filtration directly

Explanation

Loop diuretics inhibit the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle, reducing sodium reabsorption and promoting diuresis. This action disrupts the medullary gradient and increases excretion. They do not directly raise filtration rate or block ADH.

Question 15Renal Anatomy, Physiology and Pathophysiology

The glomerular filtration barrier restricts the passage of which component into the filtrate?

  1. Glucose
  2. Large plasma proteins Correct answer.
  3. Sodium ions
  4. Water

Explanation

The filtration barrier, composed of fenestrated endothelium, basement membrane, and podocyte slits, prevents large plasma proteins such as albumin from entering the filtrate. Small molecules like water, sodium, and glucose pass freely. Proteinuria signals injury to this barrier.

Question 16Renal Anatomy, Physiology and Pathophysiology

A dialysis patient develops muscle weakness and an ECG shows peaked T waves. Which electrolyte imbalance is most likely?

  1. Hypocalcemia
  2. Hypernatremia
  3. Hyperkalemia Correct answer.
  4. Hyponatremia

Explanation

Peaked T waves and muscle weakness are classic electrocardiographic and clinical signs of hyperkalemia, which is common in renal failure because potassium excretion is impaired. Prompt recognition matters because severe hyperkalemia can cause arrhythmias. Sodium and calcium disturbances produce different patterns.

Question 17Renal Anatomy, Physiology and Pathophysiology

Which renal process occurs primarily in the descending limb of the loop of Henle?

  1. Potassium secretion
  2. Glucose reabsorption
  3. Water reabsorption by osmosis Correct answer.
  4. Active sodium reabsorption

Explanation

The descending limb is permeable to water but not to solutes, so water moves out by osmosis as the filtrate descends into the hypertonic medulla. This step concentrates the tubular fluid. Active sodium transport occurs mainly in the thick ascending limb.

Question 18Renal Anatomy, Physiology and Pathophysiology

Which change in the afferent arteriole would tend to increase glomerular filtration rate?

  1. Vasoconstriction of the afferent arteriole
  2. Vasodilation of the afferent arteriole Correct answer.
  3. Decreased systemic blood pressure
  4. Vasoconstriction of the efferent arteriole only

Explanation

Vasodilation of the afferent arteriole increases renal blood flow and raises glomerular hydrostatic pressure, thereby increasing filtration rate. Constriction of the afferent arteriole reduces flow and lowers filtration. Systemic hypotension also reduces filtration pressure.

Question 19Renal Anatomy, Physiology and Pathophysiology

In a patient with nephrotic syndrome, which finding is most consistent with damage to the glomerular filtration barrier?

  1. Massive proteinuria Correct answer.
  2. Glycosuria
  3. Hematuria without protein loss
  4. Hyperkalemia

Explanation

Nephrotic syndrome is characterized by increased permeability of the glomerular barrier to protein, producing massive proteinuria along with hypoalbuminemia and edema. Hematuria is more typical of nephritic syndromes. Glycosuria and hyperkalemia reflect tubular or excretory dysfunction instead.

Question 20Renal Anatomy, Physiology and Pathophysiology

Which of the following best explains why patients with chronic kidney disease often develop hypocalcemia?

  1. Impaired activation of vitamin D and phosphate retention Correct answer.
  2. Increased intestinal calcium absorption
  3. Increased renal calcium excretion
  4. Excessive parathyroid hormone secretion

Explanation

Failing kidneys cannot adequately convert vitamin D to its active form, reducing intestinal calcium absorption, while phosphate retention binds calcium and lowers serum levels. Together these produce hypocalcemia and stimulate secondary hyperparathyroidism. Increased absorption or excretion would not explain low calcium.

Question 21Renal Anatomy, Physiology and Pathophysiology

Which segment of the nephron is responsible for the active secretion of hydrogen ions that helps maintain acid-base balance?

  1. Descending limb of the loop of Henle
  2. Renal pelvis
  3. Glomerulus
  4. Proximal convoluted tubule and collecting duct Correct answer.

Explanation

Hydrogen ion secretion occurs mainly in the proximal convoluted tubule and is further regulated in the collecting duct, where intercalated cells contribute to acid excretion. This process regenerates bicarbonate and maintains acid-base balance. The glomerulus and pelvis do not perform this tubular function.

Question 22Renal Anatomy, Physiology and Pathophysiology

A patient's dialysis prescription is being reviewed. Which physiologic function of the kidney is NOT replaced by conventional hemodialysis?

  1. Endocrine functions such as erythropoietin production Correct answer.
  2. Correction of electrolyte imbalance
  3. Regulation of fluid volume
  4. Removal of urea

Explanation

Conventional hemodialysis clears wastes and corrects fluid and electrolyte balance, but it does not restore the kidney's endocrine functions such as erythropoietin and activated vitamin D production. Patients therefore often need erythropoiesis-stimulating agents and vitamin D analogs. Waste removal and volume control are core dialysis functions.

Question 23Renal Anatomy, Physiology and Pathophysiology

Which statement about the renal handling of glucose is accurate?

  1. Glucose is reabsorbed completely until the transport maximum is exceeded Correct answer.
  2. Glucose is actively secreted into the filtrate
  3. Glucose is not filtered at the glomerulus
  4. Glucose reabsorption occurs mainly in the collecting duct

Explanation

Glucose is freely filtered and reabsorbed almost completely in the proximal tubule until the transport maximum is exceeded, after which glycosuria appears. This threshold concept explains glucose in the urine when blood glucose is very high. Secretion and collecting duct reabsorption are not significant.

Question 24Renal Anatomy, Physiology and Pathophysiology

A patient with acute kidney injury has a fractional excretion of sodium below 1 percent. This finding most suggests which type of injury?

  1. Acute tubular necrosis with tubular damage
  2. Postrenal obstruction
  3. Chronic glomerulonephritis
  4. Prerenal azotemia with intact tubular reabsorption Correct answer.

Explanation

A low fractional excretion of sodium suggests the tubules are intact and avidly reabsorbing sodium in response to reduced renal perfusion, typical of prerenal azotemia. In intrinsic tubular damage such as acute tubular necrosis, sodium reabsorption is impaired and fractional excretion rises. This distinction guides fluid management.

Question 25Renal Anatomy, Physiology and Pathophysiology

Which structure is the functional unit of the kidney responsible for urine formation?

  1. Renal artery
  2. Renal pyramid
  3. Nephron Correct answer.
  4. Ureter

Explanation

The nephron is the functional unit of the kidney, consisting of the glomerulus and its associated tubule, and it performs filtration, reabsorption, and secretion. Each kidney contains about one million nephrons. Pyramids, arteries, and ureters are supporting or transport structures.

Question 26Renal Anatomy, Physiology and Pathophysiology

Which hormone is released by the posterior pituitary and directly increases water reabsorption in the collecting duct?

  1. Atrial natriuretic peptide
  2. Parathyroid hormone
  3. Antidiuretic hormone Correct answer.
  4. Aldosterone

Explanation

Antidiuretic hormone inserts aquaporin-2 water channels into the collecting duct membrane, allowing water to move down its osmotic gradient and concentrate the urine. Its release rises when plasma osmolality increases or blood volume falls.

Question 27Renal Anatomy, Physiology and Pathophysiology

Which portion of the nephron is the principal site of active reabsorption of the majority of filtered sodium and water under normal conditions?

  1. Proximal convoluted tubule Correct answer.
  2. Distal convoluted tubule
  3. Collecting duct
  4. Glomerular capsule

Explanation

The proximal convoluted tubule reabsorbs roughly two-thirds of the filtered sodium and water, largely coupled to active sodium transport and glucose and amino acid cotransport. This bulk reabsorption occurs before the fine-tuning segments.

Question 28Renal Anatomy, Physiology and Pathophysiology

A patient with advanced chronic kidney disease has an arterial blood gas showing pH 7.28 and bicarbonate 14 mEq/L. Which additional finding would most support that the acidosis is primarily metabolic in origin?

  1. An increased serum potassium concentration
  2. An elevated arterial carbon dioxide tension
  3. A compensatory decrease in arterial carbon dioxide tension Correct answer.
  4. A normal arterial carbon dioxide tension

Explanation

In metabolic acidosis the lungs compensate by increasing ventilation, which lowers arterial carbon dioxide tension toward the expected value predicted by the bicarbonate level. A primary respiratory acidosis would instead show an elevated carbon dioxide tension.

Question 29Renal Anatomy, Physiology and Pathophysiology

A patient with severe heart failure has reduced renal perfusion and a low effective circulating volume. Which sequence best describes the resulting renal response?

  1. Renin release increases, angiotensin II forms, aldosterone rises, and sodium and water are retained Correct answer.
  2. Atrial natriuretic peptide rises and directly increases renin secretion
  3. Aldosterone falls and potassium retention causes sodium excretion
  4. Renin release decreases, angiotensin II falls, and sodium is excreted

Explanation

Reduced effective circulating volume activates the renin-angiotensin-aldosterone system: renin converts angiotensinogen to angiotensin I, which becomes angiotensin II, a potent vasoconstrictor that stimulates aldosterone release. Aldosterone then promotes sodium and water retention, worsening volume overload.

Question 30Renal Anatomy, Physiology and Pathophysiology

A patient with acute kidney injury has a urine sodium of 8 mEq/L and a fractional excretion of sodium of 0.5 percent while not receiving diuretics. Which interpretation is most consistent with these values?

  1. Prerenal physiology with avid tubular sodium reabsorption Correct answer.
  2. Excess atrial natriuretic peptide effect causing natriuresis
  3. Intrinsic tubular damage with impaired sodium reabsorption
  4. Postrenal obstruction with a salt-wasting pattern

Explanation

A low urine sodium and fractional excretion below 1 percent indicate that functioning tubules are reabsorbing sodium avidly in response to reduced renal perfusion, a pattern typical of prerenal azotemia. Intrinsic tubular injury usually impairs reabsorption and raises these values.

Question 31Dialysis Principles, Modalities and Prescription

During a hemodialysis treatment, the dialysate sodium concentration prescribed is 138 mEq/L while the patient's predialysis serum sodium is 132 mEq/L. What is the primary clinical effect of this sodium gradient across the dialyzer membrane?

  1. It has no effect because sodium is not dialyzable
  2. It forces potassium into cells and causes hypokalemia
  3. It drives diffusive sodium gain that supports plasma refilling and reduces intradialytic hypotension Correct answer.
  4. It causes net sodium loss and worsens cramps and hypovolemia

Explanation

A dialysate sodium higher than serum sodium creates a diffusive gradient that moves sodium into the patient, raising osmolality and supporting vascular refilling. This reduces the risk of hypotension and cramping during ultrafiltration. The gradient direction, not just the absolute value, determines whether sodium is gained or lost.

Question 32Dialysis Principles, Modalities and Prescription

Which clearance mechanism predominates for removal of small solutes such as urea during conventional low-flux hemodialysis?

  1. Diffusion down a concentration gradient across the dialyzer membrane Correct answer.
  2. Adsorption of solute onto the membrane surface
  3. Convective drag carried by solvent flow through the membrane
  4. Metabolic degradation of urea within the dialysate circuit

Explanation

In low-flux hemodialysis, small solutes like urea are removed mainly by diffusion, driven by the concentration difference between blood and dialysate. Convection becomes important for larger middle molecules when high-flux membranes and substantial ultrafiltration are used. Adsorption and metabolic degradation play negligible roles in routine clearance.

Question 33Dialysis Principles, Modalities and Prescription

A patient is prescribed a blood flow rate of 300 mL/min and a dialysate flow rate of 500 mL/min. What is the dialysate-to-blood flow ratio, and what is the usual rationale for this relationship?

  1. 0.6:1, chosen to limit dialysate consumption
  2. 1.67:1, chosen to provide adequate concentration gradient along the dialyzer Correct answer.
  3. 3:1, chosen to maximize ultrafiltration
  4. 1:1, chosen to match clearance exactly to blood flow

Explanation

Dividing 500 by 300 gives a dialysate-to-blood flow ratio of about 1.67:1. A dialysate flow moderately higher than blood flow helps maintain the concentration gradient along the dialyzer so clearance is not limited by exhausted dialysate. Ratios far above this yield diminishing returns in small-solute clearance.

Question 34Dialysis Principles, Modalities and Prescription

Which statement accurately describes the purpose of the dialysate bicarbonate concentration in a standard hemodialysis prescription?

  1. It sterilizes the dialysate before it reaches the dialyzer
  2. It prevents clotting in the extracorporeal circuit during treatment
  3. It acts as the primary osmotic agent driving ultrafiltration
  4. It corrects the metabolic acidosis common in kidney failure by providing a buffer source Correct answer.

Explanation

Patients with kidney failure typically have metabolic acidosis, and bicarbonate in the dialysate diffuses into the blood to buffer excess hydrogen ions. Typical dialysate bicarbonate is around 32 to 39 mEq/L, adjusted to the patient's acid-base status. This is a core prescription parameter distinct from anticoagulation and osmotic effects.

Question 35Dialysis Principles, Modalities and Prescription

A patient on hemodialysis has a prescribed ultrafiltration goal of 3 liters over a 4-hour treatment. What average ultrafiltration rate does this represent, and why is the rate clinically relevant?

  1. 12 mL/min, relevant because it determines dialyzer clearance
  2. 1,200 mL/hour, relevant because it sets the blood flow rate
  3. 750 mL/hour, relevant because high rates are associated with intradialytic hypotension and cardiovascular stress Correct answer.
  4. 300 mL/hour, relevant because it determines dialysate flow

Explanation

Three liters over four hours equals 750 mL/hour, or about 12.5 mL/min/kg depending on body weight. Ultrafiltration rate is clinically important because rapid fluid removal is linked to hypotension, cramping, and myocardial stunning. Prescribers often cap the rate relative to body weight to protect cardiovascular stability.

Question 36Dialysis Principles, Modalities and Prescription

Which formula correctly expresses the urea reduction ratio (URR) for a patient whose predialysis BUN is 70 mg/dL and postdialysis BUN is 21 mg/dL?

  1. URR = (70 + 21) / 70 × 100, giving about 130%
  2. URR = 70 / 21 × 100, giving about 333%
  3. URR = (70 − 21) / 70 × 100, giving about 70% Correct answer.
  4. URR = 21 / 70 × 100, giving about 30%

Explanation

The urea reduction ratio is the fractional fall in BUN, calculated as (pre-BUN minus post-BUN) divided by pre-BUN, then multiplied by 100. With these values, (70 − 21) / 70 equals 0.70, or about 70%. A URR of 65% or higher generally indicates adequate small-solute clearance.

Question 37Dialysis Principles, Modalities and Prescription

Which parameter most directly reflects the adequacy of delivered dialysis dose when using Kt/V?

  1. The postdialysis serum potassium concentration
  2. The ratio of dialysate flow to blood flow during treatment
  3. The transmembrane pressure required to achieve the ultrafiltration goal
  4. The product of dialyzer urea clearance and treatment time divided by the urea distribution volume Correct answer.

Explanation

Kt/V combines the dialyzer clearance of urea (K), treatment time (t), and the patient's urea distribution volume (V), which approximates total body water. A commonly targeted single-pool Kt/V is at least 1.2 per treatment for thrice-weekly hemodialysis. The other parameters influence delivery but do not define the dose metric itself.

Question 38Dialysis Principles, Modalities and Prescription

In peritoneal dialysis, which characteristic of the peritoneal membrane primarily determines the rate at which solutes equilibrate between blood and dialysate?

  1. The concentration of glucose in the dialysate bag
  2. The patient's residual urine output
  3. Its effective surface area and permeability, often assessed by a peritoneal equilibration test Correct answer.
  4. The dwell time of the previous exchange only

Explanation

Peritoneal transport status reflects membrane surface area and permeability and is classified with a peritoneal equilibration test using the dialysate-to-plasma creatinine ratio. Transport status guides prescription of dwell times and solution strengths. Residual kidney function and glucose concentration affect total clearance and ultrafiltration but do not define membrane transport characteristics.

Question 39Dialysis Principles, Modalities and Prescription

A peritoneal dialysis patient is classified as a high transporter on a peritoneal equilibration test. Which prescription adjustment is most appropriate to improve ultrafiltration?

  1. Lengthen dwell times to allow more complete solute equilibration
  2. Increase the fill volume indefinitely to raise intra-abdominal pressure
  3. Shorten dwell times so glucose osmotic gradient is not lost before drainage Correct answer.
  4. Switch to a lower dextrose concentration to reduce absorption

Explanation

High transporters absorb glucose rapidly, so the osmotic gradient dissipates quickly and long dwells produce poor ultrafiltration and sodium removal. Shortening dwell times preserves the gradient during the period when ultrafiltration is most efficient. This often means more frequent, shorter exchanges during the day.

Question 40Dialysis Principles, Modalities and Prescription

Which statement best describes the difference between hemodialysis and hemofiltration regarding solute removal?

  1. Hemofiltration removes solutes primarily by diffusion, while hemodialysis relies mainly on convection
  2. Both modalities remove solutes exclusively by adsorption onto the membrane
  3. Hemofiltration does not require an extracorporeal blood circuit
  4. Hemofiltration removes solutes primarily by convection with replacement fluid, while hemodialysis relies mainly on diffusion Correct answer.

Explanation

Hemofiltration achieves clearance through high-volume convective flow, requiring replacement fluid to maintain volume and electrolyte balance. Hemodialysis removes small solutes mainly by diffusion across the dialyzer membrane. Hemodiafiltration combines both mechanisms for broader clearance.

Question 41Dialysis Principles, Modalities and Prescription

During a treatment, the transmembrane pressure is increased to achieve the prescribed fluid removal. What is the direct effect of increasing transmembrane pressure?

  1. It reduces the risk of membrane clotting
  2. It decreases the dialysate flow requirement
  3. It increases the diffusive clearance of urea
  4. It increases the rate of ultrafiltration across the membrane Correct answer.

Explanation

Transmembrane pressure is the pressure gradient driving solvent across the membrane, so raising it increases the ultrafiltration rate. Diffusion of urea is governed by concentration gradients and flows, not by transmembrane pressure. Excessive transmembrane pressure can also promote protein fouling and reduce membrane performance over time.

Question 42Dialysis Principles, Modalities and Prescription

Which dialyzer membrane property describes the tendency of a membrane to allow water to pass under a given pressure gradient?

  1. Priming volume
  2. Sieve coefficient for albumin
  3. Mass transfer-area coefficient for urea
  4. Hydraulic permeability, expressed as the ultrafiltration coefficient Correct answer.

Explanation

The ultrafiltration coefficient (Kuf) quantifies hydraulic permeability, describing how much water crosses the membrane per unit of transmembrane pressure. The mass transfer-area coefficient describes diffusive clearance of a solute, and the sieve coefficient describes rejection of solutes by size. Priming volume refers to the blood-side volume needed to fill the dialyzer.

Question 43Dialysis Principles, Modalities and Prescription

A patient receives continuous venovenous hemodiafiltration in the intensive care unit. Which combination of mechanisms provides solute clearance in this modality?

  1. Convection only, because no dialysate is used
  2. Adsorption only, because continuous circuits rely on membrane binding
  3. Both diffusion from dialysate flow and convection from filtrate generation with replacement fluid Correct answer.
  4. Diffusion only, because continuous therapies cannot generate filtrate

Explanation

Continuous venovenous hemodiafiltration combines a dialysate circuit for diffusion with a filtrate circuit and replacement fluid for convection. This dual mechanism improves clearance of both small and middle molecules in hemodynamically unstable patients. Continuous therapies can generate substantial filtrate volumes, so replacement fluid is required.

Question 44Dialysis Principles, Modalities and Prescription

Which factor most limits the clearance of middle molecules such as beta-2 microglobulin during high-flux hemodialysis?

  1. The patient's serum sodium level
  2. Membrane pore size and the balance of convective and diffusive transport Correct answer.
  3. The dialysate bicarbonate concentration
  4. The anticoagulant dose used during treatment

Explanation

Middle-molecule clearance depends on membrane pore size and the extent of internal filtration and backfiltration that drive convective transport. High-flux membranes with larger pores remove more middle molecules than low-flux membranes. Dialysate bicarbonate, serum sodium, and anticoagulant dose do not primarily determine middle-molecule clearance.

Question 45Dialysis Principles, Modalities and Prescription

A patient's prescribed dry weight is being reassessed. Which finding best supports lowering the estimated dry weight?

  1. A rising predialysis BUN with stable weight
  2. Frequent episodes of postdialysis fatigue
  3. Recurrent intradialytic hypotension and cramping near the end of treatment
  4. Persistent hypertension with edema despite achieving the current dry weight Correct answer.

Explanation

Fluid overload manifesting as hypertension and edema at the current target suggests the dry weight is set too high. Lowering the target gradually allows additional fluid removal while monitoring tolerance. Hypotension and cramping suggest the target may already be too low or the ultrafiltration rate too aggressive.

Question 46Dialysis Principles, Modalities and Prescription

Which laboratory parameter is used to guide the prescribed dialysate calcium concentration for a hemodialysis patient?

  1. Predialysis BUN and the urea reduction ratio
  2. Serum calcium and parathyroid hormone levels along with the patient's medications Correct answer.
  3. Serum potassium and the dialysate potassium gradient
  4. Serum albumin and the patient's protein intake

Explanation

Dialysate calcium is selected based on the patient's calcium balance, parathyroid hormone level, and use of calcium-based binders or vitamin D analogs. A higher dialysate calcium provides net calcium gain, while lower concentrations promote loss. Potassium, urea, and albumin parameters guide other aspects of the prescription.

Question 47Dialysis Principles, Modalities and Prescription

Why is the dialysate potassium concentration typically set lower than the patient's serum potassium in a standard hemodialysis prescription?

  1. To prevent potassium from entering the blood and causing hyperkalemia
  2. To drive potassium into cells through osmotic effects
  3. To create a diffusion gradient that removes excess potassium during treatment Correct answer.
  4. To maintain the dialysate pH within the circuit

Explanation

A dialysate potassium lower than serum potassium establishes a gradient for diffusive removal of potassium accumulated between treatments. The concentration is individualized because overly low values can cause hypokalemia and arrhythmias. Potassium movement into cells is influenced by pH and insulin, not by the dialysate gradient alone.

Question 48Dialysis Principles, Modalities and Prescription

A patient on thrice-weekly hemodialysis has a single-pool Kt/V of 1.0. Which prescription change is most likely to raise the delivered dose?

  1. Reducing blood flow to improve dialyzer efficiency
  2. Decreasing the surface area of the dialyzer
  3. Lowering the dialysate flow rate
  4. Increasing treatment time while maintaining the same blood flow Correct answer.

Explanation

Kt/V is proportional to treatment time and clearance, so extending time increases the delivered dose when clearance is held constant. Reducing blood flow, lowering dialysate flow, or using a smaller dialyzer all tend to reduce clearance. Access recirculation and treatment interruptions should also be evaluated when the dose is low.

Question 49Dialysis Principles, Modalities and Prescription

Which statement correctly describes the role of residual kidney function in peritoneal dialysis prescription?

  1. It contributes meaningfully to total solute and fluid clearance, so prescriptions may be adjusted as it declines Correct answer.
  2. It has no effect on total clearance once peritoneal dialysis begins
  3. It determines the dialysate glucose concentration needed for ultrafiltration
  4. It replaces the need for peritoneal equilibration testing

Explanation

Residual kidney function adds measurable solute and water clearance in peritoneal dialysis patients and often preserves quality of life. As it declines, the peritoneal prescription may need more exchanges, larger volumes, or higher glucose concentrations. It does not eliminate the need for transport testing or dictate glucose strength directly.

Question 50Dialysis Principles, Modalities and Prescription

Which factor would most likely cause a discrepancy between the prescribed and delivered dialysis dose?

  1. A stable dry weight over several treatments
  2. A dialysate bicarbonate concentration within the target range
  3. Use of a high-flux rather than low-flux membrane
  4. Access recirculation reducing the effective solute clearance Correct answer.

Explanation

Access recirculation means already-cleared blood returns to the dialyzer, lowering effective clearance and delivered dose despite an adequate prescription. High-flux membranes generally increase clearance rather than reduce it. Stable dry weight and appropriate bicarbonate do not lower delivered dose.