1. Peritoneal dialysis (PD) differs from hemodialysis in which of the following ways?
a. PD requires both vascular access and abdominal access.
b. PD cannot be done at home.
c. PD access is by an intra-abdominal catheter.
d. Sterile dialysate is not required for PD.
2. The main difference between an arteriovenous shunt (AVS) and an arteriovenous fistula (AVF) is an:
a. AVS is entirely within the arm.
b. AVF is entirely within the arm.
c. AVF is more likely to become clotted or infected.
d. AVF requires an external tube.
3. Which of the following dialyzers is used currently?
b. Flat plate
d. Hollow tube
4. Which of the following kidney structures connects with and delivers urine directly to the ureter?
5. The glomerular filtration rate is an important index of renal function and in the normal adult is approximately:
a. 50 mL/min/1.73 m2.
b. 75 mL/min/1.73 m2.
c. 125 mL/min/1.73 m2.
d. 200 mL/min/1.73 m2.
CCHT Answers and Explanations
1. C: Hemodialysis requires vascular access since the blood flows out of the patient, through the dialysis machine’s semipermeable membrane, and then back into the patient. The membrane keeps certain waste products or excess water from returning to the patient, while electrolytes and blood cells are returned. Peritoneal dialysis is performed with an intra-abdominal catheter without blood ever leaving the body. Vascular access is not required. The blood vessels of the abdominal cavity act as a filter similar to the semipermeable membrane used in hemodialysis. Peritoneal dialysis may be performed at home with a cycler machine to exchange fresh sterile dialysate, often overnight 7 days a week. Manual exchange of dialysate may also be done.
2. B: Since hemodialysis must be carried out repetitively, usually three times a week for 4 hours, repeated vascular access is required. Arterial blood is sent to the dialyzer and returned to the patient by an arm vein. Arteriovenous shunts connect the artery and vein by an external tube, which has a connecting port so that blood may be sent to the dialysis machine from the artery and returned to the vein. These shunts are subject to infection and clotting so that surgically implanted arteriovenous fistulas were developed, which connect artery and vein entirely within the arm. These are still standard for most dialysis patients.
3. D: Dialysis machines have evolved since their initial frequent use in the 1960s. The initial type, the so-called Kiil, consisted of 70 lb flat plates covered by sheets of cellophane. They required cleaning and storage after each use, and membranes had to be replaced. The coil dialyzer was supported by a mesh screen coiled around a central core. It required complete sterilization with a large amount of blood in a canister that was bathed in the dialysate. The Gambro flat plate dialyzer used a new membrane type named cuprophane. These early machines were replaced by the so-called hollow fiber dialyzer, which is the type in use today. In this model, the blood flows through tiny hollow tubes (fibers) while the dialysate flows around the outside of these fibers. Biocompatible membranes, sophisticated alarms, and automatic functions characterize the modern dialyzer.
4. A: The kidney is a fist-sized bilateral organ with a tough outer capsule. The most external portion of the organ is called the cortex. The renal medulla or interior portion of the kidney contains sections called pyramids with points referred to as papillae. Each papilla delivers urine into a receptacle-like calyx, which then transmits urine into the renal pelvis. The pelvis connects to the ureter and delivers urine for excretion. The functional unit of the kidney is the nephron, present in the cortex and extending into the medulla. The nephron is composed of a glomerulus, a tangled bunch of capillaries, which produces the glomerular filtrate, and a renal tubule, which acts on the filtrate to reabsorb water and exchange electrolytes. Blood is conducted to the glomerulus via an afferent arteriole and is filtered by the glomerular capillaries, which retain blood cells and large molecules, such as proteins. The blood is then returned by way of an efferent arteriole.
5. C: The normal adult has a glomerular filtration rate (GFR) of about 125 mL/min, although there is some variability due to age and sex. Clinically, this value is often expressed as GFR/m2 body surface area. It is usually measured by the so-called creatinine clearance in which blood and urine creatinine concentrations and the urine volume are measured, and the GFR calculated. Little creatinine is reabsorbed by the renal tubules, thus making it a valuable standard for estimating glomerular function. In end stage renal disease, the GFR is often below 15 mL/min/1.73 m2, and dialysis is required. Many drugs are excreted by the kidneys, and dosage adjustments based on GFR are often necessary.