FREE CHBT Biomedical Technology and Dialysis Water Treatment Questions and Answers
The ultrafiltration coefficient of a dialyzer refers to the:
The dialysis machine can alter the hydraulic pressures in the blood and dialysate compartments and thus control the ultrafiltration rate of the fluid transfer. Each dialyzer has an ultrafiltration coefficient (Kuf) determined by the manufacturer. This refers to the volume of fluid (in mL) that passes through the membrane at a given pressure difference in 1 hour. Thus, a dialyzer with a Kuf of 5 and a transmembrane pressure of 50 mm Hg transfers 250 mL (5 x 50) of fluid in 1 hour of dialysis. Patients with kidney failure are often edematous with excess water in the interstitial compartment so removal by dialysis represents an efficient way of controlling fluid volume and weight. Since the patient's kidneys are not functioning, diuretic drugs are of little benefit.
The term "sieving coefficient of a membrane" refers to the:
As water moves through the membrane from the blood to the dialysate (convection), it drags molecules along with it (solvent drag). The size of the molecule and the size and number of the pores in the membrane determine the fraction of solute that undergoes convective transport. Small molecules pass easily and quickly, but large molecules pass more slowly. The term "sieving coefficient of a membrane" refers to the amount of a given solute that passes through the membrane from the blood into the dialysate. A sieving coefficient of 1.0 indicates that 100% of a given solute passed through the membrane, while a sieving coefficient of 0.4 indicates that only 40% of a given solute passed through the membrane by a convective mechanism.
The main difference between an arteriovenous shunt (AVS) and an arteriovenous fistula (AVF) is an:
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 surgically implanted arteriovenous fistulas were developed, which connect artery and vein entirely within the arm. These are still standard for most dialysis patients.
Which site in the hemodialysis pathway has the highest positive pressure?
In hemodialysis, arterial blood is conducted through tubing to a pump, which forces the blood through the hollow fibers in the dialyzer. The pre-pump blood usually has a negative pressure, while the post-pump blood (arterial header) about to enter the hollow fibers has the highest positive pressure, the value depending on the resistance of the fibers. Pressure then diminishes over the length of the fiber, and the pressure in the venous return is the lowest positive pressure in the system. The dialysis machine can control the pressure differential between the dialysate and the blood, the so-called transmembrane pressure. This may be adjusted to control the amount of fluid removal. The average pressure difference between blood entering and leaving the dialyzer fibers determines the net hydraulic pressure, forcing fluid out of the blood, through the membrane, and into the dialysate.
All of the following substances are produced by the kidney EXCEPT:
In addition to its role in water and electrolyte balance and acid-base control, the kidney also produces substances that are of importance in erythropoiesis, vitamin D metabolism, and blood pressure control. Production of the hormone erythropoietin by juxtaglomerular renal cells is important in controlling red blood cell production in the bone marrow. In the presence of anemia, the resulting hypoxia stimulates the hypoxia-inducible transcription factor in these cells, and increased amounts of erythropoietin are produced. A decrease in renal perfusion leads to increased production of renin by the kidney; this enzyme catalyzes the conversion of angiotensinogen to angiotensin 1, which is subsequently converted to angiotensin 2 by an angiotensin-converting enzyme. The latter stimulates aldosterone secretion by the adrenal gland. The renin-angiotensin-aldosterone system is of great importance in the regulation of blood pressure. The active form of vitamin D, calcitriol, is also produced in the kidney.
Which of the following dialyzers is used currently?
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.
Which of the following kidney structures connects with and delivers urine directly to the ureter?
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.