Doalysis Flashcards
Dialysis
filtering metabolic waste products from blood:
separation of dissolved substances from a solution by allowing the solution to diffuse through a semipermeable membrane
Hemodialysis
Removing waste products such as creatinine and urea, as well as free water from the blood when the kidneys are in renal failure.
Peritoneal Dialysis(PD)
A treatment for patients with severe chronic kidney disease. The process uses the patient’s peritoneum as a membrane across which fluids and dissolved substances (electrolytes, urea, glucose, albumin and other small molecules) are exchanged.
Continuous Ambulatory Peritoneal Dialysis(CAPD).
Fluid is introduced through a tube in the abdomen and flushed out either every night while the patient sleeps or via regular exchanges throughout the day PD is used as an alternative to hemodialysis (especially in kidlets)
The dialysis solution in the dialyzer (filter) helps _____ and contains ______
remove wastes/fluid from blood. Contains chemicals in concentrations similar to blood, a mixture of purified water and measured chemicals, which flows countercurrent on the outside.
Substances that must remain in the bloodstream, such as glucose, sodium, calcium, and magnesium, are in
the dialysate in concentrations similar to blood.
The composition of the dialysate determines
which solutes pass out of and which stay in the blood during dialysis.
Dialyzer
an artificial kidney filter designed to provide controllable transfer of solutes and water across a semi permeable membrane separating flowing blood and dialysate streams.
the tranfer processes for a dialyzer
diffusion (dialysis) and convection (ultrafiltration).
three basic dialyzer designs
coil, parallel plate, and hollow fiber configurations.
convection
transport of a constituent by bulk motion of a fluid
diffusion
transport due to concentration gradients
acute renal failure
sudden loss of kidney function due to illness injury or toxin
chronic kidney disease
long slow process where kidney loses their function
end stage renal disease
kidneys have completely and permanently shut down
Renal failure is described as
a decrease in glomerular filtration rate (GFR).
Biochemically, renal failure is
typically detected by an elevated serum creatinine level.
CLASSIFICATIONS OF RENAL FAILURE
I. Acute Kidney Injury II. Chronic Kidney Disease
ARF
Rapid loss of kidney function (hypovolemia). Causes include low blood volume Exposure to harmful substances
ARF diagnosed by
the basis of lab findings elevated blood urea nitrogen (BUN)
Elevated creatinine inability of the kidneys to produce sufficient amounts of
urine.
complications of ARF
Complications: metabolic acidosis, high potassium levels, uremia, changes in body fluid balance, and effects to other organ systems.
ARF may be caused by
obstruction of the urinary tract
Chronic kidney disease is identified by
significantly elevated creatinine.
higher levels of creatinine indicate
a falling glomerular filtration rate and as a result a decreased capability of the kidneys to excrete waste products. Creatinine levels may have been normal in the early stages
Problems frequently encountered in kidney malfunction include:
abnormal fluid levels in the body deranged acid levels abnormal levels of potassium, calcium, and phosphate anemia. hematuria (blood loss in the urine) proteinuria (protein loss in the urine)
Long-term kidney problems have significant repercussions on
other diseases, such as cardiovascular disease
Ultrafilters/Hemoconcentrators – removed total body water on the principle of
hydrostatic pressure gradients
Dialysis – utilized to treat renal failure
removal of diffusable solutes based on the principle
of a concentration gradient and solute drag established by a dialysate solution
dialysis uses a semi permeable membrane for
selected diffusion
SOLVENT DRAG (CONVECTION)
The influence exerted by a flow of solvent through a membrane on the simultaneous movement of a solute through the membrane.
COIL DIALYZER
Blood compartment consisted of one or two long membrane tubes placed between support screens and wound around a plastic core.
Serious performance limitations, which gradually restricted its use as better designs evolved.
Coil design did not produce uniform dialysate flow distribution across the membrane.
PARALLEL PLATE DIALYZER
reens, and then stacked in multiple layers ranging from 2 to 20 or more.
Allows multiple parallel blood and dialysate flow channels (lower resistance to flow).
PARALLEL PLATE DIALYZER improvements
(1) thinner blood and dialysate channels with uniform
dimensions,
(2) minimal masking or blocking of membranes on the support, and
(3) minimal stretching or deformation of membranes across the supports.
HOLLOW FIBER DIALYZER
Most effective design ->low-volume high efficiency with low resistance to flow. The fiber bundle are potted in polyurethane at each end of the fiber bundle in the tube sheet, which serves as the membrane support.
MECHANICAL ASPECTS OF DIALYSIS SYSTEMS
hemodialysis machines offer tremendous flexibility in adjusting dialysis regimens.
Hemodialysis machines use a single pass system where the dialysate circulates through the dialyzer once and is then discarded.
MECHANICAL ASPECTS OF DIALYSIS SYSTEMS
All systems require the same basic components:
dialysate heater to warm dialysate to body
temperature
dialysate pump and flow meter to regulate the rate of dialysate delivery
sensors and alarms to monitor dialysate pressure, temperature, conductivity, and air or blood leaks.
DIALYSIS TYPES
Hemodialysis Peritoneal Dialysis
When you dialyze someone, you put their blood
(hypertonic – very full of stuff that needs removing) on one side of a membrane – and put some hypotonic solution on the other side (that’s the dialysate)
hemodialysis decreases
number of BUN and creatinine molecules in the blood decreases (along with a bunch of even smaller ones like the
electrolytes, which is why we spend so much time worrying about giving them back).
HOWEVER – YOU HAVEN’T REMOVED ANY FLUID YET…
Fluid can passes thru semipermeable filter membrane, by
applying suction on the far side of the membrane, vacuum “creates a transmembrane pressure gradient” It turns out that when you do this, small solute molecules get dragged out through the membrane pores along with the water (this is what they mean by “convective transport”, or “solvent drag”)
CONVECTIVE FLUX
The movement of solutes through the membrane (“convective flux”) is calculatable using all sorts of horrid and bizarre renal mathematics
Happily, I will leave that to the engineers (or Harry)
MECHANICAL ASPECTS CIRCUIT COMPONENTS
Allsystemsrequirethesamebasiccomponents:
Aheatertowarmdialysateto37C
Adialysatepumpandflowmetertoregulatetherateof dialysate delivery
Sensorsandalarmstomonitordialysatepressure, temperature, conductivity, and air or blood leaks.
Almost all single-patient hemodialysis machines use a
single pass system where the dialysate circulates through the dialyzer once and is then discarded.
PERITONEAL DIALYSIS
Less efficient at removal vs. hemodialysis Effective in very labile cardiac states Treatment of choice in kidlets Allows more patient freedom
ALTERNATIVE HEMODIALYTIC TECHNIQUES
I. Convection based
a. CAVH (continuous arteriovenous hemofiltration) b. CVVH (continuous venovenous hemofiltration)
ALTERNATIVE HEMODIALYTIC TECHNIQUES
II. Diffusive Therapy
a. CAVHD (continuous arteriovenous hemodialysis) b. CVVHD (continuous venovenous hemodialysis)
CAVH
continuous arterio-venous hemofiltration
Blood circulates with or without a blood pump through a small hollow-fiber hemofilter.
Access - femoral artery and vein.
Heparin is infused proximal to the dialyzer.
Blood circulates through the hemofilter wherein the plasma and water is filtered and collected in the collection bag.
Replacement volume is infused into the
venous return line.
CVVH
continuous veno-venous hemofiltration
Pump assisted and achieves higher clearance. Because of its effectiveness, it is replacing the pumpless CAVH mode.
Access - double lumen catheter in the femoral, SC, or IJ vein.
Continuous diffusive solute transport is achieved by
infusing a dialysis fluid counter-current at 15 ml/min or 1 L/hr.
CAVH/CVVH MECHANISMS OF ACTION
Convection
Solute is removed by “Solvent Drag”. The solvent carries the solute through a semi-permeable membrane.
The roller pump creates hydrostatic pressure, which drives the solvent thru membrane.
The pore size limits molecular transfer More efficient removal of larger molecules than diffusion Enhanced clearance of autologous cytokines
CAVHD
continuous arteriovenous hemodialysis
This technique uses an infusion pump, dialyzer membrane and dialysate solution.
An infusion pump pushes a flow of dialysis fluid dialyzer. The blood/dialysate interfaces on the membrane. CAVHD uses the process of diffusion dialysis to rid the body of fluid, electrolytes, and nitrogenous wastes.
The preferred arterial
access site is the common femoral artery
CVVHD
continuous veno-venous hemodialysis
The process of continuous diffusion dialysis in CVVHD is less effective than the CAVHD because the lower pressure venous system does not filter as much blood per unit of time.
CAVHD/CVVHD MECHANISMS OF ACTION
Diffusion (predominantly)
Solute diffuses down an electrochemical gradient through a semi- permeable membrane in response to an electrolyte solution running counter current to the flow through the filter.
Diffusive movement of the solute- smaller molecules (ie urea) have greater kinetic energy and are removed based on the size of the concentration gradient
Convection occurs due to UF
Solute removal is proportional to the concentration gradient/size
Dialysate flow rate is slower than BFR (limiting factor to solute removal)
Solute removal is directly proportional to dialysate flow rate
ARTERIOVENOUS FISTULA
Surgically created arteriovenous fistulas are preferred over catheters for patients with chronic renal failure for ease of access and a lower infection risk.
One of the most common errors of dual lumen catheters is the placement of the arterial and venous ports on the catheters
ANTICOAGULATION
Citrate (CPD) Citrate advantages
citrate has the effect of anticoagulating the CVVH system
itself.
Citrate interrupts the clotting cascade by soaking up (chelating) free ionized calcium. the citrate is cooked off (metabolized) into the form of bicarb – (a safe result)
heparin used with
both CVVH and CVVHD
