Module 2- Nephrology and Dialysis Flashcards
Nephrology definition
The study of the kidneys, the preservation of kidney health, and the treatment of kidney disease
Cost of end stage renal disease (ESRD)
ESRD costs $33 billion dollars to Medicare each year. The patient population makes up <1% of Medicare patients, but 7-9% of the total budget
What are the three main functions of the kidney?
- Regulation of the extracellular fluid environment in the body, including volume of blood plasma, wastes, electrolytes and pH
- Secretion of hormones
- Gluconeogenesis
Structure of the kidney (macro)
Microscopic kidney structure
- The nephron is the functional unit of the kidney
- Each kidney has more than 1 million nephrons
- Nephrons consist of small tubules and associated blood vessels
- Blood is filtered, fluid enters the tubules, is modified, and then leaves the tubules as urine
Diagram of nephron
3 steps of what happens in the nephron
- Filtration — kidneys “dump” cell and protein free blood into a separate capsule (glomerular capsule)
- Reabsorption — kidneys reclaim everything body needs to keep (glucose, AA, water, salt, etc.)
- Secretion — materials from
peritubular capillaries to the renal tubular lumen
What stays in and what goes our of the kidney?
- A young, healthy adult has a kidney over-capacity — usually about ten times what is necessary.
- After age 30, renal function declines about 10% for each remaining decade of life.
The clinical determination of kidney function
- Clinical manifestation is typically increased urea or creatinine concentration in the blood, which correlates to decreased renal clearance.
- Renal clearance can be defined as the amount of blood per unit time that is cleared by the kidneys.
Glomerular filtration rate
- A glomerular filtration rate (GFR) is a blood test that checks how well your kidneys are working — GFRs can be correlated with clearance.
- Inulin: C = GFR since it is not secreted or reabsorbed. The average GFR is 180 liters per day (125 mL per minute)
What is used to measure GFR?
- A blood test to measure creatine
- Creatinine is a waste product released by muscle — it is filtered but not reabsorbed (though small amounts are secreted)
- A blood test is used to approximate GFR
An increase in creatinine in the blood indicates a decrease in GFR
Overview of kidney disease
Kidney disease is marked by the gradual loss of kidney function — the damage can be acute or chronic
When does kidney failure occur?
- When the kidney can no longer support life
- Patients typically become symptomatic when kidney function falls below 10%. At less than 5%, life can only be sustained for weeks at most.
Video explaining dialysis
https://www.youtube.com/watch?v=shFSW8VE3Gs
The physical basis for hemodialysis
- A flowing stream of blood is placed in contact with a membrane, with a flowing stream of isotonic saline on the other side.
- The natural tendency of solutes is to equilibrate by the process known as diffusion. Impurities flow from the blood to the saline (electrolytes aren’t removed)
- Proteins and blood cells are too big to fit through the membrane.
- Water filters through the membrane because of trans-membrane pressure difference.
How does a round of dialysis treatment work?
- A Patient is dialyzed for 3-5 hours, 3 times a week. Treatment is usually conducted in a freestanding Dialysis Center.
- Each treatment session removes 1-3 liters of fluid and 50 ± 20 grams of uremic toxins.
- Blood is systemically anticoagulated with heparin during treatment.
- Dialysis is an intense and exhausting treatment.
Overview of hemodialyzers
- Hemodialyzers are disposable, membrane-moderated devices for mass exchange.
- Dialyzers are designed with sufficient transport capability to reduce urea concentration in the patient’s blood and body water by about 60 to 70%.
- Dialyzers are supplied sterile. Their current cost is between 10 to 20 USD — a low cost given the 200 million manufactured worldwide every year.
Dialyzer- counter current flow
- Counter-current flow is critical to efficient removal
- Dialysate is the chemical bath used to draw impurities and toxins out of the blood and supply the blood with electrolytes
Membranes in a dialyzer
Each dialyzer has between 6,000 to 10,000 membranes
Hollow fiber membranes
- The membranes in dialyzers are in the form of very fine capillaries called hollow fibers.
- The membranes are prepared from either synthetic or naturally-occurring plastics.
- Total surface available for exchange is ~1M2 or 10 ft2.
- Blood and dialysate flow paths are generally less than 200 microns in thickness.
Facilitating vascular access
- A surgeon creates an AV fistula by connecting an artery directly to a vein, frequently in the forearm.
- Connecting the artery to the vein causes more blood to flow into the vein.
- As a result, the vein grows larger and stronger, making repeated needle insertions for hemodialysis treatments easier — the process takes up to 1 year.
Artificial vascular graft + advantages and disadvantages
- Vascular grafting is most done to bypass blockage in an artery in order to improve blood flow to the organ.
- Advantages: quicker to establish and good for people with small veins
- Disadvantages: greater risk of infection, doesn’t last as long, larger incisions
Once vascular access has been established, the patient is connected to the dialyzer set up
Urea
- Urea is nitrogenous byproduct of protein metabolism — its concentration decreases rapidly and exponentially during dialysis, yet increases linearly in between treatments.
- The net effect is a “saw tooth” pattern of concentration shown in the graph.
- Adequate hemodialysis sessions are based upon relative plasma urea levels post-session.
- Adequate hemodialysis sessions are based upon ___
Relative plasma urea levels post-session
Peritoneal dialysis
- In peritoneal dialysis, 2.5 liters of hypertonic saline are infused into the peritoneal cavity, allowed to dwell for 4-6 hours, and then withdrawn
- Fluids flow in and out by gravity — with each exchange requiring about 30 minutes
Continuous ambulatory peritoneal dialysis
- CAPD is is performed 3-5 times daily and acts as a natural membrane
- Patients are taught aseptic techniques, but every exchange potentially exposes the peritoneal cavity to bacterial microorganisms in an infection of the abdomen called peritonitis (in italics)
Diagram of subparts of peritoneal membrane
The peritoneal membrane is highly vascularized and provides an enormous amount of surface area for exchange
Graph showing concentration of dialysate to plasma vs. time from onset of exchange
Small solutes equilibrate more rapidly than large ones — but after a six hour dwell, the concentration of urea in the peritoneal cavity is about the same as plasma’s
Graph showing rate of ultrafiltration vs. time from onset of exchange
- A typical exchange removes 500 to 750 ml of fluid.
- Most of this removal occurs early on during the exchange, because the glucose eventually diffuses from the peritoneal cavity into the body.
Automated peritoneal dialysis (APD)
- A cycler performs a series of shorter exchanges overnight while the patient sleeps — typically 6 to 7 liter exchanges over 8 to 10 hours
- This is more convenient for the patient and provides the same or greater solute clearance, and the patient may have a full or dry peritoneum during the day
Future of dialysis
Nxstage system 1 portable dialysis
