Lecture 21 Renal Replacement Therapies Flashcards
(18 cards)
What is dialysis?
a tx to remove excess fluid and waste from blood when kidneys unable to
relies on diffusion, ultrafiltration and convection
2 main types: hemodialysis - uses diffusion and ultrafiltration
and peritoneal dialysis - uses diffusion, ultrafiltration and convection
What does the rate of movement of solute for dialysate depend on?
conc gradient,, permeability and SA of membrane
length of time that blood and fluid remain in contact with membrane
When is dialysis initiated in end-stage CKD (Goals?)?
initiated if one or more of following present ⇒ S&S of kidney failure (serositis, acid-base abnormalities, pruritis), anuria, inability to control volume status or blood pressure, deterioration in nutritional status, cognitive impairment
initiated based on clinical status rather than specific CrCl, typically clinical S&S of concern manifest when eGFR < 10 and not recovering
Goals: manage S&S, remove uremic toxins and other substances, restore fluid and electrolytes, reestablish normal pH
When should tx planning for dialysis start to be considered?
pt who have > 10% risk of kidney failure within one year should be referred to specialist for RRT planning
planning for dialysis should start to occur when pt kidney fxn declines to CKD stage 4
What is hemodialysis?
most common type of RRT for pt with ESRD, is extracorporeal, artificial membrane, commonly admin intermittently 3-4 x per week each session around 3-4 hours, contains dialyzer, dialysate, vascular access
involves perfusion of blood and dialysate in opposite sides of semi-permeable membrane - membrane has pores allowing for movement of smaller molecules but not larger molecules like RBCs
dialysis machine used to pump blood from body towards membrane - blood flows in counter-current to dialysate to create larger conc gradient
substances removed from blood by diffusion - creatinine, K+, urea, uremic toxins, drugs all moved to dialysate
excess water in plasma removed by ultrafiltration
What is the dialyzer in hemodialysis?
is a filter, “artificial kidney”
container that houses semi-permeable membranes that separate dialysate from pt blood, blood flows through one section and dialysate through other, selection of this can impact the removal processes
this with a semi-permeable membrane that has larger pores will allow for movement of more solutes, and one that is more permeable to water will cause increased ultrafiltration of water
What is the dialysate in hemodialysis?
cleansing liquid containing electrolytes, purified water, dextrose
composition of this can be adjusted based on pt
Bicarbonate: high conc allows for movement of bicarbonate into blood
Potassium: low amount of K+ in this prevents sudden hypokalemia as excess K+ is removed from blood
What is vascular access in hemodialysis?
access point to blood flow is required for this to occur, immediate access required: Temporary Access - insertion of venous catheter into large vein (subclavian, jugular, femoral), not preferred if plan is for ongoing dialysis as higher risk of complications
Advanced planning: Permanent Access - arteriovenous fistula, arteriovenous graft
What is an arteriovenous fistula for hemodialysis vascular access?
native fistula: created by joining a vein and an artery, typically the radial artery to cephalic vein
surgically created
requires 1-2 months of maturation before it can be used for dialysis,, is the preferred vascular access point as they have the longest survival time of vascular access methods and lower rate of complications
What is an arteriovenous graft for hemodialysis vascular access?
synthetic graft inserted to form a connection between a vein and an artery, commonly between brachial artery and basilic vein
surgically created
requires 2-3 weeks of healing time before it can be used for dialysis
have shorter survival time of the graft, higher rates of infection and thrombosis
How is hemodialysis typically run (setting, flow rates)?
In-center: 3x per week with each run lasting around 3-5 hours
Home: nocturnal - 3x per week, 8-10 hour sessions
short daily sessions consisting of 2-3 hour sessions 5-6x per week
not as common
Blood Flow Rate: 200-500 mL/min
Dialysate Flow Rate: 500-800 mL/min
What are some AEs of hemodialysis?
During: hypotension (20-30%), HTN (5-15%), cramps (5-20%), N/V (5-15%), H/A (5%), chest/back pain (5%), pruritis (5%, fever and chills (< 1%)
other: access site infections, bacteremia, sepsis, worsening of existing anemia, AV fistula/graft/catheter thrombosis
What is peritoneal dialysis?
typically admin multiple times a day to daily
distillation of dialysate into peritoneal cavity through permanent peritoneal catheter access point
peritoneal membrane acts as semi-permeable membrane between dialysate and abdominal viscera which is highly vascularized
solutes removed from blood across peritoneal membrane by diffusion and ultrafiltration
excess water in plasma removed by ultrafiltration
What are components of peritoneal dialysis?
dialyzer: peritoneum
-permeable membrane: peritoneal membrane
Access: peritoneal catheter allows for access point to instill dialysate into peritoneum, dialysate within solution bags
Blood supply: vasculature perfusing peritoneum, blood remains ‘within body’
Dialysate: supplied in bags 1-3 L, osmotic agent is dextrose which can alter the osmotic pressure by changing the amount of dextrose in dialysate which will alter amount of fluid removed
electrolyte conc similar to serum conc, instead of bicarbonate ⇒ lactate is used
What are the steps of peritoneal dialysis?
- Fill - dialysate solution is infused into peritoneal cavity, typically takes 20 minutes
- Dwell - duration for which the solution remains in the peritoneal cavity, duration is prescribed, typically around 2 hours
3.Drain - time for effluent fluid to be removed from peritoneal cavity, effluent is measured upon release, typically 10-15 minutes
one whole cycle is referred to as an EXCHANGE
What are some AEs of peritoneal dialysis?
Peritonitis - infection within peritoneal cavity
exit site infections at catheter
absorption of glucose leading to hypertriglyceridemia and weight gain/obesity
loss of albumin and other proteins may lead to malnutrition
increased glucose absorption from dialysate can also increase insulin resistance in pt with diabetes - creates increase in insulin requirement which can be managed by adding insulin to dialysate,, risk of fibrin formation in dialysate
What are the most likely causes of mortality in CKD pt on dialysis?
adjust 5 year survival rate is 40%
> 50% deaths due to CV related causes
infections second most common cause of mortality in this population
What is drug dialyzability?
refers to how much of a drug is removed from the body during dialysis - high rate = more removed and vice versa
depends on things like: molecular weight, degree of protein binding, Vd, water solubility, dialysis membrane, blood/dialysate flow rates
