Dialysis

define dialysis:

the removal of waste products and fluid from the body on the basis of particle differences in their ability to pass through a membrane

define CKD 5:

GFR < 15 mL/min

what is CKD5D

CKD stage 5 patients that undergo dialysis

what is CKD5ND

CKS stage 5 patients not undergoing dialysis

define kidney failure:

requirement of dialysis modality for > 3 months to sustain life and typically occurs once GFR < 15 ml/min

define End-Stage Renal Disease (ESRD)

related to diagnosis coding and payment structures within Medicare - an old term falling out of favor

what are the methods of drug removal during dialysis?

diffusion and convection

what is diffusion?

random movement of particles in all directions (particles tend to move across concentration gradients)

what things affect diffusion?

temperature, surface area, flux, diffusion coefficient, and membrane thickness

what is convection

fluid movement due to pressure gradient

ultrafiltration refers to

excess fluid removal from the blood during dialysis

T/F: convection is independent of concentration gradient or molecular size

true

what does the term solvent drag refer to

movement of solutes (waste products) along with fluid as it is pulled through the dialysis membrane

what are the dialysis modalities

hemodialysis (HD), peritoneal dialysis (PD), and continuous kidney replacement therapy (CKRT)

what are the hemodialysis access options

arteriovenous fistula, arteriovenous graft, and central venous catheter

which hemodialysis option has the lowest risk of infection and thrombosis

arteriovenous fistula

how long does an arteriovenous fistula take to mature after surgical creation

6-12 weeks

which hemodialysis access option is preferred for long-term access

arteriovenous fistula

what is an Arteriovenous graft

a surgically created connection between an artery and a vein connected by a synthetic tube (can be used earlier than AV fistula ~2-6 weeks)

what is the last-line option for hemodialysis access?

central venous catheter

which hemodialysis access option has the highest risk of infection and thrombosis and is used short-term (i.e. bridge to AV fistula)

central venous catheter

what does CAPD stand for

continuous ambulatory peritoneal dialysis

what is an automated PD

a machine assisted night-time peritoneal dialysis with cycler

what is continuous kidney replacement therapy

“slow hemodialysis” performed in critically ill patients with unstable hemodynamics

what are the different types/modes of CKRT?

CVVH, CVVHD, CVVHDF

what is CVVH

continuous venovenous hemofiltration - uses a filtration process to remove waste and fluid (uses convection)

what is CVVHD

continuous venovenous dialysis - involves diffusion for waste removal, similar to hemodialysiswhat

what is CVVHDF

continuous venovenous hemodialysis - combines both filtration and diffusion to remove solutes ad fluid (combination of convection and diffusion)

what is the dose of CRRT

effluent volume refers to the total volume of fluid that is processed and removed from the patient during; flow rates represent the rate at which blood is pumped through the CRRT machine; typically run continuously for 24 hours a day

what things matter when looking at CRRT filters?

the material and surface area

drug factors that influence drug removal via dialysis:

molecular weight (size), protein binding, volume of distribution (lipophilicity)

patient factors that influence drug removal by dialysis:

albumin levels, fluid status, and blood pressure

dialysis factors that influence drug removal:

conventional vs high flux, membrane type (cellulose, polyamide, polysulfone, polyacrylonitrile, polymethylmethacrylate), blood and dialysate flow rates, and length of dialysis

drug removal is increased by:

small molecular weight, low protein binding, small volume of distribution (low lipophilicity), high-flux hemodialysis, and semi-synthetic and synthetic dialysis membranes

when should drug concentrations be checked for hemodialysis patients?

prior to the session

when should drug concentrations be checked for peritoneal dialysis and CRRT

random - refer to specific medications

what is the process of hemodialysis therapeutic drug monitoring

1. obtain drug concentrations prior to session

2. estimate intra-HD drug removal

3. base additional doses on estimated post-HD concentration and target concentration

why is post-dialysis equilibrium unreliable for therapeutic drug monitoring

due to re-distribution of drug from tissue stores and/or protein binding sites, fluid shifts, and there are fluctuating drug concentrations post-HD

Notes regarding to hemodialysis

~3 sessions per week, ~4 hours per sessions, dialysis machine removes solutes, toxins, and fluid

notes about peritoneal dialysis:

continuous ambulatory peritoneal dialysis (CAPD), automatic cycler peritoneal dialysis (nighttime), peritoneal membrane used for removal of solutes, toxins, and fluid

hemodialysis dosing considerations:

dosing is complex and should always be looked up, if possible drugs should be dosed post-hemodialysis, if a large amount of drug is removed in hemodialysis give a supplemental dose after hemodialysis

what are some examples of intra-dialytic medications

erythropoiesis stimulating agents (ESAs) and activated vitamin Ds

if a drug is significantly removed during HD, when should it be administered?

post-hemodialysis

supplemental dose =

normal dose * fraction removed by hemodialysis

why are supplemental doses given to dialysis patients?

to replace the amount of drug that was removed by the HD procedure

what % of drug removed during HD qualifies for a supplemental dose

if > 30-40% is removed by HD

which form of dialysis does not effectively remove drugs

peritoneal dialysis

when can significant drug removal occur in peritoneal dialysis?

if drug has very low Vd, low protein binding, few other routes of elimination, and rapid exchanges

T/F: drugs given by peritoneal route can move in and out of the membrane

true

what should you be aware of when administering drugs by peritoneal route?

it can achieve potentially toxic serum levels

why does peritoneal dialysis have substantially less drug removal than with hemodialysis?

has a 10mL/min maximum clearance and the majority of the pores are small (95% of the SA) whereas the large pores account for #% of the SA

when would drugs be administered via peritoneal/systemic dialysis?

treatment of peritonitis, systemic infections, hyperglycemia, and anemia\

what is critical to evaluate regarding the drug and dialysate fluid for peritoneal dialysis?

the stability and compatibility

which form of dialysis has the most drug removal?

continuous kidney replacement therapy

T/F: it is difficult to predict drug removal in CKRT/CRRT

true

what is the drug clearance for CKRT

most fall into 25-50 mL/min

common complications of hemodialysis:

hypotension, cramping, fatigue, infection, thrombosis, bleeding

causes of hypotension with hemodialysis

hypovolemia, excessive fluid removal, antihypertensive administration prior to HD, autonomic dysfunction

how to help prevent hypotension associated with hemodialysis

appropriate ‘dry weight’ selection, hold antihypertensive medications prior to HD

how to manage hypotension associated with hemodialysis

small fluid bolus (100-250 mL) 0.9% sodium chloride or lactated ringers, decrease fluid removal (ultrafiltration), and midodrine

MOA of midodrine

alpha-1 agonist which leads to peripheral vasoconstriction (Pro-drug)

Dosing of midodrine for hemodialysis hypotension

2.5-10 mg PO 30 minutes prior to HD

ADRs of midodrine

bradycardia, HTN, peripheral ischemia (PVD patients), urinary retention.dru

drug interactions with midodrine

MAOIs and other sympathetic activating drugs

causes of cramping in dialysis patients

hypovolemia and decreased muscle perfusion

prevention of cramping in hemodialysis patients

selecting appropriate ‘dry weight’

how to manage cramping in hemodialysis

small fluid bolus (100-250 mL) 0.9% sodium chloride or lactated ringers, decrease fluid removal (ultrafiltration), vitamin E 400 IU PO QHS

what medication is thought to help cramps but does not!

quinine 324 mg PO daily

ADRs of quinine

arrythmias, thrombocytopenia, and hypersensitivty reactions

what is the #2 cause of mortality in hemodialysis

infections

which type of infections are associated with dialysis the most?

blood stream (some infections are pneumonia)

which medication is frequently used to treat MRSA dialysis associated infections?

vancomycin

causes of thrombosis with dialysis access:

Virchow’s triad (hypercoagulable state, endothelial damage, and stasis of blood), and patients have higher risk if using erythropoiesis stimulating agents (epoetin alfa or darbepoetin alfa)

how to prevent thrombosis with dialysis access?

heparin with dialysis (but long-term risk of HIT) and systemic anticoagulants/antiplatelet may be used but is controversial

how to manage thrombosis from dialysis access?

alteplase (Cathflo) 2 mg/mL instilled for 30-120 minutes

how does alteplase work?

plasminogen activation which leads to plasmin activation and fibrinolysis (breakdown of clot)

what are the complications of peritoneal dialysis?

peritonitis, fluid overload, and hyperglycemia