dialysis prescription 2
TRANSCRIPT
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By
Dr. Iheme, C.P.
M.B.B.Ch
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Outline Introduction
Epidemiology
Haemodialysis apparatus
Mechanisms of solute transport
Indications for dialysis
Components of dialysis prescription
Dialysis Adequacy
Complications of Haemodialysis
Conclusion
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Introduction Definition: Dialysis is a process whereby the solute
composition of blood is altered by exposing it to a dialysate through a semipermeable membrane.
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Introduction ctd Functions of the kidney
• Remove excess salt, water, and acid.
• Remove or regulate other electrolytes (e.g. K + , Ca 2+ , Mg 2+ , PO 4 ).
• Remove waste products of metabolism (Ur and Cr routinely measured, but there are many others).
• Make erythropoietin.
• 1 ά -hydroxylates and activates vitamin D.
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Epidemiology US: 490,000 ESRD patients, 300,000 currently on HD
UK: 23,500 HD patients, 74000 PD patients
White population predominant
Diabetes is the most common underlying diagnosis, followed by hypertension in the US.
Nigeria:17ooo new cases yearly. Prevalence of 79,050
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Renal Replacement Therapies
offered to the patients
556, 73%
9, 1%
7, 1%
188, 25%
Haemodialysis
CAPD
RenalTransplant
ConservativeArogundade et al, WCN 2009
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Epidemiology Mortality rate in RRT patients age 30–34 is 25x higher
age >85,mortality is 73x higher
Median survival
age 45–54 is currently 10.5 years
age 55–64 it is 5.6 years
age 65–74, 3 years
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Haemodialysis apparatus
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Mechanisms of solute transport1. Diffusion: movement of substances from an area of
higher concentration to an area of lower concentration of solutes.
2. Ultrafiltration (convective Transport): water driven by a hydrostatic is pushed through the membrane .
Solutes that can pass easily through the membrane pores are swept along with the water ( “solvent drag”).
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Mechanisms of solute transport Hemodiafiltration: hemodialysis and hemofiltration
are combined. Seen in newer models of machines
“Countercurrent” flow : Maximize the concentration difference of waste products between blood and dialysate in all parts of the dialyzer.
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Indications for dialysis in AKI
AEIOU
Acidosis: pH<7.2
Electrolyte abnormalities:
life-threatening hyperkalemia associated with ECG changes
symptomatic hypermagnesemia and hypercalcemia
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Indications for dialysis Intoxications: Xtics of dialysable substances
Low molecular weight (<500 Da)
High water solubility
Low degree of protein binding
Small volumes of distribution (<1 L/kg)
High dialysis clearance relative to endogenous clearance
E.g. barbiturates, bromides, chloral hydrate, alcohols, lithium, theophylline, procainamide, salicylates, atenolol, and sotalol.
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Indications for dialysis in AKI
Overload: fluid overload or pulmonary edema not responsive to aggressive diuresis
Uremia: mental status changes attributable to uremia, uremic pericarditis, or neuropathy, bleeding diatheses, or vomiting associated with uremia.
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Initiation of dialysis in CKD CKD stage 4 (GFR < 30 mL/min/1.73 m2) pts and
family members, should receive education about kidney failure and options for its treatment.
Initiate maintenance dialysis after an assessment of
uremic features
evidence of protein-energy wasting
metabolic abnormalities and/or volume overload mgt
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Components of dialysis Prescription Haemodialysis is a form of treatment and requires a
prescription
Prescription depends on individual characteristics and should be tailored to suit the individual needs
Choosing a prescription depends on the dialysis modality to be employed
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Goal of HD is to achieve
Dialysis adequacy
Electrolyte balance
Volume regulation
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Dialysis Prescription For the goal of attaining adequate Kt/V and URR
values, the principle variables are:
duration of treatment,
Frequency
blood flow,
dialysate flow,
dialyzer size.
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Dialysis Prescription Duration of treatment:
typically btw 3-4 hours in length
thrice weekly
Time can be ↑ if Kt/V and/or URR reflect poor dialysis
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Dialysis Prescription Frequency: Different dialysis modalities exist
Intermittent in-center HD: usually 3x weekly
Intermittent home HD
Short daily HD (about 6x weekly)
Nocturnal HD (6-8hrs, 6x weekly)
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Dialysis Prescription KDOQI guidelines recommend in-center short
frequent hemodialysis as an alternative to conventional Rx after considering
individual patient preferences,
the potential quality of life and
physiological benefits, and
the risks of these therapies.
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Dialysis Prescription
Blood flow rate: Largely depends on type
of access used.
1. Arteriovenous fistulas (AVFs): Best. Flow rates of 600-800cc/min. Can maintain patency at flows of 200cc/min.
2. Arteriovenous grafts (AVG): Flow rates of 1000 to 1500 cc/min.
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Dialysis Prescription3. Cuffed tunneled dialysis catheters: Placed in IJV
4. Femoral catheters
Aim is to achieve blood flow rates of 400-500cc/min for fistula and graft, 350-400cc/min for catheters.
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AV Fistula
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PTFE Graft
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Cuffed TunneledCatheter
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Dialysate flow: btw 500-800cc/min. Increasing the flow beyond 800 has no added benefit
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Dialyzer size: A dialyzer is a rigid polyurethrane shell ( ≈30cm long), containing hollow fibres (capillaries) of dialysate membrane.
A larger exposed surface area can be used to help improve adequacy
Dialyser efficiency: measured as KoA (mass transfer urea coefficient). Could be high flux >600 or low flux <300
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Electrolyte balance Dialysate: A solution of ultrapure water,
Na + (132-150mmol/L),
K + (usually 1.0 – 3.0mmol/L),
Ca 2+ (1.0 – 1.25mmol/L),
Mg 2+,
Cl – ,
dextrose,
Buffer(usually HCO3)
Ultrapure water is generated in a treatment plant
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Dialysate Potassium concentration Depends on the patient’s pre-HD K+ concentration.
Serum K+ ≥5.5 mEq/L→ a dialysate K+ of 2- 3 mEq/L
If propensity toward arrhythmias, 3 mEq/L bath is preferred to avoid precipitating hypokalemia.
A dialysate K+ of 4 mEq/L →patients with hypokalemia or persistent serum K+ <3.5 mEq/L.
Serum K+ >6.5 to 7.0 mEq/L or ECG changes hyperkalemia, → 0 or 1 mEq/L dialysate K+.
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Sodium modelling 140 - 145 mEq/L is appropriate in most cases
↓ serum Na+ levels indicate excessive free water intake and managed through fluid restriction.
Serum sodium <130mEq/L→ the dialysate sodium conc<= 15 - 20 mEq/L above the serum levels.
Hypernatremia should also be corrected slowly.
Dietary Na+ <100mmol/day intake (equivalent to 6g NaCl)
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Calcium concentrations Guidelines recommend ↓ dialysate Ca 2+ to maintain
neutral or negative Ca 2+ balance to prevent vascular calcification.
↑ patient: dialysate gradients associated with SCD
Dialysate Ca 2+ of 1.25mmol/L normally used.
May be increased to 3-3.5mmol/l in persistent hypercalcemia,
concurrent acidosis
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Dialysate bicarbonate Usually of 35 - 38 mEq/L to correct the metabolic
acidosis associated with chronic renal failure.
For those susceptible to alkalosis, lower bath of 20 - 28 mEq/L can be used. E.g.
total parenteral nutrition (TPN),
vomiting or nasogastric suction,
poor protein intake,
Respiratory alkalosis.
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Volume Regulation: Ultrafiltration Fluid restriction to limit intradialytic weight gains to
<4 kg
Ultrafiltrate should not be ˃ 10% of patient’s body water
>4 to 5 L of ultrafiltrate → uncomfortable fluid shifts and intradialytic hypotension.
Patients with low residual kidney function (< 2 ml/min) undergoing 3x weekly HD require 3 hours minimum.
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Volume Regulation: Ultrafiltration Additional sessions or longer treatment times for pts
with
large weight gains,
high ultrafiltration rates,
poorly controlled blood pressure,
difficulty achieving dry weight,
poor metabolic control (such as hyperphosphatemia, metabolic acidosis, and/or hyperkalemia).
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Anticoagulation Heparinization during HD minimizes clotting of the
dialysis circuit during the treatment.
For patients with evidence of bleeding, no heparin is prescribed. This includes
Uraemic gastritis,
GI bleeding
Pericardial effusion
Haemorrhagic stroke
Recent surgery
Post transplant patients
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Anticoagulation
Risk factors for Clotting include
high hemoglobin and hematocrit,
a high rate of ultrafiltration,
low blood flow on dialysis.
Both unfractionated and LMWH can be used.
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Dialysis Adequacy Dialysis can be considered adequate if it
provides relief of uraemic symptoms
controls acidosis, fluid balance, and serum K +.
It should also allow a feeling of physical and psychological well-being.
Adequacy is mainly modelled by 2 equations
Kt/V
urea reduction ratio.
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Urea as a surrogate marker Small, water-soluble breakdown of amino acids and
dependent on protein intake and breakdown.
Now considered a good surrogate marker for other pathogenic solutes
Advantages include
Abundance in renal failure
Ease of measurement,
Wide volume of distribution
Good dialyzability
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Dialysis Adequacy Kt/V: is a ratio that relates the volume of cleared
plasma (Kt) to the volume of urea distribution (V).
K = dialyser urea clearance.(ml/min)
t = time on dialysis.(min)
V = volume of distribution of Ur (estimated from patient size).(ml)
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Dialysis Adequacy Describes the volume of urea cleared during a dialysis
session relative to the volume of urea distributed throughout the body.
spKt/V: single pool urea clearance
eKt/V: equilibrated urea clearance
stdKt/V: Weekly standard urea clearance
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KDOQI guidelines on Adequacy A target single pool Kt/V (spKt/V) of 1.4 per session
for patient treated thrice weekly, with a minimum delivered spKt/V of 1.2.
If significant residual native kidney function (Kr), the dose of hemodialysis may be reduced.
For hemodialysis schedules other than thrice weekly, a target standard Kt/V of 2.3 volumes per week with a minimum delivered dose of 2.1
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Dialysis Adequacy Urea reduction rate (URR) similarly reflects the
removal of urea
URR = (BUNpre–BUNpost)/BUNpre
K/DOQI guidelines recommend the attainment of a minimal URR of 65% and a target URR of 70%.
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Complications of Haemodialysis The most common complications during hemodialysis
are,
hypotension,
cramps,
nausea and vomiting,
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Complications of Haemodialysis headache,
chest pain,
back pain,
itching.
Haemolysis
Clotting of extra-corporeal unit
First use syndrome/dialyser reaction
Accidental disconnection
Hard water syndrome,
Air embolism
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Intradialytic hypotension IDH is defined as a fall in SBP >20mmHg (or MAP
>10), associated with symptoms, or a fall to SBP <100mmHg.
Symptoms associated with IDH include:
Cramps, abdominal pain, or nausea (reduced gut perfusion).
Yawning, sighing, anxiety, or dizziness (reduced cerebral perfusion).
Chest pain or arrhythmias
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IDH Causes
Volume-related
Large weight gain (high ultrafiltration rate)
Short weekly dialysis time (high ultrafiltration rate)
Excessively low target (“dry”) weight
Antihypertensive medications
Eating during treatment
Anemia
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IDH
2. Inadequate vasoconstriction
High dialysis solution temperature
Autonomic neuropathy
3. Cardiac factors
Diastolic dysfunction
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IDH 4. Other causes
a. Pericardial tamponade
b. Myocardial infarction
c. Occult hemorrhage
d. Septicemia
e. Dialyzer reaction
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Immediate management of IDH:
Stop ultrafiltration (UF).
Trendelenburg position.
IVF 0.9% NaCl as a 250mL bolus.
Recheck BP.
Thorough clinical review (including medications) to prevent future episodes
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Disequilibrium Syndrome
Clinical features: nausea and vomiting, agitation, headache, seizures, loss of consciousness.
Cause: high blood urea levels being reduced too rapidly. Usually occurs during first dialysis session (with high blood flows). Leads to cerebral edema
Prevention: use a dialyser with small surface area, commence blood flow rate at 150-200mL/min. Limit first session to 2h. Mannitol infusion,50% dextrose infusion
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Conclusion Haemodialysis is a life-sustaining procedure for the
treatment of ESRD
In AKI, it provides rapid correction of fluid and electrolyte abnormalities that pose an immediate threat to the patient’s well-being.
In CKD, it results in a dramatic reversal of uremic symptoms and helps improve the patient’s functional status and survival.
To achieve these goals, the dialysis prescription must ensure that an adequate amount of dialysis is delivered to the patient.
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Thanks for listening
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References Cheng,S., Vijayan,A. The Washington Manual Nephrology
Subspecialty Consult.3rd Edition.St. Louis,Missouri: Lippincott Williams and Wilkins; 2012: 538-562
Daudirdas,J.T.,Blake,P.G., Ing,T.S. Handbook of Dialysis. 5th
Edition. Philadelphia: Lippincott Williams and Wilkins; 2015 Steddon,S., Ashman,N.,Chesser, A.,Cunningham,J. Oxford
Handbook of Nephrology.2nd Edition. Oxford, UK: Oxford University Press;2014:274-308
Bamgboye,E.L. The looming epidemic of kidney failure in Nigeria. MetroHealth: 2015
Hemodialysis Prescription & Adequacy, KDOQI guidelines,Oct2015
Palmer,B.F., The Dialysis Prescription and Urea modelling. www.kidneyatlas.org