By

Dr. Iheme, C.P.

M.B.B.Ch

Outline Introduction

Epidemiology

Haemodialysis apparatus

Mechanisms of solute transport

Indications for dialysis

Components of dialysis prescription

Dialysis Adequacy

Complications of Haemodialysis

Conclusion

Introduction Definition: Dialysis is a process whereby the solute

composition of blood is altered by exposing it to a dialysate through a semipermeable membrane.

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.

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

Renal Replacement Therapies

offered to the patients

556, 73%

9, 1%

7, 1%

188, 25%

Haemodialysis

CAPD

RenalTransplant

ConservativeArogundade et al, WCN 2009

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

Haemodialysis apparatus

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”).

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.

Indications for dialysis in AKI

AEIOU

Acidosis: pH<7.2

Electrolyte abnormalities:

life-threatening hyperkalemia associated with ECG changes

symptomatic hypermagnesemia and hypercalcemia

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.

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.

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

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

Goal of HD is to achieve

Dialysis adequacy

Electrolyte balance

Volume regulation

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.

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

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)

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.

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.

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.

AV Fistula

PTFE Graft

Cuffed TunneledCatheter

Dialysate flow: btw 500-800cc/min. Increasing the flow beyond 800 has no added benefit

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

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

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+.

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)

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

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.

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.

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).

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

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.

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.

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

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)

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

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

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%.

Complications of Haemodialysis The most common complications during hemodialysis

are,

hypotension,

cramps,

nausea and vomiting,

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

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

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

IDH

2. Inadequate vasoconstriction

High dialysis solution temperature

Autonomic neuropathy

3. Cardiac factors

Diastolic dysfunction

IDH 4. Other causes

a. Pericardial tamponade

b. Myocardial infarction

c. Occult hemorrhage

d. Septicemia

e. Dialyzer reaction

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

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

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.

Thanks for listening

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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