Magdy El-MasryProf. of Cardiology

Tanta University

CHANGES IN BLOOD PRESSURE AFTER HEMODIALYSIS

HemodialysisRemoval of Fluid and Solutes with the Goal to Achieve

“Dry Weight”

What the cardiologist should know?

Hemodialysis Basics

5

Diffusion

Convection

Goals of Dialysis

–Solute clearance• Diffusive transport (based on countercurrent

flow of blood and dialysate)• Convective transport (solvent drag with

ultrafiltration)

–Fluid removal

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Figure 3-2

Body Fluid Compartments

Appropriate Removal Ratesetting the fluid removal rate to not exceed the plasma refill rate (PRR) will minimize risk of hypovolemia, hypotension

“Never too fast, never too much”

VascularSpace

Plasma Refill Rate

Intravascular

HemodialysisUF rate

Extravascular

UFR ≤ PRR

Fluid Removal by Ultrafiltration (UFR)illicits compensatory mechanisms, termed plasma or intravascular refill, aimed at minimizing this reduction

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Dialysate Buffer• Acetate: in the early 1960s became the

standard dialysate buffer used to correct uremic acidosis

In the mid 1980s some reported the linking between acetate and cardiovascular instability and hypotension during HD

• Bicarbonate: emerged the buffer of choice

Dialysis Solution Sodium Level

Plus Minus

Low dialysate sodium

Less weight-gain, thirst &hypertension

More hypotension, cramps

High dialysate sodium

Less hypotension, cramps

More weight gain, thirst & hypertension

EXCESS FLUID WEIGHT

Body weight at which composition of body fluid compartments is normal.

At higher weights there is expansion of compartments

At lower weights there is depletion of compartments.

Both these states have adverse clincal consequences.

CONCEPT of DRY WEIGHT

DRY WEIGHT

(euvolemia)

In short, among all these elements, the 2 essential clues are the BP and the weight

Intradialytic Hypotension

Acute complications of dialysis HHCCBNF

• Hypotension — 25 to 55 %• Cramps — 5 to 20 % • Nausea and vomiting — 5 to 15 % • Headache — 5%• Chest pain — 2 to 5 %• Back pain — 2 to 5 %• Itching — 5 %• Fever and chills — Less than 1 %

Intradialytic Hypotension

K/DOQI• ↓SBP≥20mmHg or ↓MAP 10mmHg with symptoms:

abdominal discomfort,yawning, sighing, N/V, cramps,restlessness, anxiety, fainting

Cardiac output

Arterial Blood Pressure

Diastolic fillingAtrial kick

Systemic vascular resistance

Stroke volume

preload afterload contractility

Heart rate / rhythm

Ultrafiltration

Osmolality Fall

Warm Dialysate

Bio-incom-patibility

Endotoxin

AcetateInfusion

Volume

Vasopressors

Vasodilatator

Cell Dysfunction

ComplementActivation,

Cytokine release

Hypoxemia

Heart Disease

Vascular Disease

Autonomic Dysfunction

Hormonal Dysfunction

Medications

SepsisInfection

Vasovagal stim.

HYPOTENSION

CARDIACOUTPUT

PERIPHERAL RESISTANCE

PATHOGENESIS MEDIATORS PATHOPHYSIOLOGY PATIENT

Acute management of low blood pressure associated with hemodialysis

Ultrafiltration should either be stopped or the rate decreased.

The patient should be placed in the Trendelenburg position.

The blood flow rate should be reduced. Intravascular volume may be replaced with

mannitol or saline. Currently the use of an intravenous bolus of saline is the first-line therapy for hypotension.

PREVENTION

• Accurate setting of the "dry weight"• Steady, constant ultrafiltration • Increased dialysate sodium concentration and

sodium modeling • Bicarbonate dialysate buffer • Decrease dialysate temperature from 37C to

34-35C

Prevention – Con’tImprovement in cardiovascular Performance in

cardiac patients.Midodrine (the selective alpha-1 adrenergic

agonist) in patients with autonomic neuropathy and perhaps others with severe hemodialysis hypotension not responsive to the above measures.

Avoidance of food.Avoid large interdialytic weight gainNo antihypertensive before dialysis

Intradialytic Hypertension

The growing problem of intradialytic hypertension(5 – 15 % of HD patients )

Intradialytic HypertensionClinical Definitions

• ↑MAP of ≥ 15 mmHg during or immediately post dialysis

• Hypertension during 2nd or 3rd hr of HD after significant UF removed

• ↑BP that is resistant to UF

The Etiopathogenesis of Intradialytic Hypertension

HypervolemiaSodium balance positive and extracellular volume expand

Increased systemic vascular resistanceIncreased sympathetic activity

Renin-angiotensin system hyperactivity

Endothelial cell dysfunctionElevated concentration of endothelin 1

Calcification of the arterial treeIncreased hematocrit

Erythropoietin Therapy

Increased vascular stiffnessNitric oxide deficiency

Hypertension in dialysis( (Another World

• There are limited studies on controlling blood pressure in patients on dialysis.

• No consistent guidelines available due to the fact that no one knows what blood pressure to target.– Pre, Post, intradialytic, non-dialysis day.

Blood pressure measurement in dialysis patients

Majority of Uremic patients lack diurnal variation in BP

Immediate pre dialysis and post dialysis are misleading and not ‐ ‐reflective of true interdialytic BPHowever, a post dialytic BP is more reflective of interdialytic BP

*Continuous monitoring is warranted in poor control patients (those with large interdialytic weight gain)

*“Systolic load “ > amount of time SBP exceeds 140 mmHg per ‐‐day as correlates to incidence of LVH

K/DOQIBlood Pressure Goals in Hypertensive ESRD Patients

• Target BP ≤ 140/90 mmHg (predialysis)

• ≤ 130/80 mmHg (postdialysis)

Treatment of hypertension in patients on hemodialysis

Treatment of hypertension is often a multiple-step, multidisciplinary process to reach KDOQI guidelines of predialysis BP values of <140/90 mm Hg.

The key to successful treatment is patience; it often takes 4-6 weeks to achieve results. (This represents the lag phenomenon )

Chronic volume expansion

Vascular Na/K ATPase

NO SynthetaseADMA

DLIS etc

NO

iCa++

Vaso-constriction

Sustained UF & Na restriction

ECV

DLIS etc

ADMA

LAG

BP

Lag period between normalisation of ECF and optimal control of BP

DLIS:digoxin-like immunoreactive substance ADMA:asymmetric-dimethyl arginine

Treatment of Intradialytic Hypertension The step-by-step approach

Choice of antihypertensive drugs

All classes of antihypertensive drugs can be used in dialysis patients, with the sole exception of diuretics, which are not commonly used because of their lack of efficacy.

Therefore, with the exceptions of diuretics, the criteria for drug selection are quite similar to those used in non-dialysis patients.

Dialysis Clearance of Drugs

In general, removal of drugs on HD has NOT been tested and is based on theoretical considerations of molecular size and chemical makeup of the drug

Drugs with low MW, limited volume of distribution (Vd) , and that are water-soluble are most likely to be removed by HD and will require extra dosing

Postdialysis dosing or extra doses after HD may be necessary for certain antihypertensive agents:

•Angiotensin converting enzyme inhibitors (ACE-I): all are dialyzable except fosinopril

•Angiotensin receptor blockers (ARB): none are dialyzed

•B-blockers: atenolol and metoprolol are dialyzable but labetolol and carvedilol are not

•Calcium channel blocker: amlodipine is not dialyzable

Conclusions

“We can do better”

The fluctuations in BP with every dialysis is

complex

Intradialytic Blood Pressure Fluctuations

• Current StateClinically significant alteration in blood pressures is one of the biggest challenges encountered in the dialysis unit

• Ideal StateClinicians understand the physiological changes in blood pressures during hemodialysis and prevent and manage these changes effectively to ensure patient’s safety

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