Hemodialysis Prescription

Shahram Taheri M.D.Associate of Prof.

Isfahan School of Medicine

Principle of Hemodialysis

Vein

Artery

Dialysis Rx:

Time: 2-5 hoursBathBlood flow rate: 400-450cc/minDialysate flow rate: 500-800cc/minAnticoagulantAdditives:

◦ Anemia (EPO, blood)◦ Bone metabolism (vit D, calcitriol, etc)◦ Meds (antibiotics)

Dialysis adequacy 5

ADEQUACY OF DIALYSIS

• The higher mortality rate in the United States was thought to be related at least in part to inadequate dialysis.

• The weekly dialysis times declined progressively in the United States from 25 to 40 hours in the 1960s to 12 to 15 hours in the 1970s and 1980s to as low as seven to eight hours in the 1990s.

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• Studies in both Germany and the United States have documented the relationship between shorter dialysis time and poorer outcome.

• Patients dialyzed fewer than 3.5 hours three times per week have approximately twice the mortality risk compared to patients dialyzed four or more hours three times per week.

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• These patients, who were dialyzed very intensively (Kt/V of 1.67), also had a high incidence of full rehabilitation and almost all patients were rendered normotensive on no antihypertensive medications.

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How is dialysis adequacy calculated

1. Prescribed KT/V

2. Measured KT/V

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Kt/V is defined as the dialyzer clearance of urea (K, obtained from the manufacturer in mL/min, and periodically measured and verified by the dialysis team) multiplied by the duration of the dialysis treatment (t, in minutes) divided by the volume of distribution of urea in the body (V, in mL), which is approximately equal to the total body water.

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K T / V

CLEARANCEIn ml/min

CLEARANCEIn ml/min

Time ofDialysis

In minutes

Time ofDialysis

In minutes

Distribution Volume of urea In ml

Distribution Volume of urea In ml

Prescribed KT/V

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Measured KT/V

Kt/V   =   -ln (R  -  0.03)  +  [(4  -  3.5R)  x  (UF  ÷  W)]

URR   =   (1  -  [postdialysis BUN  ÷  predialysis BUN])

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Cognizant of the results from the HEMO study, we continue to aim for a single-pool Kt/V of approximately 1.4 to 1.6

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A number of factors contribute to Kt/V including: The size of the dialysis membrane,

since larger surface area membranes can remove more urea per unit time.

The blood flow rate to the dialyzer (Qb), since presenting new plasma with a high urea concentration maintains the favorable gradient for urea removal.

The dialysate flow rate (Qd), since delivering new fluid containing no urea also maintains the urea concentration gradient.

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Ultrafiltration, which removes urea by convection in a concentration similar to that in the plasma, also plays a contributory role.

Convective loss of small solutes is of minor importance with standard dialysis, but is the primary route of urea removal with continuous dialytic therapies for acute renal failure.

Hemodialysis Filter (Dialyzer)

Hemodialysis Filter (Dialyzer)

Hemodialysis Vascular Access

Polytetrafluoroethylene

Arteriovenous (AV) Fistula

Question 1

• Which type of vascular access is associated with better outcomes in hemodialysis patients? (choose one answer):

1. Central venous cuffed catheter

2. Arteriovenous graft

3. Arteriovenous fistula

4. Temporary central venous catheter

Which Vascular Access and When Should It Be Placed?

CKD Progression

05

10152025303540

Dates

eGF

R c

c/m

in/1

.73m

2

Initial presentation:HTN, CKD, proteinuria

HD

Vascular Access (AVF)

SODIUM

Ideally, dialysate sodium should be slightly lower, than the patient’s sodium level

Currently, sodium is viewed more as a way to stabilize intra-dialytic blood pressure rather than a way to “ultrafiltrate” and reduce circulating volume

Traditional “sodium modeling” results in a gain of sodium, an increase in post-dialytic thirst, resulting in increased interdialytic wt gain

Sodium 

The choice of dialysate sodium concentration for individual patients depends upon the predialysis serum sodium concentration and the hemodynamic status of the patient

Patients with normal serum sodium

For most patients with normal or near-normal serum sodium levels, we use a sodium dialysate concentration of approximately 137 mEq/L.

Hypernatremia 

 If the serum sodium concentration is only mildly elevated, we use a dialysate sodium concentration that is within 2 mEq/L of the plasma sodium concentration for the first dialysis session.

Hypernatremia 

The use of dialysate sodium concentrations more than 3 to 5 mEq/L below the plasma sodium concentration is associated with hypotension, muscle cramps, and, most importantly, disequilibrium syndrome. Subsequently, correction of the hypernatremia is performed with the administration of hypotonic solutions.

TEMPERATURE

Normal dialysate temperature (37° C) results in positive thermal gain, resulting in vasodilation and drop in B/P

Lower temperature dialysate prevents the thermal gain and results in greater stability of B/P

Lowering dialysate temperature should be one of the first considerations in improving intra-dialytic stability

Potassium 

Patients with severe hyperkalemia are often treated medically prior to dialysis.

Patients with potassium <4.0 mEq/L

If the predialysis serum potassium level is <4.0 mEq/L, we use a dialysate potassium concentration of 4.0 mEq/L.

This concentration prevents the development of hypokalemia and its complications.

Patients with potassium between 4.0 and 5.5 mEq/L

If the predialysis serum potassium level is between 4.0 and 5.5 mEq/L, the typical dialysate potassium concentration ranges from 2.0 to 4.0 mEq/L.

We generally use a dialysate potassium of 3.0 mEq/L if the predialysis serum potassium is between 4.5 to 5.5 mEq/L.

Patients with potassium between 5.5 and 8.0 mEq/L

If the predialysis potassium level is between 5.5 mEq/L and 8.0 mEq/L, then we generally use a 2.0 mEq/L dialysate potassium bath.

An exception may be made for patients who are at risk for arrhythmias related to potassium removal, for whom some nephrologists do not use a dialysate potassium <3.0 mEq/L

Buffer solutions

The main dialysate buffer used in intermittent hemodialysis is bicarbonate.

Bicarbonate is inexpensive and generally well tolerated, without the hemodynamic problems that may be observed with acetate.

Buffer solutions

A disadvantage of bicarbonate is that it precipitates as an insoluble salt when stored together with the divalent cations, calcium and magnesium, thereby requiring the buffer and electrolytes to be stored separately prior to hemodialysis.

Buffer solutions

The dialysate bicarbonate concentration varies based upon the acid-base status of the patient.

The acid-base status should be assessed using both the serum bicarbonate and pH.

Buffer solutions

In addition, possible side effects of bicarbonate include hypoxemia due to decreased respiratory drive related to the higher pH, and altered mental status, weakness, cramping, and lethargy due to acute metabolic alkalosis.

Mild or moderate metabolic acidosis

For patients with mild or moderate metabolic acidosis (ie, serum bicarbonate 10 to 23 mEq/L and an acidemic pH), we generally use dialysate bicarbonate concentration of approximately 30 to 35 mEq/L.

Severe metabolic acidosis

For patients with severe metabolic acidosis (ie, serum bicarbonate <10 mEq/L and a severely acidemic pH), the concentration of the bicarbonate solution may be increased to approximately 35 to 40 mEq/L.

For such patients, an extended duration of hemodialysis may be necessary.

Calcium 

For patients with significant hypocalcemia (total plasma calcium level <8.0 mg/dL [<2.0 mmol/L], corrected for hypoalbuminemia), particularly if the patient is symptomatic, we use a dialysate calcium concentration of 3.0 to 3.5 mEq/L.

For patients with severe hypercalcemia (total plasma calcium level >12.0 mg/dL [>3.0 mmol/L]), we use a dialysate calcium concentration of 2.0 to 2.5 mEq/L.

Calcium 

For patients with mild hypocalcemia, normocalcemia, or mild hypercalcemia (total plasma calcium level between 8.0 to 12.0 mg/dL [2.0 to 3.0 mmol/L]), we use a dialysate calcium concentration of 2.5 mEq/L.

Magnesium 

The usual dialysate magnesium concentration is 0.5 to 1.0 mEq/L.

Chloride 

The amount of dialysate chloride is dependent upon the dialysate sodium and bicarbonate concentrations.

Glucose

The standard dialysate glucose concentration is generally either 100 mg/dL (5.5 mmol/L) or 200 mg/dL (11.1 mmol/L).

BLOOD FLOW RATE

 We select the blood flow rate based, at least initially, by the duration of significant azotemia (ie, blood urea nitrogen [BUN] >100 mg/dL) prior to starting dialysis.

BLOOD FLOW RATE

Among patients with severe, longstanding azotemia, the rapid reduction of solute should be avoided, in order to prevent dialysis dysequilibrium syndrome.

BLOOD FLOW RATE

If the BUN has been >100 mg/dL for at least three days in the patient with acute kidney injury (AKI), we use a blood flow rate less than 200 mL/min for the first treatment.

If the BUN has not been >100 mg/dL for at least three days, we use a dialysis blood flow rate of 300-350 mL/min.

ULTRAFILTRATION

The approach to volume overload is different for end-stage renal disease (ESRD) patients undergoing chronic maintenance dialysis and for critically ill AKI patients.

ULTRAFILTRATION

The target weight of a chronic dialysis patient is usually determined empirically as the weight at which clinical signs of extracellular fluid expansion are absent and below which clinical signs of extracellular depletion arise.

ULTRAFILTRATION

In contrast, in critically ill acute renal failure (ARF) patients, the volume expansion that is frequently observed is often necessary to maintain optimal circulatory and oxygen transport status.

ULTRAFILTRATION

In hemodynamically stable patients, the estimation of target intravascular volume can be made in the usual fashion utilized for ESRD patients.

ULTRAFILTRATION

In hemodynamically unstable patients, target intravascular volume should be titrated to invasive or noninvasive monitoring (such as bioimpedance analysis, pulse contour analysis [PiCCO], or echocardiography), which should guide the UF goals for a given intermittent hemodialysis session.

Hemodialysis anticoagulation

Hemodialysis and continuous renal replacement therapies require extracorporeal blood flow.

Some form of anticoagulation, usually with heparin, is required to prevent thrombosis in the blood circuit.

STANDARD ANTICOAGULATION

Anticoagulation in routine hemodialysis consists of a standard dose of heparin given as a bolus at the start of the dialysis treatment, with a mid-treatment dose to maintain suitable anticoagulation.

Heparin modeling can be performed using an initial bolus followed by a constant fixed infusion of heparin to maintain an activated clotting time (ACT) of 200 to 250 seconds (normal = 90 to 140 seconds).

No-heparin hemodialysis

No-heparin hemodialysis was developed for use in the patient at high risk of bleeding.

The protocol requires pretreating both the dialyzer and blood lines with 2000 to 5000 units of heparin contained in a liter of normal saline.

The heparinized saline is flushed from the extracorporeal lines prior to the start of the dialysis treatment so that heparin is not administered to the patient.

No-heparin hemodialysis

Extracorporeal blood flows are rapidly increased to 250 to 500 mL/min and maintained throughout the treatment, and 25 to 30 mL saline flushes are administered every 15 to 30 minutes into the arterial (predialyzer) limb to minimize hemoconcentration and to wash fibrin strands from the kidney into the bubble trap.

No-heparin hemodialysis

The volume of saline administered with such frequent flushing must be removed during the dialysis to prevent hypervolemia.

One-to-one nursing is required, with careful monitoring of the arterial and venous pressure alarms to detect early clotting.

Minimum-dose heparin

The use of minimum-dose heparin has been shown to reduce bleeding complications in high-risk patients when compared with regional heparinization with protamine neutralization (10 versus 19 percent).

The protocol usually involves boluses of 500 units of heparin every 30 minutes to keep the activated clotting time >150 but <200 seconds.

Minimum-dose heparin

Alternately, a continuous infusion of heparin with frequent activated clotting time (ACT) monitoring can be used to achieve the same degree of anticoagulation.