Fig. 4.1
Schematic demonstration of hemodialysis prescription
4.1.1 Preparation of Items
Arterial and venous blood tubes (or blood tube set).
Dialyzer .
Two needles (15, 16, or 17 G) for hemodialysis.
Normal saline 1 L and infusion solution set.
Heparin .
Syringes (e.g., 5, 10, 20, or 30 mL) for heparin administration.
Dressing set (2% chlorhexidine with 70% propyl alcohol, 70% alcohol, and/or 10% povidone-iodine sponge), sterilization drape.
4.1.2 Anticoagulation
Hemodialysis requires extracorporeal blood flow . Some form of anticoagulation is required to prevent thrombosis in the extracorporeal blood circuit (dialyzer and arterial/venous blood tubes) during the procedure. Anticoagulation protocols used in hemodialysis differ according to dialysis center. Anticoagulants used in hemodialysis are unfractionated heparin, low-molecular-weight heparin , regional anticoagulation with citrate or protamine reversal, direct thrombin inhibitor , antiplatelet agents, prostacyclin, heparinoids, and heparin-protamine. Strategies to decrease the risk of bleeding include using low-dose heparin and the fast-flow no-heparin method. The most commonly used anticoagulant is heparin. Each dialysis center may have its own heparin protocol. A commonly used heparin protocol in routine hemodialysis consists of an initial dose of heparin administered as a bolus at the start of the hemodialysis treatment and a continuous dose of heparin administered during hemodialysis to maintain suitable anticoagulation (Hemodialysis Adequacy 2006). An initial dose of heparin (10–50 units/kg, usually 50 units/kg) is bolus injected just after needle insertion into the arteriovenous fistula or through a central venous catheter (Santos and Peixoto 2008). A continuous dose of heparin (500–1500 units/h, usually 1000 units/h) is administered during the session of hemodialysis. A strategy to maintain the patency of the extracorporeal circuit and to minimize bleeding risk is needed in anticoagulation.
4.1.3 Heparin Rinsing
Rinsing is a process of washing the extracorporeal circuit with rinsing solution. After setting up the hemodialysis machine with the arterial/venous blood tubes and dialyzer, 2000–5000 units (usually 3000 unit) of heparin in 1 L of normal saline is infused into the extracorporeal circuit. Then, the heparinized saline is flushed from the extracorporeal lines with unheparinized normal saline prior to the start of the dialysis treatment. Because the heparin is not administered to the patient during the rinsing process, it can be used in the rinsing process of a heparin-free protocol, which is indicated for patients with a high risk of bleeding. However, heparin should not be used in the rinsing sequence for a patient with heparin-induced thrombocytopenia. This rinsing process is optional, and thus this process can be omitted.
4.1.4 Priming
Because the dialyzer and arterial/venous blood tubes are filled with air or foreign materials (e.g., sterilant), performing the priming process with normal saline is essential to remove such materials from the extracorporeal circuit. Therefore, after priming, there should be no air within the extracorporeal circuit.
Set up the hemodialysis machine with the arterial/venous blood tubes and dialyzer.
After connecting the venous or arterial blood tube to normal saline, start the blood pump at a low rate (50–100 mL/min). The nurse or technician operates the machine to fill the extracorporeal circuit with normal saline. In some dialysis machines, the priming process is automatically completed by a computerized program. After connecting between arterial and venous blood tube ends, recirculation process is performed in the extracorporeal circuit. During recirculation, remnant air bubble can be removed from arterial/venous blood tubes and dialyzer. However, the recirculation process is optional and can be omitted.
4.1.5 Obtaining Vascular Access
4.1.5.1 Patients with Central Venous Catheter
The operator washes his or her hands and assesses the condition of the hemodialysis machine. After priming the extracorporeal circuit, heparin should be prepared for initial bolus (10–50 units/kg) and maintenance (500–1500 units/h) administration.
The operator is recommended to wear clean gloves. After opening the dressing set and preparing the items to be used, the gauze and tape previously used for dressing are removed. The catheter insertion site should be inspected for the color, blood clots, swelling, and pus discharge.
Antiseptics including 2% chlorhexidine with 70% alcohol or 70% alcohol and/or 10% povidone-iodine can be used for disinfection, and the catheter insertion site is sterilized, starting from the center and moving outward in a circular pattern. After removing the heparin cap at the end of the catheter , disinfect the both ends of catheter. After disinfection, the catheter tip must be handled with aseptic techniques and minimum exposure to air.
After the antiseptics have dried, the catheter insertion site and both suture sites are fixed with gauze.
The patency of the catheter lumen is verified using normal saline (e.g., 20 mL in a 20-mL syringe). If flushing is unsuccessful, obstruction is suspected.
Blood sample should be taken immediately after obtaining vascular access to prevent dilution by fluid.
The prepared heparin (10–50 units/kg) is injected into the venous end of the catheter.
4.1.5.2 Patients with Arteriovenous Fistula or Graft
The operator washes his or her hands and prepares the items to be used for hemodialysis.
Any abnormalities of vascular access should be inspected by checking thrill, bruit, and pulsation.
The operator wears gloves to sterilize the arterial and venous areas of the arteriovenous fistula puncture site by rubbing a 2% chlorhexidine gluconate with 70% isopropyl alcohol or 70% alcohol and/or 10% povidone-iodine-soaked cotton ball in a circular pattern with a diameter up to 5 cm. Wait 3 min to allow it to dry if you use povidone-iodine.
The area to be sterilized is secured by spreading the sterilization wrap below the patient’s arm to the arteriovenous fistula site.
4.1.6 Cannulation (Needling)
- 1.
The operator should verify the absence of abnormalities in the patient’s vascular access (thrill, bruit, pulsation, redness, or swelling of arteriovenous fistula or graft) and inspect arteriovenous fistula for a cannulation site.
- 2.
Three types of cannulation techniques:
- (a)
Rope-ladder technique: The cannulation site should be at least 5–10 mm from the previous puncture site to promote proper healing.
- (b)
Buttonhole technique: This technique can be used only in the arteriovenous fistula . If there is a limited number of puncture sites available, insert the needle into the same site, and create a hole by the repeated needle insertion. This method may also be less painful.
- (c)
Area puncture technique: One or two areas of vascular access are repeatedly used for cannulation. Thus, repeated puncturing of the same site can weaken the blood vessel walls and produce aneurysm or pseudoaneurysm.
- (a)
- 3.
The operator should wear sterile gloves.
- 4.
Apply a tourniquet to facilitate needle insertion and prevent damage to the inside of the vessel. Even if the blood vessel appears thick enough, a rubber band is recommended to prevent damage of blood vessel.
- 5.
Needles can be inserted into the vessel with an angle at 20–35° for arteriovenous fistula and at 45° for arteriovenous graft using a needle because steep angles during needle insertion can cause injury at the site of vascular access . Thus, this procedure should be cautious . If flashback of blood occurs, the needle must be inserted with a less steep needle angle:
- (a)
For arterial sites, needle insertion should be at least 3 cm away from the arteriovenous anastomosis. For venous sites , cannulation site should be at least 5 cm away from the arterial needling site in order to minimize access recirculation.
- (b)
Blood sample should be taken immediately after access cannulation to prevent dilution by fluid.
- (c)
The syringe containing heparin with normal saline is connected to the venous needle line to remove the air and is then clamped to prevent an air embolism .
- (d)
Hemodialysis session will start 3 min after injection of the initial heparin into the venous needle line in order to allow the heparin to mix in the body.
- (a)
4.1.7 Complications of Cannulation
4.1.7.1 Infiltration
An infiltration is made if the needle makes more than one hole with going into the fistula and out the other side. If infiltration occurs before the heparin injection, the needle should be removed, and two fingers should be used to press an area at least 2.5-cm wide. If infiltration occurs after the heparin injection, perform dialysis without removing the needle if the hematoma size does not increase. If the hematoma size increases, remove the needle and apply an ice bag on the area.
When puncturing the venous site, the puncture should be made above the infiltration area whenever possible. If the puncture must be below the infiltration area, it should be 5 cm below it to prevent clots from being trapped in the needle.
4.1.7.2 Thrombosis or Stenosis of Vascular Access
Vascular access thrombosis is highly associated with dehydration and hypotension caused by excessive hemodialysis, slow blood flow from venous stenosis , hematoma due to inexperienced puncturing , excessive pressure during hemostasis after hemodialysis, sleeping on one’s arm, improper blood vessel selection, and initial use of immature blood vessels. Intimal proliferation is the main cause of stenosis, though vascular intimal damage from repeated puncturing and deficiency in the puncture technique are also causes.
4.1.8 Initiating Hemodialysis
The inlet of the patient’s arterial needle line should be connected to the end of the arterial line of the blood tube.
The blood pump should be started with low flow rate (usually 50 mL/min) and gradually increase (to 100 mL/min) until the entire blood circuit is filled with blood. At first time, the blood circuit is filled with priming fluid. After starting blood pump, the priming fluid inside of blood circuit is replaced by blood. During this procedure, the priming fluid is disposed through the other end of blood circuit.
After the extracorporeal circuit is filled with blood, the blood pump should be turned off, and the inlet of the patient’s venous needle line and the end of venous blood tube are connected to each other.
The blood pump is turned on after the lines are connected. At this time, the hemodialysis starts at a blood flow rate of 100 mL/min and is gradually increased to the patient’s target blood flow rate. If the blood flow rate is increased too quickly, symptoms such as hypotension , sweating, and chest discomfort can occur.
4.1.9 Monitoring of Parameters
4.1.9.1 Body Weight
Patient weight should be measured before and after hemodialysis to ensure that the target weight loss is being achieved. Dry weight refers to the post-dialysis weight when all or most of the excess body fluid has been eliminated.
4.1.9.2 Vital Signs
It is important to assess the changes of blood pressure from the previous state of the individual patient during hemodialysis. Treatment may be required for systolic blood pressure ≥160 mmHg or diastolic blood pressure ≥100 mmHg. If a patient’s pulse rate increases, it may relate with anemia, ischemic heart disease, and hypotension. In many cases, body temperature may increase during hemodialysis due to high dialysate temperature or an infectious condition. Peripheral vasoconstriction as a result of hypovolemia leads to reduced dissipation of heat from the skin.
4.1.9.3 Pressure Monitors on the Arterial Blood Line
Pressure can be monitored in the arterial blood line between patient’s vascular access (arterial) and the blood pump (pre-pump pressure monitor). Pressure in the arterial blood line usually ranges from −80 to −200 mmHg. When the blood volume is insufficient from the vascular access, the pressure in the arterial line (pre-pump pressure) could decrease, which causes an alarm to sound.
There are many causes of decreased pressure in arterial line: improper positioning of catheter, the presence of thrombus or fibrin clot inside of the catheter, abnormal position of the arterial needle, inadequately inserted needle, needle touching the blood vessel wall, hypotension , stenosis of the arterial anastomosis, twisting of the arterial line, and blood vessel collapse due to elevation of patient’s arm.
Management of decreased pressure in arterial line includes fluid administration, repositioning or reinsertion of the arterial needle, extension of the time with reducing blood flow rate , and revascularization of the stenotic vascular access.
4.1.9.4 Pressure Monitors on the Venous Blood Line
Pressure can be monitored in the venous blood line between the blood pump and vascular access (venous side) (post-pump pressure monitor). Normal pressure in the venous blood line is between 50 and 250 mmHg.
Causes of increased pressure in venous blood line are high arterial pressure, using a small-caliber needle, a clot in the venous line filter, stenosis or cramping in the venous side of the vascular access , improper insertion of the venous needle, and a twisted venous line.
When a clot is suspected in the venous line or filter, the dialyzer is washed with saline. If a clot is found in the dialyzer, the venous line is exchanged for a new one, and dialysis is continued after adjusting the heparin dose.
Obstruction in the venous needle or in a venous-side vessel can be assessed by checking for resistance while washing the needle with saline after separating the venous line from the blood pump, which has been temporarily turned off.
4.1.9.5 Venous Air Trap and Detector
The air trap is used to prevent air embolism when returning the blood back to the patient. Thus, the air detector should be turned on at all times during dialysis.
4.1.9.6 Food and Water Intake During Dialysis
Food intake during hemodialysis is not usually recommended. Pulmonary aspiration can be induced by hypotension or vomiting , while the food is being digested. But access to the amount of food and water intake during dialysis and the same amount of water should be removed during hemodialysis to achieve the desired post-dialysis dry weight.
4.1.10 Termination of Hemodialysis
Heparin infusion should be discontinued usually 30 min prior to terminating hemodialysis in patients with arteriovenous fistula or graft for the proper hemostasis after removing needles from vascular access.
Blood from the extracorporeal circuit should be returned to the patient’s body using normal saline. If the patient’s blood pressure is low upon termination of hemodialysis, more normal saline can be administered.
4.1.11 Removing the Needle and Hemostasis
If pressure is applied to the vascular puncture site to control bleeding before the needle is completely removed, there may be vascular injury caused by the tip of the needle, which can result in significant bleeding and delayed hemostasis. Vascular injury can be avoided by removing the needle at the same angle and in the same direction as it was inserted.
Hemostasis should be performed with sterile gauze, applying constant pressure for 10–15 min. Adequate pressure should be applied to the puncture site after removing the needles for proper hemostasis without clotting the vessels. If there is clotting in the vessel, there is no thrill and pulsation. After the operator sterilizes the site with disinfectant (e.g., povidone/iodine), sterile gauze should be applied to the puncture site. The patient can remove the gauze after 6–8 h.
Post-dialysis thrill and bruit are always assessed. A swollen fistula can be treated by applying a cold compress on that day and a hot compress on the next day. Compresses should be applied for 20–30 min, with a 1-h interval between applications.
4.1.12 Post-dialysis Evaluation
- 1.
Vital signs : Blood pressures in supine and standing positions, temperature , heart rate, and respiratory rate
- 2.
Changes of body weight:
The patient body weight should be measured before and after hemodialysis, and calculate the changes of bodyweight during hemodialysis. There may be a difference between calculated ultrafiltration volume and measured pre- to post- weight change, because of failure to account for the volume of administered fluid to the patient during hemodialysis, hyperalimentation, or oral fluid ingestion.
- 3.
Post-dialysis blood values for hemodialysis adequacy:
The method and timing of obtaining the blood sample may have an effect on concentrations of urea, potassium, and bicarbonate (rebound effect) at the end of hemodialysis.
Adequacy of dialysis, access recirculation , and cardiopulmonary recirculation based on urea nitrogen measurement can be affected by the method and timing of blood sampling. According to the KDOQI guideline, the post-dialysis blood sample for hemodialysis adequacy should be drawn after decreasing the blood flow rate (100 mL/min for 15 s) or stopping the dialysate flow rate (3 min) (Hemodialysis Adequacy 2006).
4.2 Hemodialysis Prescription
4.2.1 Rationale for Hemodialysis Prescription
Hemodialysis is a treatment that removes waste products (uremic toxins ) and extra fluid and balances electrolytes (sodium , potassium , bicarbonate , chloride, calcium , magnesium , phosphate , etc.) in patients with decreased renal function. To maintain physiologic state in hemodialysis patients and improve their quality of life, proper guidelines regarding many factors should be followed. In this chapter, prescriptions involved in the regulation of the blood flow rate, dialysate flow rate, dialysate sodium, potassium , calcium , magnesium , temperature , and the selection of a dialyzer are described.
4.2.2 Basic Mechanisms Applied to Hemodialysis Prescription
4.2.2.1 Diffusion
Diffusion is the movement of a solute from a high-concentrated compartment to a low-concentrated compartment through a semipermeable membrane (Fig. 4.2a). In hemodialysis, some solutes are removed from the blood compartment by diffusion (e.g., urea and creatinine), while others are added (e.g., bicarbonate in patients with metabolic acidosis and calcium in patients with hypocalcemia). The clinical significance of diffusion during dialysis is that low-molecular-weight substances, such as urea , creatinine, endotoxin fragments, uric acid, and ammonia, can be removed. Large molecules, such as albumin, red blood cells, and bacteria, cannot pass through the semipermeable membrane. Thus, the amount of diffusion depends on the degree of each solute’s concentration gradient between compartments and the molecular weight, electrical charge, and lipid solubility of the solutes. Other factors that determine diffusion are surface area, pore size, and numbers of pores (mass transfer coefficient to the solute) in the dialyzer membrane. Maximizing diffusion during dialysis requires a dialysate flow in the direction opposite the blood flow (counter current), a higher concentration gradient between the blood and dialysate compartments, a large surface area, and a high-flux membrane.
Fig. 4.2
Diffusion and the Gibbs-Donnan effect. (a) Diffusion is the movement of small molecules through a semipermeable membrane because of the concentration gradient of small molecules between the two compartments. Large molecules cannot cross the semipermeable membrane. The small black circles indicate small molecules, such as urea. The large circles indicate large molecules, such as albumin . (b) The Gibbs-Donnan effect occurs when nondiffusible albumin (an anion) attracts diffusible sodium (cation) in the blood compartment of the dialyzer and the attracted sodium crosses the dialyzer membrane less readily than sodium without albumin. Arrows indicate the diffusion of sodium
In hemodialysis, the diffusion of sodium ions is partially inhibited by nondiffusible protein in the blood compartment of dialyzer . Because positively charged sodium ions (cations) are attracted by large negatively charged proteins (anions) in the blood compartment of the dialyzer (Gibbs-Donnan effect), sodium will not cross the membrane as readily as small anions (Fig. 4.2b). This effect lowers sodium diffusion through the dialyzer membrane by 4–5% and varies with blood pH during hemodialysis (Santos and Peixoto 2008).
An error occurs when measuring plasma and dialysate sodium concentrations. Plasma consists of water (93% of the plasma volume) and nonaqueous components such as lipids and proteins (7% of the plasma volume). Water represents nearly 100% of the dialysate volume. Sodium is distributed only in the water component of plasma and dialysate. Over time, the plasma sodium level becomes 6–7 mEq/L higher than that of the dialysate. In practice, overestimation of plasma sodium and suppressed diffusion via the Gibbs-Donnan effect compensate for each other.
4.2.2.2 Ultrafiltration
When hydrostatic pressure changes in one compartment, water passes through a semipermeable membrane from the high-hydrostatic-pressure compartment to the low-hydrostatic-pressure compartment. That movement results in ultrafiltration (Fig. 4.3). Ultrafiltration is positively related to the pressure gradient between the blood and dialysate compartments, which is generated by a difference in the hydrostatic, osmotic, or oncotic pressure gradient. During hemodialysis, the hydrostatic pressure gradient produced by the blood pump induces ultrafiltration. Clinically, ultrafiltration is a critical mechanism for removing excessive fluid from a patient during hemodialysis. Decreased oncotic pressure in the blood compartment caused by pre-dilution can increase ultrafiltration during continuous renal replacement therapy.
Fig. 4.3
Ultrafiltration and convection. (a and b) Ultrafiltration is the movement of water through a semipermeable membrane because of the hydrostatic (a) or osmotic (b) pressure gradient between the two compartments. The large pentagons indicate osmotic molecules, such as sodium or glucose and open arrows indicate the movement of fluid (water). (c) Convection is the movement of small molecules through a semipermeable membrane during fluid movement. The small black circles indicate small molecules, such as urea, and open arrows indicate the movement of fluid (water)
4.2.2.3 Convection
During the movement of water, small molecules can pass through the semipermeable membrane. Convection is the movement of small molecules through a semipermeable membrane during fluid movement even when the solute concentration is the same in both compartments. Because convection can co-occur with ultrafiltration, the transport of small molecules might not be related to the concentration gradient of the solute (diffusion).
Some higher-weighted molecules, including β2-microglobulin, can be removed by convection. Convective removal of higher-molecular-weight solutes can be significant when using high-flux dialyzers (Fig. 4.3).
4.2.3 Parameters Related to Hemodialysis Prescription
Hemodialysis prescription is an integral area in nephrology. Many parameters should be considered in prescribing hemodialysis, and all hemodialysis prescriptions must be modified to account for the individualized conditions of each patient. In particular, each hemodialysis patient’s electrolytes should be screened, and the dialysis protocol for each patient should correct any underlying or associated conditions. The parameters commonly used during chronic hemodialysis prescription are ultrafiltration; dialysis time and frequency; dialysate sodium , potassium , calcium, bicarbonate , magnesium , temperature , and glucose; the type of dialyzer; blood flow rate; and dialysate flow rate (Table 4.1). Prescriptions in hemodialysis may require a comprehensive approach based on medications, laboratory test findings, and patient conditions.
Table 4.1
Compositions of normal serum and dialysate for hemodialysis
Normal serum level | Dialysate level | |
|---|---|---|
Sodium (mEq/L) | 135–145 | 135–140 |
Potassium (mEq/L) | 3.5–5.0 | 2.0–4.0 |
Calcium (mmoL/L) | 1.12–1.32 | 1.25–1.50 |
Chloride (mEq/L) | 102–109 | 98–124 |
Bicarbonate (mEq/L) | 24 | 32–39 |
Magnesium (mmoL/L) | 0.7–1.0 | 0.5–0.75 |
Glucose (mg/dL) | 70–150 | 100–200, 0 |
pH | 7.4 | 7.1–7.3 |
4.2.3.1 Adequacy of Hemodialysis
Brief Summary of Hemodialysis Adequacy
A target single-pool Kt/V of 1.4 per hemodialysis session for patients treated thrice weekly is recommended.
The minimum delivered single-pool Kt/V is 1.2 per session for thrice weekly hemodialysis patients.
Small solute (urea) clearance is the best method for measuring hemodialysis adequacy , and Kt/V is the most commonly used measure. A target single-pool Kt/V of 1.4 and a minimum delivered single-pool Kt/V of 1.2 per hemodialysis session are recommended for patients treated thrice weekly. Adequacy of hemodialysis is described more in detail in the “Adequacy of hemodialysis” chapter.
4.2.3.2 Ultrafiltration (Amount of Fluid Removal)
Summary of Ultrafiltration Prescriptions
Determination of ultrafiltration volume from body weight before and after hemodialysis based on dry weight.
Ultrafiltration rate higher than 13 mL/kg per hour is not recommended due to increased mortality rate.
Diet education for dialysis patients: Low-sodium diet.
For patients with severe hypervolemia, additional prescription with more frequent or longer hemodialysis may be needed for volume control.
(Optional) Measurement of body fluid composition by bioimpedance analysis can be used for proper evaluation of volume status.
(Optional) Automatically regulating ultrafiltration volume based on blood volume monitoring via a biofeedback system significantly reduces the frequency of hypotensive episodes.
The amount of fluid removed by ultrafiltration varies according to patient condition, with a range of 0–4 L per hemodialysis session. Fluid removal might not be needed in a patient with adequate urine volume and no edema. Those prescribing ultrafiltration should consider: (1) cardiac function, (2) volume status before hemodialysis, (3) number of antihypertensive drugs, and (4) vascular or autonomic response. A large volume of fluid removal can cause muscle cramps , nausea , vomiting , hypotension, decrease in residual renal function, or cardiac damage (Table 4.2). One report demonstrated that a 1 L increase in ultrafiltration was associated with a 5.1-fold increased risk of hemodialysis-induced cardiac injury (Burton et al. 2009). An ultrafiltration rate higher than 13 mL/kg per hour significantly increased the all-cause of mortality rate in the US-based Hemodialysis (HEMO) Study (Flythe et al. 2011). Therefore, an ultrafiltration rate lower than 13 mL/kg per hour is warranted during hemodialysis. To maintain hemodynamics in physiologic state, minimizing the ultrafiltration rate is recommended.
Table 4.2
The effects of high and low ultrafiltration rates
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