Blood Conservation Summary

Introduction 

The necessity of blood conservation and the avoidance of using Allogeneic blood (donor blood) has grown tremendously in the past few years.  The danger of using banked blood has been recognized and there is a growing move to find new ways to conserve blood.  There is inherent risk of transmitting certain diseases and immunosuppression is unavoidable.  Practitioners are now aware that non-screenable transmittable diseases are a risk when allogeneic blood is given.  With this new awareness, blood use has dropped considerably and will continue to fall as new conservation techniques are devised.  Much of the decreased blood usage has come from perfusionists developing and utilizing ways to remove all blood from the perfusion circuit at the end of the case.  Manufacturers have also contributed to this reduction in allogeneic blood use.  Lower prime oxygenators, condensed circuits and other equipment are fast becoming the routine.  The standard of care has now become one that uses all measures to prevent allogeneic blood use.  Blood banks have benefited from decreased usage by having more blood available for emergencies.  Patients have benefited with reduced exposure to the hazards inherent in banked blood. This article focuses primarily on perioperative blood management techniques which can be implemented in cardiac surgery.

Blood Management Program

The cornerstone of all blood conservation efforts should be a well-conceived, multidisciplinary, multimodality approach to blood conservation.  Such an approach should incorporate documented policies and procedures, rigid transfusion criteria, evidenced-based techniques (described herein) and most importantly the organization of a blood management committee to oversee all aspects of the program.  Individuals participating on the blood management committee should include physicians, blood bank directors, nursing supervisors and perfusionists.  It is recommended that individuals participating on the committee obtain certification from the International Board of Blood Management (IBBM) to become certified Perioperative Blood Management Technologists (PBMT) or Perioperative Blood Management Specialists (PBMS).

Autologous Blood

The patient’s own blood, autologous blood, eliminates many of the disadvantages of allogeneic blood.  Many patients will accept their own blood, but will not accept transfusions of allogeneic blood.  Some adherents to the Jehovah’s Witnesses religion will allow this type of transfusion.  As mentioned above, the risk of disease transmission is eliminated.  Cross-matching errors are also eliminated with the use of autologous blood.  Some patients are difficult to obtain blood for if they have multiple red blood cell antibodies or unusual blood phenotypes.  There are several ways that the patient’s blood can be salvaged and returned to the patient. 

 

PERIOPERATIVE BLOOD CONSERVATION TECHNIQUES

Autologous Blood Donation

The patient can donate his or her blood in preparation of a major surgery.  The procedure is excellent for non-emergent cases where there is enough time to employ the technique.  The patient’s blood is collected gradually over the weeks before surgery.  The patient is brought in every two weeks and a small amount of blood is removed and stored.  The total amount collected this way is usually about the equivalent of 2 units of packed red blood cells.  Major drawbacks of this system are the time and numerous visits required to accumulate a sufficient amount of blood.  Costs of drawing and storing the blood can also be considerable. 

In heart surgery, another method of obtaining the patient’s blood can be adopted.  Blood can be removed just prior to starting cardiopulmonary bypass (CPB).  After heparinization and cannulation, blood can be removed by way of the venous line and a Y connection to a collection bag.  The venous line is unclamped and the priming volume is allowed to enter the venous reservoir.  When the patient’s blood reaches the Y connection, a clamp is applied and the blood is diverted to the collection bag.  The patient can be infused through the arterial cannula to maintain adequate arterial blood pressure.  The process is done slowly to prevent arrhythmias and drops in blood pressure.  One of the safety features of this technique is that, in most cases, CPB can be initiated immediately if the patient becomes unstable.  The patient is heparinized for the bypass procedure before the blood is removed, therefore the blood is fully anticoagulated when giving back to the patient after CPB.  Heparin in this blood must be taken into consideration when the protamine reversal dose is given.  The blood collected this way retains all clotting factors. This blood contains platelets that will not be exposed to the pump circuit and bypass.  Some teams perform ANH or Acute Normovolemic Hemodilution and remove blood from the central line or 14 gage IV line and replace this blood with a colloid.  Removing blood in this manner can require more time but also eliminates the safety of being able to initiate CPB if done before cannulation.  Blood saved before CPB is begun and reinfused after CPB has been shown in some studies to decrease post-op bleeding and coagulation defects.  This method is valuable in preventing allogeneic blood administration.  The problem with removal of blood in the OR is that the patient must have a high enough hematocrit to allow removal of the blood.  With the dilution of CPB small patients or those with a low hematocrit are not candidates for this procedure.  Some surgeons are reluctant to use this method because of the dangers associated with ischemic heart disease.

Autologous Priming

In on-pump cardiac surgery, another technique can be employed which is essentially the opposite of collecting and saving pre-bypass autologous blood.  With this technique, the crystalloid in the CPB circuit is removed and replaced with the patient’s own blood just prior to initiation of CPB.  This method is called Autologous Priming, and it can decrease the amount of hemodilution that would normally take place upon initiation of CPB, thereby preserving the patient’s hematocrit.

Removal of the crystalloid via autologous priming can be done at virtually any point in the CPB circuit, however it must be done slowly and must be carefully coordinated with anesthesia in order to ensure that the patient’s blood pressure is not compromised.  The recirculation line on the oxygenator is the most commonly used site for removal of the crystalloid.  Blood from the patient is allowed to flow into the CPB circuit from either the venous line (Autologous Priming) or retrograde from the aortic line.  When done in the retrograde fashion from the aortic line, it is typically termed Retrograde Autologous Priming or “RAP” for short.  The displaced crystalloid can be collected in a bag or diverted to the cell saver for processing.  Either way, the volume of the displaced crystalloid should be measured and subtracted from the initial priming volume for fluid balance calculations.  Autologous priming is most effective on patient’s who have sufficient volume to tolerate the removal of 500ml-1500ml or their blood volume.  Patients with high pulmonary pressures and enlarged hearts tend to tolerate the procedure particularly well.  In the event that there is insufficient volume to operate the heart lung machine safely after initiation of CPB, the removed crystalloid can always be returned to the CPB circuit.

Autotransfusion Machine (Cell Washer)

These machines have become common place in heart surgery and their employment is likely to increase as new uses are conceived.  These machines allow the salvage of blood that is apparently lost.  Blood on the surgical field can be aspirated with a special suction line into a holding cardiotomy.  In addition, blood remaining in the CPB oxygenator and circuit, can be salvaged at the end of the operation.  Blood can also be aspirated from post- op drainage devices such as chest tube collection containers.

The main functions of the cell saver are collection in a heparinized container, concentration of the fluid via centrifugation, washing the red cells and diverting the washed RBCs to an infusion bag (See Animation Below).  The aspiration tube used to suction blood from the surgical field is a double line with heparinized saline constantly dripping down the line and back to the collection cardiotomy with the aspirated blood and fluid.  The central component of the processor is the centrifugal bowl, known as a Latham bowl or Baylor bowl.  Fluid from the cardiotomy containing blood enters a tube in the middle of the spinning bowl and travels to the bottom.  The fluid moves to the outside where the heavier red blood cells separate and concentrate.  The leukocytes and platelets form a buffy coat layer on top of the red blood cells.  The plasma including clotting factors, plasma proteins and waste fluid accumulate on top of this layer.  An exit tube on top of the bowl allows the plasma and effluent waste to leave the bowl to a waste bag.  A sensor recognizes when the red blood cell level has risen to the top of the bowl and a wash with normal saline begins.  The normal saline wash removes any debris or other harmful elements.  It is important not to use sterile water for this wash as hemolysis would occur due to the hypotonicity of the water.  Next, the blood is emptied to a holding bag for reinfusion. 

The hematocrit of the processed cells suspended in saline is over 50% (possibly as high as 70%).  The  volume of a processed bowl in the adult set is 225 ml.  Smaller bowl sizes are available for pediatric patient’s or low blood loss procedures.  The effluent that is removed contains platelets, plasma fractions, leukocytes, free hemoglobin, heparin, saline and debris.  The blood should be infused through a filter within 6 hours of salvage if kept at room temperature.  A danger of the use of the processor is that insufficient washing may leave heparin in the red blood cells to be reinfused and bleeding may result.  Slow washes are better than fast washes for removing contaminants.  Often large volumes are processed in cases of massive bleeding and it should be remembered that the product returned is devoid of platelets and clotting factors.  It would be necessary, in this case, to also administer platelets and fresh frozen plasma.

Contraindications of Processor Use:

• Gross contamination or Infection
  
• Malignancy of the surgical area
  
• Cesarean Section (Amniotic fluid should not be aspirated.)
  
• Use of topical hemostatic agents

Hemostatic Agents That Preclude Processor Use:

• Antivene
  
• Gelfoam
  
• Helistat
  
• Hemopad
  
• Instat

Detrimental Factors Affecting Processor Use:

• Antibiotics aspirated should be washed slowly and thoroughly.
  
• Betadine solution should not be aspirated due to hemolysis.
  
• Hot solutions should not be aspirated due to hemolysis.
  

Other Uses of Blood Processors:

Uses of these machines other than the traditional blood salvaging have increased recently.  Blood left in the pump circuit can be salvaged.  The blood can be pumped through the arterial cannula after the case into the processor sucker.  There the blood enters the reservoir and can be processed.  It is necessary to flush the circuit with priming solution to remove all the blood.  This leaves a pump and circuit that is primed and ready to use in case of the reinstitution of CPB.  The blood salvaged from the circuit is excellent for processing due to the lack of contamination and debris. The only drawback is the loss of platelets, plasma proteins and clotting factors.

Relatively new advancements in the field of autotransfusion are devices which allow for automatic processing of wound drainage postoperatively.  These devices are capable of processing, washing and returning shed blood that is suctioned from surgical drains postoperatively.  These devices are particularly effective in cardiac surgery, where postoperative blood loss can be significant.  An example of such a device is the CardioPAT manufactured by Haemonetics Corporation.

Use as a rapid infusion device is another capability of processors.  The processor tubing is adapted by disconnecting the tube before it enters the centrifugal bowl.  This tubing can be connected to a 1/4 in. line that leads to various IV sites for infusion.  The air detector with automatic stop makes an excellent safety feature during this adaptation.  The speed of the pump should be low to avoid over-pressurizing the IV sites.

Plasmapheresis and Plateletpheresis

Plasmapheresis and plateletpheresis are terms used to describe the removal of those portions from whole blood while separating the red blood cells and giving them back to the patient.  The products may then be given to the patient after bypass.  The purpose of this procedure is to conserve the platelets and other clotting factors while not reducing the hematocrit of the patient during bypass.  The processor is used for this procedure.  Uncontaminated blood is drawn into the centrifuge where it is spun to separate the products.  The products are collected in transfer bags where ordinarily the waste liquid is contained and the red blood cells are collected as usual.  The collected RBCs can be given back immediately or held until later.

Hemoconcentrators 

Excess fluid can be removed from the patient’s vascular system with a hemoconcentrator.  The hematocrit of the patient will increase as the fluid is removed.  During CPB these devices may be connected to the pump circuit and are a great asset for fluid management.  There are no absolute contraindications to the use of these devices as there are with the autotransfusion blood processors-washers.  Perfusionists do not ordinarily use the dialysate irrigating solution to affect electrolyte control.  The fluid removed is plasma water along with solutes.  Other solutions can be added to the pump volume to control electrolyte concentrations if necessary.  This is often used for control of potassium.  Plasma water, potassium and other electrolytes are removed and normal saline is added to reduce the amount of circulating potassium.  If a normal saline irrigating dialysate was used  the process might be faster because the gradients of solutes in the solution and the blood would be different.  However, this is usually not necessary during CPB.

The hemoconcentrator works by forcing fluid and small solutes across a semi-permeable membrane.  The formed elements of the blood are too large to cross this membrane.  Globulins and other large proteins (fibrinogen and albumin) are also not removed.  The sizes of the pores range from 15,000-55,000 daltons and this allows sodium, potassium, chloride, creatinine, urea and glucose to cross the membrane for removal.  Heparin can also be removed or concentrated in small amounts.  The size of heparin is 6,000-20,000 daltons, therefore a portion will cross the membrane and activated clotting times should be monitored often.  The amount of circulating drugs may be decreased by the removal of the plasma and this should be considered when determining the patient’s response to medications.   

There are many places to incorporate the device in to the pump circuit.  Some perfusionists let the pressure of the arterial line provide the pumping force to remove the fluid.  This is done by a Y connector and tubing coming off the arterial line.  Pump flows should be increased to account for the flow that is diverted to the hemoconcentrator.  Care should be taken to clamp this line when the pump flow is decreased due to the backflow that can occur.  Other perfusionists desire a dedicated pump head to control the flow through the hemoconcentrator.  This allows more control and avoids problems with diminished arterial pump flow.  The disadvantage of this technique is that it requires a pump head for use.  A way to have the ability to quickly utilize a hemoconcentrator is to have a Y connector with a short length of tube built into the pump circuit.  This tube comes off the arterial line and is kept clamped if use of a hemoconcentrator is not needed.  If it becomes necessary to hemoconcentrate, one can be connected quickly to the tube.

The residual blood left in the pump circuit can be salvaged and concentrated with the hemoconcentrator after CPB is completed. New technologies such as separate hemoconcentrating reservoirs allow for quick, safe and  reproducible blood salvaging with quality control and also keep the circuit safely primed with chased crystalloid fluid.  An example of such a device is the Hemobag manufactured by Global Blood Resources LLC.  Alternative methods can be used where the blood is circulated through joined arterial and venous lines or through an A-V bridge and the hemoconcentrator is allowed to filter till you get to the bottom of the venous reservoir.