GUIDELINES FOR BLOOD CONSERVATION DURING ADULT CARDIAC SURGERY AND CARDIOPULMONARY BYPASS.

BACKGROUND

Cardiac surgery and cardiopulmonary bypass have placed a tremendous demand on blood banking facilities. Open heart surgery has historically been associated with a high rate of blood transfusion. Efforts to decrease such a burden have allowed for a reduction in the blood units transfused per patient, during the last decade.

The well known risks associated with blood transfusions have prompted the search for methods and techniques designed to further decrease the exposure of patients to homologous blood.

Religious belief and the right to choose have led some patients to refuse transfusion of allogenic blood or blood products under all circumstances.

Factors reinforcing the avoidance of blood transfusion:

Transfusion-transmitted infections ABO incompatible transfusion reactions Transfusion-associated immunomodulation: Increased infection risk Dissemination of malignant cells Negative effects of the storage lesion Dwindling blood supplies Increasing cost of haemovigilance Improved patient outcomes Evidence suggesting reduced overall costs Litigation Religious belief Motivation for more discriminating transfusion practice Health care team satisfaction Accomodates patient preference

OBJECTIVES

In today's multicultural healthcare system, patients who request alternatives to blood transfusion are not only moved by religious beliefs. Cardiac surgery with cardiopulmonary bypass can be performed without the administration of homologous blood as a result of the employment of several combined strategies. A comprehensive blood conservation program designed to avoid blood transfusion must be a team group endeavour, and should include all phases of treatment, from the preoperative period to the post hospital discharge. A coordinated multidisciplinary approach is central to the success of any blood conservation program.

The increased risk of transfusion associated with open heart surgery is predominantely related to the coagulopathy and hemodilution that occur as a result of the use of cardiopulmonary bypass to perform the operations. Conservation of red cell mass and prevention of coagulopathy are the most important objectives of a guideline/protocol designed to avoid blood transfusion.

General strategies developed to guide the prevention of blood transfusion are usually centered around a few ideas, such as:

Lowering the risks that are associated with bleeding Use of meticulous surgical techniques Optimization of CPB circuit and prime Use of hemostatic agents Begin medical treatment well in advance of upcoming surgeries Maintaining a high level of critical care

MINIMUM ACCEPTED HEMATOCRIT LEVELS

Mortality risks related to hematocrit levels during cardiac surgery have been disclosed from large series of cases. Based on this body of experience, a minimum hematocrit of 15% for normal risk patients (17% for high-risk patients) during bypass and 22% (24% for high-risk patients) postoperatively should allow for an adequate oxygen transport and delivery and should also reduce the risks of increased morbidity and mortality. Successful management of Jehovah's Witness patients has revealed a remarkable tolerance of severe acute normovolemic anemia. The tight adderence to a specific guideline will allow for the vast majority of cases to be performed with hematocrits above the minimum levels described. Most hospitals and blood bank facilities have stablished standards to the minimum accepted hematocrit on a surgical patient, and these values should be adopted by the cardiac surgical team in order to orient the efforts at a bloodless surgery and perfusion.

STRATEGIES TO AVOID BLOOD TRANSFUSION

1. PRE-OPERATIVE STRATEGIES

Check blood cell mass and blood coagulation. Correct anemia and investigate and treat any coagulation disorder.

1.1. Anemia type and etiology should be sought and corrected to the normal value or to the closest possible. A few drugs and nutritional supplements may be indicated, such as:

Iron (ferrous sulphate), folic acid, vitamin B12 and erithropoietin.
Nutritional adjustments should help to normalize hematocrit and hemoglobin values.

1.2. Coagulation disorders if present should be investigated and treated whenever possible.

Vitamin K1 administration, discontinuance of platelet inhibitors or changing to a short acting reversible platelet inhibitor may be necessary.

The majority of patients will have normal hematocrits (hemoglobin levels) and blood coagulation. These patients can benefit from erithropoietin administration in order to enhance their red cell production.

2. INTRA-OPERATIVE STRATEGIES

The main blood conservation goals during the intraoperative period of cardiac surgery are to minimize blood loss, and preserve both red cell mass and coagulation function. These can be attained with a meticulously conducted surgical technique and cardiopulmonary bypass.

2.1. Acute normovolemic hemodilution. Blood is collected from patients immediately after anesthetic induction and before starting the operation. After collecting the first blood bag, removed volume is replaced by cristalloids and colloids infusion, guided by the collected volume and by changes in heart rate and mean arterial pressure. Two to three units of autologous blood can be collected from an adult patient without significant side effects. During surgery the blood remains in the operating room, ready for use. This technique allows for the autotransfusion of blood rich in functioning red blood cells and platetets, and containing intact all clotting factors.

2.2. Administer an antibribrinolytic agent to minimize perioperative and postoperative blood loss. Aprotinin or tranexamic acid have been reported as equaly effective to reduce blood loss by an average of 50-60%.

2.3. Surgical technique. A crucial factor in "bloodless surgery" is the meticulous nature of hemostasis required during surgical dissection and procedure. Technical aids help facilitate this, such as electrocautery, argon beam coagulator, microwave coagulation scalpels, and topical hemostatic agents, according to the surgeon experience and preferences. Blood loss from surgical field can be minimal with a carefully performed surgical exposure, even during reoperations.

2.4. CPB circuit. Perfusion team should adjust the customized cardiopulmonary bypass circuit normally used in order to minimize hemodilution via circuit priming volume. The CPB circuit can be taylored to accomodate a prime of 1,000-1,200 ml of crystalloids.

2.5. Autologous priming. The use of autologous priming to replace most of crystalloids from the circuit will contribute to reduce the degree of hemodilution and mantain adequate oxygen transport during cardiopulmonary bypass.

2.6. Ultrafiltration (Hemoconcentration). Ultrafiltration should be considered as an excellent complement to remove the excess of water administered during autogenous blood collection. Either conventional or modified ultrafiltration can be employed with good results. With an ultrafilter in the circuit, at the end of operation the hematocrit can be on the 32--36% range.

2.7. Surgical hemostasis. After weaning from bypass, meticulous hemostasis is secured. Pump residual blood is administered as necessary to adjust the hemodynamic function and to increase hematocrit. Diuretics should be liberally used to eliminate the excess of water.

2.8. Anticoagulation. Heparin administration and its effect on clotting time should be criteriously monitored during the procedure. Protamin should be cautiously administered in a dose sufficient to neutralize the heparin effect. Heparin neutralization should be monitored by the ACT return to baseline.

2.9. Intraoperative blood cell salvage. Whenever available, intraoperative blood salvage may be performed by the use of a cell saver. Otherwise all blood aspirated from the surgical field returns to the circuit. Blood remaining in the circuit at the end of bypass can be immediately reinfused to the patient, to adjust hemodynamic function or alternatively it may be collected in a cell saver or in blood bags for a slower venous administration.

Autologous blood collected at the start of the procedure is administered as necessary to replace immediate losses and to increase postperfusion hematocrit.

3. POST-OPERATIVE STRATEGIES

Criterious postoperative monitoring is an important adjunct of the blood conservation protocol. Residual blood from the pump system and autologous blood are administered in order to replace blood losses and to increase the hematocrit. Shed mediatinal blood can be processed in a cell saver for subsequent red cell infusion or it can just be returned to circulation by venous administration.

After leaving the ICU, patients with a low hematocrit can be subjected to the same regimen recommended to treat preoperative anemia, as described in the topic pre-operative strategies.

An experienced team can conduct practically all of their adult patients throught cardiac surgical operations without the transfusion of a single unit of blood or blood product.

SELECTED READINGS:

Martyn V, Farmer SL, Wren MN, et al. The theory and practice of bloodless surgery. Transf Apher Sci 2002; 27: 29-43.

Lewis CTP, Murphy MC, Cooley DA. Risk factors for cardiac operations in adult Jehovah's Witnesses. Ann Thorac Surg 1991; 51: 448-450.

Rosengart T, Debois W. 5. Transfusion Alternatives for Cardiac Surgery. Chapter 7: Alternatives to Allogeneic Blood Transfusion. New York, 1998.

Hardy J-F, Bélisie S, Janvier G, et al. Reduction in requirements for allogeneic blood products: Nonpharmacologic methods. Ann Thorac Surg 1996; 62: 1935-1943.

Ovrum E, Holen EA, Abdelnoor M, Oystese R. Conventional blood conservatio techniques in 500 consecutive coronary artery bypass operations. Ann Thorac Surg 1991; 52:500-505.

Dalrymple-Hay MJR, Pack L, Deakin CD, Shephard S, et cols. Autotransfusion of washed mediastinal fluid decreases the requirements for autologous blood transfusion following cardiac surgery: a prospective randomized trial. European J Cardiothorac Surg 1999; 15: 830-834