RETROGRADE AUTOLOGOUS PRIMING OF CARDIOPULMONARY BYPASS CIRCUIT.

Maria Helena L. Souza*, CCP (Br) and Decio O. Elias**, MD.

*Perfusionist, Consultant in Extracorporeal Technology.
** Pediatric Cardiac Surgeon.
Rio de Janeiro - Brazil.

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

Bleeding associated with cardiac surgical procedures is a permanent concern for a number of reasons. Blood loss reduces the adaptative capacity of cardiovascular system to support the systemic and myocardial oxygen demand. Exposure to allogeneic blood products implies a significant risk of transmission of blood-borne infections and a number of other consequences, some of which may be lethal.

Bélisle and Hardy [1] have reported a review of more than 10,000 patients from 70 cardiac centers. The postoperative mediastinal drainage averaged 917 ml (400 to 2,200 mL). This figures must be added to the intraoperative blood losses which are difficult to estimate. Speiss [2] reported that the overall transfusion rate for the cases operated in 1990 at his institution was 82%.

Currently the practice of blood transfusion in cardiovascular surgery is a matter of concern of the surgical team, the patients and their families. Decisions regarding the use of methods that contribute to reduce or avoid transfusions are discussed on the basis of religious belief and the right to choose and have led some patients to refuse transfusion of allogenic blood or blood products under all circumstances.

In an attempt to eliminate or drastically reduce the use of allogeneic blood in cardiac surgery and cardiopulmonary bypass, cardiac centers have reviewed their practices. A number of techniques emerged and have been introduced into surgical protocols. General strategies developed to guide the prevention of blood transfusion are usually centered around a few ideas, such as:

1. Lowering the risks associated with bleeding
2. Use of meticulous surgical techniques
3. Optimization of CPB circuit and prime
4. Use of hemostatic agents
5. Begin medical treatment well in advance of upcoming surgeries
6. Maintaining a high level of critical care

These general ideas can be condensed into two broad groups of methods and techniques:

A. Methods and techniques devised to reduce blood loss;
B. Methods and techniques devised to decrease administration of allogeneic blood and blood products.

Reducing the degree of hemodilution and priming volumes have been demonstrated to be of paramount importance in the armamentarium of several surgical teams, in order to decrease bleeding and transfusion requirements. Autotransfusion, under several modalities have contributed to avoid the use of allogeneic blood and minimize hemodilution. A technique known as retrograde autologous priming is a variant of autotransfusion and is the subject of this review.

RETROGRADE AUTOLOGOUS PRIMING (RAP)

The first reference to the elimination of donor blood prime from the CPB circuit is credited to Panico and Neptune in 1960 [3]. These authors initially primed the circuit with 1 liter of physiologic saline. After arterial cannulation, a portion of the patient's blood was drained retrograde into the CPB circuit. Immediately after venous cannulation the patient's blood volume was routed into a reservoir located in the bubble oxygenator. The bloodless prime was helpful in reducing blood usage. DeBois and Krieger [4] modified this technique and incorporated it into their successful blood conservation program.

The use of patient's own blood to prime the CPB circuit has been shown to reduce hemodilution and transfusion requirements. It also maintains higher hemoglobin levels, and does not require extra disposables. Retrograde autologous priming is a very inexpensive technique [4].

The basic technique of priming the CPB circuit with autologous blood has been modified by several authors. A simple and practical modification has been reported by Balachandran [5] et cols. This technique has the advantage of using venous blood to prime most of the CPB circuit. It produces less hemodynamic instability and is performed as the first step to start cardiopulmonary bypass.

DESCRIPTION OF RAP

The CPB circuit consists of a hollow fiber membrane oxygenator with an integral isolated cardiotomy reservoir, roller or centrifugal pumps, an arterial line filter and a set of tygon tubing. Ideally the circuit should be designed to accomodate the lowest priming volume possible. The CPB circuit is initially primed with 1 liter of Hartmann's solution, 1 liter of gelofusine solution, and 5,000 units of porcine heparin. After removing the prebypass filter the volume remaining in the circuit is approximately 1,700 ml. The hematocrit during bypass is maintained above 22-24%, or even higher if no blood is collected for postpump autotransfusion.

In order to implement the retrograde autologous priming technique a one quarter-inch recirculation line is diverted off the arterial line into the cardiotomy reservoir. A side branch from the recirculation line is connected to an Y piece which ends into empties 1 liter prime bags. These collecting bags are suspended in the pump console IV pole. In this position the bags are at a higher level than the heart and eliminates the chance of entraining air into the aorta. Autologous blood will replace the circuit's prime by alternating clamps applied in the positions A, B, and C, during the various stages of the RAP (figure 1).

Figure 1. Modified from Balachandran S [5].

Step 1. Connecting the cannulas and arterial and venous lines.
After clear prime recirculation and prior to aortic cannulation, clamps are applied at positions A, B, and C, as represented in figure 1. The aortic cannula is connected to the arterial line, the clamps at positions A and B are removed and the aortic pressure is confirmed in the pressure gauge. After evaluating aortic pressure, the clamp at position B is reapplied. The venous cannula is connected to the venous line.

Step 2. Displacement of prime from arterial line.

The clamp at position C is slowly and partially removed to allow blood to flow retrograde from the patient's aorta into the arterial line, as illustrated in figure 2. This will displace a volume of approximately 150 mL of clear priming solution into the prime bag. When the arterial blood reaches the clamp at position B, the line clamp is reapplied at position A.

Step 3. Displacement of Prime from Venous Side.

After reappling the clamp in position A, the clamp at position B is removed (figure 3). The variable occlusion clamp on the venous line is slowly released. This will allow the venous blood to drain from the patient. At the same time the arterial pump is slowly rotated at a sufficient flow (400 to 500 mL/min) to maintain a constant level in the venous reservoir. When venous blood has displaced the priming solution in the venous reservoir, the membranes compartment, and the arterial line filter and reached the recirculation line, the line clamp is removed from position A and reapplied at position C (figure 4).

Step 4. Starting Bypass.

After the clamp is reapplied at position C, the venous line clamp is then widely opened and the pump flow is increased to establish full CPB. The time taken to displace the prime from the venous side is less than two minutes. If necessary, hemodynamic stability can be maintained during this period using a small bolus of phenylephrine (50 - 200 mcg) to maintain a systolic pressure above 100 mmHg. It is not unusual a small arterial pressure drop of 20 to 40 mmHg which usually resolves with the initiation of CPB. Cardiopulmonary bypass is conducted in the usual manner.

If fluids are required during CPB, the clear prime collected in the prime bags can be introduced into the circuit by the recirculation line.

COMMENT

Autotransfusion under the modality of RAP has only gained popularity during the last few years. A few authors have reported their techniques which depended on their CPB circuit design and protocols [6-8]. Low hematocrits during CPB are associated with increased risk of in-hospital mortality, intra or postoperative placement of an intra-aortic balloon, and return to the pump after initial weaning [7]. The technique above described has the potential to allow for the perfusionist to lower the hematocrit to a desired level by adding aliquots of clear prime from the prime bags. Another advantage of this technique is that most prime displacement occurs in an antegrade direction, from the venous line. This contributes to avoid hemodynamic instability at the start of CPB. The technique also can be considered as the initial steps to start CPB instead of a pre-CPB procedure.

CONCLUSION

Retrograde autologous priming is an invaluable adjunt to any protocol intended to minimize the use of allogeneic blood during cardiac surgery and cardiopulmonary bypass. The technique is a variation of autotransfusion and allows for the conduction of CPB with no donor blood requirements. This technique also allows for a controlled pump hematocrit which can contribute to reduce morbidity and the hospital mortality.

A variation of RAP is a frequent component of all protocols intended to eliminate the necessity of blood transfusions during cardiac surgery with the assistance of cardiopulmonary bypass.

REFERENCES

1. Bélisle S, Hardy J-F. Hemorrhage and the use of blood products after adult cardiac operations: Myths and realities. Ann Thorac Surg 1996; 62: 1908-1917.

2. Speiss BS, Gillies SA, Chandler W, Verrier E. Changes in transfusion therapy and reexploration rate after institution of a blood management program in cardiac surgical patients. J Cardiothorac Vasc Anesth 1995; 9: 168-173.

3. Panico FG, Neptune WB. A mechanism to eliminate the donor blood prime from the pump oxygenator. Surg Forum 1960; 10: 605-609.

4. De Bois, Krieger KH. The influence of oxygenator type ad priming volume on blood requirements. In Krieger KH and Isom OW. Blood Conservation in Cardiac Surgery, Springer-Verlag, New York, 1998.

5. Balachandran S, Cross MH, Karthikeyan S, Mulpur A, Hansbro SD, and Hobson P. Retrograde autologous priming of the CPB circuit reduces blood transfusion after coronary artery surgery. Ann Thorac Surg 2002; 73: 1912-8.

6. Cormack JE, Groom RC. Hematocrit prediction and preservation for cardiopulmonary bypass. http://perfline.com/ejournal/2002/jec0102.html.

7. Cromer MJ, Wolk DR. A minimal priming technique that allows for a higher circulating haemoglobin on cardiopulmonary bypass. Perfusion 1998; 13: 311-13.

8. Saxena P, Saxena N, Jain A, Sharma VK. Intraoperative autologous blood donation and retrograde autologous priming for cardiopulmonary bypass: A safe and effective technique for blood conservation. Annals of Cardiac Anesthesia 2003; 6: 47-51.