CEREBRAL PERFUSION

Retrograde Cerebral Perfusion

PURPOSE:

To provide an alternative method of cerebral protection during procedures which require the cessation of cardiopulmonary bypass.  To provide an alternative method of cerebral protection during procedures where no other means of aortic perfusion, and thus cerebral perfusion, can or will be performed.  To provide an adjunctive therapy for the management of, and treatment for, cerebral embolic events (Air, atheromatous material, clot, etc.).

This procedure is routinely performed in conjunction with policies relating to Cardiopulmonary Bypass and Deep Hypothermia Circulatory Arrest.  Usage involves a variety of emergency procedures which include, but are not limited to, the following:   Massive Air Embolism, Aortic Aneurysm Repairs (ascending, transverse, or thoraco-abdominal), etc..  The above listed procedures and repairs cannot normally be performed successfully under standard operating conditions.  The technique of utilizing retrograde cerebral perfusion during circulatory arrest with profound hypothermia has proven to lessen the chance of neurological morbidity following the above listed surgical interventions or repairs.

INTRODUCTION:

Aortic aneurysmal disease with or without dissection is an extremely serious condition that carries an extremely high morbidity if not treated.  The surgical repair of this defect poses one of the greatest technical challenges in the cardiac operative suite today.  From 1957, when DeBakey, et al., first reported this procedure (Aortic Aneurysm Repair). Until the 1980’s, this procedure has carried with it a high morbidity and mortality rate.  The primary contributory components to this high morbidity and mortality are central nervous system ischemic damage and uncontrollable perioperative bleeding.

Deep Hypothermic Circulatory Arrest (DHCA) has proven to be one of the greatest advances in the treatment of this, as well as many other, technical challenges.  DHCA provides a dry, quit, motionless surgical field in which to operate while at the same time providing hypothermic protection to the major organs such as the brain and kidneys.  This protection is presumably achieved by the decreased metabolic activity and demand of these organs as a direct response to lower temperatures.    Studies have shown a limited period for DHCA, (40-45 minutes).  With this finding, techniques were created to try and increase the “safe period” allotted to DHCA with respect to recovery of cerebral function post-operatively.

Initially, distal clamping of the aorta was performed with selective cerebral antegrade perfusion of the arch vessels (innominate, left common carotid, or left subclavian arteries).  This technique does provide an increased “safe period” for the cerebral tissue but has been associated with a high incidence of intra/post operative problems.  The perfusion circuit required to perform antegrade cerebral perfusion has proven to be cumbersome and often provides excessive crowding in the already limited surgical field.  The result being distortion of the aortic lumen.  In the acute dissection patient, antegrade flow up the arch vessels often resulted in further dissection or increase fragmentation of the vessel wall with debris being forced (perfused) directly into the cerebral circulation.  This technique has therefore been associated with a high incidence of stroke.

Retrograde Cerebral Perfusion (RCP) has proven to be a safe and effective alternative in providing cerebral protection past the “safe period” while maintaining a simple, non-encumbered surgical field.  RCP is carried out through a superior vena cava cannula.  There is no need for additional cannula or clamps.  There is also no need for invasion of the cerebral arch vessels.  This technique provides maintenance of deep hypothermia in the cerebral tissues, decreases the risks of cerebral injury by reducing blood cell microaggregation, provides nutrients (metabolic substrates), and provides back washing of toxic metabolites, potential embolic debris, and/or air bubbles.

PROCEDURE FOR IMPLEMENTATION:

A.    Circuit Design:

1.    A variety of circuit designs have been reported in the literature or forwarded to our attention.  The following is a LIST ONLY and is not to be considered as all inclusive.  As a reminder, this technique is most often utilized in the presence of disease processes requiring femoral arterial cannulation.  The following descriptions are for ADULT perfusion circuits, and assume the use of a 3/8” arterial line, and 1/2” venous line.  Dual venous cannulation (SVC & IVC) is required.

a.    Femoral Arterial Line to SVC Cannula:

1.    All connections can be made on the surgical field. This procedure can be used in the presence of direct IVC and SVC cannulation or in the presence of direct SVC and femoral vein cannulation.  The procedure as written assumes direct SVC and IVC cannulation.

2.    Place 3/8” Y- connector in the arterial line distal to the arterial filter and approximately 6-8” proximal to the projected attachment site of femoral arterial cannula (A).

3.    Attach a piece of 3/8” tubing to the non-used arm of the Y-connector and clamp the tubing (A’).

4.    Have the surgeon approximate and cut 3/8” length to the end of the SVC cannula, after the cannula has been inserted into the SVC.

5.    Place a 3/8” Y-connector in the 3/8” tubing (A’) in the most straight forward fashion.  Your connections should be made with the intention of connecting the SVC cannula to the base of the 3/8” Y-connector and A’ to one arm of the connector.

6.    To the unused arm of the Y-connector, attach a 6”  piece of 3/8” tubing and clamp the tubing (V’).

7.    In the venous line (V), place the standard venous connector (1/2 x 3/8 x 3/8).

8.    Attach the 6” piece of 3/8” tubing described in #6 above (V’) to one of the 3/8” arms of the venous line connector.

9.    Insert the SVC cannula and attach to the bottom of the 3/8” Y-connector which is positioned on the arterial line extension (A’).

10.    Insert the IVC cannula and attach to the non-used 3/8” arm of the venous connector.

11.    Insert the femoral arterial cannula and attach to the arterial line (A).

**    Be sure that ALL tubing and connectors are de-aired prior to initiating CPB.

**    Clamps should remain on the arterial line extension (A’) while conducting normal CPB and the cooling/warming phases of DHCA. **

12.    Initiate CPB and DHCA procedures in the usual fashion.  Conduct cooling, flows, and drug administrations as per written protocol and surgeon preference.

13.    When desired core temperature has been achieved, initiate the exsanguination portion of the DHCA protocol by placing a clamp on the arterial line while leaving the venous line open.

**    The surgeon should place a tubing clamp on the 6” piece of arterial tubing where it is attached to the femoral arterial cannula at the same time.

14.    When adequate drainage of patient volume has been achieved (DO NOT ALLOW THE CVP TO REACH ZERO OR GO NEGATIVE), place a clamp on the venous line at the pump location.

15.    Ask the surgeon to visualize the SVC cannula and the femoral arterial-SVC tubing (A’) to assure an air-free environment.

16.    Have the surgeon place a clamp on the 6” piece of 3/8” tubing connecting the SVC connector to the venous line (V’) and remove the clamp off of the femoral arterial-SVC tubing (A’).

NOTE:  In this configuration, there is no need to clamp the IVC cannula.  The decision to clamp the IVC or not is to be made by each individual account.

17.    If using a centrifugal pump, decrease the RPM’s to 800.

18.    Remove the clamp from your arterial line slowly (at the pump location while leaving the clamp on the femoral artery) and begin RCP across the bridged tubing into the SVC.

19.    Flows should be maintained between 200-500 ml/min. while maintaining the patient CVP < 25 mmHg.  Blood return to the pump is by cardiotomy suction.  The surgeon should visualize retrograde flow from the aortic arch vessels.  If flow is not visible, turn the pump off, clamp all lines and check for proper orientation and flow path from the arterial pump to the SVC cannula.

20.    The heater/cooler should be kept on the cold setting while not allowing the blood temperature to fall below 14C (as per DHCA protocol).

21.    When the surgical repair has reached the point where standard CPB is required, stop the RCP flow and place a clamp on the arterial line at the pump location.

22.    Have the surgeon:

–    place a clamp on the arterial bridge tubing (A’)
–     remove the clamp from the venous bridge tubing (V’)
–    remove the clamp from the femoral arterial cannulation site
*    if a clamp was placed on the IVC cannula, remove it at this time.

23.    At the surgeon request, increase pump RPM’s to ~ 1500, remove the clamp from the arterial line tubing (pump location) and begin forward flow into the femoral arterial cannula.

24.     After seeing a mild increase in the CVP (~ 5 mmHg), or at the surgeon command, the venous clamp may be removed from the pump location and normal CPB resumed.  Follow DHCA protocol for re-initiation of CPB ( Trendelenburg position with carotid compression).

NOTE:  Communication is critical at this time.  Repeat ALL commands to the surgeon prior to doing them and remain focused

25.    Rewarming is per standard protocol relating to DHCA and CPB.

b.    Arterial Line to Venous Line:

1.    All connections are made off of the surgical field (at the pump).

2.    Place a 3/8” Y-connector in the arterial line approximately 6-8” distal to the arterial filter.

3.    Place a 1/2” Y-connector in the venous line (in an easy to reach and convenient location) between the oxygenator and where the tubing attachment to the sterile field.

4.    Attach a 6” piece of 1/2” tubing to the unused arm of the 1/2” Y-connector.

5.    Place a 1/2” x 3/8” straight connector on the end of the 6” piece of 1/2” tubing.

6.    By using 3/8” tubing, attach the 1/2” x 3/8” connector  to the unused arm of the 3/8” Y-connector that was placed in the arterial line distal to the arterial filter.

7.    Prime circuit in the usual fashion.  The arterial-venous bridge may be primed by clamping the arterial and venous line distal the Y-connectors that were placed in each piece of tubing.

8.    Once you have assured that ALL tubing is primed and de-aired, place clamps on the arterial-venous bridge (double clamping of the A-V bridge is suggested for safety).

9.    Place clamps on the arterial and venous lines in the normal fashion.

10.    As stated in the previous technique ( a.) , femoral arterial cannulation will most likely be used.  Venous cannulation will consist of either direct SVC and IVC cannula or a combination of femoral vein and SVC cannula.

11.    Once cannulation has been achieved, initiate CPB and DHCA procedures in the usual fashion.  Conduct cooling, flows, and drug administrations as per written protocol and surgeon preference.

12.    When desired core temperature has been achieved, initiate the exsanguination by placing a clamp on the arterial line distal (patient side) to the 3/8” Y-connector (which you placed during the initial set-up) while leaving the venous line open.

13.    When adequate drainage of patient volume has been achieved (DO NOT ALLOW THE CVP TO REACH ZERO OR GO NEGATIVE), place a clamp on the venous line proximal (oxygenator side) to the 1/2” Y-connector which you placed in line during the set-up.

14.    Ask the surgeon to visualize the SVC to assure an air-free environment.

15.    Have the surgeon place a clamp on the cannula that is positioned to drain the IVC.  This will be found directly in the IVC or in the femoral vein.

16.    If using a centrifugal pump, decrease the RPM’s to 800.

17.    Remove the clamps from your arterial-venous bridge line slowly and begin RCP across the bridged tubing, up the venous line, and into the SVC.

18.    Flows should be maintained between 200-500 ml/min. while maintaining the patient CVP < 25 mmHg.  Blood return to the pump is by cardiotomy suction.

19.    The heater/cooler should be kept on the cold setting while not allowing the blood temperature to fall below 14C .

20.    When the surgical repair has reached the point where standard CPB is required, double clamp the arterial-venous bridge line.

21.    Have the surgeon remove the clamp from the cannula positioned in the IVC or femoral vein.

22.    At the surgeon request, increase pump RPM’s to ~ 1500, remove the clamp from the arterial line tubing and begin forward flow into the femoral arterial cannula.

23.     After seeing a mild increase in the CVP (~ 5 mmHg), or at the surgeon command, the venous clamp may be removed from the pump location and normal CPB resumed.

24.    Rewarming is per standard protocol relating to CPB.

c.    IVC Direct Cannulation with Retrograde Cardioplegia Cannula:

(This technique assumes the use of a blood cardioplegia circuit.)

1.    Set-up and priming of circuit is per standard written procedure.

2.    Initiation of CPB are per standard written procedure.

3.    Exsanguination portion of DHCA is per standard written procedure.

4.    After arterial and venous lines are both clamped, the surgeon may pull the retrograde cardioplegia cannula out of the coronary sinus and into the right atrium.

5.    The retrograde cardioplegia cannula may then be advanced into the SVC by manual manipulation.

6.    One or more of the following should be performed prior to initiating RCP with this set-up:

–    Remove the crystalloid tubing from the cardioplegia pump raceway and clamp, OR

–    Clamp the crystalloid tubing where it exits the cardioplegia pump raceway (not recommended due to the high flows which will be used), OR

–    In the presence of a “bridged” cardioplegia circuit, clamp the crystalloid line out and open the bridge in the circuit thus allowing both lines to be filled with blood.  This provides accurate flow measurements to the system.

7.    At the surgeon’s or institutional preference, it may be advisable to disconnect the cardioplegia cannula from the cardioplegia infusion line and clear the tubing of the cardioplegia solution which is still in the circuit.

8.    Be sure the temperature of your cardioplegia heat exchanger is set to maintain the desired level of cerebral hypothermia without inducing hypothermic injury to the tissues being perfused. Temperature of the RCP blood should not fall below 14C as is stated in the DHCA procedure.  **Be Careful, the cardioplegia circuit is capable of delivering the blood at temperatures of 4-8C.

9.    Cardioplegia system pressure should be monitored closely and automatic shut-off set for the cardioplegia pump to correlate with a CVP pressure of 25 mmHg.

10.    Flows should be maintained between 200-500 ml/min. while maintaining the patient CVP < 25 mmHg.  Blood return to the pump is by cardiotomy suction.

11.    When the surgical repair has reached the point where standard CPB is required, turn off the cardioplegia pump and clamp the infusion line.

12.    Return the circuit to its normal position thus allowing the delivery of cardioplegia should it be requested or required by the surgeon.

13.    The surgeon will withdraw the cardioplegia cannula from the SVC and replace it in the coronary sinus, assuming more cardioplegia will be given.  If the administration of cardioplegia will not be necessary for the remainder of the procedure, the cannula may remain in the right atrium or removed from the heart.

14.    The standard SVC cannula will be replaced thus restoring the original venous drainage circuit design.

15.    At the surgeon request, increase pump RPM’s to ~ 1500, remove the clamp from the arterial line tubing and begin forward flow into the femoral arterial cannula.

16.     After seeing a mild increase in the CVP (~ 5 mmHg), or at the surgeon command, the venous clamp may be removed from the pump location and normal CPB resumed.

17.    Rewarming is per standard protocol relating to DHCA and CPB.

NOTE:    The technique just listed would provide a quick, easy, and excellent choice for the administration of RCP in the presence of Air Embolism.  In the presence of a 2-stage venous cannula, no SVC cannula manipulation would be required and the RCSP cannula could be place in the SVC in a very quick fashion.

V.    CONDUCT OF RCP:

A.    Flows:

1.    RCP flow is between 200 – 500 ml/min..

B.    Pressures:

1.    CVP pressure is monitored and should remain < 25 mmHg.

C.    Temperature:

1.    Blood temperature is to remain > 14 degrees centigrade as per  protocol.

D.    Blood Gas:

1.    All blood gas values are to be maintained according to protocol and Alpha-Stat blood gas management.

E.    Lab Values Monitored:

1.    ACT’s – every 30 minutes as per CPB protocol.

2.    ABG’s – every 30 minutes as per CPB protocol.

3.    Glucose – every 30 minutes during RCP and for the remainder of the procedure.