The Ultimate Guide to Assisted Venous Drainage

This article was written as a basic guide to Assisted Venous Drainage (AVD). The techniques and results described in this article should be taken merely as suggestions and should be followed only at your own risk! While many of the techniques are currently used at one center or another, no one technique is being endorsed.  We are currently aware of three primary methods of “assisting” the venous flow from the patient. 

1. Placing a non-occlusive pump in the venous line
   
2. Vacuum applied to a cardiotomy
   
3. Modification of and use of a roller head to provide controlled occlusion and limited negative pressure
   Some centers are also using dual venous lines for certain types of applications. 

Primary uses and applications of AVD:

1. Heartport
   
2. Operations requiring femoral cannulation
   
3. Minimally invasive Valve Surgery
   

   
   

   a. Requiring bi-caval cannulation
   b. Requiring single atrial cannulation
   c. Requiring femoral cannulation

   
   
4. Normal Coronary Artery Bypass or Valve Replacement
   
5. Any Time Small Venous Cannulae Are Used
   
6. Lower Half Mini sternotomy cases where the atrium is cannulated via the internal jugular
   
7. Prime reduction;  using smaller venous lines and initiating bypass with an unprimed venous line

Vortex Pump Assisted Venous Drainage

Using a Non-Occlusive vortex type pump (eg. Medtronic Biomedicus) in the venous line is  the most common method of assisting venous return. A favorite term for this technique is KAVD or Kinetic Assisted Venous Drainage. This method is accomplished by placing a Biopump (usually a Biomedicus) in the venous line between the venous cannula and the venous reservoir. An effective way to do this is to create a shunt in your venous line by placing 2 Y connectors in line (facing in opposite directions) and placing the bio-head in the diverted blood path. (See Figure 1.)

Clamping the venous line in the right place (shunt line) then diverts blood through the bio-head, while removing the clamp allows for free venous flow. The bio-head can also be placed in the venous line without a shunt, but using a shunt can be beneficial in case of massive air influx to the bio-head. 

The “Y’s” in the venous line can alternatively be placed and “stubbed” out with 3/8″ connectors. Leaving each stump clamped, the Biopump (and it’s associated costs) can be withheld until its need is confirmed. The same effect can be attained by simply adding a small loop in the venous line. Keeping the loop clamped so that it doesn’t fill with blood allows a clean site to cut into and add a Biopump.

All of the HeartPort™ cases use some derivative of this system. The system works well and is sometimes used with and without measuring negative pressures. Those that measure venous line pressures (figure 1, DLP) have max pressures from n50 to n100mmhg with n80mmhg being a popular value. Simple DLP pressure monitors (the red boxes) work well for this purpose. Those that do not measure negative pressures generally have measured them in the past and are comfortable with the performance of the pump. The universal drawback to the Biopump seems to be the cost. 
 
 

Vacuum Assisted Venous Drainage

Vacuum assisted venous drainage is normally accomplished by attaching a regulated suction line to the cardiotomy and closing all vented ports (leave them capped). Vacuum regulators can be placed on the cardiotomy, and suction can be applied with either wall or sucker line. 

By using a regulator (Figure 2) to limit the negative pressure to n20mmHg to n50mmHg, one then has a nicely controlled suction unit. With VAVD, the negative pressure can be monitored from the cardiotomy  or the venous line.  Currently a proprietary systems are available, but most perfusionists are assembling the various components in their own design.  Sorin Biomedical, Gish,  Medtronic and Baxter are all sources of sealed cardiotomies. Since the suckers and vent are pumping into (read  positive pressure) the cardiotomy, it is possible to pressurize the system and pump air up the venous line.   Most commercially available cardiotomies. have positive pressure relief valves to ostensibly prevent this. In massive “sucker bypass nightmares” one might need to manually relieve the pressure. 

Additionally, vacuum could be inadvertently shut off (or stepped on) and with a massive amount of sucker return occurring simultaneously, one could  pump so much pressure in the cardiotomy that a massive air embolus could move up the venous line to the atrium. This is not likely, but this remains a concern. Lines open to air with a clamp  in place can provide a manual bailout of vacuum (or positive pressure). A separate cardiotomy for sucker return can also be used. 

Most often, a roller pump is used with VAVD, but a non-occlusive (Biopump) pump can also be used. What would happen if the negative pressures were high enough to pull air from the membrane?  This is an inherent concern regarding the flow when you are using a non-occlusive pump on a vacuum system.  However, as long as positive flow is maintained this is not a problem.  Also, if using a non-occlusive pump, you should remember to always release the vacuum before weaning from bypass.  Air can be pulled across the membrane depending on where you clamp the arterial line.  Drawbacks of this system include a frequent reluctance to apply negative pressure to the bypass system and an occasional occlusion of venous return from the vacuum.  This can occur when you are filling the heart by partially occluding the venous line.  This necessitates vacuum release momentarily.
 
 

Roller Pump Assisted Venous Drainage

Using a roller pump is probably the least frequently used method to provide assisted venous drainage. The principal is simple however. This method is achieved by placing a shunt line between the line going into the pump head and the line coming out of the pump head. When the pump is off and there is no clamp on this line then the line acts as a  passive venous line. Just clamping the shunt and turning on the pump head is, however, not a suitable method of AVD. With the shunt clamped and the roller on one QUICKLY finds pressures (negative) rising to a dangerous level. This occurs even without obstruction of the inflow. If the shunt line is only partially occluded (say 90%) then the identical negative pressures (measured via DLP on the negative side of the pump head) provide much greater flows. 

I’ve run the numbers with flow probes and pressure monitors throughout the circuit and it is repeatable. For example,  if you run the negative pressure to n60 with the shunt line totally occluded but without any inflow occlusion (30 French cannula in a pool) the flow is 2.9L. With the shunt only partially occluded and the negative pressure at the same n60 (our selected max) (of course Rpm’s come up because of the now under-occlusion) flow jumps to 4.2L. This is measured flow into the cardiotomy and the negative pressure is measured between the cannula and the roller head near the shunt takeoff. Negative pressures at the cannula remain 20 to 30mmhg (-30 to -40) lower. The partially occluded shunt line also makes collapse of venous wall and subsequent occlusion much easier to manage. Basically, one just dials whatever rpm’s give you an acceptable negative pressure. The roller head must be viewed as a device to apply negative pressure, not a true roller pump. 

A specialized use of this roller pump assisted venous circuit is demonstrated in figure 4. In this instance two separate venous lines are utilized in a Mitral Valve Repair. Because the relative flow through the SVC is substantially less than the flow through the IVC the assisted venous line is attached only to the IVC. When the assisted line is attached to both there is a substantial bouncing and repeated intermittent occlusion to the SVC line. This has been distracting to the surgeon. The assisted venous line (Figure 3 B) is passed to the field much as a sucker is passed. There is no need to prime it. Occlusion is set after cannulation. With the pump head running at about a 2L flow just enough occlusion to prime the line is utilized. This is accomplished with a clamp on the shunt. When bypass is instituted this clamp is removed as is the conventional venous clamp. After flow is established and the need for assisted venous drainage is established,  the shunt line  is partially clamped as demonstrated. The assisted pump head is rotated at a speed to produce –40 to –60 mmHg on the DLP. Prior to coming off bypass the shunt is opened and gravity drainage is used in the final stages.

AVD for Prime Reduction:

By initiating bypass with a smaller unprimed venous line one can eliminate a certain prime volume and circuit holdup.  The same result is obtained with the technique dubbed Retrograde Autologous Prime. A “Y” in the venous line near the cardiotomy allows one to drain the venous line of prime after cannulation. In this author’s experience the cases that don’t really need prime reduction seem to work the best. The LOL’s (little ole ladies) seem to need the volume replaced anyway. I have spoken with other perfusionists who swear by the technique. 
 

AVD Caveats, Opinions, Precautions:

Placing a vacuum on a bypass cardiotomy can be helpful and with a little practice can become routine. The technique is not without potential complications. Understanding when to release vacuum is critical. If one leaves a circuit clamped and “on vacuum” for a period of time (just for illustrative purposes) strange things happen.   Observe the tiny bubbles actually pulled into the line via the visible connector. This occurred at n45mmHg. 

In this instance a non-occlusive pump is simulated in the off position with vacuum still applied to the cardiotomy. The air (liters of it) is seen rushing up the pump line and into the cardiotomy. 
 

AVD Summary Table: