Thursday, July 12, 2007

Computerized Perfusion Circuits

Vitrification perfusion circuits should be monitored for the following parameters:

1. Pressure

2. Air emboli

3. Reservoir level

4. Temperature

5. Concentration of the vitrification solution.

Computerized perfusion systems, have been around for decades, in the form of heart-lung machines. Though these may not turn out to be the ideal systems to build on, for vitrification perfusion, I think they are at least worth looking at. In speaking with people involved in cryonics, I’m not sure many people realize exactly what a heart-lung machine is, or does.

Typically, a heart-lung machine consists of 3-5 pumps that are monitored, and servo-controlled, by a computer. The computer is usually about the same size and shape as one of the pumps. The pumps, along with the computer are positioned on a rolling base that also accommodates a monitor, as well as holders for various perfusion components, (reservoirs, oxygenators, filters, etc.).

Cables are connected between the computer and the pumps. Desired parameters are entered into the computer. For instance, the computer can be set to alarm if pressure in a circuit exceeds 150mmHg, (or any other set value) and/or to turn off one of the pumps and clamp the associated lines, if the pressure in that pump’s circuit exceeds a higher value, (such as 200mmHg). Defaults for values such as these are simple to program, and easy to adjust, or override, during a case, if necessary.

The computer is not restricted to monitoring the perfusion circuit; you can monitor a variety of inputs such as patient temperatures and pressures.

There are pumps designed to deliver increasing/decreasing concentrations of certain solutions, such as the cardioplegia solutions used to stop the heart, during open-heart surgery. This may be of use, in the ramping of the vitrification solution concentration.

Someone who is familiar with Alcor has taken a lot of time to graciously explain to me why that company has approached their circuit the way they have. At this point, I feel they are doing what is best for their institution, given the history, their goals, their budget, and a few other factors. However, I think even they would agree that, if they were starting at “Square One,” and they could afford to write a check for a new heart-lung machine, they might take a different route.

I feel starting with a heart-lung machine that will measure, display and respond to four of the five desired parameters is a lot more practical than started from scratch. I have not priced heart-lung machines, recently, but I would estimate the cost of a new one with quite a few whistles and bells, to be in the neighborhood of 100,000K. That’s probably not as much as it would cost to have someone buy all the components and program a comparable system. Also, it is often possible to get used, or refurbished, models for much less. I think this course of action is at least worth exploring for companies that are just beginning to work toward the goal of vitrification.

***Please note: This article contains ideas and suggestions based on my education and my decade of experience as a clinical perfusionist in heart surgery. I have not participated in any cryonics procedures, and I have a lot to learn about the vitrification process. I am open to any, and all, constructive comments and criticisms.


Phil said...

What's the most essential difference between what Alcor's perfusion machine and a standard heart lung machine?

Melody said...

I hope to attain more details than I already have, regarding the Alcor cryoprotectant circuit, (not to be confused with the washout circuit), soon.

The main difference is that heart lung machines come with the safety features I mentioned in regard to automatic clamping of the lines and shutdown of the pump, in the event air is detected in the lines, or a critical pressure that might blow the circuit apart is exceeded.

Alcor is working toward monitoring the concentration of the cryoprotectant agent and adjusting the dosing, accordingly.

As I wrote in my post, for a company starting from scratch, it might be wise to start with a heart-lung machine which provides a lot more safety features than Alcor has, and build a stand-alone system for the monitoring and administration of the cryoprotectant.

Phil said...

So the most critical distinction seems to me to be the safety features that alert users to air in the circuit and too much pressure.

Does SA have a standard heart lung machine? I can't remember that specifically after all the CF posts.

Melody said...

I think the main distinction would be that the features of these machines are fully integrated, not put together, piecemeal, as those systems currently being used in cryonics are. No doubt Cobe-Sorin, Sarns, Medronics and other companies that sell perfusion equipment have spent many decades and billions of dollars designing, building and testing this equipment. Heart-lung machines have proven performance in millions of surgical cases. Maybe comparing buying a Ferrari, as opposed to building your own car out of parts from a variety of sources, would be appropriate. ;)

No, SA does not have a heart-lung machine. When I suggested to Saul that we get one and find a way to add monitoring of the concentration of the cryoprotectant, and any other features we might want, he was all for it. However, Charles was sure we needed to design and build our own, without even looking at the heart-lung machines.

Did I mention charting? Newer heart-lung machines feature automatic charting of temperatures, flow rates, pressures, etc.