## Tuesday, January 31, 2006

Problem Solving (By Dr Who)

Here is a little something for you fellow nerds/geeks out there.

One of the things we keep track of in the OR for a really sick person with a bad heart is called Cardiac Output (CO), which is essentially how well the heart pumps blood to the rest of the body. It is defined as CO=SVxHR, where SV is Stroke Volume and HR is Heart Rate. Well, you can imagine HR is easy to measure, but how the hell do you measure the amount in milliliters of blood that the heart is pumping out?

Well, you can look at it with an ECHO machine. This is where you put a probe down someone's throat and use ultrasound to look at the heart. It is not very accurate and is very subjective. So they had to come up with another way to effectively measure CO that most anesthesiologists and Intensive Care Unit nurses could use. This is what they came up with.....

So you put a specialized catheter down one of the veins in a person's neck. This catheter goes through the right side of the heart and into the Pulmonary artery (which carries all of the blood in the body to the lungs to get oxygen) until it can go no further. (It actually has a balloon on the end of it that we inflate to help it "float" through the maze of the veins, heart and arteries.) You have to be careful not to "tickle" the heart with this catheter or you could send the heart into a fatal rhythm.

Then, we inject fluid through a hole in the first chamber of the heart. The fluid is of a known rather low temperature. The tip of this specialized catheter which is in the Pulmonary Artery measures the temperature of the blood. The temperature should go down as this colder fluid makes its way through the heart. Our computer then plots out the changes in temperature on a graph and the area under the curve is calculated. This number is then used to calculate the Cardiac Output. If the heart pumps poorly, then it will take a long time for the cooler blood to reach the end of the catheter. If the heart pumps well, then the cooler fluid will reach the end of the catheter very quickly with a small volume under the curve.

Pretty cool, huh?