Week 3

Week 3 felt like it flew by! I cannot believe that we are almost halfway done with immersion already. This week, I saw three more CABGs, two TAVRs, and a thoracic surgery performed using cameras. One of the CABG’s that I saw this week was a re-operation. Performing open heart surgery for a second time is very challenging because scar tissue forms around the heart after the first surgery, and can be difficult to work around. Furthermore, after open heart surgery the heart can stick to the sternum, making it dangerous to re-open the chest in the conventional way. Because of this, Dr. Worku, one of Dr. Tranbaugh’s colleagues, used a special oscillating saw to cut through the sternum. The grafting of this surgery was also more difficult than normal, because some of the grafts typically used for CABG had already been used for the patient’s first CABG procedure. Additionally, I saw a CABG of a diabetic patient this week. The patient had significant calcification in their radial arteries that were used for the bypass. Though the patient still had an intact right internal mammary artery that may have been in better condition, Dr. Tranbaugh said that it is better to leave one internal mammary artery intact because diabetics have a higher risk of chest infection.

This week, I also had a long discussion with Dr. Tranbaugh about pressure measurements and catheters. In order to measure pulmonary arterial pressure, a Swan Ganz catheter is used. These catheters are able to travel through the heart using a balloon that floats with the blood. The balloon and catheter travel with the blood through the superior vena cava, right atrium, right ventricle, and pulmonary artery until they reach a small arteriole. The pressure here can be read by the catheter, and it is called the “wedge pressure”. Additionally, many of these catheters are equipped with a thermister, which can be used to measure cardiac output. Cardiac output, along with the patient’s body surface area, is used to measure their cardiac index, which must be kept minimally above 2 liters/min/m^2. Cardiac output can be measured by the thermister on the catheter if a cold saline solution is injected into the heart. The integral of the change in temperature with time can be used along with some other factors as an approximation of the output, or blood flow. Some of these concepts were a bit complicated to understand- I want to do a little more reading next week on pressure measurements and cardiac output, as we could potentially use this in our rat in-vivo MI models in the fall.

I also was able to see a camera-guided thoracic surgery with Dr. Reyes. The patient had significant fluid buildup in the lungs, and the procedure was to drain the fluid and attach the lungs to the chest cavity, preventing lung collapse. The entire procedure was performed thoracoscopically using cameras and a few small incisions, and took only an hour to complete. Dr. Reyes pointed out many anatomical structures of the lungs on the camera during the procedure- it was amazing how much could be seen by one or two small incisions!

One interesting concept that I learned about medicine this week was from a doctor I met while watching the TAVR cases, whose name escapes me. He said that in surgery, the enemy of “good” is “better”. This means that taking the time or the necessary steps to make a good procedure better can often put the patient at higher risk. This higher risk may come from increased time spent in the procedure or additional steps added. I am not used to this way of thinking, as my main experiences with clinical products have been on the R&D end, when I worked at GSK. There, it was always crucial that every step of manufacturing was perfect no matter the extra time or steps required. I carry this same mentality in my PhD research now. The doctor that I spoke with said these two ways of thinking are very different, but it is important for us, as engineers, to make our devices as perfect as possible.