Due to the Joint Commission inspection of New York - Presbyterian this week, our involvement in clinical shadowing was limited. On Monday, I did have the opportunity to observe an aortic valve replacement.
This surgery was actually a little difficult to understand, because none of the surgeons, nurses, or technicians were willing to explain what was going on, despite there being an approximately 30 minute window during which everyone just stood around and waited. I tried asking the technician operating the bypass machine what they were waiting for, to which she replied, "Go ask somebody else. Can't you see I'm working? I'm busy here." Minutes later (and throughout the surgery, actually), I saw her chatting and joking with her colleague sitting beside her.
Thankfully, there was a medical student present who was also observing the surgery. She wasn't entirely sure of the procedure, but she explained to me what she knew, which helped me understand why everyone was just waiting. Because they were stopping the patient's heart, they wanted to cool the body so as to reduce metabolism, and thus minimize cell death. She wasn't sure why the surgeons decided to stop blood flow throughout the entire body except to the brain, as she told me that the bypass machine is usually used to pump blood continuously through the rest of the body during the surgery.
We asked the anesthesiologist if we could watch the procedure from her side, because we had already spent an hour just staring at backs of surgeons operating on the patient, but not the surgery itself. The anesthesiologist took pity on us, and allowed us to take turns watching the surgery up-close. Because of this, I finally got a glimpse of the patient's heart, which took me some time to identify because it just appeared to be a massive lump of fat.
During the surgery, I saw the bag of cardioplegia solution that was used to induce cardiac arrest. I was unable to get someone to explain to me how that worked, so I did a little search online and found some information on http://www.drugs.com/pro/cardioplegic.html.
Apparently, cardioplegia is induced by varying the ion concentrations in the heart muscles. The ion that precipitates cardiac arrest is potassium. The swiftness of the arrest induction preserves adenosine triphosphate (ATP) for myocardial contraction when the heart is made to function again. Magnesium ions are used to inhibit a myosin phosphorylase, further conserving ATP stores. A low calcium ion concentration is used to maintain cell membrane integrity. While sodium and chloride ions do not produce cardiac arrest, they maintain "ionic integrity of myocardial tissue", and electroneutrality of the cardiopledic solution, respectively. Finally, bicarbonate anions are used to counteract the metabolic acidosis resulting from ischemia.
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