# March 2013

Written by Sonia Spindt (class of 2012-2013)

I thought I could forget about physics after I took the final for that class last spring. Most of the topics covered in my class seemed to be surrounded by facts that I, nor any other pre-med student, would ever use again after taking the MCAT—there was always a question of relevance present when studying physics’ material. However, Dr. Harken surprised me when he began his morning lecture with the question, “what is Ohm’s law?” Sadly, my mind drew a blank! Thankfully, the residents remembered that the equation simply states R=V/I.  My mind quickly reverted back to last spring and I immediately began to struggle with an issue of relevance here. How could a patient’s health fit into this equation that talks about the behavior of circuits? According to Dr. Harken, Ohm’s law can be modified to discuss Systemic Vascular Resistance (SVR) and its roll in shock.  In this case, the resistance found in the systemic vasculature of a patient would be equal to (Mean Arterial Blood Pressure (MABP)-Central Venous Pressure(CVP))*80/Cardiac Output (CO). All of these can be measured to determine if the patient falls into the normal SVR range of 800-1200 dyn. Having set the stage, Dr. Harken then went on to describe the following three scenarios:

Patient 1

A patient comes into the emergency department with a BP of 90/60, a MABP of 74, a CO of 4 L/min., and a CVP of 4. What is his SVR? What is the subsequent plan of treatment? After using the above equation, the physician would find that the patient’s SVR is 1400 dyn, a value that falls above of the normal range. In this case, the increased SVR is indicative of hypovolemic shock, or having a state of decreased blood volume. Consequently, the treatment would simply be to give the patient more volume. The causes of hypovolemia can include: external/internal bleeding, severe burns (leads to a loss of plasma), loss of body sodium and intravascular water (vomiting, diarrhea, sweating), and vasodilation (can happen after a trauma inhibits the vasomotor center in the brain).

Patient 2

A patient comes into the emergency department with a BP of 85/60, a MABP of 62, a CO of 4 L/min, and a CVP of 12. In this case, CVP falls into a normal range, so no additional volume is needed. The physician notes this difference and calculates the SVR for this patient and finds that it is 1,000 dyn. Some additional tests would have to be performed to confirm that this patient is experiencing cardiogenic shock, a type of shock that implies that there is inadequate circulation of the blood. In this case, the patient’s doctor would order a Beta 1 agonist to increase the heart’s pump action.

Patient 3

A patient comes into the emergency department with a BP of 85/60, a MABP of 62, a CO of 8 L/min, and a CVP of 12. The doctor calculates the SVR to be 500 and notices that the patient is warm. The doctor concludes that the patient has an infection and is experiencing septic shock. In this case, the doctor would order an Alpha agonist.

Essentially, Dr. Harken used these scenarios to argue that three types of treatment should be considered when a patient exhibits symptoms of shock. Ultimately, the doctor should 1. give the patient volume, 2. administer a chemical agent like a Beta 1 or Alpha agonist, or 3. increase hemoglobin to increase oxygen saturation. In the medical field, this is called “Early Goal Directed Therapy” and Dr. Harken is a firm believer in this system of treatment.  It was nice to hear this lecture because it reminded me that even the smallest of things learned in our undergraduate years can still be important in a later career. The morning meeting was soon finished and I made my way up to the OR.

While looking at the board, I ran into Dr. Krosin, who immediately told me that I should go to OR 3 to watch a Tram Flap Reconstruction. I eagerly took his advice and dashed off to OR 3, where the very jolly Dr. Allen greeted me. I explained who I was, and Dr. Allen happily volunteered to describe the procedure and to answer any questions that may arise during the 6 hour surgery. Of course, I was curious about the patient’s history, so I asked Dr. Allen about her story. The patient was a 38 year old woman who had had a mastectomy because of breast cancer. She opted for reconstruction with an expander (an implant) but that soon failed when the implant became infected. Dr. Allen offered to try the expander again but sadly, it too failed. The state of the breast tissue was too mangled by infection to be salvaged, so Dr. Allen suggested the Tram Flap Reconstruction. The patient was very hesitant at first to undergo this extensive procedure, and after watching the surgery, I don’t blame her.

Dr. Allen first began by removing the infected expander from the patient’s left breast. He removed the infected issue and scraped/irrigated the resulting cavity. After this, he began to cut out a section of the patient’s abdomen, to mobilize the rectus muscle. There is a crude drawing at the end of my journal to help illustrate the size of the piece of abdomen being removed (about 25 cm by 25 cm). It was divided up into four quadrants, two of which would be utilized for the breast reconstruction. For the next 2 hours, Dr. Allen and his resident began to slowly expose the abdominal wall found beneath the mesentery and fascia. A few times during the procedure, Dr. Allen would excitedly point out the amazing anatomical features found in this surgery, asking me to literally stand next to him, only inches away from the table. My favorite point in the procedure was when Dr. Allen was clipping blood vessels that were entangled with nerves. Every time Dr. Allen cauterized the vessel with the bovie, the electricity found in the tool would cause the rectus muscle to violently contract. It was really exciting to see this because it was only something I hypothetically read about in my physiology textbooks. Here I was, standing an inch away from a human muscle that was very alive and very active. When the piece of mesentery was finally free from the patient’s abdominal wall, Dr. Allen asked me to stand by his side again so that he could point out the infamous linea semicircularis. According to Dr. Allen, this is one of very few surgeries where this line is exposed.

After this, Dr. Allen had to make a tunnel from the abdominal flap up to breast cavity. It essentially had to be a hole big enough for a human fist to fit through and it had to transverse the entire human torso. To do this, Dr. Allen took both of his fists and pushed them into the patient until they were touching. As you can imagine, Dr. Allen had to vigorously shimmy his arms through the patient’s torso and of course, he worked up quite the sweat doing this. Once the tunnel was large enough, he lifted up the abdominal flap and rotated it 90 degrees, so that the rectus muscle was essentially lying 180 degrees on top of itself. From here, he started to push this baby-sized piece of tissue through the tunnel until it emerged from the breast cavity. At this point, the anesthesiologist, all of the nurses, the graft specialist, Dr Krosin, and I were all silently watching this amazing feat being performed. It was an ingenious technique that allowed for the healthy vascularization of the new breast tissue and stability of said tissue from the rectus muscle found beneath. It allowed the breast to feel natural and it had the added bonus of a tummy tuck. Of course, this procedure was insanely invasive, and the pain would be about the same as the pain felt by those who are struck by trucks.

For the next two hours, the surgical team worked on closing the patient. A graft made from pigs skin (which was the same price as a Ford Focus) was needed to help close the abdomen. Dr. Allen essentially removed quadrant 3 and 4 from the abdominal flap, now found in the breast cavity, because they were edge pieces and not as well vascularized as the inner 1 and 2 quadrants. This surgery was by far the most exciting surgery I have seen, and I highly recommend watching Dr. Allen perform a Tram Flap Reconstruction if given the chance.