Thursday, July 22, 2010

Week 5 - Zavrel

During this week I gained more exposure to the clinical setting and made progress with my research project.

I was able to observe cardiothoracic surgery with Dr. Leonard Girardi attending. The operation was an aortic valve replacement on a man in his 50s. While waiting outside the OR, I met two sales representatives from Edwards Lifesciences, the company that manufactures the heart valve replacements. They were on hand to field questions posed by the surgeon on the proper selection of valve replacement. If the chosen valve is too small, the pressure gradient across the valve will be too great, leading to device fatigue and premature failure. One of the sales reps. explained that the goal is to achieve a gradient as close to that associated with the natural valve as possible. The sales reps showed me a chart that indexed the cross sectional area of the valve against the BMI of the patient. This convenient chart was color coded (green corresponding to a safe match, yellow to a satisfactory match, red to a severe mismatch). Larger patients need correspondingly larger valves. Given that the pressure inside a channel exhibits a fourth power dependence on channel diameter, even minute increases in the diameter of a valve can result in substantially lower pressures and hence less likelihood of failure. The sales reps. were very knowledgeable and were able to provide a play-by-play of what was occurring during the surgery. I learned many things from my first time in the OR. For instance, I knew that the surgeons siphoned off blood from the thoracic cavity so as to facilitate surgery but I did not know that the patient’s blood was stored and then reintroduced afterward. I assumed that banked blood was used and that the patient’s blood was disposed of for reasons of contamination. One of the sales reps. pointed out the cell saver device that stored the patient’s blood and then reintroduced it. Also, they pointed out that to prevent clogging of the tubes that carry the blood to the cell saver, a blood-thinning anticoagulant agent (heparin) is administered. Upon completion of the surgery, the effects of the heparin had to be countered. Room temperature was raised when the surgery was over and the surgeons were attempting to restart the patient’s heart. I was impressed with the size of the staff on hand – nearly 20 people. The atmosphere was like that of mission control with the surgeons calling out for readings or barking out orders and the support staff flatly intoning dial readings or confirming compliance with the order.

Later in the week I was able to spend time in the emergency room (ER). Dr. Dean Straff gave me a tour. Afterward, I followed one of the senior residents on rounds and saw several cases. Dr. Straff explained that the ER sees everything from the mundane to the unprecedented. Anyone who shows up at the ER will be seen, regardless of how minor their complaint really is. Upon arrival, patients are triaged – the severity of each case is assessed and the patient is relocated accordingly. The ER is organized into three areas: A, B, C bays. Section A is nearest the ambulance drop off so usually houses the most severe cases. Among the cases I observed, several stood out.

1. An elderly man who had been the victim of a brutal physical assault late last year and suffered a stroke soon afterward was admitted from his nursing home due to a feeding tube coming loose and an infection taking hold. The gentleman was in a vegetative-like state, moving his eyes and moaning in response to discomfort but otherwise unable to communicate. X-rays of his chest looked foggy so pneumonia was discerned and antibiotics prescribed.

2. Girl in her mid-20s with a family history of heart disorders (father had heart attack at young age, brother had heart defect, etc.) was admitted complaining of severe chest pains, the intensity of which changed with position. The senior resident was inclined to believe this was pericarditis, an inflammation of the sac that surrounds the heart, which is caused by a viral infection. The girl remembered having a cold a month earlier. Ordering a CT scan was one possible way to confirm this, but the senior resident cautioned against it unless it proved absolutely necessary, as the radiation dose is equivalent to about 200 x-rays – an amount inadvisable to be administered to a young woman due to the sensitive nature of the breasts and ovaries to radiation.

3. A middle-aged man presented with an abscess on his ankle. He had earlier broken his ankle and had it mended but had developed an infection. The senior resident lanced the abscess and drained it of pus, taking a culture sample for analysis. She explained that if the situation were dire, the patient would be put directly put on a general antibiotic, but because the situation was not life-threatening, they had the luxury of sending a sample to the lab for analysis to identify the specific bacteria so as to prescribe a more narrowly-focused antibiotic.

Also, a new mobile computer system was unveiled to the ER staff. This cart-mounted computer terminal was touted as being able to obtain digital signatures on consent forms and discharge papers from bedridden patients. The mobile terminal also featured an RFID reader which granted access upon swiping an ID badge, saving precious seconds that might otherwise be spent keying in a password or trying to recall a password from memory. A senior staff member at the ER was absolutely beside himself with excitement, going on at great length as to how this represented the paradigm that all emergency rooms in the nation were going to emulate in the coming years. He claimed it would free up very expensive hospital beds and result in faster turn-around time, more important than ever with cutbacks to government-supported insurance programs like Medicare and Medicaid.

The electronics needed for my research project finally arrived. I was able to verify the operation of the load cells. One observation was that the load cells exhibited a non-zero voltage output in their non-stressed state. So, I may have to account for this DC offset in the final design of the device.

My other project involves interfacing a microcontroller to a commercial sleep monitor known as a Zeo Personal Sleep Coach. The device isn’t intended as a research tool, but owing to its many features and relatively low cost, it is ideal for use in clinical studies of long duration outside the lab, i.e. at a person’s home. As the device is intended to operate as a consumer device, it isn’t terribly amenable to alteration. Consequently, I spent a good amount of time exchanging emails with technical support from the company.

Lastly, I was given a Zeo of my own to explore. The Zeo consists of a headband with a sensor that monitors brain wave activity and streams sleep stage data wirelessly to a base station for storage and display. Data can be uploaded to the company website for analysis.

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