Week 2 - John

The surgery I watched on Friday involved removing a tumor beneath the cerebellum and adjacent to the brain stem. The patient was a 3-year-old boy, who already had a previous operation to biopsy the tumor. The tumor was benign, but was slowly increasing in size, and the boy was undergoing chemotherapy to manage it. However, a part of the tumor was turning necrotic, and needed to be removed. Because of the tumor's proximity to the brain stem, extra precaution had to be taken to avoid causing any damage to the cranial nerves.

As such, neurophysiologists had to constantly monitor the patient during the entire operation, which, including the setup, lasted from 7:30 am till 4:30 pm. It was the longest operation I had seen so far because of the degree of complexity involved. Before cutting into a new area, Dr. Souweidane had to probe the tissue to ensure that it was not involved in any motor or sensory function. The neurophysiologists had attached probes to different muscle groups controlled by the cranial nerves, as well as stimuli to different sensory nerves, to determine the baseline readings at the start of the operation, and any changes that occurred during the operation. Dr. Souweidane had to use a microscope, as well as micro scissors, spatulas, and even an ultrasonic aspirator to meticulously separate the tumor from the surrounding healthy brain tissue and nerves. While large parts of the tumor were excised in whole, the remaining tumor was liquefied and aspirated away by the ultrasonic aspirator. I later found out that this ultrasonic aspirator was originally meant for shaving bone down on a microscopic level, but certainly came in very useful in this brain surgery as well.

Because the surgery took a very long time, I had the opportunity to speak with Dr. Stein, the anesthesiologist. Apparently, anesthesia has to be properly controlled - too little of it, and the patient regains consciousness; too much of it, and the patient's core organs shut down. Usually, patients are not put under anesthesia for more than 24 hours. However, if a person had a feeding tube and a ventilator attached, he or she can be under anesthesia for months. In the case of inducing a coma in patients suffering from traumatic brain injury, the rational is that when there is less activity in the brain, less oxygen is utilized, thus resulting in less oxidative damage. This principle is also used in cardiac bypasses, and is the reason for lowering the temperature of patients with cardiac arrest.

There are two IVs that go into the patient, each containing a different analgesic. In this surgery, propofol, a fast acting anesthesia, and another one I can't remember, are used. These are each connected to a bag of 0.9 sodium chloride solution. Another small bag of saline is also attached to the patient. This attachment actually involves a blood pressure gauge, and the saline is merely to prevent clotting. Also, if blood is required at any time during the surgery for testing, it is drawn via this tube. Antibiotics are also given to the patient during the surgery, although I am not sure why this is the case. The patient is also attached to a ventilator for respiratory function, where initial and final lung pressure, as well as the duration of inhalation, exhalation, and intervals can be determined. In this patient, the duration of inhalation is slightly shorter than that of exhalation. During the surgery, heart rate, pulse rate, blood pressure, blood oxygen content, and hematocrit is constantly monitored. Every so often, a blood sample is drawn to determine oxygen content, hematocrit, and ion levels, so that they can be adjusted if necessary. Some of the tests are redundant for an added layer of precaution in case one device fails to function. The hematocrit is regularly monitored because if it drops too low, blood transfusion is needed. The average hematocrit for a person is 45%, but a young healthy patient can withstand a level of 20%, while geriatric patients can withstand a level of 30%. These numbers are obviously approximate, because each patient is different. The goal is to avoid blood transfusions, because even though blood is tested before transfusion, there is still a risk of contracting HIV or hepatitis C (1 in 2,000,000 for both) or hepatitis B (1 in 205,000), or for an immune-compromised patient, the natural antibodies in the donor's blood may be too detrimental for the patient's own immune system to handle.