One last case to get you thinking about the difference between TCOM and perfusion pressure is that of a 35-year-old female pharmacist who underwent incision and drainage of a left index finger abscess 3 months before I saw her. The day after the I&D a dark discoloration was noted at the tip of the finger under the nail which continued to enlarge and eventually she necrosed the tip of her finger. When I saw her she needed 4 Norcos per day for pain control.
The skin perfusion pressure of her index finger was totally normal at 91mmHg and the PVR of the digital artery was normal. In other words, her digital artery was not occluded. However, the TCOM on the finger as close as I could come to the distal tip was only 48mmHg. That’s too low for the hand and for someone whose digital artery we just proved was patent. But, when I gave her oxygen to breathe, the TCOM increased to over 200mmHg. So, whatever the cause of her tissue hypoxia to the finger, it could be overcome with a little oxygen breathing. That also confirms that the artery was patent and whatever was keeping her tissue oxygen levels down was reversible. To me, that suggested she had vasospasm. She had no significant past medical history but I sent her to a rheumatologist and sure enough, she was eventually given the diagnosis of an autoimmune disease.