Dr. Neil Melendez was a patient in episodes 3×19 Hurt and 3×20 I Love You.
Dr. Melendez was caught in the earthquake at the brewery. Blunt force trauma from debris falling on him caused a retroperitoneal bleed (internal bleeding in the abdominal cavity). Melendez assumed he was most likely bleeding from the pancreas.
Dr. Lim suggested Angio (an angiogram) for embolization to stop the bleed (angiogram = using dye to make the blood flow visible; embolization = using a tube to inject materials into the blood vessel to clog it up and stop the bleed), but Claire recommended an open surgery to explore and resect (remove unhealthy or dead tissue).
They found during the surgery that a branch of the SMA (superior mesenteric artery – a large vessel that supplies internal organs with blood) was torn, and it was the right decision to do open surgery rather than the Angio-supported embolization, which would not have been able to stop the bleeding.
They resected (removed) the devitalized (dead) tissue, but then they found additional injuries all the way up the celiac trunk (a major artery of the abdomen). The lack of blood flow to the bowel caused ischemic bowel colitis (inflammation of the bowel, which can lead to the bowel tissue ceasing function and dying).
During surgery they restored full blood flow to the bowel and reperfused (another word for restoring blood flow) via mesenteric bypass (bypassing the damaged artery to restore blood flow to the bowel again), but his lactate was 4 (probably mmol/L, lactic acid is a biomarker that can detect tissue damage in the bowel), already indicating some failure to the bowel wall.
They retested his lactate later (presumably at least an hour, probably more), and it went up to 8.1, which suggested more bacterial leakage and progressing ischemia (loss of blood flow to part of the bowel). Melendez was past the point of treatment by that time.
Dr. Lim suggested to resect more bowel and do a trauma Whipple (surgery to remove the head of the pancreas) to Dr. Glassman, but Glassman refused because it wasn’t a viable solution. Significant revascularization (restoring blood flow to the bowel) was out of the question, and even if by some miracle Melendez survived the surgery, he would end up being severely impaired for the rest of his life.
They had to stand by helplessly to watch Dr. Melendez die from intestinal necrosis (and possibly other organs in its wake), which we know progressed quickly, and he passed away the same day.