[Perioperative minimum acceptable hematocrit level in highly invasive head and neck surgery]

We examined the perioperative balance between oxygen delivery and oxygen consumption under hemodilution in 24 patients who underwent head and neck surgery of long duration and with massive blood loss. Intraoperative mixed venous oxygen saturation (SVO2), which decreased according to a decrease in hematocrit (Hct), was almost always kept above 60% when Hct was more than 20%. The longer the duration of surgery, the lower was SVO2 at the end of surgery. Postoperative SVO2 correlated positively with SVO2 at the end of surgery, and negatively with the duration of surgery and blood loss, but did not correlate with Hct. In 9 cases, SVO2 at the recovery from anesthesia decreased to below 60%, because oxygen consumption increased remarkably with shivering. These results suggest that in highly invasive head and neck surgery, the intraoperative minimum acceptable Hct level is 20%. On the other hand, there is no general postoperative minimum acceptable Hct level, because postoperative oxygen demand and supply balance depends on the degree of surgical invasion and increase of VO2. SVO2 at the end of surgery is useful in predicting postoperative oxygen demand and supply balance.