To the Editor:—
In a recent reply to a letter to the editor, 1Drs. Spahn and Casutt state that the “efficacy [of hypotensive anesthesia] has been challenged recently” and cited an article in which I was a coauthor. 2I believe they have misrepresented the thrust of the paper, which was to demonstrate the safety of hypotensive epidural anesthesia in elderly higher risk patients. Although we found no significant difference in blood loss between groups (mean arterial pressure [MAP], 50 vs. 65 mmHg), this unexpected finding was addressed in the Discussion. I believe that this probably reflected “imprecision in the measurement technique.” In a previous study in which blood loss was more carefully measured and surgical assessments of bleeding were recorded, there was a small but statistically significant difference in blood loss between 50 and 60 mmHg MAP during primary total hip replacement (THR). 3
In primary total hip replacement, there is a clear relation between MAP and intraoperative blood loss. The results of four randomized studies 2,3,5,6performed in the 1990s using epidural or spinal anesthesia clearly show that intraoperative blood loss is related to MAP with most of the benefits occurring when pressures are reduced within the normotensive range (MAP, 90–100 mmHg). Reduction in MAP below 60 mmHg produces less-dramatic benefits.
The authors also state that “a majority of surgical bleeding is venous bleeding.” This may be true for some procedures, such as liver resection, but is not so for the majority of surgical procedures. We studied this in primary total hip replacement and found that central venous pressure had no relation to intraoperative bleeding (r2= 0.005). 3Venous blood tends to be blue; arterial blood tends to be red. One merely has to look into most surgical wounds to realize that the majority of bleeding is arterial. I agree with Klowden et al. 4that it is time for the anesthesia community to stop criticizing hypotensive anesthesia and start practicing the technique.