Oxygen Tension During Laminectomy

To the Editor:—  Frequently during laminectomy, the surgeon complains that the blood from the epidural space is "dark" despite the fact that the anesthesiologist is administering oxygen concentrations of 40% or more in the anesthetic gas mixture. There is generally no concurrent indication of hypoxemia in terms of respiratory or circulatory signs and there is no obvious cyanosis in the upper regions of the body. Nevertheless, the dark blood in the wound is disquieting. The conservative anesthesiologist may discontinue all anesthetic agents and administer 100% oxygen in an attempt to correct the situation with the result that the anesthesia becomes light and the patient begins to cough due to the endotracheal tube. Other anesthesiologists question the powers of observation of the surgeon which may result in an unpleasant altercation.In order to determine whether the observation of dark blood was apparent or real and, if real, to determine its significance,