Combined Use of Spinal Anesthesia and Midazolam Sedation Increases the Risk of Hypoxemia

Abstract

To the Editor: We read with interest the article entitled "The Influence of High Spinal Anesthesia on Sensitivity to Midazolam Sedation" by Ben-David et al. [1]. The authors explain that their study did not address the central clinical question "Does the combined use of high spinal anesthesia and midazolam sedation increase the risk of hypoventilation and hypoxemia?" The answer is yes, at least in patients over 65 years of age, as was demonstrated in our prospective, randomized, and double-blind study evaluating oral benzodiazepine premedication 60-90 minutes before surgery (with 1 mg flunitrazepam, 1 mg lorazepam, or 7.5 mg midazolam) and the incidence of hypoxemia during surgery under spinal anesthesia [2]. The incidence of hypoxemia (arterial O2 saturation < 90% with room air) was 60% in patients who received midazolam compared with 15% in unpremedicated controls (overall, 42% of premedicated patients presented hypoxemia during surgery). Key factors for the development of hypoxemia were drowsiness during surgery (66% vs 11% in awake patients) and the level of anesthesia (49% in patients with an anesthetic level of T-6 or higher compared with 21% in those with T-7 or lower). Using these factors, we designed a risk score for hypoxemia: 0 points = awake and anesthetic level T-7 or lower; 1 point = drowsy or anesthetic level T-6 or higher; 2 points = drowsy and anesthetic level T-6 or higher. The incidence of hypoxemia was significantly different among the three groups: 0 points, 7%; 1 point, 30%; and 2 points, 74%. Thus, the results of our study underscore the fact that sedation during spinal anesthesia may lead to potentially dangerous complications and should be used with caution and monitored. Hernan R. Munoz, MD Jorge Dagnino, MD Department of Anesthesiology Catholic University of Chile School of Medicine Santiago, Chile