背景：笑气在麻醉中应用广泛，常用吸入浓度为70%。虽然笑气影响vitamin B12、叶酸代谢及脱氧核糖核酸合成，并能避免高浓度氧的使用，但是这些作用的最终结果尚不清楚。
方法：预期手术时间超过2小时的外科手术患者随机分为两组：非笑气组（80%氧，20%氮气）；笑气组（70%笑气，30%氧）。患者和观察者均采取盲法。试验的第一个中止时点为患者住院期间；第二个中止时点包括ICU和术后并发症的持续时间；最后一个中止时点包括严重的恶心、呕吐及下列较大并发症：肺炎、气胸、肺栓塞、伤口感染、心肌梗塞、静脉血栓栓塞、中风、术中知晓以及术后30天内死亡。
结果：3187名符合条件的患者中有2050名经签署同意书后参加了试验。非笑气组患者较大并发症（优势比0.71；95%可信区间0.56-0.89；P = 0.003）严重恶心、呕吐（优势比0.40；95%可信区间0.31-0.51；P < 0.001）的发生率明显较低，但平均住院时间组间无差异（7.0 vs. 7.1 days；P = 0.06）。术后进入ICU的患者中，非笑气组比笑气组更快的转出ICU（hazard ratio，1.35；95% confidence interval，1.05-1.73；P = 0.02）。
结论：避免使用笑气同时增加吸入氧浓度，可降低较大外科手术后并发症的发生，但对住院时间无明显影响。接受较大外科手术的患者常规使用笑气麻醉值得商榷。
or Surgery A Randomized Controlled Trial.part1.rar (292.97k) or Surgery A Randomized Controlled Trial.part2.rar (8.69k) Avoidance of Nitrous Oxide for Patients Undergoing Major Surgery: A Randomized Controlled Trial.
Clinical Investigations
Anesthesiology. 107(2):221-231, August 2007.
Myles, Paul S. M.B., B.S., M.P.H., M.D., F.C.A.R.C.S.I., F.A.N.Z.C.A. *; Leslie, Kate M.B., B.S., M.D., M.Epi., F.A.N.Z.C.A. +; Chan, Matthew T. V. M.B., B.S., F.A.N.Z.C.A. ++; Forbes, Andrew M.Sc., Ph.D. [S]; Paech, Michael J. M.B., B.S., D.M., D.R.C.O.G., F.R.C.A., F.A.N.Z.C.A., F.F.P.M.A.N.Z.C.A. [//]; Peyton, Philip M.B., B.S., M.D., F.A.N.Z.C.A. #; Silbert, Brendan S. M.B., B.S., F.A.N.Z.C.A. **; Pascoe, Elaine B.Sc. ++; the ENIGMA Trial Group ++++
Abstract:
Background: Nitrous oxide is widely used in anesthesia, often administered at an inspired concentration around 70%. Although nitrous oxide interferes with vitamin B12, folate metabolism, and deoxyribonucleic acid synthesis and prevents the use of high inspired oxygen concentrations, the consequences of these effects are unclear.
Methods: Patients having major surgery expected to last at least 2 h were randomly assigned to nitrous oxide-free (80% oxygen, 20% nitrogen) or nitrous oxide-based (70% N2O, 30% oxygen) anesthesia. Patients and observers were blind to group identity. The primary endpoint was duration of hospital stay. Secondary endpoints included duration of intensive care stay and postoperative complications; the latter included severe nausea and vomiting, and the following major complications: pneumonia, pneumothorax, pulmonary embolism, wound infection, myocardial infarction, enous thromboembolism, stroke, awareness, and death within 30 days of surgery.
Results: Of 3,187 eligible patients, 2,050 consenting patients were recruited. Patients in the nitrous oxide-free group had significantly lower rates of major complications (odds ratio, 0.71; 95% confidence interval, 0.56-0.89; P = 0.003) and severe nausea and vomiting (odds ratio, 0.40; 95% confidence interval, 0.31-0.51; P < 0.001), but median duration of hospital stay did not differ substantially between groups (7.0 vs. 7.1 days; P = 0.06). Among patients admitted to the intensive care unit postoperatively, those in the nitrous oxide-free group were more likely to be discharged from the unit on any given day than those in the nitrous oxide group (hazard ratio, 1.35; 95% confidence interval, 1.05-1.73; P = 0.02).
Conclusions: Avoidance of nitrous oxide and the concomitant increase in inspired oxygen concentration decreases the incidence of complications after major surgery, but does not significantly affect the duration of hospital stay. The routine use of nitrous oxide in patients undergoing major surgery should be questioned.
(C) 2007 American Society of Anesthesiologists, Inc.
http://www.anesthesiology.org/pt/re/anes/abstract.00000542-200708000-00008.htm;jsessionid=GspWGxxJTp8MvVfXBmFTYm1vVL2V8YzdPThyp54QVnrMfDLppxdv!1267112738!181195629!8091!-1!1185688054514
EDITORIAL VIEWS
Is It Time to Retire High-concentration Nitrous Oxide?
Hopf, Harriet W. M.D.
Department of Anesthesiology, University of Utah, Salt Lake City, Utah. harriet.hopf@hsc.utah.edu
http://www.anesthesiology.org/pt/re/anes/fulltext.00000542-200708000-00005.htm;jsessionid=GsPMfSPt5QV4TG14bSvR2Qp1R54t4Z1Gnr214Mnq5b1hGlvJ3TCK!1267112738!181195629!8091!-1
ime to Retire High-concentration Nitrous Oxide.pdf (102.3k)
