Departmento de Anestesiología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Anesth Analg. 2011 Jul;113(1):70-6. doi: 10.1213/ANE.0b013e31821f105c. Epub 2011 May 19.
The onset and offset of action of anesthetic gases might be delayed by respiratory changes and gas exchange alterations present in obese patients. In this study, we assessed the influence of obesity on the hysteresis between sevoflurane and its effect as measured by the bispectral index (BIS). Because the use of positive end-expiratory pressure (PEEP) in obese patients has improved gas exchange, we also assessed the influence of PEEP on hysteresis.
Fifteen obese and 15 normal-weight patients, ASA physical status I and II, 20 to 50 years old, scheduled to undergo general anesthesia for elective laparoscopic surgery, were prospectively studied. Anesthesia was induced with propofol and maintained with sevoflurane and fentanyl. At the end of surgery and after stable BIS values of 60 to 65, the inspired concentration of sevoflurane was increased to 5 vol% for 5 minutes or until BIS was <40 and then decreased. Sevoflurane transitions were performed once in normal-weight subjects (without PEEP) and twice in obese patients (one without PEEP and one with a PEEP of 8 cm H(2)O). The hysteresis between sevoflurane end-tidal concentrations and BIS during these transition periods was modeled with an inhibitory Emax model using a population pharmacokinetic/ pharmacodynamic (PK/PD) approach with NONMEM VI. A descriptive analysis of sevoflurane inspired and expired concentrations, BIS values, and time to reach different BIS end points was also used to compare the PK and PD characteristics.
All patients completed the study. The data were adequately fit with the PK/PD model. The hysteresis expressed as the effect-site elimination rate constant was not influenced by body mass index or PEEP (P > 0.05). Neither obesity nor PEEP showed any influence on the PK/PD descriptors.
Our results do not support the hypothesis that obesity prolongs induction or recovery times when sevoflurane, a poorly soluble anesthetic, is used to maintain anesthesia from 90 to 120 minutes.
肥胖患者的呼吸变化和气体交换改变可能会延迟麻醉气体的作用开始和结束时间。在这项研究中，我们评估了肥胖对七氟醚及其效应之间滞后的影响，这种效应是通过双频谱指数（BIS）来测量的。由于在肥胖患者中使用呼气末正压通气（PEEP）可以改善气体交换，我们还评估了 PEEP 对滞后的影响。
本前瞻性研究纳入了 15 名肥胖患者和 15 名体重正常患者，ASA 身体状况 I 级和 II 级，年龄 20 至 50 岁，计划接受全身麻醉下的择期腹腔镜手术。麻醉诱导采用丙泊酚，维持采用七氟醚和芬太尼。在手术结束时，当 BIS 值稳定在 60 至 65 之间后，将七氟醚的吸入浓度增加到 5 体积%，持续 5 分钟，或直到 BIS 值<40 ，然后降低。在体重正常的患者中（无 PEEP）进行一次七氟醚转换，在肥胖患者中进行两次转换（一次无 PEEP，一次有 8 cm H2O 的 PEEP）。使用群体药代动力学/药效学（PK/PD）方法和 NONMEM VI 采用抑制 Emax 模型对这些转换期间七氟醚呼气末浓度和 BIS 之间的滞后进行建模。还使用描述性分析来比较 PK 和 PD 特征，包括七氟醚吸入和呼出浓度、BIS 值以及达到不同 BIS 终点的时间。
所有患者均完成了研究。数据与 PK/PD 模型拟合良好。以效应部位消除速率常数表示的滞后不受体重指数或 PEEP 的影响（P>0.05）。肥胖或 PEEP 均未对 PK/PD 描述符产生任何影响。
当使用七氟醚维持麻醉 90 至 120 分钟时，我们的结果不支持肥胖会延长七氟醚诱导或恢复时间的假设，七氟醚是一种不易溶解的麻醉剂。
