Heinze J, Rohrbach M
Klinik für Anästhesiologie, Universität Tübingen.
Anaesthesist. 1992 Nov;41(11):673-9.
Benzodiazepines for sedation may decrease the PaO2, the arterial O2 saturation (SaO2), and the CO2 response more in the elderly than in the young. The purpose of this study was to assess changes in blood gases due to i.v. midazolam or sublingual flunitrazepam given as premedication in elderly patients for unilateral cataract surgery. METHODS. Fifty patients over 65 years of age with treated arterial hypertension and other co-existing diseases (ASA III-IV) were randomly assigned to have: (1) i.v. midazolam titrated until they became drowsy (17 patients; 2.85 +/- 0.84 mg [mean +/- SD]); (2) sublingual flunitrazepam (16 patients; 0.005 mg/kg); or (3) no sedation (17 patients; controls). On entering the operating theatre, the radial artery was cannulated and the first blood gas analysis was obtained. The premedication was then given. At 5, 10, 20, and 30 min after premedication, before and 10 min after retrobulbar block, before operation, 5 and 15 min after the beginning of the operation, 10 and 20 min after administration of 500 mg acetazolamide i.v. during the operation, and 10 and 20 min after the operation additional arterial blood samples were analysed (a total of 15 measuring points). Pulse oximetry, invasive blood pressure, and ECG were continuously monitored. All patients received oxygen 3 l/min during the operation by nasal cannula. Differences between the three groups were analysed by Student's t-test or U-test and a P value < 0.05 was considered significant. RESULTS. The patient demography, including duration of anaesthesia and operation, was similar in the three groups (Table 1). No significant differences were seen in heart rate, mean arterial pressure, PaO2, pulse-oximetric oxygen saturation (SpO2), base excess, or serum bicarbonate levels. The PaCO2 increased in patients after midazolam (P < 0.01) and flunitrazepam (P < 0.05) until the beginning of the operation compared with the control group (Fig. 3); 20 min after the operation there was still a significant difference between the midazolam group and the controls. SaO2 was significantly (P < 0.05) lower in the midazolam group 10 and 20 min after administration of premedication compared with the control group, but was within physiological limits (Fig. 5). Despite titration, 2 patients had severe respiratory insufficiency 3 min after midazolam: the SpO2 decreased below 85% and the paO2 below 55 mmHg. The paCO2 was higher (P < 0.05) in the midazolam group 10 min after acetazolamide compared with the controls. CONCLUSIONS. The results of the study show the potential hazards of i.v. midazolam in the elderly. If sedation is required for cataract surgery under local anaesthesia, we recommend sublingual flunitrazepam or the use of benzodiazepines with lower hypnogenic effects in the elderly. A thorough preoperative discussion of anaesthesia and the operation might be an adequate substitute for any premedication in high-risk patients; the best blood gas analysis results were obtained in the control group.
用于镇静的苯二氮䓬类药物对老年人动脉血氧分压（PaO₂）、动脉血氧饱和度（SaO₂）及二氧化碳反应的降低作用，相较于年轻人更为明显。本研究旨在评估老年患者单侧白内障手术术前静脉注射咪达唑仑或舌下含服氟硝西泮对血气的影响。方法：50例65岁以上患有动脉高血压及其他并存疾病（ASAⅢ - Ⅳ级）的患者被随机分为三组：（1）静脉注射咪达唑仑直至患者出现嗜睡（17例；2.85±0.84mg[均值±标准差]）；（2）舌下含服氟硝西泮（16例；0.005mg/kg）；（3）不进行镇静（17例；对照组）。进入手术室后，穿刺桡动脉并进行首次血气分析。随后给予术前用药。在术前用药后5、10、20和30分钟，球后阻滞前、后10分钟，手术前，手术开始后5和15分钟，术中静脉注射500mg乙酰唑胺后10和20分钟，以及术后10和20分钟分别采集动脉血样进行分析（共15个测量点）。持续监测脉搏血氧饱和度、有创血压及心电图。所有患者术中经鼻导管吸氧，流量为3L/分钟。三组间差异采用Student's t检验或U检验分析，P值<0.05被认为具有统计学意义。结果：三组患者的人口统计学资料，包括麻醉及手术时长相似（表1）。心率、平均动脉压、PaO₂、脉搏血氧饱和度（SpO₂）、碱剩余或血清碳酸氢盐水平未见显著差异。与对照组相比，咪达唑仑组（P<0.01）和氟硝西泮组（P<0.05）患者的PaCO₂在手术开始前升高（图3）；术后20分钟，咪达唑仑组与对照组仍存在显著差异。与对照组相比，咪达唑仑组在术前用药后10和20分钟时SaO₂显著降低（P<0.05），但仍在生理范围内（图5）。尽管进行了滴定，但2例患者在咪达唑仑注射后3分钟出现严重呼吸功能不全：SpO₂降至85%以下，PaO₂降至55mmHg以下。与对照组相比，咪达唑仑组在静脉注射乙酰唑胺后10分钟时PaCO₂更高（P<0.05）。结论：本研究结果显示静脉注射咪达唑仑对老年人存在潜在危害。若局部麻醉下白内障手术需要镇静，我们推荐老年人使用舌下含服氟硝西泮或催眠作用较弱的苯二氮䓬类药物。对于高危患者，术前充分讨论麻醉及手术情况可能足以替代任何术前用药；对照组的血气分析结果最佳。
