术前夜禁食后的水合状态（经尿渗透压浓度评估）对低风险患者全麻期间低血压程度的影响

背景组织间隙的晶体液分布增多可能减少患者的有效血容量。我们研究了术前整夜禁食患者体内的水合状态对组织间液再分布和全麻期间低血压程度的影响。方法60例ASA分级I级或II级的中耳整复术患者从午夜12时开始禁食。麻醉诱导用芬太尼和丙泊酚，维持用七氟烷和瑞芬太尼。从麻醉诱导开始，前印分钟内静脉滴入醋酸林格液15ml/kg，之后30分钟输注1ml／kg。我们测定麻醉诱导后和研究期间的尿渗透压浓度（pre-Uosm和post—Uosm），以及研究结束时全身细胞外液生物电阻相对于基础值降低的百分数（ARe）。pre-Uosm低于25百分位的患者和高于75百分位的患者分别被列入水化组和脱水组。比较两组之间一系列的变量，包括30—90分钟内相对于基础值的平均动脉压和ARe。结果与水化组（pre-Uosm〈378．5mOsm／妇，n=15）相比，脱水组（pre-Uosm〉759．5mOsm／kg，n=15）年龄较低（44岁坩．52岁，P=0．049），而post．U05m较高（181mOsm／kgw．55mOsm／kg，P=D．DOJ）。水化组和脱水组之间，30—90分钟内相对于基础值（0．67w．0．67，P：0．85）的平均动脉压均数差值（-0．070—0．084）的95％可信区间以及ZXRe（5．6％vs.6.0％，P=n58）均数差值（-J．85％-1.06％）的95％可信区间均相似。结论由尿渗透压浓度测得经一夜禁食后的体内含水状态对低风险患者全麻期间的血压降低程度并无影响。这一结论表明，对于整夜禁食的低风险患者，用晶体液扩充血容量以防止全麻期间血压过低的做法缺乏事实依据。

BACKGROUND： The increased distribution of crystalloid solution into the interstitial space may decrease the effectiveness of intravascular volume loading in patients. We investigated whether preoperative hydration status after overnight fasting affects interstitial fluid redistribution and thus the magnitude of hypotension during general anesthesia. METHODS： Sixty ASA physical status I/II patients undergoing tympanoplasty fasted from midnight. Anesthesia was induced by fentanyl and propofol and maintained with sevoflurane and remifentanil. Coinciding with the induction of anesthesia, 15 ml/kg acetated Ringer solution was infused 1V over 60 minutes followed by 1 ml/kg acetated Ringer solution over the next 30 minutes. Urine osmolalities after induction of anesthesia and during the study period （pre-Uosm, post-Uosm） and percent decreases of whole-body bioelectrical resistance for extracellular fluid relative to baseline at the end of the study period （ARe） were measured. Patients with a pre-Uosm 〈 the 25th percentile or with a pre-Uosm 〉 the 75th percentile of pre-Uosm were categorized in the hydrated or the dehydrated group, respectively. A range of variables, including mean arterial blood pressure during the 30- to 90-minute period relative to baseline, and ARe, were compared between the groups. RESULTS： The dehydrated group （pre-Uosm 〉 759.5 mOsm/kg, n = 15） had a lower age （44 vs 52 years, P = 0. 049） and had a higher post-Uosm （181 vs 55 mOsm/kg, P = 0.00l） compared with the hydrated group （pre-Uosm 〈 378.5 mOsm/kg, n = 15）. Mean arterial blood pressure during the 30- to 90-minute period relative to baseline （0.67 vs 0.67, P = 0.85） with 95% confidence interval for the difference of means （ - 0. 070 to 0. 084） and Re （5.6% vs 6.0%, P = 0.58） with 95% confidence interval for the difference of means （-1.85% to 1.06%） were similar for the hydrated and dehydrated grotps. CONCLUSIONS： Preoperative dehydration after overnight fasting as measured by urine osmolality did not alter the magnitude of hypotension during general anesthesia. This finding suggests that intravascular volume loading with crystalloid solution to prevent hypotension during general anesthesia is an unfounded practice for low risk patients after overnight fasting.