Ng Ka Ting, Alston R Peter, Just George, McKenzie Chris
1 Department of Anaesthesiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
2 Department of Anaesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, Edinburgh, UK.
Perfusion. 2018 Mar;33(2):148-155. doi: 10.1177/0267659117735883. Epub 2017 Oct 6.
Bispectral index (BIS) and monitoring of end-tidal concentration may be associated with a reduction in the incidence of awareness during volatile-based general anaesthesia. An analogue of end-tidal concentration during cardiopulmonary bypass (CPB) is measuring exhausted isoflurane concentration from the oxygenator as an estimate to blood and, so, brain concentration. The aim of this study was to determine the relationships between oxygenator exhaust and blood concentrations of isoflurane and the BIS score during CPB when administering isoflurane into the sweep gas supply to the oxygenator.
Seventeen patients undergoing elective cardiac surgery using CPB and isoflurane with BIS monitoring were recruited in a single-centre university hospital. Isoflurane gas was delivered via a calibrated vaporiser at the beginning of anaesthetic induction. Radial arterial blood samples were collected after the initiation of CPB and before aortic cross-clamping, which were analysed for isoflurane by gas chromatography and mass spectrometry. The BIS score and the concentration of exhausted isoflurane from the oxygenator membrane, as measured by an anaesthetic gas analyser, were recorded at the time of blood sampling.
The mean duration of anaesthetic induction to arterial blood sampling was 90 min (95%CI: 80,100). On CPB, the median BIS was 39 (range, 7-43) and the mean oxygenator exhaust isoflurane concentration was 1.24 ± 0.21%. No significant correlation was demonstrated between BIS with arterial isoflurane concentration (r=-0.19, p=0.47) or oxygenator exhaust isoflurane concentration (r=0.07, p=0.80). Mixed-venous blood temperature was moderately correlated to BIS (r=0.50, p=0.04). Oxygenator exhaust isoflurane concentration was moderately, positively correlated with its arterial concentration (r=0.64, p<0.01).
In conclusion, in patients undergoing heart surgery with CPB, the findings of this study indicate that, whilst oxygenator exhaust concentrations were significantly associated with arterial concentrations of isoflurane, neither had any association with the BIS scores, whereas body temperature has moderate positive correlation.
双谱指数（BIS）和呼气末浓度监测可能与挥发性全身麻醉期间术中知晓发生率的降低有关。体外循环（CPB）期间呼气末浓度的类似物是测量氧合器排出的异氟烷浓度，以此作为血液及进而脑部浓度的估计值。本研究的目的是确定在向氧合器的吹扫气体供应中给予异氟烷时，CPB期间氧合器排出物与异氟烷血液浓度及BIS评分之间的关系。
在一家单中心大学医院招募了17例接受CPB和异氟烷麻醉并进行BIS监测的择期心脏手术患者。在麻醉诱导开始时，通过校准蒸发器输送异氟烷气体。在CPB开始后和主动脉交叉钳夹前采集桡动脉血样，通过气相色谱和质谱法分析其中的异氟烷。在采血时记录BIS评分以及通过麻醉气体分析仪测量的氧合器膜排出的异氟烷浓度。
从麻醉诱导到动脉采血的平均持续时间为90分钟（95%CI：80,100）。在CPB期间，BIS的中位数为39（范围7 - 43），氧合器排出的异氟烷平均浓度为1.24±0.21%。BIS与动脉异氟烷浓度（r = -0.19，p = 0.47）或氧合器排出的异氟烷浓度（r = 0.07，p = 0.80）之间未显示出显著相关性。混合静脉血温度与BIS呈中度相关（r = 0.50，p = 0.04）。氧合器排出的异氟烷浓度与其动脉浓度呈中度正相关（r = 0.64，p < 0.01）。
总之，在接受CPB心脏手术的患者中，本研究结果表明，虽然氧合器排出浓度与异氟烷动脉浓度显著相关，但两者均与BIS评分无关，而体温具有中度正相关性。
