Anesthetic agent consumption is often calculated as the product of fresh gas flow (FGF) and vaporizer dial setting (F_VAP). Because F_VAP of conventional vaporizers is not registered in automated anesthesia records, retrospective agent consumption studies are hampered. The current study examines how F_VAP can be retrospectively calculated from the agent’s inspired (F_IN) and end-expired concentration (F_ET), FGF, and minute ventilation (MV). Theoretical analysis of agent mass balances in the circle breathing reveals F_VAP = [F_IN − (dead space fraction * F_IN + (1 − dead space fraction) * F_ET) * (1 − FGF/MV)]/(1-(1 − FGF/MV)). F_IN, F_ET, FGF and MV are routinely monitored, but dead space fraction is unknown. Dead space fraction for sevoflurane, desflurane, and isoflurane was therefore determined empirically from an unpublished data set of 161 patient containing F_VAP, F_IN, F_ET, MV and FGF ranging from 0.25 to 8 L/min delivered via an ADU® (GE, Madison, WI, USA). Dead space fraction for each agent was determined empirically by having Excel’s solver function calculate the value of dead space fraction that minimized the sum of the squared differences between dialed F_VAP and predicted F_VAP. With dead space fraction known, the model was then prospectively tested for sevoflurane in O₂/air using data collected over the course of two weeks with one FLOW-i (Getinge, Solna, Sweden) and one Zeus workstation (Dräger, Lübeck, Germany). Because both workstations use an electronically controlled vaporizer/injector, the dialed F_VAP were available to allow the calculation of median performance error (MDPE) and median absolute performance error (MDAPE). MDPE and MDAP are reported as median and interquartiles. The empirical dead space fraction for isoflurane, sevoflurane, and desflurane were 0.59, 0.49, and 0.66, respectively. For prospective testing, a total of 149.4 h of useful data were collected from 78 patient with the Zeus and Flow-i combined, with FGF ranging from 0.18 to 8 L/min. The model predicted dialed F_VAP well, with a MDPE of −1 (−11, 6) % and MDAPE of 8 (4, 17) %. F_VAP can be retrospectively calculated from F_IN, F_ET, FGF, and MV plus an agent specific dead space fraction factor with a degree of error that we believe suffices for retrospective sevoflurane consumption analyses. Performance with other agents and N₂O awaits further validation.

麻醉剂消耗量通常计算为新鲜气体流量 (FGF) 和蒸发器刻度盘设置 (F _VAP ) 的乘积。由于传统汽化器的 F _VAP未在自动麻醉记录中注册，因此回顾性药物消耗研究受到阻碍。当前的研究检查了如何根据药剂的吸入浓度 (F _IN ) 和呼气末浓度 (F _ET )、FGF 和分钟通气量 (MV)回顾性地计算 F _{VAP 。}循环呼吸中药剂质量平衡的理论分析表明 F _VAP  = [F _IN  − (死腔分数 * F _IN  + (1 − 死腔分数) * F _ET) * (1 − FGF/MV)]/(1-(1 − FGF/MV))。F _IN、 F _ET、 FGF 和 MV 被常规监测，但死腔分数未知。因此，七氟醚、地氟醚和异氟醚的死腔分数是根据 161 名患者的未发表数据集凭经验确定的，该数据集包含 F _VAP、 F _IN、 F _ET、 MV 和 FGF，范围从 0.25 到 8 L/min，通过 ADU® (GE ，美国威斯康星州麦迪逊）。_{每个试剂的死腔分数根据经验确定，方法是让 Excel 的求解器函数计算死腔分数的值，该值最小化拨出的 F VAP}和预测的 F _VAP之间的平方差之和. 已知死腔部分后，使用一台 FLOW-i（Getinge，瑞典索尔纳）和一台 Zeus 工作站（德尔格，德国吕贝克）在两周内收集的数据，对模型进行 O 2 /空气中七氟醚的前瞻性_测试). 因为两个工作站都使用电子控制的汽化器/注射器，所以拨打的 F _VAP可用于计算中值性能误差 (MDPE) 和中值绝对性能误差 (MDAPE)。MDPE 和 MDAP 报告为中位数和四分位数。异氟醚、七氟醚和地氟醚的经验死腔分数分别为 0.59、0.49 和 0.66。对于前瞻性测试，使用 Zeus 和 Flow-i 组合从 78 名患者收集了总共 149.4 小时的有用数据，FGF 范围为 0.18 至 8 L/min。该模型很好地预测了拨号 F _VAP，MDPE 为 −1 (−11, 6) %，MDAPE 为 8 (4, 17) %。F _{VAP可以从 F IN} , F _ET追溯计算、FGF 和 MV 加上具有一定程度误差的药剂特定死腔分数因子，我们认为足以进行回顾性七氟醚消耗分析。与其他试剂和 N ₂ O 的性能等待进一步验证。