Sturesson L W, Bodelsson M, Jonson B, Malmkvist G
Section of Anaesthesiology and Intensive Care, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden
Section of Anaesthesiology and Intensive Care, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden.
Br J Anaesth. 2014 Sep;113(3):508-14. doi: 10.1093/bja/aeu102. Epub 2014 May 28.
The anaesthetic conserving device AnaConDa (ACD) reflects exhaled anaesthetic agents thereby facilitating the use of inhaled anaesthetic agents outside operating theatres. Expired CO₂ is, however, also reflected causing a dead space effect in excess of the ACD internal volume. CO₂ reflection from the ACD is attenuated by humidity. This study tests the hypothesis that sevoflurane further attenuates reflection of CO₂. An analysis of clinical implications of our findings was performed.
Twelve postoperative patients received mechanical ventilation using a conventional heat and moisture exchanger (HME, internal volume 50 ml) and an ACD (100 ml), the latter with or without administration of sevoflurane. The ACD was also studied with a test lung at high sevoflurane concentrations. Reflection of CO₂ and dead space effects were evaluated with the single-breath test for CO2.
Sevoflurane reduced but did not abolish CO₂ reflection. In patients, the mean dead space effect with 0.8% sevoflurane was 88 ml larger using the ACD compared with the HME (P<0.001), of which 38 ml was due to CO₂ reflection. Our calculations show that with the use of the ACD, normocapnia cannot be achieved with tidal volume <6 ml kg(-1) even when respiratory rate is increased.
An ACD causes a dead space effect larger than its internal volume due to reflection of CO₂, which is attenuated but not abolished by sevoflurane administration. CO₂ reflection from the ACD limits its use with low tidal volume ventilation, such as with lung protection ventilation strategies.
Clinical Trials NCT01699802.
麻醉保存装置AnaConDa（ACD）可反射呼出的麻醉剂，从而便于在手术室之外使用吸入麻醉剂。然而，呼出的二氧化碳也会被反射，导致死腔效应超过ACD的内部容积。湿度可减弱ACD对二氧化碳的反射。本研究检验七氟醚可进一步减弱二氧化碳反射这一假设。并对我们研究结果的临床意义进行了分析。
12例术后患者使用传统的热湿交换器（HME，内部容积50 ml）和ACD（100 ml）进行机械通气，后者在给予或未给予七氟醚的情况下使用。还在高七氟醚浓度下用测试肺对ACD进行了研究。采用二氧化碳单次呼吸试验评估二氧化碳反射和死腔效应。
七氟醚可减少但不能消除二氧化碳反射。在患者中，使用ACD时，0.8%七氟醚下的平均死腔效应比使用HME时大88 ml（P<0.001），其中38 ml是由二氧化碳反射所致。我们的计算表明，使用ACD时，即使增加呼吸频率，潮气量<6 ml·kg⁻¹时也无法实现正常碳酸血症。
由于二氧化碳反射，ACD导致的死腔效应大于其内部容积，七氟醚给药可减弱但不能消除这种效应。ACD对二氧化碳的反射限制了其在低潮气量通气（如肺保护通气策略）中的应用。
临床试验编号NCT01699802。
