Apan A, Muluk N Bayar, Güler S, Budak B
Department of Anaesthesiology, Kirikkale University Faculty of Medicine, Ankara, Turkey.
B-ENT. 2013;9(2):141-50.
The aim of this study was to investigate the effects of N2O-O2 mixture (Inspired O2 30%) on middle ear pressure (MEP) in children compared with the effects of an air-oxygen mixture (Inspired O2 50%).
The study included thirty child patients who underwent general anaesthesia for different reasons, with the exception of ENT problems and ear interventions. They were randomly divided into two groups. Group 1 (15 children: 10 male and 5 female) received a N2O-O2 mixture (Inspired O2 30%); and group 2 (15 children: 10 male and 5 female) were given an air-oxygen mixture (Inspired O2 50%). MEP was measured using a portable impedance analyser before the operation (PreO),10 minutes after intubation (10AEn), 30 minutes after intubation (30AEn), 10 minutes before extubation (10BEx), 15 minutes after the operation (PO15), 30 minutes after the operation (PO30), 1 hour after the operation (PO1h) and 6 hours after the operation (PO6h).
The pressure and compliance values were the same in groups 1 and 2. The pressure-time graphs for the two groups were different: in Group 2, MEP rose quickly at 10AEn and positive pressure values were seen in the middle ear. MEP then fell rapidly until the end of the surgery and lower and negative pressures (Mean -50 daPa) were observed at PO6h. In Group 1, MEP was elevated at 10AEn and positive pressure was found (but not as high as in Group 2). MEP then fell more slowly. In other words, positive pressure in the middle ear persisted longer and the middle ear was subjected to positive pressure and nitrogen over a longer period. Separate analyses were made in Groups 1 and 2 of pressure differences and of compliance values at eight measurement points using the Friedman test. Differences in pressure values were found to be statistically significant in both Group 1 (p = 0.000) and Group 2 (p = 0.000). In Group 1, all the 10AEn and 30AEn values were significantly higher than the PreO, PO30, PO1h and PO6h values. The 10BEx value was significantly higher than the PreO and PO1h values. The PO15 value was significantly higher than the PreO value. In Group 2, the PO6h value was significantly lower than the 10BEx, 10AEn and 30AEn values. The PO1h value was significantly lower than the 30AEn values. The MEP values increased in Group 1 in younger and taller children and in children receiving anaesthesia for shorter periods. MEP values increased in Group 2 in younger and taller children, and in heavier children. MEP values fell with the length of anaesthesia.
In brief anaesthesia, nitrogen was not removed from the middle ear quickly in Group 1: middle ear pressure values were higher. The nitrous oxide remained in the middle ear longer and so the possibility of ear toxicity may increase. In Group 2, 50% O2 was rapidly absorbed and removed from the middle ear and so middle ear pressure was not as high. It may be concluded that air-oxygen mixture (Inspired O2 50%) anaesthesia should be recommended as being more reliable in tympanoplasties and other middle ear interventions than a N2O-O2 mixture (Inspired O2 30%).
本研究旨在比较氧化亚氮-氧气混合气（吸入氧浓度30%）与空气-氧气混合气（吸入氧浓度50%）对儿童中耳压力（MEP）的影响。
该研究纳入30例因不同原因接受全身麻醉的儿童患者，但不包括耳鼻喉问题及耳部手术患者。他们被随机分为两组。第1组（15名儿童：10名男性和5名女性）接受氧化亚氮-氧气混合气（吸入氧浓度30%）；第2组（15名儿童：10名男性和5名女性）给予空气-氧气混合气（吸入氧浓度50%）。在手术前（PreO）、插管后10分钟（10AEn）、插管后30分钟（30AEn）、拔管前10分钟（10BEx）、术后15分钟（PO15）、术后30分钟（PO30）、术后1小时（PO1h）和术后6小时（PO6h）使用便携式阻抗分析仪测量MEP。
第1组和第2组的压力和顺应性值相同。两组的压力-时间图不同：在第2组中，MEP在10AEn时迅速升高，中耳出现正压值。然后MEP迅速下降直至手术结束，在PO6h观察到较低的负压（平均-50 daPa）。在第1组中，MEP在10AEn时升高并出现正压（但不如第2组高）。然后MEP下降得更慢。换句话说，中耳正压持续时间更长，中耳在更长时间内承受正压和氮气。使用Friedman检验对第1组和第2组在八个测量点的压力差异和顺应性值进行了单独分析。发现第1组（p = 0.000）和第2组（p = 0.000）的压力值差异具有统计学意义。在第1组中，所有10AEn和30AEn值均显著高于PreO、PO30、PO1h和PO6h值。10BEx值显著高于PreO和PO1h值。PO15值显著高于PreO值。在第2组中，PO6h值显著低于10BEx、10AEn和30AEn值。PO1h值显著低于30AEn值。第1组中年龄较小、身高较高且接受麻醉时间较短的儿童MEP值升高。第2组中年龄较小、身高较高且体重较重的儿童MEP值升高。MEP值随麻醉时间延长而下降。
简而言之，在第1组中，麻醉期间氮气不能迅速从中耳排出：中耳压力值较高。氧化亚氮在中耳停留的时间更长，因此耳部毒性的可能性可能增加。在第2组中，50%的氧气被迅速吸收并从中耳排出，因此中耳压力没有那么高。可以得出结论，在鼓膜成形术和其他中耳手术中，空气-氧气混合气（吸入氧浓度50%）麻醉比氧化亚氮-氧气混合气（吸入氧浓度30%）麻醉更可靠，应予以推荐。
