Section of Critical Care & Anesthesia, Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, USA.
Equine Vet J. 2009 Nov;41(8):747-52. doi: 10.2746/042516409x416198.
It is unknown whether administration of gas-mixtures high in inspired fraction of oxygen (FiO2) under general anaesthesia may increase formation of pulmonary atelectasis and impair gas exchange.
To evaluate the effects of different FiO2 on pulmonary gas exchange in isoflurane-anaesthetised horses breathing a helium/oxygen (He/O2) mixture.
Thirty healthy mature horses were sedated with i.v. acepromazine (0.02 mg/kg bwt), detomidine (0.002 mg/kg bwt) and xylazine (02-0.4 mg/kg bwt). General anaesthesia was induced with i.v. 5% guaifenesin to effect, diazepam (0.1 mg/kg bwt) and ketamine (2 mg/kg bwt), and maintained with isoflurane. Fifteen horses (Group HX) were ventilated mechanically with gas mixtures of successively increasing FiO2 (0.25-030, 0.50-0.55, > 0.90), obtained by blending 02 with Heliox (70% He/30% O2). The other 15 horses (Group O) were ventilated immediately with 100% O2 (FiO2 > 0.90). After 20 min of ventilation at the different FiO2 levels in Group HX and after 60 min in Group O, PaO2 and PaCO2 were measured and the alveolar to arterial PO2 gradient (P(A-a)O2) was calculated. Data analysis included robust categorical regression with clustering on horse (P < 0.05).
Inhalation of a He/O2 mixture with FiO2 as low as 0.25-030 ensured adequate arterial oxygenation and was associated with a smaller P(A-a)O2 gradient than inhalation of pure O2 (P < 0.05). In Group HX, PaO2 increased with each rise in FiO2 and so did P(A-a)O2 (P < 0.05). The PaO2 was significantly lower and the P(A-a)O2 higher in Group O compared to Group HX at a FiOz >0.90 (P < 0.05).
Administration of a He/O2 gas mixture low in FiO2 can better preserve lung function than ventilation with pure oxygen. A step-wise increase of FiO2 using a He/O2 gas mixture might offer advantages with respect to pulmonary gas exchange over an immediate exposure to 100% 2O2.
全麻下吸入高氧分数（FiO2）混合气体是否会增加肺不张形成并损害气体交换尚不清楚。
评估异氟醚麻醉下呼吸氦/氧（He/O2）混合气体时不同 FiO2 对肺气体交换的影响。
30 匹健康成熟马静脉注射乙酰丙嗪（0.02 mg/kg bwt）、地西泮（0.002 mg/kg bwt）和二甲苯胺噻嗪（0.2-0.4 mg/kg bwt）镇静。静脉注射 5%瓜非西林至起效，给予地西泮（0.1 mg/kg bwt）和氯胺酮（2 mg/kg bwt）诱导全身麻醉，并使用异氟醚维持。15 匹马（HX 组）通过混合 02 与 Heliox（70% He/30% O2），依次增加 FiO2（0.25-0.30、0.50-0.55、>0.90），用机械通气。另外 15 匹马（O 组）立即用 100% O2（FiO2>0.90）通气。在 HX 组的不同 FiO2 水平通气 20 分钟后，在 O 组通气 60 分钟后，测量 PaO2 和 PaCO2，并计算肺泡-动脉 PO2 梯度（P（A-a）O2）。数据分析包括基于马的稳健分类回归（P<0.05）。
吸入 FiO2 低至 0.25-0.30 的 He/O2 混合物可确保足够的动脉氧合，与吸入纯 O2 相比，P（A-a）O2 梯度较小（P<0.05）。在 HX 组中，随着 FiO2 的每次升高，PaO2 增加，P（A-a）O2 也增加（P<0.05）。与 HX 组相比，O 组在 FiOz>0.90 时 PaO2 明显较低，P（A-a）O2 较高（P<0.05）。
与纯氧通气相比，低 FiO2 的 He/O2 混合气体可更好地维持肺功能。与立即暴露于 100% 2O2 相比，使用 He/O2 混合气体逐步增加 FiO2 可能在肺气体交换方面具有优势。
