不同程度过度通气对蛛网膜下腔出血犬脑氧代谢的影响

Effects of graded hyperventilation on cerebral oxygen metabolism in a cisterna magna blood injection model of snbarachnoid hemorrhage in dogs

目的评价不同程度过度通气对蛛网膜下腔出血犬脑氧代谢的影响。方法健康雄性犬，体重12～18kg，采用枕大池二次注血法制备犬蛛网膜下腔出血模型，取模型制备成功犬24只，随机分为4组（n=6）：正常通气组[N组，呼气末二氧化碳分压（PETCO2）35～40mmHg]、轻度过度通气组（L组，PnCO2 30～35mm Hg）、中度过度通气组（M组，PETCO2 25～30mmHg）和重度过度通气组（H组，PETCO2 20～25mmHg）。调整呼吸机参数使各组PETCO2分别达到所需数值，维持机械通气4h。分别于二次注血完毕稳定后30min（T0）、机械通气1、2、3、4h（T1-4）时记录基本生命体征，测定颅内压、颈静脉血氧饱和度（SjvO2）、颈静脉血氧分压（PjvO2）、颈动脉．静脉血氧含量差（Da—jvO2）、脑氧摄取率（ERO2）和颈静脉-动脉血乳酸浓度差（Djv—aL）。分别于T0-4、机械通气结束后4、12、20、44、92和188h（L5-10）时采集前肢内侧皮下头静脉血测定S-100B蛋白浓度。结果与N组比较，其余各组T1～4时颅内压降低，M组和H组Da—jvO2、ERO2升高，H组Djv—aL升高，M组T2～4时Djv—aL升高，H组T2-3时SjvO2降低，H组T1-10时血清S-100B蛋白浓度升高（P〈0．05）；与T0时比较，N组、M组和H组T5-6时、L组T4～8时血清S-100B蛋白浓度升高（P〈0．05）。结论对蛛网膜下腔出血犬，轻度及中度过度通气不会加重脑损伤；重度过度通气时脑氧供需失衡，脑损伤加重。

Objective To investigate effects of graded hyperventilation on cerebral oxygen metabolism in a cisterna magMa blood injection model of subarachnoid hemorrhage in dogs. Methods A model of subarachnoid hemorrhage in dogs was established by using two injections of autologous blood into cisterna magma. Twenty-four male dogs weighing 12-18 kg were randomly divided into four groups （ n = 6 each） ： group N normally ventilated （PETCO2 35-40 mm Hg）, group L lightly ventilated （PET CO2 30-35 mm Hg）, group M moderately ventilated （PETCO2 25-30 mm Hg） and group P profoundly ventilated （PETCO2 20-25 mm Hg）. The expected PETCO2 levels were maintained through adjustment of respirator parameters. The dogs were ventilated for 4 h and the anesthetics were discontinued. Vital signs, intracerebral pressure （ICP）, jugular venous oxygen saturation （SjvO2）, jugular venous oxygen pressure （PjvO2）, arterio-jugular venous oxygen content difference （Da-jvO2）, cerebral oxygen extraction ratio （ERO2） and arterio-jugular venous differences of lactate （Djv-aL） were recorded at 30 min after two injections of blood （T0 ） and at 1, 2, 3, 4 h（T1- 4 ） following mechanically ventilated. Blood samples were drawn from cephalic vein of forelimb to determine S-100B protein before the first injection of blood, at To 4 and at 4, 12,20,44,92 and 188 h （T5-10）after ventilation. Results Compared with group N,ICP at Tj4 was significantly decreased in the other groups, Da-jvO2 and ERO2 significantly increased in group M and H, Djv-aL significantly increased in group H and at T2-4 in group M, SjvO2 significantly decreased at T2,3 in group H and S-100B protein concentration significantly elevated at T1-10 in group H （P 〈 0.05）. Compared with To, S-100B protein concentration significantly elevated at T5-8 in group N, M and H and at T4-8 in group L （P 〈 0.05）. Conclusion Mild hyperventilation and moderate hyperventilation does not aggravate brain injury, while profound hyperventilation exacerbates brain injury due to imbalance between cerebral oxygen supply and consumption after subarachnoid hemorrhage in dogs.