急性颅内高压时呼气末正压通气对脑氧代谢的影响

目的 观察呼气末正压通气（PEEP）对急性高颅压犬脑氧代谢的影响。方法 8只犬,全麻、机械通气,自体血凝块注入右额叶脑内制成颅内高压模型,静脉滴注脂多糖诱发急性肺损伤,PEEP从0cmH2O开始每次增加3cmH2O水柱,直到18cmH2O,每个水平持续20min,在左侧额顶部用光纤颅内压探头监测颅内压（ICP）的变化,记录平均动脉压（MAP）并计算脑灌注压（CPP）。股动脉、左颈内静脉球部逆行置管采血,行血气分析并计算脑氧摄取（CEO2）和脑动静脉氧含量差（Da-jO2）,分析其与MAP、ICP和CPP的相互关系。结果 随着PEEP的递增,MAP下降,ICP,CPP均有不同程度下降,Da-jO2、CEO2呈上升趋势。血流动力变化与脑氧代谢之间无明显相关性。结论 PEEP通气可改善氧合,但使脑灌注下降,血流动力指标与脑氧代谢指标之间无明显一致性,单用ICP、CPP不能完全判断组织灌注是否充分,有必要监测脑氧代谢,以指导设置PEEP水平。

Effect of PEEP on cerebral oxygen metabolism in dogs with induced intracranial hypertension

Objective To investigate the influence of positive end-expiratory pressure (PEEP) on cerebral oxygen metabolism in dogs with induced intracranial hypertension.Methods The intracranial hypertension were induced by auto blood clotting injected into the right frontal lobe of 8 anesthesiaed and mechanical ventilated dogs, and then the lipopolysaccharide was infused to induce the acute lung injury. PEEP was applied in increments of 3 cm H2O from 0 to 18 cm H2O with each level last for 20 min. The intracranial pressure (ICP) was monitored by an optical fiber transducer implanted into left frontal lobe. Mean arterial pressure (MAP) were recorded simultaneously and cerebral perfusion pressure (CPP) was calculated. The blood sampling was collected from femoral artery and jugular bulb to undertake the blood gas analysis. Cerebral extraction of oxygen (CEO2) and cerebral arteriovenous difference of oxygen (Da-jO2) were observed. The correlation was analyzed among MAP, ICP, CPP, CEO2 and Da-jO2.Results With increasing of PEEP level, MAP, ICP and CPP all decreased in different various extent while CEO2 and Da-jO2 displayed a rising tendency. There were no significant relationship among the changes of hemodynamic data and cerebral oxygen metabolism.Conclusion Applying PEEP can improve the oxygenation and damaged the CPP. The changes of hemodynamics are in discrepancy to the parameter of cerebral oxygen metabolism. It is doubtful to assess whether the perfusion of brain tissue is sufficient singly based on the ICP and CPP. It is necessary to monitor the cerebral oxygen metabolism to set up the level of PEEP in order to ensure the oxygenation and cerebral oxygen supply.