过度通气能够改善幕上开颅术的手术条件吗？一项多中心随机交叉试验研究

背景过度通气作为神经外科手术麻醉中的重要方法，其有效性还缺乏验证。我们在由手术医师评估脑肿胀分级和测定颅内压（ICP）的条件下，选择中度低碳酸血症和正常血液碳酸数值两种情况对接受开颅手术的幕上脑肿瘤患者进行一项双周期随机交叉试验研究。方法275例幕上脑肿瘤患者随机接受以下治疗程序：一是过度通气（动脉二氧化碳分压，PaCO2=25±2mmHg）继以正常通气（动脉二氧化碳分压，PaCO2=37±2mmHg）；二是正常通气继以过度通气。通气和呼气末CO2分压保持稳定20分钟。患者随机接受丙泊酚输注或异氟烷吸入麻醉。在每一试验阶段末由不了解治疗程序的手术医师测定ICP，并以4级评定方法评估脑肿胀分级。结果以通用估计方程模型分析，我们发现过度通气降低了45％脑肿胀加重的风险，P=0．004，95％可信区间为22％-61％，需要治疗患者数为8。过度通气期间ICP均数±标准差为12．3±8．1mmHg，低于正常通气时的16．2±9．6mmHg，P〈0．001。麻醉方式对脑肿胀评估和ICP无影响。结论对幕上脑肿瘤患者而言，手术中过度通气可改善与ICP降低相关的由手术医师评估的脑肿胀程度。

BACKGROUND： Hyperventilation has been an integral, but poorly validated part of neuroanesthefic pracrice. We conducted a two-period, crossover, randomized trial to evaluate surgeon-assessed brain bulk and measured intracranial pressure （ICP） in patients undergoing craniotomy for removal of supratentorial brain tumors during moderate hypocapnia or normocapnia. METHODS： Two-hundred and seventy-five adult patients with supratentorial brain tumors were randomized to one of two treatment sequences： hyperventilation （arterial carbon dioxide tension, PaCO2 25 ± 2 mm Hg） followed by normoventilation （PaCO2 37 ± 2 mm Hg） or normovenfilation followed by hyperventilation. Ventilation and endtidal CO2 tension were kept constant for 20 min. Patients were also randomly assigned to receive a propofol infusion or isoflurane anesthesia. At the end of each study period, subdural ICP was measured and the neurosurgeon, blinded to the treatment group, was asked to rate the brain bulk using a four-point scale. RESULTS： Using a generalized estimation equation model, we found that hyperventilation decreased the risk of increased brain bulk by45%, P =0. 004, 95% confidence intervals 22% to 61%, and the number needed to treat was 8. The mean （±SD） ICP during hyperventilafion, 12.3 ±8. 1 mm Hg, was lower than that during normoventilation, 16.2±9. 6 mm Hg, P 〈0. 001. Anesthetic regimen did not affect brain bulk assessment or ICP. CONCLUSIONS： In patients with supratentorial brain tumors, intraoperative hyperventilation improves surgeon-assessed brain bulk which was associated with a decrease in ICP.