呼吸频率对容量控制机械通气脓毒性休克患者动脉血和中心静脉二氧化碳分压差的影响

Effects of respiratory rate on venous-to-arterial CO2 tension difference in septic shock patients with volume mechanical ventilation

目的探讨机械通气脓毒性休克患者呼吸频率(RR)设定对动脉血和中心静脉二氧化碳分压差(CO2-gap)的影响.方法选择2017年1月至2018年12月中国人民解放军第九○一医院收住的脓毒性休克成人住院患者.所有患者均接受机械通气,模式为容量控制.通过呼吸机调节RR.RR从10次/min开始,每60 min加2次RR,直至16次/min.每时段同时采集动脉及中心静脉血气进行组织灌注指标的评价,比较患者不同时段CO2-gap、酸碱度(pH)、动脉氧分压(PaO2)、动脉二氧化碳分压(PaCO2)等指标水平变化与RR的相关性.结果随RR增加,CO2-gap、pH值和PaO2逐渐增加[CO2-gap(mm Hg):5.76±2.02 vs.9.85±1.92,pH:7.350±0.078 vs.7.430±0.078,PaO2(mm Hg):114.10-±24.96 vs.144.30±27.57],中心静脉二氧化碳分压(PcvCO2)和PaCO2均降低[PcvCO2(mm Hg):50.66±8.09 vs.41.43±12.50,PaCO2(mm Hg):44.90±7.60 vs.33.50±6.80],差异均有统计学意义(P<0.05).PaCO2的下降趋势比PcvCO2更明显.碳酸氢根(HCO3-)和二氧化碳总浓度(ctCO2)随RR的增加而明显降低[HCO3-(mmol/L):28.58±5.22 vs.22.44±4.99,ctCO2(mmol/L):56.32±21.90 vs.45.21±19.60,P<0.05];中心静脉血氧饱和度[ScvO2(%):73.1±7.7vs.75.2±8.7]有上升趋势,但无统计学意义(P>0.05).结论对于容量控制通气的脓毒性休克患者,呼吸机诱导的呼吸性碱中毒可引起CO2-gap的增加.RR设定对于此类患者可能是除心输出量低、灌注不足之外,另一个影响CO2-gap水平的指标.

Objective To explore the effects of respiratory rate(RR)on venous-to-arterial CO2 tension difference(CO2-gap)in septic shock patients with volume m echanical ventilation.Methods Adult patients with septic shock underwent volume mechanical ventilation between January 2017 and Decem ber 2018 were chosen.RR started at 10 breaths/minute and added by 2 breaths/minute every 60 minutes up to 16 breaths/minute.In different HR periods,the arterial and central venous blood gases were collected at the same time in order to evaluate the tissue perfusion indexes,and to compare the correlation of CO2-gap,pH,arterial partial pressure of oxygen(PaO2),partial pressure of carbon dioxide(PaCO2)with RR.Results CO2—gap,pH and PaO2 induced by hyperventilation increased significantly from 10 breaths/minute to 16 breaths/minute[CO2-gap(mmHg):5.76±2.02 vs.9.85±1.92,pH:7.350±0.078 vs.7.430±0.078,PaO2(mmHg): 114.10±24.%vs.144.30±27.57],and central venous carbon dioxide pressure(PcvCO2)and PaCO2 decreased respectively[PcvCO2(m m Hg):50.66±8.09 vs.41.43±12.50,PaCO2(mmHg):44.90±7.60 vs.33.50±6.80],all P<0.05.But the downward trend of PaCO2 was more obvious than PcvCO2.Hydrocarbonate(HCO3-)and concentration of total carbon dioxide(c tC 02)decreased markedly when the RR grew[HCO3-(mmol/L):28.58±5.22 vs.22.44±4.99,ctCO2(mmol/L):56.32±21.90 vs.45.21±19.60],both P<0.05.Although central venous oxygen saturation(ScvO2)had upward trends(%:73.1±7.7 vs.75.2±8.7),they were not significant(P>0.05).Conclusion In septic patients with volume controlled ventilation,respiratory alkalosis induced by hyperventilation enables the increase of CO2-gap.Clinician should make sense of cautious interpretation of CO2-gap as the low cardiac output and inadequate perfusion in the hemodynamically ventilated stable septic shock.RR is an important factor.