右美托咪啶与异丙酚镇静下允许性高碳酸血症患者颅内压及脑氧代谢的比较

Effects of sedation induced with dexmedetomidine versus propofol oxygen metabolism in patients with permissive hypercapnia

目的比较右美托咪啶与异丙酚镇静下允许性高碳酸血症患者的颅内压及脑氧代谢情况。方法行允许性高碳酸血症通气、Ramsay评分≤2分的急性呼吸窘迫综合征患者24例，年龄28～64岁，APACHE-Ⅱ评分11—18分，采用随机数字表法，将患者随机分为2组（n=12）：右美托咪啶组（D组）和异丙酚组（P组）。调节右美托咪啶输注速率或异丙酚血浆靶浓度使D组和P组患者Ramsay评分逐步达到3、4、5分。于给药前（R）、达各目标镇静水平后30min（T1-3）时采用经颅多普勒超声测定大脑中动脉脑血流速率（CBFV）、搏动指数（PI）和阻力指数（RI），抽取桡动脉血样和颈内静脉球部血样行血气分析，计算脑氧代谢率（CMR05）、动脉．颈内静脉氧含量差（Da-JvO2）、脑氧摄取率（CER02）。结果与R时比较，D组和P组T1-3时MAP、BIS值、CBFV、PI、RI和CMRO2降低（P〈0．05或0．01）；两组各时点Da-jvO2、CER02差异无统计学意义（P〉0．05）；与P组比较，D组各时点BIS值和MAP差异无统计学意义（P〉0．05），CBFV、PI和RI降低（P〈0．05）。D组和P组CBFV与CMR02均呈正相关（相关系数分别为0．80、0．76，P〈0．05）。结论在不同镇静水平，右美托咪啶较异丙酚可明显降低允许性高碳酸血症患者的颅内压，且可保持脑氧供需平衡。

Objective To compare the effects of sedation induced with dexmedetomidine and propofol on intracranial pressure and cerebral oxygen metabolism in patients with permissive hypercapnia. Methods Twentyfour patients with acute respiratory distress syndrome （ARDS） were randomly divided into 2 groups （n = 12 each） ： dexmedetomidine group （group D） and propofol group （group P）. Their APACHE 11 scores were 11-18. The pa- tients were mechanically ventilated （VT 5-7 ml/kg, RR 12-17 bpm, PEEP 6-10 cm H20, FiO2 40-60% ）. PaCO2 was maintained at 50-65 mm Hg. Radial artery was cannulated for direct BP monitoring and blood sampling. Right internal jugular vein was cannulated and the catheter was advanced cephalad until jugular bulb. Continuous infusion of dexmedetomidine was started at 0.5 μg·kg^-1·h^-1 and TCI of propofol was started at target plasma concentration （Cp） of 0.4 μg/ml. The infusion of both drugs was gradually increased until Ramsay score （1 = fully awake, 6 = asleep, unresponsive to loud verbal stimulus） reached 3, 4, 5. Transcranial Doppler monitoring was used to determine cerebral blood flow velocity （CBFV）, pulsatility index （PI） and resistance index （RI） before administration of dexmedetomidine and propofol （TO ） and at 30 min after the 3 levels of sedation were reached （T1-3 ） . Meanwhile blood samples were taken from radial artery and jugular bulb for blood gas analyses. Cerebral O2 metabolic rate （CMRO2 ）, cerebral A-VO2 content differences （Da-jvO2） and cerebral O2 extraction rate （CERO2） were calculated. Results CBFV, PI, RI and CMRO2 were significantly decreased at T1-3 as compared with the baseline values at To in both groups. CBFV was positively correlated with CMROz in both group D （ r = 0.80） and group P （ r = 0.76）. CBFV, PI and RI were significantly lower at TI 3 in group D than in group P. There was no significant change in Da-jvO2 and CERO2 at T1-3 as compared with the baseline values at To in both groups. Conclusion At different sedation levels, dexmedetomidine results in lower intracranial pressure than propofol and maintains the balance between cerebral 02 supply and demand in patients with permissive hypercapnia.