Intrathoracic Blood Volume Index for assessment on the responsiveness to volume loading in mechanically ventilated canine with hemorrhagic shock<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

邱海波

QIU Hai-bo

Department of Critical Care Medicine, Zhong-Da Hospital and School of Clinical Medicine, Southeast University, Nanjing 210009, China

Abstract

　　Objective:  To assess the significance of intrathoracic blood volume index (ITBI) on the responsiveness to volume loading in mechanically ventilated canine with hemorrhagic shock.

　　Methods:   Healthy mongrel canines were studied to standardize the modified Wiggers’ blood loss shock method. The MAP reached 50 mmHg and maintained for 60 minutes. Graded volume loading was performed with each volume loading step (VLS) consisting of 7ml.kg-1 Ringer’ given for 2 min. The same VLS were preformed after a period of 15 minutes until continuous change in SV ＜0 was reached. The values of heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), central venous pressure (CVP), pulmonary arteriole wedge pressure (PAWP), ITBI were determined immediately before and 5 minutes after volume loading. 

　　Results:   There was no significant difference between CO measured by Swan-Ganz Catheter and PICCO. The after -mode values of MAP, ITBI, and SV were significant decreased than pre-mode, and HR increased. There was no significant difference in CVP and PAWP between the values after and pre-mode. There was no significant difference in all variables between end-resuscitation and pre-mode. All variables of end-resuscitation were significant difference compared with those of after-mode. Statistically significant correlation were found between △SV after VLS and the baseline values of ITBVI,HR,MAP before fluid loading (r=0.546,－0.312 and 0.340 respectively). No correlation was found between △SV and the baseline value of CVP, PAWP  . Statistically significant correlation were also found between △SV and △ITBI (r=0.563). No correlation was found between △SV and the value of △HR, △MAP,△CVP,△PAWP. 

　　Conclusion:   Assessment of ITBI on the responsiveness to volume loading were more useful indicators than HR, MAP, CVP, and PAWP. It may help to improve resuscitation and hemodynamic management.

　　Key words:   Intrathoracic blood volume index ; Hemorrhagic shock; Canine; Volume loading test; Hemodynamic

失血性休克的复苏问题还存在着很多争论和疑问，低血压和低灌注是常见的血流动力学变化，可能继发一系列免疫功能和器官功能改变。除了尽早彻底止血外，恰当的补液和维持适当的容量状态是治疗的关键。因此在低血容量性休克的快速补液过程中，准确、有效地对治疗效果进行监测是非常重要的。经食道超声心动图(TEE)能准确地评价心功能和前负荷^[1]，但价格昂贵，操作繁琐，限制了其在治疗早期的临床应用，且不能进行持续监测。中心静脉压(central venous pressure, CVP)、肺动脉嵌顿压(pulmonary artery wedge pressure, PAWP)是目前临床常用的通过压力间接评价容量状态的指标，近年来研究显示其对容量判断的敏感性易受到胸腔内压力、心脏及血管顺应性、瓣膜返流等的影响^[2,3]，尤其在有正压通气的时候更是如此，其对容量负荷的不正确的反映会误导临床的治疗。<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

PiCCO血流动力学监测仪可通过置于股动脉的热敏探头，从颈内或锁骨下静脉注入冰盐水，通过热稀释法得到CO(cardiac output, 心输出量)、GEDV(global end diastolic volume, 全心舒张末期容积)并推算出ITBV(intrathoracic blood volume, 胸腔内血容量)和EVLW(extravascular lung water, 血管外肺水)及其指数CI、ITBVI (intrathoracic blood volume index, 胸腔内血容量指数)、GEDVI(global end diastolic volume index, 全心舒张末期容积指数)和EVLWI(extravascular lung water index, 血管外肺水指数)，PICCO 监测可在床边进行，操作简便，已有研究报道ITBVI可能是液体复苏过程中反映容量状态的良好指标^[4,5]。本实验通过建立犬的失血性休克模型，比较ITBVI、CVP、PAWP对失血性休克犬容量状态的评价的价值，以得到更好地评价容量状态的方法和指标。

材料和方法

一、材料

成年健康杂种犬共14只，体重11.7±1.1公斤，雌雄各半，由东南大学医学院实验动物中心提供。

二、复制犬失血性休克模型

动物称重后，给予2%戊巴比妥钠(30mg/kg) 静脉注射麻醉，仰卧位固定。经口气管插管(7^#)，接Evita4呼吸机 (德国德尔格公司)。模式为双水平气道正压通气 (BIPAP)，高压9-11cmH₂O (1cmH₂O = 0.098 kPa)，呼气末正压(PEEP)4cmH₂O，高压时间0.6s，呼吸频率30次/min，吸入氧浓度(FiO₂)40％。

经犬右颈内静脉置入5.5F肺动脉漂浮导管鞘 (Swan-Ganz导管,美国Arrow公司), 5F漂浮导管接压力系统，调零后在压力波形监测下将导管置入，直至出现肺动脉嵌顿波形，监测CVP、PAWP，导管鞘侧管接 PiCCO温度探头，左股动脉置 PiCCO动脉导管后接PiCCO仪(德国Pulsion Medical System)，并接压力换能器监测有创动脉压，右股动脉置单腔管以备造模，经左股静脉置中心静脉导管行液体复苏。

稳定30分钟，采用改良的Wiggers’法^[6]制备失血性休克犬模型，经右股动脉放血直至MAP下降到50mmHg (开始速度4－5ml/kg／min左右，肝素5000U预先加入储血瓶中)(1mmHg =0.133kPa)，适当放血和输血少许维持MAP在50 mmHg左右并稳定60分钟，模型成功。

三、监测指标

1. 血流动力学: 监护仪 (1500型，美国Spacelab公司) 持续监测犬心电图，记录心率 (HR)。经PiCCO导管持续监测有创平均动脉压 (MAP) ，经中心静脉导管注射4℃生理盐水5ml，利用单指示剂热稀释法原理经 PiCCO监测仪测定CO、ITBVI，并持续监测HR、SV、MAP，同时经Swan-Ganz导管测定CO、CVP、PAWP。

2. 呼吸力学：监测VT。

四、容量负荷试验

经中心静脉导管在2分钟内快速滴入林格氏液7ml/kg，作为一次容量负荷试验，稳定5分钟后测定HR、MAP、CVP、PAWP，经漂浮导管鞘注入4℃冰盐水测定CO、SV、ITBVI，15分钟后重复容量负荷试验，分别记录容量负荷试验前及试验后5分钟的HR、MAP、CVP、PAWP、CO、SV、ITBVI等指标。当SV不再增加时(即△SV小于0时)终止实验。

五、观察条件<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

实验期间，2%戊巴比妥钠10 mg/kg/h持续静脉泵入维持麻醉状态，NS2ml/kg/h持续静脉输入补充不显性失水，加盖毛毯维持犬血温在36-37℃。调整呼吸机参数维持PaCO₂在30-40mmHg。

六、统计学方法

数据以均值±标准差表示，统计学处理采用SPSS11.5软件进行。组间比较采用单因素方差分析，各监测指标及其变化与△SV(每搏输出量变化)的相关性采用Pearson相关分析，p<0.05有统计学意义。

结　果

一、一般情况

14只失血性休克犬成模平均放血量为328±36ml/只,共进行容量负荷试验98次，平均7.0±1.3次。机械通气模式BIPAP，潮气量为108±12ml。两种方法CO结果对比无统计学差异（P>0.05）。

二、造模前、造模后及复苏终点的血流动力学及容量指标

造摸后与造模前相比HR的升高、MAP、ITBVI、SV的下降有显著性差异。CVP、PAWP的改变无显著性差异，复苏终点与造模前相比各指标均无显著性差异，复苏终点与造模后相比各指标均有显著性差异(表1) 。

三、血流动力学和容量指标与△SV的相关性

ITBVI、HR、MAP与△SV之间有显著相关性，相关系数r分别为0.546、－0.312和0.340，而CVP、PAWP与△SV 无相关性，容量复苏试验后△ITBVI与SV、△SV之间有显著相关性，相关系数r为0.563，而△CVP、△PAWP、△HR、△MAP与△SV 无相关性(表2、图1) 。

　　本研究认为，ITBVI可用于机械通气的失血性休克前负荷的评价，优于HR、MAP、CVP和PAWP，对维持最佳容量状态，达到最佳的复苏效果有指导意义。而且PICCO测量ITBVI放置导管不经过心脏，创伤性较小，操作简单，并发症少，是一种简便、有效的临床监测手段。
参 考 文 献
1. Claude P T, Fergus W, David M. The use of transesophageal echocardiography for preload assessment in critically ill patients. Anesth Analg, 2000,90(2): 351-355.
2. Mark JB. Central venous pressure monitoring: clinical insights beyond the numbers. J Cardiothorac Vasc Anesth, 1991, 5(2): 163-173.
3. Connors AF, Speroff T, Dawson NV, et al. The effective of right heart catheterization in the initial care of critically ill patients. JAMA, 1996, 276(11): 889-897.
4. Sakka SG, Bredle DL, Reinhart K, et al. Comparison between intrathoracic blood volume and cardiac filling pressures in the early phase of hemodynamic instability of patients with sepsis or septic Shock. J Crit Care, 1999, 14(2): 78-83.
5. Wiesenac kC, Prasser C, Rodig G, et al. Stroke volume variation as an indicator of fluid responsiveness using pulse contour analysis in mechanically ventilated patients. Anesth Analg, 2003, 96(5):1254-1257.
5. Zollman W, Culpepper RD, Turner MD, et al. Hemorrhagic shock in dogs comparison of treatment with shed blood alone versus shed blood plus ringer’s lactate: intravascular pressures, cardiac output, oxygen consumption, arteriovenous oxygen differences, extracellular fluid PO2, electrolyte changes, and survival rates. Am J Surg, 1976, 131(3): 298-305.
6. Godje O, Peyerl M, Seebauer T, et al. Central venous pressure, pulmonary capillary wedge pressure and intrathoracic blood volumes as preload indicators in cardiac surgery patients. Eur J Cardiothorac Surg, 1998, 13(5): 533-540.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />