Hemodynamic, blood volume, and oxygen transport responses to albumin and hydroxyethyl starch infusions in critically ill postoperative patients

Hemodynamic, plasma volume, and oxygen transport effects were measured after administration of 500 ml of 5% albumin or 6% hydroxyethyl starch (HES) in hypovolemic postoperative patients using a prospectively randomized crossover design. Both agents produced marked and significant improvement in plasma volume and flow as well as small transient increases in arterial and venous pressures, urine output, colloidal osmotic pressure (COP), and oxygen transport. The authors conclude that HES is a safe, inexpensive, effective plasma expander that has hemodynamic effects similar to those of other colloids. It was apparent from these and other studies that clinically stable postoperative patients may have appreciable blood volume deficits. Routine vital signs correlated poorly with the preinfusion control hemodynamic values or the changes in blood volume status after volume loading. Normal cardiac output, central venous pressure (CVP), and pulmonary arterial wedge pressure (WP) values are commonly seen in critically ill postoperative patients who, nevertheless, may be hypovolemic. Measurement of changes in these variables after a fluid challenge is a useful way to assess plasma volume status.     

The significance of colloid osmotic pressure measurement after crystalloid and colloid infusions

Colloid osmotic pressure (COP) was followed postoperatively in 55 randomized patients. After minor operations and short-term infusion therapy only small changes of the COP could be observed and it was concluded that after such operation COP measurement is unnecessary. After major surgical interventions, however, COP measurement gave valuable hints. It was shown that even in the case of moderate blood loss replaced by crystalloids an abnormally low COP did not occur. The same applied also to preoperative hemodilution. It was unnecessary to substitute the withdrawn blood with a colloid solution. In addition, COP measurement helped to avoid expensive albumin administrations and indicated colloid overload in cases of pulmonary edema.     

Sequential cardiorespiratory patterns in septic shock

Sequential hemodynamic and oxygen transport monitoring was performed in 33 patients with septic shock to define the temporal pattern of physiologic events. Measurements taken over a 24-h period before the hypotensive crisis, defined as the lowest initial mean arterial pressure (MAP), were compared to those taken during the 48 h thereafter. In the 24-h period before the hypotensive crisis, there were increases in cardiac index (CI), central venous pressure (CVP), pulmonary capillary wedge pressure (WP), pulmonary vascular resistance index (PVRI), and pulmonary shunt (Qsp/Qt), but decreases in MAP, systemic vascular resistance index (SVRI) and oxygen delivery (Do2). When sequential cardiorespiratory patterns were examined, oxygen consumption (VO2) fell transiently to significantly low values 12 h before as well as at the time of the hypotensive crisis. SVRI fell and CI rose to values significantly different from normal in the 4 h before the low MAP. During the subsequent 48 h after the hypotensive crisis, CI, CVP, WP, PVRI and Qsp/Qt remained elevated. Values for MAP, SVRI, DO2, and VO2 were significantly reduced. These results demonstrate the existence of antecedent cardiorespiratory alterations that precede the hypotensive episode in septic shock and suggest that flow maldistribution in the systemic circulation is an early event with possible pathogenic significance.     

Intravascular volume monitoring and extravascular lung water in septic patients with pulmonary edema

OBJECTIVE: To evaluate whether different indicators using for guiding volume expansion are valuable tools to assess edematous lung injury in patients with septic shock. DESIGN AND SETTING: Prospective observational clinical study in a university intensive care unit. PATIENTS: Sixteen consecutive mechanically ventilated patients developing septic shock with evidence of pulmonary edema on chest radiograph and severe hypoxemia (PaO(2)/FIO(2) <250 mmHg). MEASUREMENTS AND RESULTS: A pulmonary artery catheter was used for the measurement of cardiac index (CI), central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP). A fiberoptic catheter was placed in the descending aorta. Measurements of extravascular lung water index (EVLWI), intrathoracic blood volume index (ITBVI), and total end-diastolic volume index (TEDVI) were obtained using the thermal dye dilution technique. Measurements were taken just after placement of catheters and 24 h later. Fluid balance was also estimated within the first 24 h. TEDVI and ITBVI were significantly correlated with EVLWI, but not CVP and PAOP. Analysis of 24-h changes showed that the changes in TEDVI and in ITBVI reflected the change in EVLWI, whereas PAOP, CVP, and fluid balance did not. CONCLUSIONS: Volume variables (TEDVI, ITBVI) are more useful indicators than pressure variables (CVP, PAOP) for assessment of EVLWI in septic patients with pulmonary edema.     

Reliability of clinical monitoring to assess blood volume in critically ill patients

Blood volumes measured by indicator dilution method in over 1500 instances of critically ill patients of various etiologies and at various times throughout their critical illness were compared with the values of concomitantly measured mean arterial pressure (MAP), CVP, pulmonary arterial wedge pressure (WP), Hct, and cardiac output. During resuscitation from hypovolemic shock, the patients' blood volumes and the monitored variables were significantly altered. However, there were poor correlations between the extent of blood volume changes and these variables during resuscitation as well as throughout the critical illness, irrespective of the etiologic type or stage of shock. With administration of a fluid load, blood volume and values of the commonly monitored variables improved appropriately, but the correlation coefficients, in general, were not good. The data suggest that the commonly monitored variables, in and of themselves, do not reflect adequately the blood volume status in critically ill patients.     

Sequential cardiopulmonary variables of infants and children in septic shock

Sequential cardiopulmonary variables were analyzed in 32 infants and children with septic shock. Variables were staged by a system based on therapeutic efforts to control blood pressure. There were 14 survivors and 18 nonsurvivors. Systemic circulation variables (MAP, cardiac index [CI], systemic vascular resistance index [SVRI], wedge pressure [WP], left cardiac work index [LCWI]) and pulmonary circulation variables (mean pulmonary artery pressure [MPAP], pulmonary vascular resistance index [PVRI], CVP, right cardiac work index [RCWI]) were similar in survivors and nonsurvivors. Pulmonary variables (intrapulmonary shunt [Qsp/Qt], fraction of inspired oxygen [FIO2], Pao2, PaCO2) revealed significantly more dysfunction in nonsurvivors than survivors during the postresuscitation (PR) and middle (M) shock stages. Even though oxygen delivery was equivalent in survivors and nonsurvivors, nonsurvivors demonstrated decreased oxygen utilization variables (oxygen consumption [Vo2], arteriovenous oxygen content difference [C(a-v)O2], O2 extraction index, core temperature) during the resuscitation (RS) and PR stages.     

Haemodynamic response to acute hypovolaemia, rapid blood volume expansion and adrenaline administration in an infant animal model

We performed a prospective experimental animal study in seven sedated and mechanically ventilated piglets weighing 9+/-0.8 kg, to assess the haemodynamic response to acute hypovolaemia, rapid blood volume expansion and adrenaline (epinephrine) administration in an infant animal model. Withdrawal of 20 mL/kg of blood (hypovolaemia), rapid infusion of 20 mL/kg of blood (expansion) and the administration of 0.01 mg/kg of adrenaline were made in each animal. Heart rate, mean blood pressure (MBP), central venous pressure (CVP), pulmonary capillary pressure (PCP), cardiac index (CI), systemic vascular resistance index (SVRI), left ventricular contractility (Dp/dtmax), blood volume variables, including intrathoracic blood volume index (ITBI), global end-diastolic volume (GEDVI) and extravascular lung water index (ELWI). Hypovolaemia produced a significant decrease in the pressure, volume and CI variables, with an increase in SVRI and a decrease in Dp/dtmax. After expansion, all variables returned towards normal, with persistence of the SVRI increase and Dp/dtmax decrease. Changes in the blood volume variables (ITBI and GEDVI) were larger than in the pressure variables (CVP, PCP) in the case of both hypovolaemia and expansion. Adrenaline caused a slight increase in heart rate, MBP, CVP, PCP and Dp/dtmax with a greater increase in SVRI. None of the interventions led to changes in ELWI. We conclude that acute hypovolaemia produces an increase in SVRI and a decrease in Dp/dtmax that does not return fully to normal with restoration of blood volume. ITBI and GEDVI are more sensitive to changes in blood volume than CVP and PCP. Rapid blood volume expansion and adrenaline administration do not affect extravascular lung water.     

Five percent human albumin in lactated Ringer's solution for resuscitation from hemorrhagic shock: efficacy and cardiopulmonary consequences

Using an ovine model of acute hemorrhagic shock, we evaluated the utility of 5% albumin in lactated Ringer's (5% ALR) solution as a resuscitation solution. After instrumentation and obtaining baseline values for BP, mean arterial pressure (MAP), pulmonary capillary wedge pressure (WP), CVP, cardiac output, extravascular lung water (EVLW), and blood gases (mixed venous and arterial), animals were rapidly exsanguinated to an MAP of 50 mm Hg. After 30 min at this pressure, measurements were repeated and 5% ALR was administered until two of three variables (WP, MAP, cardiac output) were restored to baseline values. The administration of 5% ALR was continued as needed to maintain baseline values of these variables. Sixty minutes later, data were again recorded. For induction of shock, 15.7 +/- 5.2 ml of blood/kg body weight was removed. Pulmonary artery pressure, WP, MAP, and cardiac output all significantly decreased with shock. After resuscitation, all values except MAP returned to baseline. The resuscitation volume of 5% ALR was 25.2 +/- 18.4 ml/kg. There were no changes in EVLW or intrapulmonary shunt. Oxygen delivery was significantly compromised during shock but returned to baseline after resuscitation. We conclude that in a model such as ours, 5% ALR can reverse the hemodynamic effects of acute hemorrhagic shock.     

老年患者重大手术后肺复张疗效观察

目的 观察肺复张(RM)对老年患者重大手术后肺不张及肺部感染的预防作用并评价其安全性.方法 选择2007年2月-2008年2月北京空军总医院重症加强治疗病房(ICU)收治的70岁以上老年患者40例,均为重大手术后,全麻手术持续6 h以上,麻醉、肌松状态入ICU,均为有创动脉压监测.随机分为RM试验组和非RM对照组,RM条件为吸入氧浓度0.60,呼吸频率20次/min,潮气量5 ml/kg,呼气末正压25 cm H2O(1 cm H2O=0.098 kPa),吸呼比1∶2,持续30 s,1 h后重复1次.记录RM前、后2 min及RM实施过程中心率(HR)、中心静脉压(CVP)、平均动脉压(MAP)、气道平台压(Pplat)、脉搏血氧饱和度(SpO2)的变化;RM前及末次RM 1 h后进行动脉血气分析;观察两组患者肺不张及肺部感染发生情况.结果 ①RM操作中HR、MAP、CVP有显著变化(P均<0.05),但未影响循环功能.②RM后2 min CVP迅速恢复,RM操作前后比较HR、MAP、CVP、SpO2变化不明显(P均>0.05);RM后Pplat显著降低(P<0.05).③RM组实施RM后肺不张、肺部感染的发生率均显著低于非RM组(P均<0.05).④RM后氧合指数较前变化明显(P<0.05).结论 RM可预防老年患者重大手术后肺不张及肺部感染的发生,RM在老年患者中使用较安全,并可明显改善老年患者氧合指数.     

Wedge pressure confirmation by aspiration of pulmonary capillary blood

In order to define the contribution of wedge blood composition to pulmonary artery wedge pressure (WP) measurement, we made 28 comparisons of WP and left atrial pressure (LAP) in 16 stable patients with pulmonary or cardiac failure after cardiac surgery. All technical problems associated with initial WP measurements were eliminated before simultaneously recording WP and LAP. Wedge blood samples (w), withdrawn from the distal pulmonary artery catheter port in the balloon occlusion position, were compared with paired arterial (a) blood samples. Wedge blood was defined as pulmonary capillary blood when the following three wedge-arterial gradient criteria were satisfied: (PwO2 - PaO2) greater than or equal to 19 torr; (PaCO2 - PwCO2) greater than or equal to 11 torr; and (pHw-pHa) greater than or equal to 0.08. When capillary blood was withdrawn from the wedge position, there was no difference between WP and LAP measurements. When wedge blood failed to satisfy capillary criteria, WP was significantly (p less than .05) different from LAP. Aspiration of capillary blood from the wedge position in ICU patients confirms that WP faithfully reflects LAP. It identifies those differences between WP and LAP which remain after technical problems are eliminated.     

Variation in Blood Pressure as a Guide to Volume Loading in Children Following Cardiopulmonary Bypass

OBJECTIVE: Intravascular volume loading is used to optimize cardiac output in children following weaning from cardiopulmonary bypass. Central venous pressure (CVP) is frequently used to titrate fluid administration but it is often misleading in predicting fluid responsiveness. Variation in the arterial pressure waveform is exaggerated in patients with deficient intravascular volume and has been shown to be a good predictor of fluid responsiveness in adults following cardiac surgery. The aim of this study was to compare the measures of variation in blood pressure as a guide to volume loading in children following cardiopulmonary bypass. METHODS: After ethical approval, we collected continuous real-time measurements from 25 children during volume loading after cardiopulmonary bypass. Subjects with moderate or severe tricuspid incompetence or who did not require volume loading during weaning from cardiopulmonary bypass were excluded from the study. Unstable readings were excluded from analysis. Systolic Pressure Variation (SPV), Pulse Pressure Variation (PPV) and Systolic Volume Variation (SVV) were retrospectively calculated before and after each bolus of fluid. Fluid responsiveness was classified as a change in blood pressure of > or =80 mmHg/L/m(2). RESULTS: Forty-four boluses were analyzed from the 25 children. Respiratory variables were similar. CVP was a poor predictor of fluid responsiveness and a negative relationship between change in blood pressure and Delta Down was observed. Performance in predicting fluid responsiveness as measured by the areas under the ROC curves were CVP (0.58), PPV (0.67), SPV (0.74) and SVV (0.74). CONCLUSIONS: Variation in blood pressure was a better guide to volume loading in children than CVP. Delta down was not useful in predicting fluid responsiveness in children with open chests following bypass surgery. SPV and SVV require further testing in prospective clinical trials.     

Cardiorespiratory responses to fluid administration in peritonitis

Intravascular volume expansion was studied in 59 critically ill patients with a wide variety of sepsis and in a small group of 12 patients with peritonitis; either 500 ml of 5% albumin solution or 2 units of packed red blood cells were given over a 60-min period. During the 2-h period after volume loading, significant increases in mean arterial pressure (MAP), pulmonary capillary wedge pressure (WP), central venous pressure (CVP), and oxygen consumption (VO2) were observed. One hour after fluid administration MAP had risen from 72 +/- 16 (SD) at baseline to 78 +/- 17 mm Hg (p less than .01), WP from 9 +/- 5 to 16 +/- 7 mm Hg (p less than .05), CVP from 7 +/- 4 to 9 +/- 4 mm Hg (p less than .05) and VO2 from 132 +/- 19 to 148 +/- 31 ml/min X m2 (p less than .01). Improvement in VO2 after volume loading is consistent with the concept that circulatory problems in sepsis result in less VO2 than is needed and that intravascular volume expansion in normovolemic septic patients may improve peripheral perfusion as measured by oxygen uptake.     

Dependence of oxygen consumption on cardiac output in sepsis

We studied the relationship between oxygen consumption (Vo2) and cardiac output in 17 hemodynamically stable, septic and eight nonseptic ICU patients. Each received 300 ml of fresh-frozen plasma or 25% albumin with up to 500 ml of crystalloids, in addition to regular maintenance fluids; this treatment increased pulmonary wedge pressure (WP) by 3 to 4 mm Hg. Measurements were performed before and after approximately 5 h of volume loading. Because cardiac index (CI) decreased as WP increased in four septic and three nonseptic patients, we grouped the data according to the state of flow instead of the recording time sequence. From low to high flows, mean CI increased in septic patients and nonseptic patients. Oxygen delivery (Do2) increased in septic and nonseptic patients. Vo2 remained unchanged in nonseptic patients, while it increased in septic patients. Accordingly, arteriovenous oxygen difference narrowed in nonseptic patients from 4.46 +/- 1.62 to 3.59 +/- 1.21 ml/dl (p less than .05) but did not change in septic patients. In the septic group, the difference in CI between high and low flows was significantly (p less than .05) greater in survivors than in nonsurvivors. We conclude that the septic state is accompanied by a peripheral oxygen deficit, which can be partially reversed by maintaining an above-normal CI and Do2.     

Stroke volume variations for assessment of cardiac responsiveness to volume loading in mechanically ventilated patients after cardiac surgery

OBJECTIVE: We hypothesized that measuring stroke volume variation (SVV) during mechanical ventilation by continuous arterial pulse contour analysis allows the accurate prediction and monitoring of changes in cardiac index (CI) in response to volume administration. DESIGN AND SETTING: Prospective study in an university hospital. PATIENTS: Twenty mechanically ventilated patients following cardiac surgery. INTERVENTIONS: Volume loading with oxypolygelatin (3.5%) 20 ml x body mass index over 10 min. MEASUREMENTS AND RESULTS: SVV, central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), left ventricular end-diastolic area index (LVEDAI) by transesophageal echocardiography, intrathoracic blood volume index (ITBVI) by transpulmonary thermodilution and CI were determined immediately before and after volume loading. SVV decreased, while CI, CVP, PAOP, ITBVI, and LVEDAI increased significantly. Percentage changes in CI were significantly correlated to percentage changes in SVV (r(2)=-0.59, p<0.001), ITBVI (r(2)=0.79, p<0.001), and PAOP (r(2)=0.33, p<0.05) and to baseline values of SVV (r(2)=0.55, p<0.05) and LVEDAI (r(2)=-0.68, p<0.001). CONCLUSIONS: SVV may help to determine the preload condition of ventilated patients following cardiac surgery and to predict and continuously monitor effects of volume administered as part of their hemodynamic management.     

Fluid resuscitation in circulatory shock: a comparison of the cardiorespiratory effects of albumin, hetastarch, and saline solutions in patients with hypovolemic and septic shock

Twenty-six consecutive patients in hypovolemic shock were randomized to fluid challenge with 5% albumin (A), 6% hetastarch (H), or 0.9% saline (S) solutions. Fluid challenge consisted of 250 ml of test fluid every 15 min until the pulmonary artery wedge pressure (WP) reached 15 mm Hg. Thereafter, WP was maintained at 15 mm Hg for an additional 24 h with infusions of the same test fluid. Vital signs, hemodynamic and respiratory variables, as well as arterial lactate and colloid osmotic pressure (COP) were monitored according to protocol. Chest x-rays were performed by standardized technique before fluid challenge and at 12 and 24 h of maintenance fluid therapy and were evaluated for evidence of pulmonary edema. Cardiac function and hemodynamic stability were restored by fluid challenge with A, H, and S. Two to 4 times the volume of S as A or H was required to achieve similar hemodynamic endpoints. COP was increased by fluid challenge with A or H but was markedly reduced by fluid challenge with S and throughout the 24-h maintenance period. Fluid challenge resulted in reductions in COP-WP gradient of 62% in the A, 43% in the H, and 125% in the S groups. Resuscitation with S resulted in a significantly higher incidence of pulmonary edema (87.5%) than did resuscitation with A (22%) or H (22%). Urine output was not different among the groups at any time during the study. We conclude that 6% H performs as well as 5% A as a resuscitative fluid and that resuscitation with either of these colloids is associated with a lower incidence of pulmonary edema than is resuscitation with 0.9% S.     

Correlations between cardiac output, stroke volume, central venous pressure, intra-abdominal pressure and total circulating blood volume in resuscitation of major burns

The purpose of this study was to observe the interactions between cardiac index (CI), stroke volume index (SVI), central venous pressure (CVP), intra-abdominal pressure (IAP) and total circulating blood volume index (TBVI) during resuscitation of major burns. Sixteen patients with an average TBSA of 46% (26-67%) and an average abbreviated burn severity index of 8.9 (7-11) were included into an intra-individual comparative prospective study over an 18-month period. The COLD Z-021 system (Pulsion Medical Systems, Munich, Germany) was used to obtain CI, SVI and TBVI. Two hundred and thirty-four to 278 intra-individually comparative measurements were performed for the analyses during the first 4 days after the burn injury. Correlations were shown for the interactions between CI and TBVI (r = 0.550; rs = 0.518), SVI and TBVI (r = 0.606; rs = 0.626) and for CVP versus IAP (r = 0.487; rs = 0.474). Poor or no correlations were demonstrated for the comparisons CI versus CVP (r = 0.401; rs = 0.352), CVP-PEEP versus IAP (r = 0.255; rs = 0.272). TBVI versus IAP (r = -0.120; rs = -0.169), TBVI versus CVP (r = 0.025; rs = -0.036), TBVI versus CVP-PEEP (r = -0.046; rs = -0.101), CI versus CVP-PEEP (r = 0.088; rs = 0.092) as well as for IAP versus CI (r = 0.050; rs = 0.034). An additional analysis demonstrated no correlation between TBVI and MAP (r = -0.095; rs = -0.136). Our data provide evidence that the CVP is influenced more by external pressures (IAP) than by the actual intravascular volume status of the patient. Thus, the CVP is not a suitable tool to guide fluid resuscitation during burns with shock. The TBVI may be an ideal value to guide resuscitation because the augmentation of TBVI during fluid resuscitation correlated well with improved cardiac output and stroke volume. Future randomised studies are required to demonstrate whether TBVI guided resuscitation of burns has an impact on outcome.     

Frequency of technical problems encountered in the measurement of pulmonary artery wedge pressure

A total of 2711 pulmonary artery wedge pressure (WP) measurement attempts were made prospectively from WP recordings in 44 (30 men) critically ill patients, using 77 flow-directed catheters. Of these, 322 (12%) failed to yield a WP measurement, and 521 (18%) were associated with technical problems. One half of these technical problems were due to poor dynamic response or damped pressure tracings; other problems included balloon overinflation, partial WP, and inability to aspirate blood from the pulmonary artery (PA) port. Only 50% of wedge blood sampled at the time of initial PA catheterization yielded capillary blood (PO2 greater than or equal to 10 torr higher than PaO2). In 12 stable patients in whom paired measurements were available, there were clinically important differences (-13 to +22 torr) between paired WP measurements made before and after rapid correction of technical problems. Technical problems are common and may be associated with clinically important errors. Those due to poor dynamic response are easily and rapidly detected at the bedside.     

Comparison of hydroxyethyl starch and lactated Ringer's solution on hemodynamics and oxygen transport of critically ill patients in prospective crossover studies

The cardiopulmonary effects of lactated Ringer's solution (RL) were compared with those of 10% hydroxyethyl starch, hetastarch (HES), given in 44 therapeutic interventions in 15 critically ill patients by crossover design. Each agent was given to each patient at least once; seven patients received each agent twice. Infusions were continued until the wedge pressure (WP) had increased to 16 +/- 2 mm Hg in trauma patients and 18 +/- 2.mm Hg in cardiac patients. HES 10% produced significantly increased cardiac index, left and right ventricular stroke work index, CVP, WP, oxygen delivery, oxygen consumption, and reduced pulmonary vascular resistance index (PVRI). RL increased CVP, WP, and PVRI, but did not significantly improve other hemodynamic or oxygen transport variables.     

生物电阻抗技术评价胸部大手术后患者容量状况

目的 利用多频生物电阻抗测量法评价胸外科胸部大型手术后患者体液分布变化.方法 选择2009-01-2010-12收住北京大学第三医院危重医学科的胸部大手术术后男性患者34例,利用多频生物电阻抗法Xitron4200(Xitron Technologies,San Diego,CA,USA)在患者转入危重医学科即刻检测其细胞外水(ECW)、细胞内水(ICW)数值,同时进行血气分析、测量中心静脉压和平均动脉压.按照患者转入后24 h内有无出现低血压(SBP＜90 mmHg),将患者分为低血压组和血压正常组,比较低血压组和血压正常组患者的ECW、ICW、碱剩余(BE)、血乳酸(LAC)、平均动脉压(MAP)和中心静脉压(CVP)的平均值.结果 有11例患者在术后24 h内发生低血压.术后转入危重医学科即刻的ECW值平均值在低血压组患者明显低于血压正常组患者.术后转入危重医学科即刻的ICW值、BE值、LAC值、MAP和CVP平均值在低血压组患者和血压正常组患者之间比较未见有明显差异.结论 多频生物电阻抗技术测量ECW值能在胸部大手术术后早期提示容量不足的存在.     

胸内血容量指数和中心静脉压反映容量状态的评价

目的:比较在机械通气时,随潮气量(Vt)的变化,中心静脉压(CVP)和胸腔内血容量指数(ITBVI)的变化趋势以及两者与心脏指数(CI)的相关性。方法:选取24例行有创机械通气和脉搏轮廓动脉压波形分析法(PiCCO)监测的患者,根据CI分为心功能正常组[CI≥2.2L/(min·m2)]和心功能低下组[CI<2.2L/(min·m2)]。在同步间歇指令通气(SIMV)模式下,调整Vt分别维持于6、10、15mL/kg体重水平,以上各种条件维持20min后测量呼吸力学及血流动力学指标.实验过程中以上支持条件随机选择进行。结果:(1)在所有患者,CI,ITBVI随潮气量升高而下降,平均气道压(Pmeans)随潮气量升高而升高,CVP在各组间无明显变化。(2)CVP在各实验组与CI均无相关性;在心功能低下组,ITBVI与CI有相关性(R为0.679,P<0.05)。结论:胸腔内血容量指数能更准确地反映机体容量状态和心脏前负荷,与心脏指数有较好的相关性。