Pulse pressure respiratory variation as an early marker of cardiac output fall in experimental hemorrhagic shock

Pulse pressure (DeltaPp) and systolic pressure (DeltaPs) variations have been recommended as predictors of fluid responsiveness in critically ill patients. We hypothesized that changes in DeltaPp and DeltaPs parallel alterations in stroke volume (SV) and cardiac output (CO) during hemorrhage, shock, and resuscitation. In anesthetized and mechanically ventilated mongrel dogs, a graded hemorrhage (20 mL/min) was induced to a target mean arterial pressure (MAP) of 40 mm Hg, which was maintained for additional 30 min. Total shed-blood volume was then retransfused at a 40 mL/min rate. CO, SV, right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), and continuous mixed venous oxygen saturation (SvO(2)) were assessed. Both DeltaPp and DeltaPs were calculated from direct arterial pressure waveform. Removal of about 9% of estimated blood volume promoted a reduction in SV (14.8 +/- 2.2 to 10.6 +/- 1.3 mL, P < 0.05). At approximately 18% blood volume removal, significant changes in CO (2.4 +/- 0.2 to 1.5 +/- 0.2 mL/min, P < 0.05), DeltaPp (12.6 +/- 1.4 to 15.8 +/- 2.0%, P < 0.05), and SvO(2) (82 +/- 1.4 to 73 +/- 1.7%, P < 0.05) were observed. Alterations in MAP, RAP, PAOP, and DeltaPs could be detected only after each animal had lost over 36% of estimated initial blood volume. There was correlation between blood volume loss and SV, CO, and SvO(2), as well as between blood loss and MAP, DeltaPp, and DeltaPs. Blood volume loss showed no correlation with cardiac filling pressures. DeltaPp is a useful, early marker of SV and CO for the assessment of cardiac preload changes in hemorrhagic shock, while cardiac filling pressures are not.     

Continuous monitoring of mixed venous oxygen saturation in anesthesia in pulmonary surgery

The multiplicity of potential causes of variations in mixed venous oxygen saturation (SvO2) during one lung ventilation (OLV), including a constant ventilation/perfusion mismatch, explains that it has been suggested as a routine monitoring procedure. To assess its usefulness, 12 adults undergoing OLV were monitored during surgery with an Oximetrix pulmonary catheter, placed on the side opposite to the surgical field under fluoroscopic control. Seventy two complete sets of haemodynamic measurements were obtained at 6 different times during surgery. We studied the ability of changes in SvO2 to predict changes in arterial oxygen saturation (SaO2), cardiac output (CO), and venous admixture (VA) by calculating sensitivities (Se), specificities (Sp) and predictive values with regard to these variables. There were no complications due to the protocol. However left-sided catheter placement failed in four cases. Correlation between optical and measured SvO2 was very strong (r = 0.94; p less than 0.001). SvO2, oxygen consumption (VO2) and the rate of oxygen extraction remained constant throughout the procedure, even when CO, mean arterial pressure, VA, SaO2 and PaO2 varied. Clamping the pulmonary artery returned VA, SaO2 and PaO2 values to those found before OLV, but produced a significant decrease in CO. SvO2 had low Se and Sp for changes in other variables (CO: 76 +/- 7, 48 +/- 9; PaO2: 79 +/- 6, 59 +/- 9; VA: 54 +/- 7, 48 +/- 7 respectively). In this type of surgery, alterations in variables related to oxygen are probably balanced by haemodynamic changes. In fact, according to Fick's formula, SvO2 is almost completely determined by SaO2 and CO, when VO2 and haemoglobin remain stable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mixed venous oxygen saturation during mobilization after cardiac surgery: are reflectance oximetry catheters reliable?

BACKGROUND: Oximetry catheters immediately reflect changes in mixed venous oxygen saturation (SvO2). We have used the Baxter 2-SAT system to register changes in SvO2 during early mobilizations after cardiac surgery. To assess catheter reliability, readings were compared to blood gases. METHODS: A total of 352 paired catheter and bench haemoximetry measurements were obtained at the expected highest and lowest levels of SvO2 during the mobilization procedures. The agreement between methods was explored by a Bland-Altman plot. The influence of haemoglobin (Hgb), pH, cardiac output (CO), posture, catheter identity and catheter calibration on agreement was assessed through analysis of covariance. RESULTS: Data included a substantial number of low SvO2 values, 95 paired means of SvO2 < or = 50% and 37 paired means < or = 40%. Mean oxygen saturation difference between catheter and haemoximeter readings was -1.6 +/- 5.7% (SD). Agreement between the methods depended upon the level of SvO2. At SvO2 of 65%, the two methods were virtually identical. Below 65%, the catheters increasingly underestimated the corresponding haemoximetric values by 1.5% for every 10% reduction in SvO2. Agreement was to some degree dependent on individual calibrations and catheter identity, but to a lesser extent on Hgb, CO and posture. CONCLUSION: The two methods are interchangeable for most clinical purposes. Catheter readings are, however, substantially lower than the corresponding haemoximetric measurements at low SvO2 values. Careful interpretation of the absolute values resulting from catheter measurements is recommended, especially when SvO2 readings are low.     

Goal-directed therapy in anesthesia: any clinical impact or just a fashion?

Goal-directed therapy (GDT) describes the protocolized use of cardiac output and related parameters as end-points for fluid and/or inotropic therapy administration. Identifying the patient who will benefit from it has implications throughout perioperative management. The fundamental principle behind GDT is optimizing tissue perfusion by manipulating heart rate, stroke volume, hemoglobin and arterial oxygen saturation to improve oxygen delivery by using fluids, inotropes, red blood cells and supplementary oxygen. Although cardiac output and SvO2 were previously measured using the pulmonary artery catheter, a number of less invasive methods are now available. For intraoperative GDT, the esophageal Doppler-derived Flow Time correct (FTc) is the parameter used most frequently, although other parameters such as stroke volume obtained from Vigileo, PICCO and/or LiDCO, mixed and/or central venous oxygen saturation (SvO2/ScvO2), oxygen delivery and global end diastolic volume (PiCCO system) may be applied in daily clinical practice. The correct target to be followed during the intraoperative period must be clearly established. Most parameters depend primarily on O2 consumption and are not reliable or useful during anesthesia. To date, the quantity and the type of fluids to administer during major elective surgery remain an object of continuing debate. In conclusion, in terms of evidence-based medicine, GDT during anesthesia has a clinical impact when performed using an FTc-based fluids algorithm protocol. In contrast, GDT can be considered unreliable if confusing targets such as SvO2 or ScvO2 higher than 70% during anesthesia are followed.     

Haemodynamic changes during minimally invasive coronary artery bypass surgery using high-dose esmolol

We aimed to investigate the effects of high-dose esmolol on haemodynamics and oxygen extraction in minimally invasive direct coronary artery bypass (MIDCAB) surgery patients. METHODS: In 18 patients, heart rate (HR), mean arterial (MAP), central venous (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mixed venous oxygen saturation (Sv0(2)) were prospectively measured after induction of anaesthesia (T1), start of surgery (T2), during bypass grafting with beta-blockade (T3), and at the end of surgery (T4). RESULTS: Mean esmolol dose at T3 was 0.44+/-0.2mgkg(-1)min(-1). HR was unchanged, whereas significant decreases in mean CO (3.1+/-0. 8 vs 4.8+/-1.0lmin(-1)m(-2), pre-esmolol), MAP (53+/-10 vs 89+/-14mmHg), and SvO(2) (65+/-10 vs 81+/-4%) were observed during esmolol administration. All haemodynamic parameters normalized immediately after termination of esmolol (T4). CONCLUSIONS: Despite unchanged HR esmolol reduced CO and MAP suggesting a favorable reduction of myocardial oxygen consumption. Mean Sv0(2) during esmolol administration reflects an acceptable ratio of whole-body oxygen delivery and consumption. Haemodynamic changes with high-dose esmolol during MIDCAB surgery remain within safety margins.     

Continuous monitoring of central venous oxygen saturation in neonates and small infants: in vitro evaluation of two different oximetry catheters

BACKGROUND: Accurate assessment and monitoring of the cardiocirculatory function are essential during major pediatric and pediatric cardiac surgery. Monitoring of the central venous oxygen saturation (ScvO(2)) may be a better indicator of tissue oxygenation and derangement of cellular oxygen utilization than the more commonly used vital parameters. Therefore, we compared oxygen saturation measurements with thin fiberoptic oximetry catheters and standard blood gas oximetry in an in vitro setting. METHODS: Two different size continuous fiberoptic oximetry catheters (2-4-F) were inserted in an extracorporeal circuit filled with human red blood cells in normal saline (haematocrit 30%, flow 600 ml.min(-1)). The results of fiberoptic oximetry were then compared with standard blood gas oximetry for a wide range of different oxygen saturations using linear regression. RESULTS: The oxygen saturations found ranged from 9% to 100%. The results of the two different fiberoptic oximetry catheters correlated significantly (r = 0.99, P < 0.0001) with standard blood gas oximetry. CONCLUSION: The results of fiberoptic oximetry are nearly identical with standard blood gas oximetry for a wide range of different oxygen saturations. Thin oximetry catheters can be inserted percutaneously even in neonates and small infants. The continuous monitoring of ScvO(2) may be beneficial, especially in patients who are in danger of developing low cardiac output or sudden cardiovascular collapse.     

Monitoring intravascular volumes for postoperative volume therapy

BACKGROUND AND OBJECTIVE: The feasibility of monitoring measured intravascular volumes and the cardiac filling pressures were compared to reflect the optimal volume status of postoperative patients. METHODS: In a prospective clinical study, 14 hypovolaemic adult patients were included after cardiac surgery. All patients received 1,000 mL hydroxyethyl starch after meeting the authors' criteria for hypovolaemia. Pressures were measured by use of a pulmonary artery catheter and volumes were determined by double-indicator dilution technique. RESULTS: Stroke volume index (SVI), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), intrathoracic blood volume index (ITBVI) and total circulating blood volume (TBVIcirc) increased significantlyaftervolumeloading(30.7 +/- 9.8 to 41.7 +/- 9.6 mLm(-2), 4.9 +/- 1.7 to 9.1 +/- 2.3mmHg, 6.6 +/- 1.3 to 10.6 +/- 1.9 mmHg, 858 +/- 255 to 965 +/- 163 mLm(-2), and 1,806 +/- 502 to 2,110 +/- 537 mLm(-2), respectively). During the subsequent 1 h steady-state period, CVP and PAOP decreased significantly (9.1 +/- 2.2 to 7.4 +/- 2.2 mmHg and 10.6 +/- 1.9 to 9.2 +/- 2.0 mmHg, respectively), whereas SVI and intravascular volumes remained unchanged. The changes of CVP and PAOP did not correlate with changes in stroke volume during volume loading (r2 = 0.06 and 0.03, respectively) and during steady-state (r2 = 0.17 and 0.00 respectively). On the other hand, a significant correlation was found between changes of the intrathoracic blood volume and changes in stroke volume during the volume loading (r2 = 0.67) and also during the steady-state phase (r2 = 0.83). CONCLUSIONS: Intrathoracic blood volume reflects more accurately the preload dependency of cardiac output in postoperative patients than left/right-sided cardiac filling pressures.     

Anesthetic management of surgery for a huge renal tumor with the inferior vena cava invasion--application of Vigileo as a hemodynamic monitor

In anesthetic management of surgery for a huge renal tumor with the inferior vena cava invasion, maintaining circulatory state is one of the key points. Several hemodynamic parameters are required to evaluate the circulatory state, such as central venous oxygen saturation (ScvO2), cardiac output (CO) and direct arterial blood pressure, in addition to routine hemodynamic parameters like heart rate and central venous pressure. Pulmonary artery catheter is considered as a standard apparatus to obtain those parameters; however, the catheter is invasive and may cause possible pulmonary artery damage, cardiac penetration, or severe arrhythmia. Therefore, application of pulmonary artery catheter is a relative contraindication in some cases. We used Vigileo system to obtain similar hemodynamic parameters. This system provided an arterial based pressure-based cardiac output, central venous oxygen saturation, stroke volume variation (SVV) and so on. In the present case, the system was an alternative device to pulmonary artery catheter system.     

Correlation of oxygen delivery with central venous oxygen saturation, mean arterial pressure and heart rate in piglets

BACKGROUND: Accurate assessment and monitoring of the cardiocirculatory function is essential during major pediatric and pediatric cardiac surgery. Invasive monitoring of cardiac output and oxygen delivery (DO(2)) is expensive and sometimes associated with adverse events. Measurement of central venous oxygen saturation (ScvO(2)) is less invasive and may reflect the DO(2). Therefore, we investigated the correlation of ScvO(2) with cardiac index (CI) and DO(2) and in comparison the more common monitored parameters heart rate (HR) and mean arterial pressure (MAP) with DO(2) in an animal experimental setting. METHODS: In five fasted, anesthetized and mechanically ventilated piglets CI (transpulmonary thermodilution), venous and arterial blood gases, HR and MAP was measured during normal conditions, volume loading, inotropic support, and exsanguination. RESULTS: In the five piglets 168 measurements could be performed. In a wide hemodynamic range (CI 22-335 ml x kg(-1) min(-1)) we found significant correlations of ScvO(2) with DO(2)) (r(2) = 0.91, P < 0.0001) and CI (r(2) = 0.88, P < 0.0001) and also between DO(2) and MAP (r = 0.86, P < 0.0001) and HR (r = 0.19, P < 0.05). CONCLUSIONS: ScvO(2) is a better parameter for indirect estimation of DO(2) than MAP and heart rate. Measurement of ScvO(2) is simple and does not necessitate additional invasive techniques. In the clinical setting ScvO(2) should be used in combination with other standard vital parameters, i.e. MAP, central venous pressure, lactate, base excess, and urine output.     

Effects of initiation of continuous renal replacement therapy on hemodynamics in a pediatric animal model

There are no studies analyzing the initial hemodynamic impact of continuous renal replacement therapy (CRRT) in children. We have performed a prospective observational study in 34 immature Maryland pigs to analyze the initial hemodynamic changes during venovenous CRRT. The heart rate, blood pressure, central venous pressure (CVP), pulmonary arterial occlusion pressure (PAOP), pulmonary capillary wedge pressure, temperature, and cardiac output (CO), simultaneously by pulmonary arterial thermodilution and femoral arterial thermodilution, were measured at 30-min intervals during 2 h. Venovenous CRRT induced an initial significant diminution of volemic hemodynamic parameters (intrathoracic blood volume, global end-diastolic volume, stroke volume index, PAOP, and CVP). Simultaneously, a significant increase in systemic vascular resistance index and left ventricular contractility, and a decrease in CO, was observed. We conclude that CRRT in a pediatric animal model induces initial hypovolemia, and a systemic cardiovascular response with vasoconstriction and increase in ventricular contractility.     

Effects of Initiation of Continuous Renal Replacement Therapy on Hemodynamics in a Pediatric Animal Model

There are no studies analyzing the initial hemodynamic impact of continuous renal replacement therapy (CRRT) in children. We have performed a prospective observational study in 34 immature Maryland pigs to analyze the initial hemodynamic changes during venovenous CRRT. The heart rate, blood pressure, central venous pressure (CVP), pulmonary arterial occlusion pressure (PAOP), pulmonary capillary wedge pressure, temperature, and cardiac output (CO), simultaneously by pulmonary arterial thermodilution and femoral arterial thermodilution, were measured at 30-min intervals during 2 h. Venovenous CRRT induced an initial significant diminution of volemic hemodynamic parameters (intrathoracic blood volume, global end-diastolic volume, stroke volume index, PAOP, and CVP). Simultaneously, a significant increase in systemic vascular resistance index and left ventricular contractility, and a decrease in CO, was observed. We conclude that CRRT in a pediatric animal model induces initial hypovolemia, and a systemic cardiovascular response with vasoconstriction and increase in ventricular contractility.     

Hemodynamic monitoring

The goal of hemodynamic monitoring is to maintain adequate tissue perfusion. Classical hemodynamic monitoring is based on the invasive measurement of systemic, pulmonary arterial and venous pressures, and of cardiac output. Since organ blood flow cannot be directly measured in clinical practice, arterial blood pressure is used, despite limitations, as estimate of adequacy of tissue perfusion. A mean arterial pressure (MAP) of 70 mm Hg may be considered a reasonable target, associated with sign of adequate organ perfusion, in most patients. In the approach to hypotension, which is the most common cause of hemodynamic instability in critical ill patients, increasing levels of monitoring may be used. Assuming that central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) are adequate estimates of the volume of the systemic and pulmonary circulation respectively, the following decision tree is suggested: 1) make a working diagnosis based on the relationship between pressure (CVP and PAOP) and cardiac output or stroke volume (CO or SV); 2) consider conditions that may alter reliability of CVP and PAOP in estimate adequately circulating volumes such as abnormal pressure/volume relationship (compliance) of the RV or LV, increased intrathoracic pressure (PEEP, autoPEEP, intra-abdominal pressure), valvular heart disease (mitral stenosis); 3) look at the history; 4) separating RV and LV by reciprocal variations of CVP, PAOP and SV. CVP is often used as sole parameter to monitor hemodynamic. However CVP alone may not differentiate between changes in volume (different venous return curve) or changes in contractility (different starling curve). Finally, other techniques such as echocardiography, transesophageal Doppler and volume-based monitoring system are now available.     

Marked mixed venous desaturation during early mobilization after aortic valve surgery

We investigated the physiological reaction to mobilization the first and second day after aortic valve replacement in an open, prospective study. Hemodynamic and oxygenation variables were recorded in 15 patients using a pulmonary artery oximetry catheter and bench oximetry. Serious intraoperative events occurred in 3 patients, but all patients began mobilization on the first postoperative day and mobilization was accomplished without clinical problems. Mixed venous oxygen saturation (SvO(2)) at rest was 58.0 +/- 7.7% (mean +/- SD) on the first postoperative day and 58.0 +/- 6.2% on the second day (NS). During mobilization, oxygen consumption increased by 64 +/- 41% and 58 +/- 33% on the first and second days (P < 0.01; NS between days). No compensatory increase in cardiac index and oxygen delivery was seen. Oxygen extraction increased, resulting in SvO(2) values during exercise of 35.7 +/- 6.8% on the first day and 36.7 +/- 7.7% on the second day (P < 0.01; NS between days), whereas mixed venous oxygen partial pressure was 3.0 +/- 0.4 kPa on both days. The lowest recorded value for SvO(2) was 10%. The marked and consistent mixed venous desaturation during early mobilization has not been described before and the clinical consequences and underlying mechanism require further investigation. IMPLICATIONS: During early mobilization after aortic valve replacement, a marked and consistent reduction in mixed venous oxygen saturation to 35% and mixed venous oxygen partial pressure to 3 kPa was observed.     

Critical haemoglobin concentration in anaesthetized dogs: comparison of two plasma substitutes

We have explored systemic and regional tolerance to haemodilution during anaesthesia with two different synthetic colloids. Eighteen dogs undergoing mechanical ventilation during anaesthesia with ketamine were submitted to progressive normovolaemic haemodilution with either gelatin (GEL; n = 9) or hydroxyethylstarch (HES; n = 9) administered on a 1:1 ratio. Systemic oxygen delivery was calculated from measurement of thermodilution cardiac output and arterial oxygen content, while systemic oxygen consumption was determined from expired gas analysis. Mesenteric oxygen delivery and consumption were determined using ultrasonic flow measurements, and arterial and mesenteric venous oxygen contents. The critical haemoglobin concentration (i.e. the haemoglobin value below which oxygen consumption becomes oxygen delivery dependent) was mean 3.6 (SD 0.8) g dl-1 in the GEL and 3.5 (1.5) g dl-1 in the HES group. The mesenteric critical oxygen extraction ratio (O2ER) (GEL 50.1 (12.1)%; HES 48.5 (13.4)%) was significant lower than the systemic critical O2ER (GEL 66.1 (8.4)%; HES 67.7 (7.1)%). There were no significant differences between the GEL and HES groups for any of these variables, or in the amount of colloid administered. During the study, oxygen delivery decreased almost linearly with reduction in haemoglobin, indicating a lack of cardiac output response to anaemia during ketamine anaesthesia.      

What is the role of monitoring of mixed venous blood saturation in cardiac surgery?

The equipment available for mixed venous blood saturation (Svo2) monitoring is now accurate. SvO2 is not a direct measure of cardiac output, because it depends on the balance between oxygen delivery (TaO2) and consumption (VO2). As haemoglobin affinity for oxygen increases during cardio-pulmonary bypass (CPB), the optimal level of SvO2 after CPB should be above 65-70%. There is a critical level of TaO2 below which VO2 is dependent on TaO2. Below this level, SvO2 has no clinical value as it no longer depends on TaO2. Similarly, SvO2 has no clinical value during lactic acidosis. When these limitations are taken into account, SvO2 monitoring is useful for the interpretation of intra- and post-operative haemodynamic alterations occurring during cardiac surgery. It is particularly indicated in patients with preoperative NYHA class III or IV congestive heart failure.     

Comparison of oxygen consumption calculated by Fick’s principle (using a central venous catheter) and measured by indirect calorimetry

We investigated the clinical usefulness of the Fick method using central venous oxygen saturation ScvO2 and cardiac output (CO) measured by pulse dye densitometry (PDD) for monitoring oxygen consumption VO2. This prospective clinical study was performed in 28 mechanically ventilated postoperative patients after major abdominal surgery. VO2 was determined by two methods, i.e., the Fick method and indirect calorimetry. The Fick method was employed using CO measured by PDD and VO2 obtained from a central venous catheter (CVC). VO2 measured by indirect calorimetry was averaged for 15 min. Fifty-six sets of measurements were performed. VO2 values determined by the Fick method were significantly lower than those measured by indirect calorimetry (110 +/- 29 vs 148 +/- 28 ml x min(-1) x m(-2); P < 0.01). Bland and Altma analysis showed that the mean bias and precision were 33 ml x min(-1) x m(-2) and 32 ml x min(-1) x m(-2), respectively. The correlation between the two measurements of VO2 was weak (r (2) = 0.145; P = 0.0038), indicating that the Fick method using PDD and ScvO2 is not clinically acceptable for the monitoring of VO2.     

不同时点减压对重症急性胰腺炎合并腹高压猪模型血流动力学和氧代谢的影响

目的 评价不同时点减压对重症急性胰腺炎合并腹高压模型猪血流动力学和氧代谢的影响.方法 将18只家猪进行麻醉、气管切开后接呼吸机辅助呼吸,使用含5%牛磺胆酸钠和0.5%胰蛋白酶生理盐水(1 ml/kg)胰管内注射制作重症急性胰腺炎模型.其中12只关腹后采用氮气气腹法制作25 mmHg(1 mmHg=0.133 kPa)腹高压模型,随机平均分为两组,一组腹高压持续6 h后减压(6 h组),另一组腹高压持续9 h后减压(9 h组);另外6只归为重症急性胰腺炎组.置入动脉导管和Swan-Ganz导管动态监测3组模型猪的心率(Hr)、平均动脉压(MAP)、心排血量(CO)、中心静脉压(CVP)、肺动脉嵌压(PAWP)等血流动力学指标,并行血气分析检查计算氧输送量(DO2)、氧耗量(VO2).持续24h观察不同时点减压对上述指标的影响.结果 6 h组减压后血流动力学指标与重症急性胰腺炎组相比差异无统计学意义(P＞0.05);9 h组减压后Hr、CO、MAP和CVP与另两组相比差异有统计学意义(P＜0.05).血气分析结果显示,6 h组减压后与重症急性胰腺炎组相比,氧分压(PO2)、中心静脉血氧饱和度(ScvO2)、DO2无明显差异(P＞0.05).9 h组减压3 h后PO2、ScvO2及DO2仍低于另外两组(P均＜0.05).6 h、9 h组与重症急性胰腺炎组相比,VO2在6 h时升高更明显(P＜0.05);随后VO2均呈下降趋势,差异无统计学意义(P＞0.05).结论 腹高压持续9 h后减压对重症急性胰腺炎合并腹高压模型猪的血流动力学及氧代谢产生明显影响.及时采用合适的方式减轻、解除腹高压是重症急性胰腺炎治疗的重要环节之一.

Abstract：

Objective To assess the effect of decompression in different time on systemic hemodynamics and oxygen metabolism in a 24 h lasting porcine model of severe acute pancreatitis (SAP) incorporating intra-abdominal hypertension (IAH). Methods Following baseline registrations, SAP was induced in all 18 animals. A N2 pneumoperitoneum was used to increase the intra-abdominal pressure (IAP) to 25 mmHg(1 mmHg =0. 133 kPa) in 12 of 18 SAP animals. After 6 hours,decompression was applied in 6 of these 12 pigs and the other 6 animals received decompression at 9 h since the induction of IAH. The investigation period was 24 h. Heart rate(HR), cardiac output(CO), central venous pressure (CVP), mean arterial pressure (MAP) and pulmonary arterial wedge pressure(PAWP) were continuously recorded with the aid of Swan-Ganz catheter and electrocardiography monitor; Oxygen partial pressure of artery (PaO2),carbondioxide partial pressure of artery (PaCO2) and central venous oxygen saturation (ScvO2)were measured by blood-gas analysis. Besides that, systemic oxygen delivery (DO2)and systemic oxygen consumption(VO2)were calculated according to blood-gas analysis in arterial and central venous blood.Results After decompression, HR, CO, MAP, CVP, PAWP, PaO2 and DO2 showed no significant differences in the 6 h group when compared to SAP pigs. In the 9 h group,however,CO decreased significantly and HR,CVP, PAWP increased significantly after decompression than SAP only animals (all P ＜ 0. 05). PaO2, ScvO2 and DO2 showed lower after 3 h of decompression compared with another two groups. VO2 increased higher in I AH groups during 6 h of experiment than SAP pigs (all P ＜ 0. 05). Then VO2 showed a trend to fall and no differences in three groups. Conclusions There are remarkable and relatively irreversible effects on global hemodynamics and oxygen metabolism in response to the decompression in different time after sustained IAH with the underlying condition of SAP. The results of this study are in favor of a decompression in patients of SAP with IAH in early time.     

Detection of venous air embolism by continuous mixed venous oximetry in dogs

Continuous mixed venous oxygen saturation (SvO 2) was evaluated as a monitor of venous air embolism in a canine model. Nineteen dogs were anesthetized, paralyzed, and mechanically ventilated. Invasive monitoring included SvO 2, systemic and pulmonary artery blood pressures, and thermodilution cardiac outputs. Air boluses of 0.25 and 0.5 ml/kg were injected in six dogs and 1 ml/kg in all. All 1 ml/kg emboli were detected by greater than or equal to 5% decreases in the SvO 2. The SvO 2 decreased from 82 +/- 8% to 72 +/- 11% (mean +/- SD), an average decrease of 9 +/- 5% (p = 0.004). Time to the SvO 2 nadir was 2.6 +/- 2.5 min. Of the 0.5 and 0.25 ml/kg emboli, 50% and 17% were detected, respectively. Cardiac output decreased from 2.9 +/- 0.8 to 2.1 +/- 0.8 L/min after the 1 ml/kg emboli (p = 0.02). The 1 ml/kg emboli increased pulmonary artery pressures and decreased systemic blood pressure in 100% and 75% of animals, respectively. Peak changes in pulmonary artery pressure occurred at 1.2 +/- 0.8 min. In the present study, time to maximum change was greater for SvO 2 than for pulmonary artery pressure changes. Use of fiberoptic pulmonary artery catheters for continuous measurement of SvO 2 can add a new diagnostic modality to venous air embolism detection in patients who require a pulmonary artery catheter for other medical indications.     

Comparison of central venous oxygen saturation and mixed venous oxygen saturation during liver transplantation

Central venous catheterisation is commonly performed during major surgery and intensive care, and it would be useful if central venous oxygen saturation could function as a surrogate for mixed venous oxygen saturation. We studied 50 patients undergoing living related liver transplantation. Blood samples were taken simultaneously from central venous and pulmonary artery catheters at nine time points during the pre-anhepatic, anhepatic, and postanhepatic phases. Four hundred and fifty sets of measurement were obtained. There was a good correlation between central venous oxygen saturation and mixed venous oxygen saturation. The mean (SD) difference (95% limit of agreement) was lowest at the first time point (1.06 (0.65)%, −1.94% to 2.7%) and then increased throughout the study but remained acceptable. The change in mixed venous oxygen and central venous oxygen saturations occurred mostly in parallel and as a result changes in mixed venous oxygen saturation were reflected adequately in the change in central venous oxygen saturation. The correlation between mixed venous oxygen saturation and cardiac output was poor.     

Clinical applicability of the substitution of mixed venous oxygen saturation with central venous oxygen saturation.

OBJECTIVE: To examine the clinical applicability of substituting central venous oxygen saturation (ScvO2) for mixed venous oxygen saturation (SmvO2) in monitoring global tissue oxygenation. DESIGN: Prospective clinical investigation. SETTING: University hospital. PARTICIPANTS: Seventy-three adult patients. INTERVENTIONS: Venous oxygen saturation was recorded, and oxygen saturation difference between SmvO2 and ScvO2 (DeltaSmvcv) was calculated in 2 groups of patients (group I, sepsis patients [n = 41], and group II, general anesthesia for cardiovascular surgery patients [n = 32]) during initial placement of pulmonary artery catheters. MEASUREMENTS AND MAIN RESULTS: Patients were classified as follows: class A, patients having a DeltaSmvcv >-5%; class B, patients having a DeltaSmvcv between -5% and +5%; and class C, patients having a DeltaSmvcv >+5 %. Statistically significant differences were observed in cardiac index, oxygen delivery index, and oxygen extraction ratio between class A and B in both groups. Class C of group II showed the worst correlation between SmvO2 and ScvO2 and had significantly lower arterial carbon dioxide tension values than class A and B. CONCLUSION: Pulmonary artery blood sampling should not be replaced with central venous blood. Hypocapnia and increased oxygen extraction ratio seem to be the major factors that worsen the relationship between ScvO2 and SmvO2.