'Paradoxical' rise in blood pressure during ultrafiltration in dialysis patients

In some hypertensive haemodialysis (HD) patients, blood pressurerises further during ultrafiltration (UF). We investigated sevensuch patients, who were not responsive to hypotensive drugs,including converting enzyme inhibitors. All had marked cardiacdilatation, but most were non-oedematous. They were treatedwith repeated intense UF while monitoring cardiac function byechocardiography. After a variable time period they all became(near) normotensive without medication. Mean systolic and diastolicblood pressure decreased by 46 ± 18 and 22 ± 9mmHg respectively while bodyweight decreased by a mean of 6.7± 3.0 kg. Plasma volume decreased by 22%, and mean albuminincreased from 3.9 ± 0.3 to 4.2 ± 0.3 g/dl. Cardiothoracicindex decreased from a 0.56 ± 0.02 to 0.45 ± 0.03.Mitral and tricuspid insufficiency was present in four patientsand improved or disappeared in all of them. Diameters of theinferior vena cava, left atrium, and end systolic and diastolicleft ventricle markedly decreased in all patients. Ejectionfraction increased, but remained subnormal in some patients,while cardiac output increased in five and decreased in twopatients. We conclude that paradoxical blood pressure rise withUF usually occurs in the presence overhydration and cardiacdilatation and should be treated by intensified UF. The explanationof this phenomenon remains speculative.     

Relationship between increased blood pressure and hematocrit during modified ultrafiltration for pediatric open heart surgery

Objective Modified ultrafiltration increases blood pressure after cardiopulmonary bypass in children. To investigate the cause of this hemodynamic improvement, we assessed the relationship between increased blood pressure and hematocrit. Methods We retrospectively assessed 30 consecutive patients who underwent ventricular septal defect closure, and divided them into two groups: group M (modified ultrafiltration, n = 15) and group C (conventional ultrafiltration, n = 15). We compared the intraoperative transitions of blood pressure and hematocrit, and analyzed the correlations between blood pressure and hematocrit at 15 min after cardiopulmonary bypass (immediately after modified ultrafiltration in group M) and between the percent increases in blood pressure and hematocrit during modified ultrafiltration. Results Although intraoperative central venous pressure and dopamine dosage were similar, in group M, increases in hematocrit (26.4% ± 4.9% to 31.9% ± 5.7%, P < 0.01) and systolic blood pressure (61.1 ± 10.3 to 75.6 ± 11.5 mmHg, P < 0.01) occurred during modified ultrafiltration. Furthermore, diastolic and mean blood pressure at 15 min after cardiopulmonary bypass (after modified ultrafiltration) were higher in group M than in group C. However, systolic, mean, and diastolic blood pressure were not correlated with increased hematocrit after modified ultrafiltration, and there was also no correlation between the percent increases in each blood pressure and hematocrit. Conclusion Modified ultrafiltration increased blood pressure and hematocrit immediately after cardiopulmonary bypass in children. However, no correlations were detected between the increases in blood pressure and hematocrit. These results indicate hemoconcentration is not the major cause of the increased blood pressure during modified ultrafiltration.     

Effect of increased intraabdominal pressure on cardiac output and tissue blood flow assessed by color-labeled microspheres in the pig

apd: 12 December 2000     

Cerebral blood flow during increased subarachnoid pressure

Summary In rhesus monkeys and cats cerebral intracranial pressure was increased by intracranial fluid injection. Increased liquor pressure was transferred to the superficial cerebral veins, which caused a reduction of cerebral perfusion pressure. An arterial pressure response occurred as soon as the perfusion pressure was less than 100 mm Hg. The pressure increase was dependent on the percent rate of perfusion pressure decrease in relation to the systemic arterial pressure. Carotid flow measured in monkeys showed a slight reduction as long as the perfusion pressure was higher than 50 mm Hg but was marked when it fell below that value. The systemic arterial pressure had a significant influence on cerebral vessel resistance independent from the perfusion pressure. During increased intracranial pressure the cerebral blood volume seemed to be moderately decreased.     

Hepatic extraction of indocyanine green is depressed early in sepsis despite increased hepatic blood flow and cardiac output

Although active hepatocellular function is depressed during sepsis, it is not known whether this occurs in the very early stages of sepsis and whether it is due to depressed cardiac output or hepatic blood flow. To study this, rats were subjected to sepsis by cecal ligation and puncture and hepatocellular function was determined at various intervals thereafter by assessing the ability of the liver to clear different doses of indocyanine green. The indocyanine green concentration was continuously measured in vivo with a fiberoptic catheter and an in vivo hemoreflectometer. Maximal velocity and kinetic constant of the clearance of indocyanine green, hepatic blood flow, and cardiac output were determined in experimental and sham-operated rats. The results demonstrate that hepatic blood flow and cardiac output increased 2 to 10 hours after cecal ligation and puncture, while hepatocellular function (maximum velocity and kinetic constant) was decreased even 2 hours following cecal ligation and puncture. No linear correlation between hepatocellular function and hepatic blood flow or cardiac output was found under such conditions. The extremely early depression in active hepatocellular function, despite the increased hepatic blood flow and cardiac output, may form the basis for cellular dysfunctions leading to multiple organ failure during sepsis.     

Inconsistent esophageal Doppler cardiac output during acute blood loss

Application of the Doppler principle can provide relatively noninvasive and continuous measurement of cardiac output. However, it is based on certain assumptions that may introduce error. Esophageal Doppler cardiac output was compared with Fick cardiac output during acute blood loss (35-45% estimated blood volume) in eight anesthetized pigs. Mean Fick cardiac output decreased from 4.8 to 1.9 l/min, mean Doppler cardiac output from 4.9 to 2.9 l/min. This was accompanied by a decrease in mean arterial pressure from 119 to 55 mmHg and increase in heart rate from a mean of 115 to 156 beats/min. There was an inconsistent association between the two methods both within and between individual animals. Cubic polynomial regression equations of cardiac output with time indicated small measurement error in Fick (R2: mean 0.93, range 0.99-0.75) as opposed to Doppler (R2: mean 0.67, range 0.93-0.16) cardiac output. In one animal Doppler cardiac output showed an increase with time and in one the Doppler cardiac output measurements were unrelated to time. There was highly variable association comparing Fick versus Doppler cardiac output with correlations ranging from -0.76 to 0.98. A sign test for mean differences indicated that Doppler derived cardiac output was higher than Fick cardiac output, and the chance of this occurring if the true difference was zero was less than 1 in 1,000. A test for homogeneity of correlations was also rejected. Inaccuracies in individual assumptions in the computation of esophageal Doppler cardiac output, especially unaccounted changes in aortic diameter, are responsible for the inconsistent and unpredictable values of Doppler cardiac output obtained in this experimental model of hemorrhage.     

Maintained cardiac output during positive end-expiratory pressure ventilation in open-chest pigs

Background: Does ventilation with positive end-expiratory pressure (PEEP) act to reduce cardiac output (CO) not only by impeding venous return but also by inducing myocardial depression? The present study was aimed to demonstrate the possible existence of this latter mechanism. Methods: Eight pigs of Swedish native breed weighing 20–25 kg and 10–12 weeks old were anaesthetized, tracheotomized and connected to a volume-controlled ventilator. To prevent intra-thoracic pressure from interfering with venous return, the heart and juxtacardiac vessels were exposed to atmospheric pressure by opening and retracting the chest and pericardium. Heart rate (HR), CO, stroke volume (SV), mean arterial (MAP), mean right (MRAP) and left (MLAP) atrial pressures were recorded before and after retransfusion of 500 ml of autologous blood. This procedure was carried out twice in each animal - during ventilation with zero and with 15 cm H₂O of PEEP. Results: Comparison of the two ventilation modes before volume load revealed negligible differences in HR, CO, SV, MAP, MRAP and MLAP. Moreover, the changes evoked by volume load were practically identical. Conclusions: Addition of PEEP to regular positive pressure ventilation does not induce any haemodynamically detectable myocardial depression in the piglet.     

Continuous positive pressure ventilation during epidural blockade--effects on cardiac output distribution

Background: It has been shown that when cardiac output (CO) decreases during continuous positive pressure ventilation (CPPV), its regional distribution adapts with a favouring of vital organs. Does epidural blockade modify this adaptation? Methods: Regional blood flows were assessed by the microsphere technique (15 μm) in 17 anaesthetised pigs during spontaneous breathing and CPPV with 8 cm H₂O end‐expiratory pressure (CPPV8) before and after epidural blockade. The block was induced at either the Th_6–7 (Thep) or the L₆–S₁ (Lep) level with 1 ml of lidocaine 40 mg · ml^?1. Results: When Lep was combined with CPPV8, mean arterial pressure and CO decreased significantly, and they decreased even more when combined with Thep. In contrast, the relative perfusion of the central nervous system, heart and kidneys remained stable during the four conditions studied. The adrenal perfusion during CPPV8 was obviated by epidural blockade. The absolute and relative perfusion of the skeletal muscle decreased during epidural blockade. The administered doses of epidural lidocaine did not affect blood flow in the spinal cord. Conclusions: The locally mediated nutritive vasoregulation of vital organs outweighed the sympathetic blockade induced by epidural blockade. During Thep blockade the animals were less capable of responding to the haemodynamic changes induced by CPPV8, probably due to the blockade of the cardiac part of the sympathetic nervous system.     

Cardiac output monitoring by pressure recording analytical method in cardiac surgery.

OBJECTIVE: A less-invasive method has been developed that may provide an alternative to monitor cardiac output from arterial pressure: beat-to-beat values of cardiac output can be obtained by pressure recording analytical method (PRAM). The purpose of this study was to assess the reliability of cardiac output determination by PRAM in cardiac surgery. METHODS: Cardiac output was measured in 28 patients undergoing coronary artery bypass grafting at 15 min after anaesthesia induction, 30 min after extracorporeal circulation, 1 and 3 h after arrival in the intensive care unit using thermodilution (ThD) method through a pulmonary artery catheter and PRAM. ThD cardiac output was calculated as the mean of five separate measurements. PRAM provided beat-by-beat cardiac output data continuously throughout the study and the cardiac output values displayed on a dedicated personal computer at each time point were recorded. Correlations were calculated and differences were compared by Bland-Altman analysis. RESULTS: A total of 112 measurements were obtained. Cardiac output ranged from 2.3 to 7.4 l/min, and a good linear correlation (R2=0.78, P<0.0001) was found between ThD and PRAM. The highest degree of correlation (R2=0.86) was obtained at 3 h after arrival in the intensive care unit. The lower degree of correlation (R2=0.70) was obtained 30 min after extracorporeal circulation. At Bland-Altman analysis, the overall estimates of cardiac output measured by PRAM closely agreed with ThD (mean difference, 0.027; standard deviation, 0.43; limits of agreement, -0.83 and +0.89). CONCLUSIONS: Under the studied conditions, our results demonstrate good agreement between PRAM data and ThD measurements, and this new method has shown to be accurate for real-time monitoring of cardiac output in cardiac surgery. Further studies will be required to assess this method in higher-risk patients and in the setting of haemodynamic instability or arrhythmias. This is the first study designed to assess the accuracy of PRAM in cardiac surgery.     

Transcutaneous fluorescence dilution cardiac output and circulating blood volume during hemorrhagic hypovolemia

BACKGROUND: Cardiac output and circulating blood volume are important parameters for assessing cardiac function in the intensive care setting and during major surgeries. The authors tested in an animal model of hemorrhagic hypovolemia the feasibility of measuring these parameters simultaneously by transcutaneous fluorescence monitoring of an intravenous bolus injection of indocyanine green. METHODS: Fluorescence dilution cardiac output was measured in seven anesthetized rabbits and compared to thermodilution cardiac output. The optical probe used to excite the indocyanine green fluorescence was in contact with the skin above the ear artery. Local heating enhanced blood perfusion of the measurement site. Cardiac output was measured during baseline conditions, during hemorrhagic hypovolemia, and after partial restoration of the blood volume with reinfused blood. Estimates of the circulating blood volume were simultaneously obtained from the analysis of the fluorescence dilution traces. RESULTS: Cardiac output measured by fluorescence dilution (thermodilution) averaged 455 +/- 16 (450 +/- 13) ml/min in baseline conditions and 323 +/- 15 (330 +/- 13) ml/min during hypovolemia. Fluorescence dilution cardiac output was linearly related to thermodilution cardiac output (slope = 1.13 +/- 0.05, ordinate = -50 +/- 19 ml/min, R = 0.92). Interanimal differences explained most of the variance between cardiac output estimates obtained with the two techniques. Circulating blood volume decreased from 204 +/- 5 ml in baseline conditions to 174 +/- 8 ml after bleeding and reflected blood volume changes in this acute bleeding-reinfusion model. CONCLUSIONS: The study extends the applicability of the fluorescence dilution technique for cardiac output measurement to hypovolemic conditions and demonstrates its ability to produce accurate estimates of the circulating blood volume in experimental animals.     

PiCCO技术在婴幼儿先心病术中血流动力学监测的应用

目的评价脉搏指数连续心输出量监测(PiCCO)技术在婴幼儿心脏手术中应用的价值。方法先天性心脏病患儿10例在心肺转流(CPB)下行先天性心脏病根治术。应用PiCCO监测仪监测MAP、HR、心脏指数(CI)、连续心输出量指数(CCO)、胸腔内血容量指数(ITBI)、全心舒张末期容量指数(GEDVI)、血管外肺水指数(ELWI)等指标,分别记录手术前(T1)、心脏停跳前(T2)、心脏复跳后30min(T3)、1h(T4)、术后24h(T5)数据,并观察相关置管并发症。结果10例患儿均成功完成手术。T3时MAP和CI较T1、T2时明显降低(P<0.05);T4时ITBI和GEDVI较T1、T2时明显减少,CI较T1、T2时明显增加(P<0.05)。10例患儿均未发现与PiCCO监测操作相关的并发症,股动脉与颈内静脉穿刺无一例失败。结论PiCCO技术微创科学,安全可靠,更适合先天性心脏病婴幼儿患者。     

Estimation of changes in cardiac output from the arterial blood pressure waveform in the upper limb

We have developed a new pulse contour cardiac output (PulseCO)algorithm based on frequency analysis studies of the arterialsystem. PulseCO was compared with thermodilution cardiac output(TDCO) in 10 patients undergoing cardiac surgery. Results fromone patient were unsuitable for analysis. In the remaining ninepatients, 142 TDCO determinations were compared with PulseCOafter logarithmic transformation and after being normalizedby the initial cardiac output in each patient. Each determinationwas usually the average of three measurements. Least squaresregression gave y=0.77x (r²=0.81) and the limits of agreementwere from –26% to +21%. The accuracy of PulseCO in determiningshort-term changes in cardiac output was assessed by comparingthe ratios of consecutive PulseCO determinations with the ratiosof the corresponding, consecutive TDCO determinations. Leastsquares regression gave y=0.71x (r²=0.70) and the limits ofagreement were from –21% to +25%. After phenylephrinehad been given to five patients, PulseCO showed an increasein systemic vascular resistance consistent with the known pharmacologicalactions of the drug. The PulseCO algorithm was incorporatedinto a computer program that acquires arterial pressure datafrom an analogue-to-digital converter and displays beat-to-beattrend values. Br J Anaesth 2001; 86: 486–96