The effect of the intrathoracic pressure regulator on hemodynamics and cardiac output

The intrathoracic pressure regulator (ITPR) (CirQLator; Advanced Circulatory Systems Inc, Roseville, Minn) is a novel, noninvasive device intended to increase cardiac output and blood pressure in hypovolemic or cardiogenic shock by generating a continuous low-level intrathoracic vacuum in between positive pressure ventilations. Although there are robust data supporting the benefit of the ITPR in multiple animal models of shock, the device has not been used in humans.The goals of this study were to evaluate both the safety and efficacy of the ITPR in humans. Twenty patients undergoing coronary artery bypass graft surgery were enrolled in this phase 1 study. Intraoperative use of both pulmonary artery pressure monitoring and transesophageal echocardiography (TEE) was required for study inclusion. Hemodynamic variables as well as TEE measurements of left ventricular performance were collected at baseline and after the ITPR device was activated, before surgical incision. Thermodilution cardiac output increased significantly with the application of the ITPR (4.9 vs. 5.5 L/min; P = 0.017). Similarly, cardiac output was measured by TEE (5.1 vs. 5.7 L/min; P = 0.001).There were significant increases in pulmonary artery systolic blood pressures (35 vs. 38 mmHg; P G 0.001) and mean pulmonary artery pressures (24 vs. 26 mmHg; P = 0.008). There were no significant differences in systemic blood pressures, left ventricular volumes, stroke volume, or ejection fraction as measured by TEE. Using two different measurement techniques, application of the ITPR increased cardiac output in normovolemic anesthetized patients who underwent coronary artery bypass graft before sternotomy. These data suggest that the ITPR has the potential to safely and effectively increase cardiac output in humans.     

The effect of respiration on the monitoring of stroke volume and cardiac output by the electrical impedance technique

In six volunteers (5 male, 1 female) it has been shown that normal respiration made no statistical difference to the estimates of the mean stroke volume and the mean cardiac output as determined by the electrical impedance method of Kubiceket al, (1966). The coefficient of variation was usually increased by respiration. The use of those stroke volumes which occur only at end-expiration was not shown to yield a greater reproducibility with 3 other male volunteers. In the female subject it was found that the use of a digital averager triggered from the preceding R-wave of the ECG gave values for the mean stroke volume and cardiac output which were always lower than the conventional mean values obtained from a number of strokes. The expense of either of these approaches does not appear to be justified as a means of compensating for the effects of normal respiration on the impedance dZ/dt waveform.     

The effect of haematocrit on transthoracic electrical impedance and on the calculation of cardiac output by an impedance cardiograph

The Transthoracic electrical impedance (TEI) was measured using the Bomed NCCOM3 non-invasive cardiac output monitor in 27 patients with polycythemia rubra vera (PCRV) and in a control group of 27 patients with normal haematocrits. The mean haematocrit was 49.4% (SD2.61) in the patients with PCRV and 42.1% (SD 2.95) in the control group, a difference that was significant (p<0.001). The mean TEI was also significantly higher in patients with PCRV than in the control group (p<0.05), the respective values being 31.25 (5.48) Ohms and 27.5 (3.31) Ohms. The mean values for cardiac output (CO) and cardiac index (CI) were similar in both groups.     

米力农改善心脏手术后心力衰竭所致低心排血量综合征患者的肾功能

目的评价正性肌力药米力农在治疗体外循环(CPB)心脏手术后心力衰竭所致低心排血量综合征时对患者肾脏的影响。方法选取2018年1月至2020年6月间在我院心胸外科治疗的CPB心脏手术患者,在患者心脏停跳后30 min(基线期)和60 min(治疗后)进行肾脏和全身血流动力学检测。CPB术后30 min发生低心排血量综合征患者接受米力农治疗,根据患者CPB心脏手术后是否应用米力农,将患者分为米力农组(n=59)和对照组(n=82)。比较两组患者血流动力学指标和肾血流动力学指标基线期值、治疗后值、治疗后较基线期变化值。比较治疗后两组患者预后指标及并发症发生率。结果治疗后米力农组患者心脏指数变化值[(0.55±0.26) L/(min·m²) vs.(-0.35±0.28) L/(min·m²),t=19.394,P <0.001]、心搏容量指数变化值(t=8.776,P <0.001)、氧释放系数变化值(t=8.143,P <0.001)、混合静脉血氧饱和度变化值(t=9.935,P <0.001)与对照组比较显著提高,周身血管阻力指数变化值(t=10.574,P <0.001)、肺血管阻力指数变化值(t=10.654,P <0.001)与对照组比较显著降低。治疗后米力农组患者肾血流量变化值[(117.30±153.82) m L/min vs.(-63.73±157.64) m L/min,t=6.795,P <0.001]、肾脏供氧量变化值(t=4.248,P <0.001)与对照组比较显著提高,肾小球滤过分数变化值(t=6.382,P <0.001)、肾血管阻力变化值[(-0.06±0.05) mm Hg/(m L·min) vs.(0.03±0.06) mm Hg/(m L·min),t=9.407,P <0.001]和肾氧摄取率变化值(t=7.625,P <0.001)与对照组比较显著降低。结论米力农在心脏手术后早期用于治疗急性心力衰竭所致低心排血量综合征,可以增加患者心输出量和肾血流量,扩张肾血管。米力农可以改善患者易感肾脏的氧合作用,但不会引起肾小球滤过率的显著变化。     

Impaired effect of dopamine on cardiac output during octopamine infusion

The hemodynamic effects of octopamine (OCT) were studied before and during dopamine (DA) infusion in six normal dogs. Before OCT infusion, DA significantly increased cardiac index (CI) from 3.24 +/- 0.20 to 4.90 +/- 0.30 L/min X m2 and significantly decreased systemic vascular resistance index (SVRI) from 3700.2 +/- 212.5 to 2618.3 +/- 156.6 dyne X sec/cm5 X m2, without changing heart rate. During OCT infusion, DA failed to increase CI or decrease SVRI; however, it significantly increased heart rate from 153.3 +/- 12.9 to 183.0 +/- 17.0 beat/min. This suppression of a DA-related increase in cardiac output may explain why DA is ineffective in those septic patients with elevated plasma OCT levels.     

Near continuous cardiac output by thermodilution

A new thermodilution method for frequent (near continuous) estimation ofcardiac output, without manual injection of fluid into the blood, was tested.The method utilizes a pulmonary artery catheter equipped with a fluid filledheat exchanger. The technique is based on cyclic cooling of the blood in theright atrium and measurement of the temperature changes in the pulmonaryartery. Using this technique, a new estimate of cardiac output can be obtainedevery 32 s. Cardiac output estimates, obtained for a running mean of threemeasurements with this method, were compared to the mean of three conventionalthermodilution measurements. The measurements were obtained during shortperiods of stable respiration and circulation.In six pigs, we made 46 paired measurements of conventional thermodilution(TD) and near continous (TDc) thermodilution. The cardiac output(CO TD) ranged from 2.4–13.7 l/min (mean 5.4 l/min). Thebest linear fit through the paired data points was CO TDc =–0.57 + 1.01 CO TD. The mean difference between themethods was –0.50 l/min (S.D. = 0.39). The mean coefficient of variationof repeated measurements with the near continuous thermodilution was3.6%.Considering changes of more than 0.25 l/min to be significant, all changes incardiac output measured by conventional thermodilution were followed by therunning mean of three near continuous thermodilution estimates.This study demonstrates the feasibility of the new method to monitorcardiac output, and to detect all changes greater than 0.25 l/min.     

Comparison of the ability of two continuous cardiac output monitors to measure trends in cardiac output: estimated continuous cardiac output measured by modified pulse wave transit time and an arterial pulse contour-based cardiac output device

Estimated continuous cardiac output (esCCO), a noninvasive technique for continuously measuring cardiac output (CO), is based on modified pulse wave transit time, which in turn is determined by pulse oximetry and electrocardiography. However, its trending ability has never been evaluated in patients undergoing non-cardiac surgery. Therefore, this study examined esCCO’s ability to detect the exact changes in CO, compared with currently available arterial waveform analysis methods, in patients undergoing kidney transplantation. CO was measured using an esCCO system and arterial pressure-based CO (APCO), and compared with a corresponding intermittent bolus thermodilution CO (ICO) method. Percentage error and statistical methods, including concordance analysis and polar plot analysis, were used to analyze results from 15 adult patients. The difference in the CO values between esCCO and ICO was ?0.39 ± 1.15 L min^?1 (percentage error, 35.6 %). And corrected precision for repeated measures was 1.16 L min^?1 (percentage error for repeated measures, 36.0 %). A concordance analysis showed that the concordance rate was 93.1 %. The mean angular bias was ?1.8° and the radial limits of agreement were ±37.6°. The difference between the APCO and ICO CO values was 0.04 ± 1.37 L min^?1 (percentage error, 42.4 %). And corrected precision for repeated measures was 1.37 L min^?1 (percentage error for repeated measures, 42.5 %). The concordance rate was 89.7 %, with a mean angular bias of ?3.3° and radial limits of agreement of ±42.2°. This study demonstrated that the trending ability of the esCCO system is not clinically acceptable, as judged by polar plots analysis; however, its trending ability is clinically acceptable based on a concordance analysis, and is comparable with currently available arterial waveform analysis methods.     

Measurement of cardiac output by open-circuit acetylene uptake: a computer model to quantify error caused by ventilation-perfusion inequality

The ability to assess cardiac output (Q(T)) noninvasively has been the focus of interest for many researchers. While the open-circuit acetylene (C2H2) method seems promising, it is prone to error due to ventilation-perfusion (V/Q) inequality. Measurements during exercise, at high altitude or in patients with chronic obstructive pulmonary disease (COPD) could be unreliable and further validation studies under these circumstances may be needed. We used a computer model based on formulae derived from the multiple inert gas elimination technique to quantify error in Q(T) measurements resulting from V/Q inequality at rest, during exercise or at high altitude. Moreover, potential errors encountered in patients with COPD were quantified. In healthy subjects, V/Q inequality related measurement error seems negligible, under both normoxic and hypoxic conditions and especially during exercise. In COPD, errors up to 20% at rest and up to 15% during exercise are expected. It is therefore concluded from our model that the open-circuit C2H2 uptake method is expected to be accurate in normal subjects. Its validity in COPD needs further study.     

Less-invasive cardiac output monitoring by earpiece densitometry

Cardiac output was measured by thermodilution and ear densitometry in surgical ICU patients who had pulmonary arterial catheters. Overall comparison based on 56 sets of triplicate measurements revealed a correlation coefficient (r) of 0.76 between the two techniques. Although ear densitometry was more accurate with injection via the antecubital vein (r = 0.88) vs. more distal injection (r = 0.67), these data suggest that this technique lacks the accuracy for clinical application.     

Assessment of the accuracy of continuous cardiac output and pulse contour cardiac output in tracking cardiac index changes induced by volume load.

OBJECTIVE: To assess the ability to track changes in cardiac index (DeltaCI) induced by volume loading using continuous pulsed heat thermodilution (CCO), and pulse contour (PCCO) cardiac output (CO) with transpulmonary thermodilution (TD(tp)) CO as reference. DESIGN: Prospective observational clinical trial. SETTING: Intensive care unit. PATIENTS: Twelve ventilated and sedated post-operative cardiac surgery patients. MEASUREMENTS AND RESULTS: Each patient had a 7.5F CCO pulmonary artery catheter (Edwards Lifesciences) and a 5F, 20cm PCCO femoral artery catheter (Pulsion Medical Systems). Forty-five data sets were taken before and after 25 volume loadings of 5mL/kg of 4% albumin. Volume loading resulted in an increase in CI (2.84L/(minm(2)) versus 3.12L/(minm(2)), p<.05) although only nine volume loadings changed CI (DeltaCI)>/=14%. The change in CI using PCCO (DeltaPCCI) was correlated with DeltaCI (TD(tp)) (R(2)=.50, p<.0001), whilst DeltaCI using CCO (DeltaCCI) was not (R(2)=.14). The bias and limits of agreement (LOA) between DeltaTD(tp)CI and DeltaPCCI was 6.2% (95% CI, +/-5.8%) and 28.4% (95% CI, +/-38.2%) respectively. DeltaTD(tp)CI and DeltaCCI has a bias of 2.6% (95% CI, +/-8.3%) and LOA of 39.6% (95% CI, +/-63%). Both DeltaPCCI and DeltaCCI reliably tracked DeltaCI>/=14%. CONCLUSION: In this small group of patients the continuous cardiac output methods tracked changes in CI, although, in individual cases they did not change in the same direction as the thermodilution method. Critical care nurses need to critically appraise the accuracy and clinical relevance of continuous CO data within the clinical context.     

Effect of flecainide on cardiac output

The effect of intravenous flecainide (2 mg/kg) on cardiac output was evaluated by a dye dilution method in six healthy nonsmokers. The study was of a double-blind, crossover, placebo-controlled, randomized, and balanced design. Cardiac output, heart rate, and stroke volume were measured 0, 10, 30, 60, 90, 120, 150, 180, and 240 minutes after the beginning of the flecainide infusion. Flecainide reduced cardiac output and stroke volume during the first 90 minutes and heart rate increased during the first 30 minutes after flecainide. Visual analog scales for alertness and dry mouth were determined 0, 10, 60, and 240 minutes after dosing. Alertness was reduced 60 minutes after flecainide, but there was no increase in dryness of the mouth.