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Dobutamine is a newly developed catecholamine reported to have minimal direct vascular effects relative to its inotropic activity and to have less chronotropic and arrhythmogenic properties than other catecholamines used in the treatment of low output states. In this study, the acute hemodynamic effects of dobutamine were compared to those of dopamine in 13 patients with chronic low output cardiac failure. At dosages adjusted to achieve similar increments in cardiac output, dobutamine reduced left ventricular filling pressure (LVEP) from 24 +/- 2 mm Hg (SEM) to 17+/- 2 mm Hg, while dopamine increased LVEP to 30 +/- 3 mm Hg and in six patients caused arterial O2 saturation to fall below 90%. This poor response to dopamine was probably the result of its vasoconstrictive effects and illustrates the potential advantages of using a cardioselective agent such as dobutamine when the desired goal of therapy is to improve ventricular function by direct inotropic stimulation.
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Cardiac output estimation by thermodilution is carried out using room temperature or iced injectate, but the accuracy and variability of the two methods is not well documented. Room temperature and iced injectate were compared in 21 patients undergoing diagnostic cardiac catheterization. Dextrose injectate (10 ml) was administered in prefilled syringes left to stand either in iced water or in room air. Four injections were made sequentially with room temperature and iced injectate. Cardiac output by room temperature and iced injectate were not significantly different (4.70 +/- 1.22 for room temperature and 4.90 +/- 1.37 for iced injectate, n = 21, P = 0.155). There was a significant difference in the variance of the estimations by the two methods (room temperature = 0.296, iced = 0.120, P less than 0.005). From this variance the calculated number of measurements needed to estimate cardiac output to +/- 0.5 L/min with 95% confidence is seven for room temperature and four for iced injectate. For five patients with cardiac output less than 4.00 L/min with room temperature injectate, cardiac output with iced injectate was significantly higher (3.33 +/- 0.34 for room temperature vs. 3.69 +/- 0.49 for iced injectate, P = 0.05). Thus room temperature injectate generally gives a satisfactory cardiac output estimation but with significantly greater variability than iced injectate. Sample size for accurate cardiac output estimation must be greater with room temperature injectate. Iced injectate may over-estimate output when cardiac output is low.
Cardiac output was measured by two-dimensional echocardiographic Doppler technique in 55 adult patients in the intensive care unit. Doppler cardiac output determinations were measured from four sites (suprasternal long axis of the ascending aorta, suprasternal long axis of the descending aortic, apical left ventricular outflow tract, and parasternal long axis of the main pulmonary artery) and were compared to cardiac output determined by thermodilution for a total of 101 observations (r = 0.84). Mean cardiac output was 5.3 L/min (range 1.8 to 9.5 L/min) by Doppler technique and 5.1 L/min (range 1.6 to 8.9 L/min) as measured by thermodilution. Correlation of Doppler cardiac output with thermodilution cardiac output gave r values of 0.85, 0.83, 0.90, and 0.81 from the ascending aorta, descending aorta, left ventricular outflow tract, and pulmonary artery, respectively. Averaging of data in patients in whom more than one determination was possible resulted in improved correlation (r = 0.94). Thus, cardiac output can be measured with reasonable accuracy by Doppler from a variety of sampling sites and averaging of data from more than one site may improve these results.
Cardiac output estimation is an important and much needed measurement for assessing patients in heart failure. In hypertension, it is vital for understanding the haemodynamic basis of the disease and the mode of action of drugs. Measurements of blood pressure and cardiac output provide the only means of estimating peripheral resistance. Of the available methods to determine cardiac output, thermodilution is the most practical, although it has its difficulties and care has to be exercised in its use. When intra-arterial blood pressure measurements are needed, the dye-dilution method is equally valid, and if respiratory techniques are available the Fick principle may also be used. Of the non-invasive methods, none is yet developed to a stage suitable for general clinical use. Doppler velocimetry is the most promising technique, but it requires complex computer analysis and, as yet, can reliably be used only to measure changes in cardiac output in an individual. The technique has been assessed against the electromagnetic flowmeter in man and gives reasonable accuracy and repeatability. Echocardiography and impedance cardiography are not yet satisfactory for clinical use; neither are the radionuclide methods, apart from the 'first pass' method, but this also needs further verification.
Cardiac output is determined by the interaction of cardiac pump function and the mechanical properties of the peripheral circulation that govern venous return. Increasing pleural pressure impedes peripheral venous return but aids cardiac ejection; on the other hand, decreasing pleural pressure can augment venous return but impedes the emptying of the left ventricle, creating an increase in aortic pressure. Whether a fall in pleural pressure leads to an increase or decrease in cardiac output depends upon the functional state of the heart and its sensitivity to changes in afterload. Understanding the effect of pleural pressure on cardiac output may lead to the development of therapeutic or diagnostic techniques using altered pleural pressure.
Cardiac output was determined by means of radioactive microspheres, 15 +/- 5 microns in diameter. Blood flow in the ascending aorta was measured by an electromagnetic flowmeter. In eight cats thirty-eight simultaneous measurements were made of cardiac output and aortic flow. The observations correlated well (r = 0.89), with a mean difference of 5.2%, probably corresponding to coronary blood flow. Continuous flow recordings showed no alterations in aortic flow during the injections of microspheres; arterial blood pressure and heart rate remained unchanged even after six injections, each consisting of about 2 x 10(5) spheres per kg body weight. Tests for shunting of microspheres were performed and revealed shunt fractions in the systemic circulation of about 8%, with no significant shunting through the lungs. The microsphere method for determining cardiac output is thought to be an accurate method, suitable for small and medium sized animals.
We studied 99 adult patients after elective cardiac surgery who had low cardiac output (cardiac index less than 2.5 L/min/m2) in spite of adequate cardiac filling pressure (pulmonary capillary wedge pressure less than 8 mm Hg). Patients received milrinone by loading dose (50 micrograms/kg over a 10-minute period), followed by a continuous infusion of either 0.375, 0.5, or 0.75 micrograms/kg/min (low-, middle-, and high-dose groups, respectively) given for a minimum of 12 hours. Patients were allocated to each dosage group sequentially, not randomly. Hemodynamic measurements were made before the loading dose and at 15, 30, 45, and 60 minutes, 3, 6, and 12 hours after the start of milrinone therapy. Further measurements were made at 2 and 4 hours after treatment was stopped. Milrinone therapy was associated with a rapid, well-sustained, and highly significant increase in cardiac index in all three dose groups (p less than 0.001), and a similar fall occurred in pulmonary capillary wedge pressure in all groups (p less than 0.001). Significant increases occurred in heart rate in all three groups (p less than 0.001). Systemic and pulmonary vascular resistance also fell significantly, although changes in this latter parameter were less predictable and more dose dependent. Few serious treatment-related adverse effects were seen. We conclude that intravenous milrinone is an effective and safe therapy for the treatment of low output states after cardiac surgery.
Cardiac output is determined by heart rate, by contractility (maximum systolic elastance, Emax) and afterload, and by diastolic ventricular compliance and preload. These relationships are illustrated using the pressure-volume loop. Diastolic compliance and Emax place limits determined by the heart within which the pressure-volume loop must lie. End-diastolic and end-systolic pressures and hence the exact position of the loop within these limits are determined by the peripheral circulation. In the presence of minimal sympathetic tone, some 60% of total blood volume is hemodynamically inactive and constitutes a blood volume reserve (the unstressed volume). The remainder of the blood volume (the stressed volume) and the compliance of the venous system determine the venous pressure. This venous pressure together with venous resistance determines venous return, right atrial pressure, cardiac preload, and hence cardiac output. Venoconstriction causes conversion of unstressed volume to the stressed volume, the blood volume reserve is converted into hemodynamically active blood volume. After hemorrhage this replaces the lost stressed volume, while in other situations where total blood volume is not reduced, it allows a sustained increase in cardiac output. The major blood volume reserve is in the splanchnic bed: the liver and intestine, and in animals but not man, the spleen. A major unsolved problem is how the conversion of unstressed volume to stressed volume by venoconstriction is reflexly controlled.
We have studied the haemodynamic effects of i.v. milrinone, a new phosphodiesterase inhibitor, in patients with low cardiac output after cardiac surgery. Thirty-five patients with a cardiac index (Cl) less than 2.5 litre min-1 m-2 and a pulmonary capillary wedge pressure (PCWP) greater than 8 mm Hg were given a loading dose of milrinone 50 micrograms kg-1 followed by an infusion at one of three rates: 0.375 micrograms kg-1 min-1, 0.5 micrograms kg-1 min-1 or 0.75 micrograms kg-1 min-1 for 12 h. After 1 h there were increases in Cl (35%) (P less than 0.001), heart rate (13%) (P less than 0.01) and stroke volume index (19%) (P less than 0.005). There were decreases in mean arterial pressure (12%) (P less than 0.01), systemic vascular resistance (35%) (P less than 0.001) and PCWP (24%) (P less than 0.05). Pulmonary vascular resistance was unchanged or reduced and left ventricular stroke work index was unchanged or increased. The haemodynamic improvements were sustained throughout the infusion period. Milrinone was tolerated well: three patients developed tachycardia greater than 125 beat min-1, one patient developed atrial fibrillation and one patient had a short run of atrial bigemini. We conclude that milrinone is a useful agent in the treatment of patients with a reduced cardiac output after cardiac surgery.
Cardiac output was measured 120 times in 27 critically ill patients using the thermodilution and transthoracic electrical impedance methods. Both the minimum and mean values for the distance between the inner electrodes, and a variety of values for the resistivity of blood (rho) were substituted in the Kubicek's empiric formula for calculating cardiac output by transthoracic electrical impedance. Using the mean distance between the inner electrodes and a rho-value of 150 ohm X cm gave the best agreement between the methods (mean difference 0.17 +/- 2.4 L/min). Ventilation alone or with positive end-expiratory pressure did not significantly affect the bias of the estimate, but both affected its precision when compared with measurements in spontaneously breathing patients (SD of mean difference 2.4 and 3.2 L/min, respectively, vs. 1.5 L/min). The pulmonary artery wedge pressure was significantly higher in patients with an abnormal diastolic impedance waveform (zero-wave), but there was no relationship between wedge pressure and base impedance per unit length between the measuring electrodes.
Circulatory failure after cardiac surgery often calls for active hemodynamic management with fluids, inotropes, and vasodilators. Dopexamine hydrochloride is a new combined beta 2-adrenergic and DA1-dopaminergic receptor agonist and an inhibitor of the uptake-1 mechanism of endogenous catecholamines. As a result, it exerts inotropic and vasodilator effects on the heart and systemic vasculature. The effects were examined over a mean of 22 hours, using 1 to 4 micrograms/kg/min of dopexamine to treat low cardiac output states following coronary bypass and valvular/ventricular repair surgery. In 8 out of 14 patients, low cardiac output was readily reversed by 1 microgram/kg/min of dopexamine. Six patients required higher doses (2 to 4 micrograms/kg/min) to achieve a satisfactory cardiac index. Significant changes from control values were observed throughout the infusion for heart rate (67 to 102 beats/min), cardiac index (2.0 to 3.4 L/min/m2), and systemic vascular resistance (1,545 to 914 dyne.s.cm-5). Pulmonary vascular resistance, pulmonary artery wedge pressure, and right atrial pressure were also significantly reduced during the infusion. Most of these changes reversed when dopexamine was discontinued, suggesting a drug-specific effect and a lack of tolerance. Nausea was a frequent complaint, but was no more frequent than in a random sample of similar patients. Titration of dopexamine, 1 to 4 micrograms/kg/min, was efficacious in producing circulatory improvement in patients with a low cardiac output after cardiac surgery.
Eleven hypervolemic and oliguric children with low cardiac output after cardiac operations were treated by slow continuous ultrafiltration or continuous arteriovenous hemofiltration. A mean negative fluid balance of 1.63 +/- 0.37 ml/kg/hr (standard error of the mean [SEM]) significantly improved the hemodynamic status within 59 +/- 6.1 hours (SEM). Although the central venous pressure decreased significantly from 15.2 +/- 0.84 to 8.8 +/- 0.92 mm Hg (p less than 0.0001), the mean arterial pressure increased significantly from 41.5 +/- 2.54 to 53.5 +/- 2.21 mm Hg (p less than 0.001). In addition, pH increased significantly from 7.31 +/- 0.01 (SEM) to 7.43 +/- 0.001 (SEM) (p less than 0.001) and oxygenation index (arterial oxygen tension/inspired oxygen fraction) from 119 +/- 15.2 (SEM) to 214 +/- 27.0 (SEM) (p less than 0.001). Hemodynamic improvement during slow continuous extracorporeal fluid removal allowed a significant decrease of the catecholamine infusion rate. After normovolemia had been achieved, continuous arteriovenous hemofiltration had to be continued in four children because of persistent anuria. Eight patients could be weaned from artificial ventilation and vasopressor support. Two patients died without recovery of renal function and one with restored renal function. Slow continuous ultrafiltration and continuous arteriovenous hemofiltration improve the cardiovascular function in children with low cardiac output by optimizing the preload conditions of the failing heart. In addition, they improve acid-base balance and pulmonary gas exchange.
The variety of volume flow calculation methods described for determination of cardiac output by Doppler and the controversy surrounding their relative accuracy is to some extent a result of how difficult they are to use and the fact that they break down in patients whose anatomic and physiologic flow cross sections do not match, in patients who may have flow in vessels with flow profiles that are not flat, and in patients who are difficult to examine in one view or another or who do not give clean Doppler waveforms. Nonetheless, most of the methods work to some extent in most patients. Discovering those patients who do not fit the assumptions in these methods and whose cardiac output can therefore not be accurately calculated will probably be a major contribution of the new flow mapping Doppler technologies. We believe these new technologies may provide more sophisticated methods for calculating volume flows, cardiac outputs, regurgitant fractions, and shunt volumes.
The present paper describes a new method for the measurement of cardiac output (CO) and cardiac shunt (CS). The CO method is based on the accurate determination of the concentration of the indicator in large vessels. For the measurement of the left to right shunting volumes, a double tracer technique is used by which radioactively labeled transferrin or erythrocytes are applied together with radioactively labelled human-serum-albumin (HSA) microspheres. The results obtained using these methods were compared with the data obtained by invasive methods. High correlation of both sets of data suggests that the proposed methods might provide an excellent extension of noninvasive procedures in the first months of a childs life.
During anaesthesia haemodynamic measurements were performed with pulsed ultrasound Doppler in six patients with a Swan-Ganz catheter. Cardiac output (CO), heart rate (HR), arterial blood pressure (AP), systemic vascular resistance (SVR) and left cardiac work (LCW) were measured simultaneously with the velocity measurements of the bloodstream in the ascending aorta. Six to fourteen (median 9) simultaneous measurements were done in each patient. Sixty-two measurements were made. The velocity (V) and the product of velocity and heart rate (VHR) were compared with CO in order to establish a non-invasive index of the cardiac output. The product of velocity, the heart rate and the arterial blood pressure (VHRAP) was compared with LCW, showing a good correlation between VHR and CO (V = maximum velocity) (rho = median 0.85), as was the case between VHRAP and LCW (rho = 0.88). Furthermore, a negative correlation between V and SVR was found, illustrating that the velocity of the bloodstream in the aorta obviously depends on the afterload. It is concluded that pulsed ultrasound Doppler in combination with HR and AP can measure relative changes in CO and LCW.
A system has been developed to monitor continuously the components of the oxygen Fick equation: oxygen consumption by a gas exchange analyzer and arteriovenous oxygen difference by pulse and fiberoptic oximetry. A computer-based system was developed which calculates cardiac output and other variables every 20 sec. Continuous Fick (CF) cardiac output was compared to thermodilution (TD) cardiac output in 21 ventilated post-cardiac surgery patients. A total of 237 simultaneous cardiac output measurements had a range between 2 and 11 L/min. The correlation between CF and TD cardiac outputs was r = .86, with an equation of TD cardiac output = 0.92 CF cardiac output + 1.16. There was a significant (p less than .001) difference between the two methods of cardiac output estimation. The CF method was consistently lower than TD; this difference was greater at lower flows. CF cardiac output measurement is practical; it offers distinct advantages in viewing cardiac output together with oxygen demand and oxygen extraction.