SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Cardiac bypass in late-gestation fetal lambs causes severe placental vasoconstriction, which leads to fetal death from hypoxemia and respiratory acidosis. This response can be blocked by the administration of indomethacin; however, a fatal metabolic acidosis then gradually develops in the fetus. Because the fetus is known to mount an intensive catecholamine response to stress, and because the fetal myocardium is particularly sensitive to increased afterload, we hypothesized that elevated afterload as a result of fetal stress contributes to diminished cardiac output after bypass. Twenty fetal lambs at 80% gestation underwent 30 minutes of normothermic cardiac bypass at flow rates of 200 to 500 ml/kg per minute. All ewes received general anesthesia with ketamine. In 10 fetuses general anesthesia was specifically designed not to inhibit the release of stress-related catechols (ketamine); the remaining 10 fetuses received a "high" (cisterna magna) total spinal anesthetic with tetracaine, to block the fetal stress response. In each anesthetic group, 5 of the 10 lambs received indomethacin. During operation, normal hemodynamics were preserved in the spinal anesthetic group. Cardiac output, placental blood flow, and arterial carbon dioxide tension were all improved relative to results in the ketamine group. When spinal anesthesia and indomethacin are both given, hemodynamics also approach normal after bypass, and gas exchange is further improved. These data suggest that the inhibition of the stress response by spinal anesthesia improves the hemodynamic status of the fetus during operation and, in combination with indomethacin, allows maintenance of near-normal placental function after fetal cardiac bypass. Similar responses may also be possible in human fetuses with use of a high-dose narcotic technique.
The relationship between effective renal plasma flow (ERPF) and cardiac output was examined in 46 patients (22 with congestive heart failure and 24 following cardiac surgical procedures) by simultaneously measuring the global ERPF by the single-injection method and cardiac output by the thermodilution method. Of the patients in the heart-failure group, 21 also had pulmonary artery end diastolic pressure (PAEDP) recorded at the same time. ERPF and cardiac output were found to be related by the regression equation: cardiac output = 2.08 +/- 0.0065 ERPF (r, 0.80), with a SE of estimate of 0.81 l/min. ERPF and PAEDP were related by the regression equation: PAEDP = 45.02-0.0675 ERPF (r, 0.86), with a SE of estimate of 5.5 mm Hg. ERPF may be a useful noninvasive method of estimating cardiac output if it is known that no intrinsic kidney disease is present, and if the error of 0.81 l/min (1 SE of estimate) is within the range of clinical usefulness. The error is principally attributable to the determination of cardiac output by the thermodilution method.
The dependence of cardiac output measurement precision on ambient temperature and cardiac output stability was assessed by concurrent continuous and bolus thermodilution methods in postoperative cardiac surgery patients. The degree of agreement between the two methods was depended on room temperature (0.1 L/min for each degree below 25 degrees C). The agreement was also closer in trials where cardiac output was stable (< 10% variation). The continuous thermodilution method shows sufficient agreement with the bolus method for use in critical care; however, improved precision of cardiac output thermodilution measurements can be achieved by use of correction factors for cardiac instability and for ambient temperature.
Explore the source record for details and available documents.
A pulmonary artery catheter (PAC) capable of continuous cardiac output (CCO) determination by thermodilution has recently been introduced. The purpose of this study was to compare CCO with two other methods of cardiac output (Ot) determination: electromagnetometry (EM) and standard bolus thermodilution cardiac output (BCO). Following median sternotomy and pericardiotomy, an EM ring probe was placed around the ascending aorta in 25 adult cardiac surgical patients and connected to an EM flowmeter interfaced with a calibrated strip recorder. Measurements were obtained over a 15- to 20-minute interval during a period of stable EM-determined Ot prior to initiation of cardiopulmonary bypass and in the absence of surgical stimulation. The CCO system averages Ot over a 3-minute interval, updating the measurement every 30 seconds. Cardiac output determined by the CCO system was compared with EM Ot averaged from the prior 3-minute period and with BCO obtained immediately after changing the Ot monitor from the continuous to bolus mode. Compared with EM, the bias for CCO was -0.48 L/min, precision 0.56 L/min, and the limits of agreement 1.12 L/min. Bias, precision, and limits of agreement of CCO compared with BCO were 0.41, 0.82, 1.64 L/min, respectively. Correlation between EM and CCO was r = 0.80 and between CCO and BCO r = 0.64. Cardiac output determined by CCO was within 10% of the EM determination for 37 measurements, between 10% and 20% for 17, and greater than 20% for 7 measurements.(ABSTRACT TRUNCATED AT 250 WORDS)
Most pulse contour methods are unreliable under changing haemodynamic conditions, because no corrections are made for pressure-dependent compliance and reflections of pressure waves. The pulse contour method of Wesseling includes such corrections. Four thermodilution measurements equally spread over the ventilatory cycle were used to calibrate and evaluate this pulse contour method. We designed a prototype incorporating a combination of the thermodilution method and pulse contour method and evaluated its potential for monitoring patients undergoing coronary bypass graft operation. Eight to 12 times during the operation, cardiac output was estimated by pulse contour and by thermodilution. The results were compared: the linear regression between the methods was COpc = 0.3 + 0.94. COth, (r = 0.94). The standard deviation for the difference between the methods against the mean of the methods was 10.6%. We concluded that the corrected pulse contour method estimates cardiac output accurately, even when heart rate, blood pressure, and total peripheral resistance change substantially.
In anesthetized dogs cardiac output was measured directly (by the method of Fick and by electromagnetic flowmetry) and indirectly (by the method of Bremser-Ranke and by rheography). The measurements were carried out before and after drug tests. The absolute values of cardiac output at rest differed depending on the method used. After the drug test all the methods revealed distinctly changes in cardiac output. A good correlation between flowmetric and rheographic methods was demonstrated. In view of this, they can be recommended to be used in rapidly changing hemodynamic situations. The method of Bremser-Ranke proved more suitable for the processes developing within 30-40 sec.
In three clinical centres, we compared a new method for measuring cardiac output with conventional thermodilution. The new method computes beat-to-beat cardiac output from radial artery pressure by simulating a three-element model of aortic input impedance, and includes non-linear aortic mechanical properties and a self-adapting systemic vascular resistance. We compared cardiac output by continuous model simulation (MF) with thermodilution cardiac output (TD) in 54 patients (18 female, 36 male) undergoing coronary artery bypass surgery. We made three or four conventional thermodilution estimates spread equally over the ventilatory cycle. In 490 series of measurements, thermodilution cardiac output ranged from 2.1 to 9.3, mean 5.0 litre min(-1). MF differed +0.32 (1.0) litre min(-1) on average with limits of agreement of -1.68 and +2.32 litre min(-1). Differences decreased when the first series of measurements in a patient was used to calibrate the model. In 436 remaining series, the mean difference became -0.13 (0.47) litre min(-1) with limits of agreement of -1.05 and +0.79 litre min(-1). When consecutive measurements were made, the change was greater than 0.5 litre min(-1), on 204 occasions. The direction of change was the same with both methods in 199. The difference between the methods remained near zero during surgery suggesting that a single calibration per patient was adequate. Aortic model simulation with radial artery pressure as input reliably monitors changes in cardiac output in cardiac surgery patients. Before calibration, the model cannot replace thermodilution, but after calibration the model method can quantitatively replace further thermodilution estimates.
Cardiac output is a hemodynamic parameter used by critical care nurses to guide and evaluate therapy. The thermodilution method of cardiac output measurement has allowed this parameter to be obtained at the bedside that is easily performed, timely, and reliable. Despite the relative simplicity in measuring cardiac output with the thermodilution method, it is not without problems. Potential physiologic and technical problems may yield erroneous cardiac output values. Critical care nurses must strive to maintain up-to-date knowledge and skill in performing thermodilution cardiac output measurements to ensure accurate and reliable values.
The measurement of cardiac output has many clinical applications and the development of a reliable, non-invasive measurement technique would be of considerable value to clinicians, cardio-respiratory physiologists and cardiovascular pharmacologists. Currently-used methods of measuring cardiac output are either invasive, and therefore potentially dangerous, or require the use of expensive, sophisticated, complex equipment which often has to be kept exclusively for the purpose of measuring cardiac output. We describe a method based on the recently modified and validated acetylene rebreathing technique which avoids the necessity for on-line computer acquisition of data by employing semi-manual digitization of hard copy recordings. The method is non-invasive, accurate, sensitive and relatively inexpensive. In addition, the whole technique can be rapidly performed by minimally trained personnel.
Cardiac output and organ blood flows were measured in 6 nonpregnant and 24 pregnant ewes from 38 to 141 days of gestation employing radionuclide-labeled microspheres. From the nonpregnant state to term increases in cardiac output, from 73.7 +/- 4.6 ml/min-kg of maternal weight to 148 +/- 2.4 ml/min-kg, and heart rate, from 88.5 +/- 10.3 to 106 +/- 4.6 beats/min, were noted, while mean arterial blood pressure was unchanged. Near term, the blood flows to the uterus and mammary gland represented approximately 18% of cardiac output. The blood flow to nonreproductive organs increased from 76.6 +/- 6.8 ml/min-kg of nonreproductive tissue in the nonpregnant state to 132 +/- 3.5 ml/min-kg at 130-140 days' gestation (P less than 0.01). No significant changes in renal blood flow were detected.
INTRODUCTION: Cardiac output (CO) monitoring is indicated only in selected patients. In cardiac surgical patients, perioperative haemodynamic management is often guided by CO measurement by pulmonary artery catheterisation (COPAC). Alternative strategies of CO determination have become increasingly accepted in clinical practice because the benefit of guiding therapy by data derived from the PAC remains to be proven and less invasive alternatives are available. Recently, a device offering uncalibrated CO measurement by arterial waveform analysis (COWave) was introduced. As far as this approach is concerned, however, the validity of the CO measurements obtained is utterly unclear. Therefore, the aim of this study was to compare the bias and the limits of agreement (LOAs) (two standard deviations) of COWave at four specified time points prior, during, and after coronary artery bypass graft (CABG) surgery with a simultaneous measurement of the gold standard COPAC and aortic transpulmonary thermodilution CO (COTranspulm). METHODS: Data from 30 patients were analysed during this prospective study. COPAC, COTranspulm, and COWave were determined in all patients at four different time points prior, during, and after CABG surgery. The COPAC and the COTranspulm were measured by triple injection of 10 ml of iced isotone sodium chloride solution into the central venous line of the PAC. Measurements of COWave were simultaneously taken at these time points. RESULTS: The overall correlation showed a Spearman correlation coefficient between COPAC and COWave of 0.53 (p < 0.01) and 0.84 (p < 0.01) for COPAC and COTranspulm. Bland-Altman analysis showed a mean bias and LOAs of 0.6 litres per minute and -2.2 to +3.4 litres per minute for COPAC versus COWave and -0.1 litres per minute and -1.8 to +1.6 litres per minute for COPAC versus COTranspulm. CONCLUSION: Arterial waveform analysis with an uncalibrated algorithm COWave underestimated COPAC to a clinically relevant extent. The wide range of LOAs requires further evaluation. Better results might be achieved with an improved new algorithm. In contrast to this, we observed a better correlation of thermodilution COTranspulm and thermodilution COPAC measurements prior, during, and after CABG surgery.
OBJECTIVE: To evaluate the accuracy of a new pulse contour method of measuring cardiac output in critically ill patients. DESIGN: A prospective criterion standard study. SETTING: Cardiac surgery intensive care unit in a university hospital. PARTICIPANTS: Nineteen cardiac surgery patients requiring intensive care treatment with pulmonary artery catheters after surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The pulse contour cardiac output monitor uses transpulmonary bolus thermodilution measurements to calibrate the system. In each patient, the pulse contour cardiac output values were compared with conventional thermodilution. The method described by Bland and Altman and linear regression analysis were used for comparison. The mean difference (bias) +/- standard deviation of differences (precision) was 0.31 +/- 1.25 L/min for pulmonary bolus thermodilution cardiac output versus pulse contour cardiac output and 0.21 +/- 0.73 L/min for pulmonary bolus thermodilution cardiac output versus transpulmonary bolus thermodilution cardiac output. Linear regression (correlation) analyses were pulse contour cardiac output = 0.97 thermodilution + 0.53 (r = 0.88), and transpulmonary cardiac output = 0.87 thermodilution + 1.09 (r = 0.96). There was a small increase 60 minutes after recalibration but not a statistically significant difference between pulse contour cardiac output and pulmonary bolus thermodilution cardiac output (p = 0.52). CONCLUSIONS: Bias and precision are acceptable, and the system provides results that agree with conventional thermodilution. This study demonstrates the clinical applicability of the pulse contour cardiac output monitoring system.
We have developed novel implantable Doppler microprobes to monitor beat-by-beat stroke volume and cardiac output (CO) after cardiac surgery. In 11 adults undergoing either coronary artery bypass grafting (n = 6) or valve replacement (n = 5), Doppler microprobes were implanted on the ascending aorta or the main pulmonary artery to measure aortic blood flow (ABF) or pulmonary artery blood flow (PBF). The diameters of both vessels were determined before surgery using two-dimensional echocardiography. Stroke volume was obtained from velocity tracings measured by a 4-MHz zero-crossing pulsed Doppler flowmeter. Simultaneous measurements of Doppler and thermodilution CO (TDCO) were compared. We found the following: ABF = 1.03 TDCO - 0.22 L/min (r = 0.89); while PBF = 0.69 TDCO - 1.24 L/min (r = 0.75). Furthermore, peak flow velocity and maximum acceleration of blood in the ascending aorta were measured after inotropic stimulation with dobutamine; both values increased significantly from control values (25.2 +/- 6.1 percent and 44.6 +/- 8.6 percent, respectively, at 7.5 micrograms/kg/min). We conclude that implanted aortic Doppler microprobes provide a sensitive and reliable method to measure aortic blood flow velocity after surgery and then allow monitoring of stroke volume and CO and analysis of left ventricular function after cardiac surgery.
Current methods of measuring cardiac output require the invasive insertion of a thermodilution catheter with its concomitant risks and complications. We examined the noninvasive method of transthoracic electrical bioimpedance (TEB) in comparison with thermodilution cardiac outputs in a sample of 44 critically ill patients with poor left ventricular function (left ventricular ejection fraction less than 30%) and with either ischemic or idiopathic dilated cardiomyopathy. Dyspnea, mitral regurgitation, tricuspid regurgitation, and difference between real and ideal weight had the most marked effects on the correlation between the two methods, with lesser influence by left ventricular ejection fraction, height, weight, hemoglobin, hematocrit, and aortic regurgitation. TEB and thermodilution cardiac outputs were correlated, at r = 0.51 (p less than 0.00009), but the low reliability and low percentage of TEB readings within 0.5 L/min of thermodilution cardiac outputs (31%) renders TEB inadequate for clinical measurement of cardiac outputs in this patient population.
A continuous cardiac output monitoring system has been developed in the laboratory to allow the real-time measurement of the cardiac output. This form of continuous cardiac output measurement allows the doctor to view the beat-to-beat cardiac output and can be employed to measure artery constrictions as well. The sensor comprises a laser Doppler velocimeter and an impedance measurement unit. The laser Doppler velocimeter is capable of measuring bi-directional blood flow within the vessel while the impedance measurement unit determines the cross-sectional area of the vessel. In laboratory tests, it was demonstrated on a heart-lung machine that the product of the two parameters measured is proportional to the actual flow volume of up to 6 lmin(-1) with a mean percentage error of 12.4% and a mean square error of 0.09 (using the lmin(-1) scale) were obtained. This is significantly more accurate than the measurement made using the thermodilution cathether.
Cardiac output was measured by the thermodilution method in three young harbor seals, at rest and while swimming up to the maximum effort for which they could be trained. Stroke volume was determined by counting heart rate simultaneously with determination of cardiac output. Cardiac outputs varied widely between surface breathing (7.8 ml.kg-1.s-1) and breath-holding while swimming under water (1.8 ml.kg-1.s-1). Stroke volume while at the surface was almost twice the volume while submerged. Surface cardiac output was always near maximal despite work effort, whereas submerged cardiac output gradually increased at higher work efforts. The cardiovascular performance of seals at the maximum MO2 we could induce from them is equivalent to that of the domestic goat.