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Non-invasive Doppler-derived cardiac output: a validation study comparing this technique with thermodilution and Fick methods.

The high mortality and morbidity related to cardiac events remains a considerable problem in vascular surgery. Predicting high risk patients is difficult except perhaps by coronary angiography which is invasive, costly and impractical. It would be useful to have a technique which could easily measure cardiac output and stratify cardiac risk in patients needing vascular surgery. Doppler-derived cardiac output may be such a technique. It offers considerable advantages over Swan-Ganz thermodilution measurement in that it is non-invasive, continuous, inexpensive, and requires only limited technical skill and training. In order to assess and validate a Doppler cardiac output monitor (ACCUCOM 2, Datascope Medical Co. Ltd.), we undertook a prospective study comparing Doppler-derived measurements with those obtained by thermodilution and Fick methods. Twelve patients undergoing elective coronary angiography were studied. Swan-Ganz thermodilution catheters were inserted on completion of cardiac catheterisation and five consecutive thermodilution and Doppler measurements made in each patient. Oxygen saturation from pulmonary artery and aortic blood samples, and a single indirect Fick cardiac output, were calculated. Linear regression analysis for Doppler against thermodilution gave a correlation co-efficient (r) of 0.81 (p less than 0.002), and (r) for Doppler against the Fick method was 0.76 (p less than 0.02). Bland and Altman's statistical method showed the differences to be normally distributed. The mean difference (thermodilution minus Doppler) was 0.32 l/min SD 0.48 l/min, 95% confidence limits -0.64 to +1.28 l/min. Doppler-derived cardiac output compares well with traditional methods of measurement and may be a useful tool in the assessment and monitoring of the high risk vascular patient.

Adult↗

Noninvasive monitoring of cardiac output in critically ill patients using transesophageal Doppler.

Measurement of cardiac output using thermodilution technique in mechanically ventilated patients is associated with significant morbidity. The goal of the present study was to assess the validity of cardiac output measurement using transesophageal Doppler in critically ill patients. Forty-six patients from three different intensive care units underwent 136 paired cardiac output measurements using thermodilution (COTH) and transesophageal Doppler (COTED). In addition, simultaneous suprasternal Doppler and indirect calorimetry (Fick principle) were used to measure cardiac output in 26 patients from one center. A good correlation was found between COTH and COTED (r = 0.95), with a small systematic underestimation (bias = 0.24 L/min) using transesophageal Doppler. The limits of agreement between COTH and COTED were +2 L/min and -1.5 L/min. Variations in cardiac output between two consecutive measures using either transesophageal Doppler or thermodilution techniques were similar in direction and magnitude (bias = 0 L/min; limits of agreement = +/-1.7 L/min). Suprasternal Doppler and indirect calorimetry yielded similar correlations and agreements in the subset of patients in whom they were used. These results confirm that transesophageal Doppler can provide a noninvasive, clinically useful estimate of cardiac output and detect hemodynamic changes in mechanically ventilated, critically ill patients.

Adult↗

Cardiac output measurements in congenital heart disease: validation of a simple, portable Doppler method.

Noninvasive Doppler cardiac output measurements are clinical standards in adults and children. Presently, these standard Doppler methods generally require relatively expensive and large imaging equipment with complex signal-processing techniques. Thus, universal access to these important measurements has been limited. Simple, portable Doppler methods have been validated previously and applied to infants and children without cardiac disease. Nevertheless, these specific, inexpensive techniques have not been validated in children with complex congenital heart disease. Accordingly, we compared a noninvasive, suprasternal, non-image-guided, pulsed Doppler cardiac output with standard invasive Fick cardiac outputs in 20 patients (age range, 1 month to 15 years) with congenital heart disease. Doppler cardiac output was displayed by multiplying the mean velocity with an operator-selected angiographic or echographic estimate of the aortic diameter. The values from linear regression analysis were r = 0.96; Doppler cardiac output = 0.98 x Fick cardiac output - 0.08 L/min (range, 0.55-3.10 L/min). The 95% confidence limits were less than 35% of the mean of Doppler and Fick cardiac outputs across the range of measurements. We conclude that relatively linear and accurate measurements of cardiac output can be made by this simple, inexpensive, portable method in selected infants and children with various forms of congenital heart disease.

Adolescent↗

[Cardiac output determination with transpulmonary thermodilution. An alternative to pulmonary catheterization?].

UNLABELLED: Cardiac output measurements are often helpful in the management of critically ill patients and high risk-patients. In this study an alternative technique for measurement of cardiac output by the transpulmonary indicator dilution technique (TPID) was evaluated in comparison to conventional thermodilution using a pulmonary artery catheter. With TPID, a thermistor-tipped catheter (the smallest available is 1.3 F) is placed in the aorta via a femoral artery introducer. Thus, TPID can also be used in very small children in whom placement of a pulmonary artery catheter may be difficult or even impossible. In principle, TPID is less invasive since the possible complications of the pulmonary catheters are avoided. We investigated the accuracy and reproducibility of transpulmonary thermodilution in patients over a broad range in age and body surface. METHODS: Following approval by the ethics committee and written consent, the data were obtained from 21 patients without a circulatory shunt undergoing diagnostic heart catheterization. The patients were between 0.5 and 25.2 years old, their body surface between 0.35 and 1.89 m2. Measurements were performed in duplicate with bolus injections of ice-cold normal saline (0.15 ml/kg), randomly spread over the respiratory cycle. In total 48 thermodilution curves were measured simultaneously in the pulmonary artery and in the aorta. Thermodilution curves were monoexponentially extrapolated for elimination of recirculation and cardiac output was calculated with a standard Stewart Hamilton procedure. RESULTS: The amplitude of the typical arterial thermodilution curve shows a smaller and more delayed course than the pulmonary artery thermodilution curve. There was a very good correlation between the values found by pulmonary and TPID cardiac output measurements (R = 0.968). There was a slightly smaller cardiac output value measured by the TPID (Bias = -4.7 +/- 1.5% sem) The reproducibility of duplicate measurements with the two methods were nearly the same, the standard deviation of the difference was 10.9% for the pulmonary thermodilution method and 11.7% for TPID. DISCUSSION. TPID gives an alternative technique for measurement of cardiac output. We showed over a broad range in age and body surface a very good correlation with thermodilution measurements in the pulmonary artery. The slightly smaller values for TPID are explained by early recirculation, for clinical purposes the difference is negligible. However, the reproducibility of a method is clinically very important. Both methods showed in duplicate measurements basically the same reproducibility. The disadvantage of TPID in being more sensitive to baseline alteration is counterbalanced by less respiratory variability in comparison to the conventional thermodilution technique. However, by increasing the amount of injected indicator (i.e., 0.2 ml/kg approximately equal to 15 ml in an adult) it is possible to reduce the effect of baseline alteration. By using fiberoptic catheters it is even possible to use TPID as double-indicator dilution technique to measure intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). We conclude that in many patients TPID might be an attractive, less invasive and reliable alternative to conventional cardiac output measurement by pulmonary artery catheter.

Adolescent↗

End-tidal carbon dioxide during extremely low cardiac output.

STUDY OBJECTIVE: A number of studies have shown that expired CO2 concentration is closely related to cardiac output, but that cardiac output was not controlled as an independent variable. In addition, the partial pressure of end-tidal CO2 (PETCO2) during extremely low cardiac output has not been reported. The objective of the present study was to measure PETCO2 during well-controlled, very low blood flow rates under conditions of constant minute ventilation. DESIGN: Ten anesthetized, intubated, and mechanically ventilated swine (weight, 43 to 102 kg) were placed on two ventricular assist devices in order to control cardiac output. Minute ventilation was measured and kept constant. Ventricular assist device output (measured with an ultrasonic flow probe); PETCO2; and aortic, pulmonary artery, and central venous pressures were recorded continuously. INTERVENTIONS: After electrical induction of ventricular fibrillation, pump output was decreased in steps. MEASUREMENTS AND MAIN RESULTS: Cardiac index ranged from 0 to 5,371 mL/min/m2; 59% of PETCO2 measurements were made at cardiac indexes of less than 1,313 mL/min/m2 (30 mL/min/kg). The relationship of PETCO2 levels to cardiac index was determined with linear regression analysis; P < .05 was statistically significant. PETCO2 correlated significantly with cardiac index (P < .0001). The best-fit line by least-squares analysis produced the equation: PETCO2 = 4.98 + 0.012 [cardiac index] (r2 = .82). CONCLUSION: Under conditions of constant minute ventilation, PETCO2 correlated closely with cardiac index over a large range of blood flow rates, including extremely low rates.

Animals↗

Thermodilution: an advanced technique for measuring continuous cardiac output.

A thermodilution method of obtaining continuous cardiac outputs represents an improvement in the assessment and treatment of critically ill patients. The critical care nurse assists in placement of the pulmonary artery catheter, which includes a thermal filament for continuous readings of cardiac output, and uses the continuous cardiac output readings to make assessment decisions and trouble-shoot the equipment.

Aged↗

Impedance cardiography by use of a spot-electrode array to track changes in cardiac output in anesthetized dogs.

Transthoracic impedance cardiography is a noninvasive method to determine changes in cardiac output on the basis of the cardiac-induced impedance change measured across the thorax. In this report, we describe a new, easily applied, tetrapolar spot-electrode configuration for use in canine transthoracic impedance cardiography. The array is a convenient alternative to use of the traditional circumferential band-electrode array which, in the dog, is prohibitive because of the extensive skin preparation required. The spot-electrode array was used to compare changes in cardiac output measured by transthoracic impedance cardiography, with changes measured by a reference indicator-dilution technique. A spot-electrode array, composed of 4 standard ECG electrodes, was used to measure transthoracic impedance in 10 anesthetized dogs. Variations in cardiac output were produced by controlled hemorrhage (200- to 250-ml increments). Simultaneous reference measurements of cardiac output were made before hemorrhage (control) and at each level of hemorrhage, using the saline-dilution method. The beat-by-beat impedance changes were measured by use of a Minnesota impedance cardiograph, which also recorded the first derivative of impedance (dZ/dt). An index of cardiac output was defined as the product of the maximal value of the first time derivative of impedance, ejection time, and heart rate for each beat during inscription of a saline-dilution curve. The average of the beat-by-beat indices was calculated and then normalized relative to the initial control value. Linear regression analysis was performed to evaluate the correlation of the index of cardiac output with the reference cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗

Effect of insulin on the distribution of cardiac output in the fetal lamb.

Three to five measurements of fetal cardiac output and its distribution were made using radiolabeled microspheres in each of 12 sheep fetuses in whom fetal plasma insulin concentration was varied by exogenous infusion of insulin to the fetus. Blood concentrations of oxygen and glucose as well as blood gases, pH, hematocrit, and plasma insulin concentrations were also measured. Both fetal arterial oxygen content and whole blood glucose concentration fell as fetal insulin concentration rose. Fetal cardiac output rose as insulin concentration increased and was accompanied by an increase in fetal heart rate. Increased insulin concentration was associated with increased flow to the heart, stomach, placenta, and carcass while blood flow to the fetal brain, lungs, liver, kidneys, spleen, and intestines was not affected. As plasma insulin concentration rose, the percentage of the cardiac output distributed to the fetal heart and upper carcass increased; that distributed to the fetal brain, lungs, liver, stomach, intestines, and lower carcass remained unchanged; while that distributed to the kidneys, spleen, and placenta decreased. When expressed as a fraction of cardiac output, an additional 7% (from 39 to 46%) of the cardiac output was distributed to carcass over the range of insulin concentrations studied. Most of the increased portion of the fetal cardiac output distributed to the fetal carcass during hyperinsulinemia was accounted for by a decrease in the percentage of fetal cardiac output perfusing the placenta.

Animals↗

A simple method for reducing cardiac output in the conscious lamb.

We have developed a method for reducing cardiac output in a controlled stepwise fashion using awake, intact, unsedated lambs. The method involves placing a balloon-tipped (Foley) catheter into the right atrium from a jugular vein isolated by a small neck incision. Systemic venous return and cardiac output are limited by balloon inflation. With each balloon inflation the animal reaches a new and stable cardiac output, which allows the measure of steady-state hemodynamic and metabolic variables. We have been able to decrease cardiac output to as low as 20% of the resting cardiac output and maintain a stable preparation. The reductions in cardiac output are quickly reversible by balloon deflation. Animal survival allows repeated study. We present data from five lambs studied between 26 and 36 days of age. Alterations in O2 consumption, O2 transport, O2 extraction, blood pressure, and arterial lactate concentration are examined in response to decrements in systemic blood flow and are consistent with changes seen in response to a reduction of cardiac output by other methods.

Animals↗

Relationship of changes in cardiac output to changes in heart rate in medical ICU patients.

OBJECTIVE: To determine whether changes in cardiac output are correlated with changes in other commonly measured covariables (heart rate, respiratory rate, mean arterial pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and temperature). DESIGN: Case series. SETTING: Medical intensive care unit (ICU) in a Veterans Administration Medical Center. PATIENTS: Twenty-three patients with Swan-Ganz catheters placed by the primary care team were studied on 25 occasions. Patients were managed by the primary team as clinically indicated. INTERVENTIONS: Thermodilution cardiac output and covariables were determined at baseline and at hourly intervals for the next 5 h. Each cardiac output measurement was calculated by averaging the last four of five individual measurements at each time point. RESULTS: The mean cardiac output (9.21/min), heart rate (107/min), and pulmonary artery occlusion pressure (19 mmHg) were elevated. The hourly mean change in cardiac output was 10.2%. Using least-squares linear regression analysis, we found clinically significant changes in cardiac output (> 6.4%) to be most closely correlated with changes in heart rate (R2 = 0.29, p < 0.001). Stepwise linear regression analysis showed that none of the other covariables added significantly to this relationship. No significant relationship was found between changes in cardiac output and changes in pulmonary artery occlusion pressure. Despite these correlations clinically significant changes in cardiac output were accompanied by changes in heart rate in the same direction only 62% of the time. CONCLUSION: Changes in cardiac output were best correlated with changes in heart rate. Changes in pulmonary artery occlusion pressure were not correlated with changes in cardiac output in this population of medical ICU patients. A change in any of the covariables (alone or in combination) cannot be reliably used to indicate a simultaneous change in cardiac output.

Adult↗

Radionuclide determination of cardiac outputs and indices.

A radionuclide procedure for the determination of cardiac output is presented. Cardiac outputs estimated by the proposed method are compared to those obtained by the temperature dilution method during right heart catheterization. A new index of cardiac performance is also presented: cardiac output as a percentage of total blood volume. This index is determined by a totally external count-based procedure.

Adult↗

Cardiac output measurement by thermodilution.

The accuracy of thermodilution for measuring cardiac output was studied by comparing this method with measurements obtained by an electromagnetic flowmeter in the dog. Thermal curves were computed by a cardiac output computer and absolute flows were obtained by pump calibration of the flowmeter. Regression analysis showed an excellent correlation (P less than 0.001) between thermodilution measurements with injectates at 0 degrees C and flowmeter measurements using either cannulating probes (n = 105, r = 0.98) or periaortic probes (n = 100, r = 0.96). With the use of normal room temperature injectates, a good correlation was also found with absolute flows (n = 75, r = 0.92, P less than 0.001). Thermodilution overestimated cardiac output by 3% to 9%. In 32 pairs of successive cardiac output determinations by thermodilution, there was no significant difference between the two measurements (P greater than 0.05). In eight patients cardiac output was measured postoperatively by thermodilution with injectates at 0 degrees C and 24 degrees C administered in rapid succession. Regression analysis of 50 pairs of measurements at the two temperatures showed a strong correlation between the two techniques (r = 0.96) and the two results were not significantly different (P = 0.00001).

Animals↗

Comparison of impedance cardiography and dye dilution method for measuring cardiac output.

OBJECTIVE: To assess the degree of agreement between impedance cardiography, using the NCCOM3-R7 device, and the gold standard--the dye dilution method--both under basal conditions and after stimulation of cardiac output. PATIENTS: 35 paired measurements in five healthy male volunteers. INTERVENTIONS: To obtain higher levels of cardiac output, cardiac performance was stimulated with a dopamine infusion. RESULTS: In 35 paired measurements, the mean of all the impedance values was higher than that of the dye dilution values, at 10.2 v 7.4 l/min (p < 0.0001). The mean discrepancy between the two methods was 3.3 l/min, and the mean bias -2.9 l/min, with limits of agreement of -9.0 and 3.2 l/min. A change in cardiac output could not adequately be predicted by the NCCOM3-R7. In 20 of 25 measurements obtained during continuous intravenous dopamine infusions there was a rise in dye dilution cardiac output (range 0.2 to 5.9 l/min). Neither the magnitude nor the direction of the change in dye dilution values corresponded with the change measured by impedance cardiography. The mean discrepancy here between the two methods was 1.8 l/min, and the mean bias -0.8 l/min, with limits of agreement of -4.9 and 3.3 l/min. CONCLUSIONS: In healthy volunteers, impedance cardiography with NCCOM3-R7 is inadequate for assessing cardiac output when compared with the dye dilution method.

Adult↗

The fractional distribution of the cardiac output in man using microspheres labelled with technetium 99m.

To investigate the distribution of organ blood flow in patients we have developed a method of quantitating the whole-body fractional distribution of 99Tcm-labelled microspheres. The microspheres were injected into the left ventricle in nine patients with normal cardiac indices (greater than 3 1/min/m2; Group A) and 11 patients with low cardiac indices (less than 2.51 l/min/m2; Group B). The fractional organ content of the total injected dose was estimated following correction for geometry and transmission using a gamma camera. Cerebral blood flow was 579 +/- 163 ml/min (mean +/- SD) in Group A and 593 +/- 158 ml/min in Group B (p not significant (NS)). Myocardial flow in Group A was 266 +/- 82 ml/min and in Group B was 237 +/- 57 ml/min (p, NS). Total renal blood flow was 749 +/- 161 ml/min in Group A and 614 +/- 181 ml/min in Group B (p less than 0.01). There was a negative correlation between cardiac index and the percentage of the cardiac output distributed to brain (r = -0.70, p less than 0.01), heart (r = -0.67, p less than 0.01) and kidneys (r = -0.47), p less than 0.05). Low output cardiac failure is, therefore, associated with relative preservation of cerebral and myocardial blood flow and, to a lesser extent, of renal flow. A similar technique using dual labelling would allow an accurate estimation in individual patients, of the change in organ blood flow associated with transient alterations in cardiac output states.

Adult↗

Continuous versus intermittent thermodilution cardiac output measurement during orthotopic liver transplantation.

We evaluated intermittent and continuous thermodilution cardiac output data in 12 patients undergoing orthotopic liver transplantation. Measurements were performed at 16 predefined time points between induction of anaesthesia and 3 h after reperfusion of the liver graft. Cardiac output measurements yielded 192 data pairs (intermittent cardiac output range: 1.8-18.9 l.min-1, continuous cardiac output range: 3.3-20.0 l.min-1). During most of the procedure the correlation between intermittent and continuous cardiac output measurements was significant (r = 0.87, p < 0.0001), accompanied with a bias of -0.240 l.min-1 and a degree of precision of 1.789 l.min-1 (< 10.0 l.min-1:1.137 l.min-1, > or = 10.0 l.min-1:2.220 l.min-1). However, in the early phases after caval clamping and after reperfusion, accuracy was not acceptable. Only during these phases did the difference between the mean values of pulmonary artery blood temperature and rectal temperature increase (after caval clamping) or decrease (after reperfusion). In conclusion, despite acceptable levels of accuracy and precision between intermittent and continuous cardiac output measurement under stable conditions, both methods showed markedly decreased accuracy and precision in the early phases after caval clamping and after reperfusion, possibly owing to increased thermal noise.

Adult↗

Mechanisms involved in angiotensin II induced increases in cardiac output in pithed rats.

This study was conducted to determine the mechanisms by which angiotensin II (Ang-II) acutely increases cardiac output. Pithed Sprague-Dawley rats were prepared for continuous measurement of cardiac output by electromagnetic flowmetry. Ang-II (31-1000 ng/kg, i.v.) produced dose-related increases in cardiac output, heart rate and stroke volume. Although the heart rate increases were abolished by beta-adrenoceptor blockade, the cardiac output responses were unchanged due to an offsetting increase in stroke volume. The constancy of the cardiac output response following beta-adrenoceptor blockade suggested that Ang-II increased cardiac output by constricting venous smooth muscle and thereby increasing venous return. This conclusion is supported by the observation that Ang-II produced marked increases in left ventricular end diastolic pressure that paralleled the increases in cardiac output. In fact, based on volume loading with Tyrode's solution, the changes in left ventricular end diastolic pressure produced by Ang-II should have resulted in even greater increases in cardiac output. However, it appears that the significant rise in peripheral resistance to Ang-II tended to counter the effects of increased venous return on cardiac output. In addition, the Ang-II-induced elevations in cardiac output were not altered by alpha-adrenoceptor blockade. Therefore, catecholamines do not play a role in mediating the Ang-II effects. The results of this study support the conclusion that Ang-II is capable of increasing cardiac output by constriction of venous smooth muscle.

Angiotensin II↗

Comparison of two semicontinuous cardiac output pulmonary artery catheters after valvular surgery.

OBJECTIVE: To compare semicontinuous cardiac output (CCO) with bolus cardiac output (BCO), in the immediate postoperative period after valvular surgery, under hypothermic cardiopulmonary bypass with two CCO pulmonary artery catheters, based on the pulsed warm thermodilution technique, i.e., Opti-Q from Abbott or IntelliCath from Baxter-Edwards (Abbott and Baxter groups, respectively). DESIGN: Prospective study. SETTING: University hospital. PATIENTS: Forty-four adult patients scheduled for mitral and/or aortic valve surgery were randomized into two groups. Tricuspid or pulmonary valvulopathy diagnosed by echocardiography was excluded. INTERVENTIONS: Cardiac output was measured every 20 mins during the 3 postoperative hrs. BCO was the mean of three boluses (10 mL) of an ice-cold saline solution injected within 3 secs. CCO was the mean of two CCO values obtained in normal mode immediately before and after BCO measurements. MEASUREMENTS AND MAIN RESULTS: Two groups of 22 patients underwent 198 pairs of cardiac output measurements. The mean difference or bias was calculated as the difference between BCO and CCO, and precision was the SD of the mean bias. The limits of agreement were defined as bias +/- 2 SD. A two-sample Wilcoxon's test was used for comparison of bias and precision in sinus and non-sinus rhythm, and stable and unstable mean arterial pressure in each group and between the two pulmonary artery catheters. The coefficient of correlation was also calculated. Bias +/- precision was 0.066+/-0.526 L/min, r2 = .83, for the Abbott group, and 0.015+/-0.490 L/min, r2 = .85 (not significant), for the Baxter group. There was no significant difference within and between groups for bias and precision in sinus and non-sinus rhythm, nor in stable and unstable mean arterial pressure. CONCLUSIONS: This study, during the immediate postoperative period in valvular surgery under hypothermic cardiopulmonary bypass, showed a satisfactory correlation between CCO and BCO with the two systems.

Aged↗

Changes in onset time of rocuronium in patients pretreated with ephedrine and esmolol--the role of cardiac output.

BACKGROUND: We investigated the hypothesis that manipulation of cardiac output (CO) with esmolol (Es) or ephedrine (E) affects the onset time of rocuronium. METHODS: Following anesthesia induction, 33 patients received E (70 micro g kg-1), Es (500 micro g kg-1) or placebo (P) 30 s before rocuronium (0.6 mg kg-1) administration. Cardiac output was measured non-invasively after intubation every 3 min. The interval from the end of rocuronium administration to the disappearance of all twitches was considered to be the onset time. RESULTS: Onset time was shorter after E (52.2 +/- 16.5 s) and longer after Es (114.3 +/- 11.1 s) compared with P (87.4 +/- 7.3 s) (P < 0.0001). Cardiac output increased (P < 0.05) in group E for 15 min after rocuronium. In group Es, CO decreased (P < 0.05) at 3 and 6 min. Cardiac output was higher in group E vs. group Es, 3-6 min post administration of rocuronium (P=0.015). CONCLUSION: Pretreatment with E or Es appears to affect the onset time of rocuronium by altering CO as measured with the NICO (Non-Invasive Cardiac Output) monitor (Novametrix Medical Systems Inc., Willingford, CO).

Adolescent↗