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The non-invasive determination of cardiac output in children: a three-breath technique.

In this study, the cardiac output of 11 children (5 days to 18 yr of age) was measured following cardiopulmonary bypass. Standard dye dilution cardiac outputs and an indirect Fick-CO2 technique were simultaneously determined. A rebreathing maneuver is described to estimate the oxygenated mixed venous PCO2 (PvCO2). This estimate of PvCO2 was combined with the end tidal PCO2 and CO2 production to give a non-invasive Fick estimate of the cardiac output. Non-invasive cardiac outputs correlated well with those measured by dye-dilution (r2 = 0.94) over a range of cardiac outputs from 490-7280 ml/min. All non-invasive determinations were within 15% of the line of identity, and within 22% of averaged replicate dye-dilution values. Our results agree with previous comparisons of indirect Fick-CO2 methods with invasive determinations of cardiac output. These data suggest that the indirect Fick-CO2 technique offers a rapid, non-invasive alternative to invasive monitoring of cardiac output.

Adolescent↗

Continuous thermodilution cardiac output: agreement with Fick and bolus thermodilution methods.

OBJECTIVE: Cardiac outputs were determined with continuous thermodilution, bolus thermodilution, and the Fick method during pharmacologically varied hemodynamics. DESIGN: Prospective comparison of techniques. SETTING: University animal laboratory. PARTICIPANTS: Swine. INTERVENTIONS: Swine were anesthetized, tracheally intubated, and instrumented to measure continuous (QTDC) and bolus (QTDB) thermodilution cardiac outputs and sample arterial and mixed venous blood. Continuous thermodilution of blood was facilitated by computer modulation of a thermal filament wrapped around the portion of the pulmonary artery catheter residing in the right atrium and ventricle. QTDC was computed from the thermodilution curve monitored by the thermistor. Bolus thermodilution was performed in triplicate by injecting 10 mL of 5% dextrose in water (0 to 4 degrees C). Oxygen consumption (VO2) was calculated as the averaged minute rate of disappearance of spirometer oxygen over a 6-minute steady state. Cardiac output was determined with the direct Fick method (QF) by dividing VO2 by the difference in arterial and mixed venous oxygen content. Basal QTDC was increased and decreased with an intravenous infusion of dobutamine or labetalol, respectively. Data are summarized as mean +/- SD or 95% confidence interval (CI 95%). Agreement between methods of determining cardiac output was assessed by calculating bias, percent bias, and percent coefficient of determination (100 r2). MEASUREMENTS AND MAIN RESULTS: Eighteen swine (38.9 +/- 1.2 kg) exhibited a range of QTDC from 2.2 to 14.8 L/min. Mean measurement variance of VO2, CaO2, CvO2, and QTDB was 1.5%, 1.5%, 2.0%, and 11.8%, respectively. Mean bias, percent bias, and 100 r2 was 0.004 +/- 1.05 L/min (CI 95%: 0.18 to 0.19 L/min), -0.37 +/- 13.8% (CI 95%: -2.75 to 2.01), and 89% between QTDC and QF, respectively. Bias, percent bias, and 100 r2 was 0.05 +/- 1.09 L/min (CI 95%: -0.14 to 0.23 L/min, 1.21 +/- 13.06% (CI 95%: -1.03 to 3.46%), and 91% between QTDC and QTDB, respectively. Bias, percent bias, and 100 r2 (Fig 6) was -0.04 +/- 0.69 L/min (CI 95%: -0.16 to -.08 L/min), -1.23 +/- 9.17% (CI 95%: -2.8 to 0.35%), and 94% between QTDB and QF, respectively. CONCLUSION: Automatic cardiac output computed with continuous thermodilution appears accurate and reliable. Also, good agreement was confirmed between cardiac output derived by continuous and bolus thermodilution methods and bolus thermodilution and Fick methods.

Adrenergic Agonists↗

Validation of a novel ultrasound dilution method to measure cardiac output during hemodialysis.

A method to measure cardiac output (CO) based on ultrasound velocity dilution during hemodialysis was validated in an animal model against direct measurement using a transit time technique and a calibrated pump. In two anesthetized pigs, a 20 mm transit time ultrasound flow probe was placed on the ascending aorta to measure CO, and the right femoral artery and vein were cannulated for hemodialysis access. The dual sensor HD01 Hemodialysis Monitor was positioned on the arterial and venous tubing lines for measurement of cardiac output by ultrasound velocity dilution (COUD) by intravenous injections of 10-20 ml isotonic saline at 37 degrees C. COUD (n = 29) was compared with CO from the transit time flow probe (COT). During the second part of the experiment, the animal was placed on right atrial to left atrial bypass using a calibrated roller pump. The COUD (n = 9) was compared with cardiac output as measured by pump flow (COP). A linear relationship was observed between COUD and COT (COUD) = 0.948 x COT + 0.086 L/min, r = 0.95), and between COUD and COP (COUD = 1.06 x COP-0.327 L/min, r = 0.99). Thus, cardiac output measured by ultrasound velocity dilution during hemodialysis is in good agreement with well established, but invasive, transit time and pump standards.

Animals↗

Cardiac output: a view from Buffalo.

Cardiac output (Q) is a primary determinant of blood pressure and O2 delivery and is critical in the maintenance of homeostasis, particularly during environmental stress. Cardiac output can be determined invasively in patients; however, indirect methods are required for other situations. Soluble gas techniques are widely used to determine Q. Historically, measurements during a breathhold, prolonged expiration and rebreathing to CO2 equilibrium have been used; however, with limitations, especially during stress. Farhi and co-workers developed a single-step CO2 rebreathing method, which was subsequently revised by his group, and has been shown to be valid (compared to direct measures) and reliable. Carbon dioxide output (VCO2), partial pressure of arterial CO2 (PaCO2), and partial pressure of mixed venous CO2 (Pv(CO2)) are determined during 12-25 s of rebreathing, using the appropriate tidal volume, and Q is calculated. This method has the utility to provide accurate data in laboratory and field experiments during exercise, increased and micro-gravity, water immersion, lower body pressure, head-down tilt, and changes in gas composition and pressure. Utilizing the Buffalo CO2 rebreathing method it has been shown that the Q can adjust to a wide range of changes in environments maintaining blood pressure and O2 delivery at rest and during exercise.

Algorithms↗

Predictors of between-method differences in cardiac output measurement using thoracic electrical bioimpedance and thermodilution.

OBJECTIVES: To evaluate the usefulness of transthoracic electrical bioimpedance in trending changes in cardiac output after cardiac surgery, and to identify predictors of differences between cardiac output measured by thermodilution and transthoracic electrical bioimpedance methods. DESIGN: Prospective repeated-measures study. SETTING: University-affiliated tertiary care center. PATIENTS: Thirty-four adult patients undergoing elective cardiac surgery with routine pulmonary artery catheter placement. INTERVENTIONS: Simultaneous paired cardiac output measurements by transthoracic electrical bioimpedance and thermodilution were made at four time points: within 2 hrs of intensive care unit (ICU) admission; when the patient reached a normothermic temperature; after extubation; and 24 hrs after ICU admission. MEASUREMENTS AND MAIN RESULTS: Mean measurements by each method over time did not differ, except at ICU admission, when compared by repeated-measures analysis of variance. For each time point, bias and precision between methods were calculated. Bias calculations ranged from 0.02 to 0.21 L/min/m2. Precision calculations ranged from 1.06 to 1.52 L/min/m2. Predictors of between-method differences identified by a multiple regression model of hemodynamic variables were: increased systemic vascular resistance index, decreased mean arterial pressure (MAP), and the presence of atrial or ventricular pacing. CONCLUSIONS: While mean postoperative cardiac output measurements did not differ by method over time, agreement between transthoracic electrical bioimpedance and thermodilution methods was poor in the immediate postoperative period, with precision calculations indicative of clinically significant differences. Increased systemic vascular resistance index and decreased MAP were predictive of larger between-method differences.

Aged↗

Thermodilution method overestimates low cardiac output in humans.

We compared 57 cardiac output measurements by the thermodilution and Fick methods in 26 patients and found that thermodilution values were higher in all 16 cases in which Fick outputs were less than 3.5 l/min. In 10 cases where Fick values were less than or equal to 2.5 l/min, thermodilution and Fick measurements differed by an average of 35%. When combined with the results of previous studies comparing the thermodilution, dye dilution, and Fick techniques, these findings suggest that the thermodilution method overestimates true cardiac output in the low output range. This overestimation probably is due to heat loss under conditions of low flow. Because the thermodilution method is used widely in patients with low output states, these findings have potentially important clinical implications.

Adolescent↗

Influence of sampling site and flow area on cardiac output measurements by Doppler echocardiography.

In 40 patients cardiac output was simultaneously determined by pulsed Doppler echocardiography and thermodilution (range 4.0 to 10.2 liters/min). The sample volume was located in the center of the mitral anulus, at the tips of the mitral leaflets and in the center of the aortic anulus. Circular cross-sectional areas of the mitral anulus, aortic anulus and aortic bulbus were calculated from M-mode and two-dimensional echocardiographic diameters. The varying short axis of the elliptical mitral opening area was obtained from the diastolic leaflet separation in the M-mode, and the long axis was derived from the maximal mitral orifice area or mitral anulus diameter. Cardiac output was calculated by multiplying time-velocity integrals with the different areas and heart rate. Doppler flow measurements correlated significantly with the thermodilution method (r = 0.79 to 0.93). Flow measurements at the aortic anulus were most accurate (r = 0.93, SEE = 0.589 liter/min) if the annular area was derived from the M-mode tracing. Measurement of the anulus in the apical five chamber view yielded a significant underestimation and the area of the aortic bulbus provided an overestimation of cardiac output. Left ventricular inflow was underestimated at the mitral leaflet tips and overestimated at the mitral anulus. The accuracy of pulsed Doppler cardiac output measurements strongly depends on the assumed flow area and sampling site. Both should be determined at the same level in the inflow or outflow tract of the left ventricle. Measurement of cardiac output in the center of the aortic anulus provided the highest accuracy.

Adolescent↗

Role of cardiac output in mediating arterial blood pressure oscillations.

The objective of this study was to determine the role of cardiac output in mediating spontaneous fluctuations in mean arterial pressure (MAP) conscious dogs. Dogs were chronically instrumented to monitor MAP and cardiac output. Atrioventricular (AV) block was induced, and left ventricular and right atrial electrodes were implanted. After recovery, MAP was observed for 5 min under two conditions: 1) normal variation in heart rate and cardiac output via triggering the ventricular stimulator with each atrial depolarization (effectively reversing the AV block, AV-linked stimulation) and 2) computer control of ventricular rate to maintain cardiac output constant on a by-beat basis at the same level as observed during normal variations in heart rate and cardiac output. When cardiac output was held constant, large-amplitude, low-frequency oscillations in MAP were readily apparent. Spectral analysis by fast Fourier transform revealed that during constant cardiac output the power observed at low frequencies in the MAP spectrum represented 95.0 +/- 2.7% of the total power compared with 75.5 +/- 4.6% during normal variations in heart rate and cardiac output (P < 0.05). In addition, when cardiac output was held constant, the power observed at higher frequencies markedly decreased from 24.5 +/- 4.6% of total power during AV-linked stimulation to only 5.0 +/- 2.7% of total power during constant cardiac output (P < 0.05). We conclude that low-frequency oscillations in MAP are due to changes in peripheral resistance, whereas a significant amount of high-frequency changes in MAP stems from spontaneous changes in cardiac output.

Animals↗

A novel vasopressin peptide lowers blood pressure through decreases in cardiac output.

The changes in blood pressure, cardiac output, and total peripheral conductance evoked by the novel hypotensive arginine vasopressin (AVP) - like peptide, d(CH2)5[D-Tyr(Et)2,Arg3,Val4,Arg7,Eda9]AVP (HYPO-AVP), were recorded in conscious unrestrained Sprague-Dawley rats implanted with radiotelemetry pressure transducers and ultrasonic transit-time flowprobes. Intravenous infusions of 0.6, 1.0, 2.0, and 4.0 microg x kg(-1) x min(-1) of HYPO-AVP evoked dose-related decreases in blood pressure. At the lowest dose of 0.6 microg x kg(-1) x min(-1), the fall in blood pressure was associated with a small but significant increase in total peripheral conductance. Cardiac output was unchanged. In contrast, at the three higher doses of 1.0, 2.0, and 4.0 microg x kg(-1) x min(-1), the fall in blood pressure was related to a dramatic fall in cardiac output. Indeed, total peripheral conductance decreased, preventing blood pressure from falling further. These hemodynamic findings should help to direct future research into the mechanism of the putative hypotensive property of vasopressin, a property that attenuates the well established blood pressure elevating actions of the peptide.

Animals↗

Measurement of cardiac output in anesthetized rats by dye dilution using a fiberoptic catheter.

A method is described for the measurement of cardiac output and oxygen saturation in closed-chest rats using a small (2.4 F) commercially available fiberoptic catheter and a reflection-spectral-photometer. Positioned in the aortic arch, the catheter functions as an oxymeter for oxygen saturation and as a densitometer for measurement of indocyanine green, obviating the need for blood removal and passage through a densitometer. The sensitivity and reproducibility of this method were characterized in 90 rats by thermodilution, radiolabeled microspheres, and electromagnetic flow methods as standard references. Basal cardiac output as well as changes in cardiac output during isoproterenol infusion and blood removal and replacement were measured. In addition, multiple measurements of cardiac output over 1 min were used to document the method's suitability in constructing a ventricular function curve. With the fiberoptic catheter, cardiac output varied predictably with anesthesia, with rats on dial-urethane (n = 23) having values of 150 +/- 39 (SD) ml/min/kg and 2 and 1% enflurane (18-35 rats per group) yielding cardiac outputs of 190 +/- 60 and 236 +/- 77 ml/min/kg, respectively. Pentobarbital produced the least cardiovascular depression (n = 15) with an average cardiac output of 322 +/- 22 ml/min/kg. The average cardiac output with this method in 90 rats (regardless of anesthesia) was 214 +/- 91 (SD). This value was comparable to cardiac output values determined in paired experiments from radiolabeled microspheres (9 rats) 220 +/- 43, electromagnetic flow (11 rats) 177 +/- 33, and a subset of rats with thermodilution (231 +/- 45 ml/min/kg). The within measurement (repeat measurements) variability with the fiberoptic method was consistently less than the rat-to-rat variability when compared to the thermal and radiolabeled microsphere methods, but it was comparable to electromagnetic flow. The method can be used when rapid measurements (4 measurements within 60 s) of cardiac output are required, as in constructing a ventricular function curve, and can readily detect small changes in cardiac output during controlled hemorrhage and isoproterenol infusion. In summary, this method gives measurement of oxygen saturation and cardiac output by dye dilution without blood removal. There is less surgical preparation than required for electromagnetic cardiac output, and it is an alternative to the thermodilution method.

Animals↗

Continuous noninvasive cardiac output as estimated from the pulse contour curve.

We developed a noninvasive computer-based system for estimating continuous cardiac output by a modified pulse contour method using a finger pressure waveform. The method requires no individual patient calibration or baseline cardiac output. First, we calibrated the system in a "learn" group of 20 patients. The computer-based cardiac output was then compared with thermodilution cardiac output in 27 patients undergoing coronary artery bypass surgery. A total of 94 cardiac outputs were performed (three averaged per determination) at four predetermined time periods: preinduction, postinduction, prebypass, and postbypass. During determination of each thermodilution cardiac output, the pulse wave data were simultaneously recorded on cassette tape. The patients had cardiac outputs ranging from 2.9 to 6.4 L/min. The correlation coefficient was 0.75. The average thermodilution cardiac output was 4.50 (+/- 0.83 SD) L/min, while the cardiac output derived from the finger pressure wave was 4.48 (+/- 0.7 SD) L/min (95% confidence interval [CI] of difference, 0-3.2%). The mean difference between the two methods was 0.02 (+/- 0.55 SD) L/min. The 95% CI for the bias was 0.0001 to 0.036 L/min. The 95% CI for the lower limit of agreement was -1.12 to -1.06 L/min; the upper limit for the 95% CI was 1.09 to 1.16 L/min. The program demonstrated that information about cardiac output can be obtained by using the Finapres device (Ohmeda, Boulder, CO). The cardiac output values obtained by this continuous noninvasive technique were within +/- 20% of the simultaneous thermodilution values 87% of the time. This was true over the narrow range of cardiac outputs (2.9 to 6.4 L/min) and wide range of heart rates (45 to 140 beats/min).

Adult↗

Evaluation of radiocardiographic methods for determination of cardiac output and right and left ventricular ejection fractions using a cardiac phantom.

Cardiac output and ejection fractions of the cardiac ventricles are valuable measures of cardiac function. Noninvasive radionuclide techniques for determination of these measures are based on analysis of different data: first passage low frequency, first passage high frequency and multigated equilibrium data. We have evaluated the principles of these methods using a dynamic cardiac phantom. Radiocardiographic determinations of cardiac output and right and left ventricular ejection fractions showed excellent correlation against true phantom values: r = 0.993 (p less than 0.001), r = 0.978 (p less than 0.01) and r = 0.943 (p less than 0.05), respectively. Thus, the findings of the present study demonstrate a high validity of current radiocardiographic measures of cardiac function.

Cardiac Output↗

A fully automated cardiac output analysis system.

An automatic cardiac output analysis system is described in which indicator dilution studies are performed serially without operator assistance. Indicator dye injection, blood sampling, and monitoring for air entry into the system are performed automatically through a present program sequence. Sampled blood is returned to the subject through a venous cannula resulting in an absence of blood loss. This system may be used in performing cardiac output analyses on a serial basis and in infants and small animals where blood loss is critical.

Automation↗

An assessment of cardiac output by thermodilution in infants and children following cardiac surgery.

A 4 F thermodilution catheter for measuring cardiac output was evaluated for accuracy and linearity in the laboratory and by comparison with the dye dilution method in infants and children following cardiac surgery. When 2 ml of 0 degrees C injectate were used, the correlation of computer determined flows to calibrated pump flows, over a range encountered clinically, was r = 0.998. The means of triplicate determinations by both the thermal and dye methods were compared in 8 of 25 patients and the comparison found to be favorable (r = 0.976). The complications of thermodilution catheter placement are described and related to the need for post-surgical chest x-ray and thermodilution recordings. The simplicity of the thermodilution technique and other advantages over the dye method in children, such as repeatability, and ease of calibration are discussed in relation to the increased flexibility in management which accrues.

Cardiac Catheterization↗

Phentolamine in low cardiac output states: an assessment with ECG-gated cardiac scintigraphy.

We examined the effect of parenteral phentolamine in 11 critically ill patients with a low cardiac output state and a high systemic resistance. Because vasodilators often affect left ventricular end-diastolic pressure-volume relationships (compliance) in acute cardiac disease, changes in the pulmonary capillary wedge pressure (WP) may conceivably not reflect the true effect of vasodilators on left ventricular preload. Hence, we measured left ventricular ejection fraction (LVEF) with ECG-gated cardiac scintigraphy and stroke volume by thermodilution before and during phentolamine infusion. We then calculated left ventricular end-diastolic volume index (LVEDVI). Phentolamine infusion was associated with an increase in the mean cardiac index (CI) (1.96 +/- .53 [mean +/- SD] to 2.45 +/- .69 L/min X m2; p less than .0025) whereas the mean WP fell (19.5 +/- 7.5 to 13.5 +/- 7.3 mm Hg; p less than .05). There was no simultaneous change in the mean LVEDVI (100 +/- 48 to 110 +/- 40 ml/m2; p = NS), implying that one of the effects of phentolamine infusion was to improve left ventricular diastolic compliance. Multiple regression analysis suggested that the major effect of phentolamine on stroke volume was mediated by concomitant changes in the LVEDVI (r2 = .64). Therefore, benefit from phentolamine in low cardiac output states is multifactorial and phentolamine likely improves left ventricular compliance in some patients.

Aged↗

Epidural analgesia and cardiac output in severe pre-eclamptics.

Labour and delivery cardiac output was assessed by thermal dilution in ten severe pre-eclamptics who received lumbar epidural analgesia. Control cardiac output was 8.8 litres/min which remained statistically unchanged following administration of lumbar epidural analgesia. At birth and delivery of the placenta, there was a moderate increase in cardiac output which increased significantly (28%) by 15 min after delivery of the placenta. Subsequently over the next hour, cardiac output returned toward baseline levels. Mother and fetus were stable throughout and infant Apgar scores were good. These results emphasise that lumbar epidural analgesia has little effect on cardiac output in severe pre-eclamptics.

Adolescent↗

[Treatment of low cardiac output syndrome in newborn infants and children].

A refractory low-cardiac-output syndrome is, in pediatric patients, most often due to impaired myocardial function after corrective surgery in congenital heart disease. Therapy has to focus on postoperative adaptation, which usually takes place within a few days. We report on three therapeutic strategies to "bridge" this phase of postoperative adaptation. Improving the contractile state of the myocardium using enoximone was attempted in 16 neonates with low-cardiac-output syndrome refractory to catecholamines (Dosage: loading-dose 1 mg/kg in 10 min intravenously, followed by an infusion of 10 mcg/kg/min). In 12/16 neonates cardiac index increased by more than 20% ("responder"), while in 4/16 neonates cardiac index remained unchanged ("non-responder"). All non-responders succumbed due to refractory low-cardiac-output syndrome, while only one responder died in low-cardiac-output syndrome. Hemodynamically, enoximone resulted in an increase of cardiac index and stroke volume (p < 0.003), a reduced systemic vascular resistance (p < 0.0022), and reduced right and left atrial pressures (p < 0.003). Heart rate and mean arterial pressure remained unchanged. No rhythm disturbances were observed. Another therapeutic approach to postoperative low-cardiac-output syndrome is atrial decompression by creating an atrial septal defect. Due to the possibility of later transcatheter closure of these defects, the acceptance for the intraoperative creation of an atrial communication to decompress the right or left atrium is increased. The defect size is critical and should be below 9 mm, so that the Rashkind-PDA-Occluder can be used for later transcatheter closure. We performed such a "surgical-interventional" decompression in 18 patients (age: 2 weeks to 7 years). In six patients the atrial defect was created because of an underdeveloped left ventricle (body weight 2.9-9.2 kg), in 12 patients for right atrial decompression during a total cavopulmonary shunt (body weight 15.2-54.2 kg). A spontaneous closure of the defect did not occurred in any of the patients, thus, transvenous closure of the defect was performed 2 to 10 weeks postoperatively. In the follow-up period of 4 to 22 months no complications such as thrombus formation, thromboembolic events or infections occurred. In low-cardiac-output syndrome refractory to all therapeutic measures mechanical circulatory support is the final method to keep the patient alive. In 11 children with refractory low-cardiac-output syndrome mechanical circulatory support was performed. In three of these, extracorporal membrane oxygenation (ECMO) was used, in eight children a ventricular assist device (Berlin Heart) was used.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Pressure↗

Advantages of continuous measurement of cardiac output 24 h a day.

To test the hypothesis that continuous measurement of cardiac output 24 h a day would provide a better day-by-day reproducibility of the daily average cardiac output than acute measurements, we developed a computer-assisted method to monitor cardiac output continuously using an electromagnetic flow transducer. Because the diastolic aortic flow, which is used as a zero-flow reference, can drift significantly with electromagnetic flow probes, automatic tracking of the diastolic flow baseline was considered essential for long-term measurements. To accomplish this, the analog pulsatile flow signal was digitally converted and processed by an IBM PC to correct for signal drift on a beat-per-beat basis. Using this computerized system in 19 chronically instrumented dogs, we compared the values of cardiac output during 5 consecutive control days, measured either for 20 h each day (allowed 4 h for special care) or for 30 min in the morning when the trained dogs were required to lie quietly in their cages. The results show that the coefficient of variation of the five daily averages in cardiac output for each individual dog was three times smaller when cardiac output was measured 20 h each day (2.9 +/- 0.3 vs. 9.7 +/- 1.0%). Whole-day coefficients of variation were also smaller for mean arterial pressure, heart rate, stroke volume, and total peripheral resistance. Because of this greater day-by-day reproducibility, continuous monitoring of cardiac output is likely to be more sensitive to small changes in cardiac output induced by experimental protocols.

Animals↗