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PubMed1991

Alternatives to Swan-Ganz cardiac output monitoring.

When we are concerned about the adequacy of peripheral oxygen delivery, our monitoring efforts focus on cardiac output as the component easiest to manipulate. Thermodilution is the current method of determining cardiac output because of logistic convenience, but by no means should it be considered the gold standard. Thoracic electrical bioimpedance is an appealing alternative because of its simplicity, noninvasiveness, and ability to track physiologic trends, but there have been a number of warnings against relying on it exclusively, at least until it is further developed. Doppler ultrasound appears to be a valid method in skilled hands, but its accuracy in quantitating cardiac output, especially in the critically ill, remains questionable. Mixed venous oximetry and transcutaneous oxygen monitoring are promising but are still being evaluated.

Blood Gas Monitoring, Transcutaneous↗
PubMed1990

Red cell volume and cardiac output in anaemic preterm infants.

To test the hypothesis that haemoglobin concentration is a poor predictor of benefit from transfusion in preterm infants, and that red cell volume is the most important indicator of anaemia, 24 preterm infants receiving red cell transfusions had red cell volume, haemoglobin concentration, and cardiac output measured before and after transfusion. Red cell volume was measured either using dilution of autologous fetal haemoglobin with donor adult haemoglobin, or with a new technique using biotin as a red cell label. The two techniques give similar results. Mean (SD) values before transfusion were 27.4 (13.3), and after transfusion 45.0 (13.7) ml/kg. Cardiac output was measured using imaging and Doppler ultrasonography, and fell with transfusion from mean 286 (121) to 251 (95.6) ml/kg/min. The red cell volume before transfusion correlated well with changes in cardiac output following transfusion, infants with a red cell volume before transfusion of less than 25 ml/kg showing a fall in cardiac output, and those with a red cell volume of greater than 25 ml/kg not showing a significant fall. There was no correlation between haemoglobin concentration, packed cell volume, or change in packed cell volume with changes in cardiac output after transfusion. A red cell volume of 25 ml/kg seems to be critical in preterm infants with anaemia, and infants with values below this are those most likely to benefit from transfusion.

Anemia, Neonatal↗
PubMed1995

Comparison of cardiac output measurement techniques: thermodilution, Doppler, CO2-rebreathing and the direct Fick method.

Simultaneously measured cardiac output obtained by thermodilution (TD), transcutaneous suprasternal ultrasonic Doppler (DOP), CO2-rebreathing (CR) and the direct Fick method (FI) were compared in eleven healthy subjects in a supine position (SU), a sitting position (SI), and during sitting exercise at a workload of 50 W (EX). The agreements between the techniques, two by two, were expressed as the bias calculated as the averaged differences between the techniques. Precision was expressed as the standard deviation of the bias. The overall agreement (bias +/- precision) between TD, DOP and CR respectively and FI were 2.3 +/- 1.6, -0.1 +/- 1.4, and -0.2 +/- 1.1 l/min. TD overestimated cardiac output consistently in SU, SI and EX. DOP was in-accurate during EX and agreed well with FI in SU and SI. CR agreed closely with FI in SI and EX, but values were underestimated in SU. The overall agreement between DOP and CR, respectively, and TD were 2.5 +/- 2.2 and 2.6 +/- 1.6 l/min. The overall agreement between DOP and CR was 0.1 +/- 1.6 l/min. In conclusion, TD overestimated cardiac output compared to the other techniques and the poor agreement has to be taken into consideration especially in measures of low values. The precision of DOP and CR against FI seems to be within clinically acceptable limits, and these methods may provide interchangeable alternatives to the invasive Fick method.

Adult↗
PubMed2004

Measurement of exercise cardiac output by thoracic impedance in healthy children.

The purpose of this study was to track changes in stroke volume during exercise by impedance cardiography in order to validate the method, and to obtain such data in a large number of healthy children for reference purposes. One hundred and fifteen healthy children (aged 7-19 years) performed progressive exercise to voluntary exhaustion with work increments every minute on a cycle ergometer. Oxygen uptake (VO(2)) was measured on a breath-by-breath system. Cardiac output was measured with an ICG-M501 impedance cardiograph. Stroke volume was normalized for body surface area and expressed as stroke volume index. Cardiac output was regressed against VO(2), and differences between stroke volume index at rest and exercise were assessed by repeated measures analysis of variance. Cardiac output increased linearly with VO(2) in all subjects: individual slopes and intercepts averaged 5.16 (1.56) l.min(-1) per l.min(-1) VO(2), and 4.25 (1.92) l.min(-1), respectively [mean (SD)]. Stroke volume index rose by an average of 29% from rest to exercise, reaching a maximum of 52 ml.m(-2) in boys and girls. Most subjects demonstrated a continuous, gentle rise in stroke volume index with increasing work rate, though a minority demonstrated a falling index as work increased above the anaerobic threshold, despite rising cardiac output. Impedance cardiography accurately tracks cardiac output and can be a useful clinical and research tool in pediatric cardiology and exercise physiology.

Adolescent↗
PubMed2002

Assessment of cardiac output from systemic arterial pressure in humans.

OBJECTIVE: To evaluate the reliability, by comparison with established techniques, of a new method to assess cardiac output, called pressure recording analytical method (PRAM), deriving from the analysis of the arterial pressure profile in the time domain the arterial-pressure-blood flow relationship. DESIGN: Criterion standard. SETTING: Hemodynamics laboratory at an university medical center. PATIENTS: Twenty-two hemodynamically stable cardiac patients scheduled for diagnostic right and left heart catheterization. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Cardiac index was simultaneously estimated by direct-oxygen Fick method, thermodilution, and PRAM applied to pressure signals recorded either invasively from an aortic catheter (PRAMa) or noninvasively at the finger (PRAMf) by photoplethysmography. Cardiac index values obtained by established techniques were significantly correlated with those estimated by PRAM: Fick method vs. PRAMa, r(2) =.88, vs. PRAMf, r(2) =.94; thermodilution vs. PRAMa, r(2) =.77, vs. PRAMf, r(2) =.77. The Bland-Altman analysis showed agreement between the Fick method and PRAM, with all data points comprised within the limits of agreement (+/-2SD) (mean difference +/- SD: -0.012 +/- 0.187 L x min(-1) x m(-2) for PRAMa; 0.024 +/- 0.167 L x min(-1) x m(-2) for PRAMf). Agreement was also found between thermodilution and PRAM, with all but one data point lying within the limits of agreement (mean difference +/- SD: -0.154 +/- 0.348 L x min(-1) x m(-2) for PRAMa; -0.108 +/- 0.348 L x min(-1) x m(-2) for PRAMf). CONCLUSIONS: In the range evaluated (cardiac index from 1.65 to 3.91 L x min(-1) x m(-2) by the Fick method), PRAM provides reliable invasive and noninvasive estimates of cardiac output in hemodynamically stable cardiac patients. PRAM may prove clinically useful for the beat-to-beat monitoring of cardiac output.

Adult↗
PubMed2004

Cardiac output determination during experimental hemorrhage and resuscitation using a transesophageal Doppler monitor.

Transesophageal Doppler (TED) monitoring has been considered a noninvasive and accurate alternative to pulmonary artery catheterization for volume replacement and cardiac output measurement in patients undergoing major surgery. This study tested the hypothesis that TED can accurately predict cardiac output during hemorrhage, shock, and resuscitation, by comparing it to total pulmonary artery blood flow (PABF) and to standard intermittent bolus cardiac output (ICO). In eight anesthetized dogs (18 +/- 1.0 kg), PABF was measured with an ultrasonic flowprobe while ICO and mixed venous O2 saturation (SvO2) were measured through a Swan-Ganz catheter. A TED probe (CardioQ, Deltex Medical Inc., Irving, TX, U.S.A.), designed for adult use (minimum 30 kg, 16 years), was placed in midesophageous to evaluate stroke volume. A graded hemorrhage (20 mL/min) was produced (H5-H35) to a mean arterial pressure (MAP) of 40 mm Hg and maintained by additional blood removal for 30 min (S1-S30). Total shed blood volume was retransfused (541 +/- 54.2 mL) over 30 min (T5-T30), after which a massive hemorrhage, 100 mL/min rate, was produced over 10 min (MH5-MH10). In general, TED overestimated PABF (r2 = 0.3472), but changes in TED paralleled PABF throughout the experimental protocol, particularly during massive hemorrhage (r2 = 0.9001). We concluded that TED accurately reflected the direction and magnitude of the changes of cardiac output over time during abrupt hemodynamic changes. Probes designed for lower weights and smaller aortas may improve its accuracy in medium size animal models under less dramatic alterations induced by hemorrhage, shock, and resuscitation.

Animals↗
PubMed1983

Cardiac output by thermodilution technique. Effect of injectate's volume and temperature on accuracy and reproducibility in the critically Ill patient.

We compared determinations of cardiac output using various combinations of injectate volumes and temperatures to results obtained with 10 ml of iced (0 degrees C) injectate (standard technique) in 33 critically ill patients. The use of a 10-ml injectate at room temperature resulted in comparable reproducibility (12.7 vs 10.8 percent; not significant) and a small and nonsignificant error (-0.013 +/- 0.543 L/min). Five milliliters at room temperature resulted in markedly decreased reproducibility (17.9 vs 8.9 percent; p less than 0.05); however, the error associated with the technique was still not significant (0.136 +/- 0.829 L/min). When a 5-ml injectate at 0 degrees C was used, a reproducibility comparable to that of 10 ml at 0 degrees C was obtained (12.3 vs 7.5 percent; not significant). The results underestimated values obtained with 10 ml at 0 degrees C (-0.360 +/- 0.857 L/minute); however, the difference did not reach statistical significance. The use of 3 ml at 0 degrees C was associated with a substantial increase in variability, with a coefficient of variation of 32.0 percent (10.4 percent for 10 ml of iced injectate; p less than 0.01); however, the differences between the average value of cardiac output obtained with this technique and the standard technique were only minimal (error, -0.063 +/- 0.455; not significant). We reached the following conclusions: (1) the use of 10 ml at room temperature and 5 ml at 0 degrees C as the indicator for thermodilution determinations of cardiac output results in small and insignificant differences in reproducibility and accuracy from the standard technique; (2) five milliliters at room temperature and 3 ml at 0 degrees C are associated with markedly decreased reproducibility; however, the error in values for cardiac output obtained with these techniques is not statistically significant; and (3) the ability to use injectate at room temperature and in small volume should substantially simplify the technique, lowering its cost, and should prevent volume overloading.

Adult↗
PubMed1997

Role of cardiac output in ethanol-evoked attenuation of centrally mediated hypotension in conscious rats.

Our previous studies have shown that ethanol selectively counteracts centrally mediated hypotensive responses. This study investigated the role of cardiac output and peripheral resistance in the antagonistic interaction between ethanol and antihypertensive drugs. Changes in blood pressure, heart rate, cardiac index, stroke volume, and peripheral resistance elicited by clonidine and subsequent ethanol or saline administration were evaluated in conscious rats. The aortic barodenervated rat was employed because it exhibits greater hypotensive responses to clonidine compared with the intact rat. Aortic barodenervation elicited acute rises in blood pressure, heart rate, and peripheral resistance, whereas cardiac index and stroke volume were not altered. The blood pressure of conscious aortic barodenervated rats returned to sham-operated levels by 48 hours due to concomitant reductions in cardiac index and stroke volume; the peripheral resistance, however, remained significantly elevated. Clonidine (30 microg/kg, I.V.) elicited greater decreases in blood pressure in aortic barodenervated compared with sham-operated rats. The hypotension was caused by decreases in cardiac index and stroke volume because peripheral resistance did not change. Ethanol (1 g/kg, I.V.) counteracted the hypotensive effect of clonidine and raised blood pressure to levels higher than preclonidine values. Significant (P<.05) increases in cardiac index and stroke volume and decreases in peripheral resistance accompanied the pressor effect of ethanol. Additional control groups were included in the study to determine the selectivity of the interaction. A dose of hydralazine (0.5 mg/kg, I.V.) was used that produced similar hypotension to that evoked by clonidine in aortic barodenervated rats. Hydralazine-evoked hypotension was similar in denervated and control rats and resulted from significant reductions in peripheral resistance. Reflex increases in heart rate and stroke volume and hence cardiac output were observed. Ethanol given after hydralazine produced a short-lived pressor effect (<5 minutes versus 40 minutes in the case of clonidine) and counteracted the sympathetically mediated increases in cardiac output, stroke volume, and heart rate. These findings support our hypothesis that ethanol selectively counteracts hypotensive responses of central origin by reversing the reduction in cardiac output elicited by clonidine.

Animals↗
PubMed1982

Validation of cardiac output estimates by digital video subtraction angiography in dogs. Correlation with thermodilution values.

To determine the validity of cardiac output estimates obtained by digital video subtraction angiography (DVSA), they were compared with thermodilution values in 6 anesthetized dogs. Multiple levels of cardiac output were produced in each dog by graded openings of peripheral arteriovenous fistulas. Both direct contrast and mask-mode images were evaluated. There was good correlation between thermodilution and direct contrast values (r = 0.88) as well as between thermodilution and mask-mode values (r = 0.89), though the mask-mode outputs were 12 +/- 1.1% less than the direct contrast values (p less than 0.05). Direct contrast and mask-mode values correlated well (n = 6; r greater than or equal to 0.95). Digital outputs exhibited little variation, indicating excellent reproducibility. These results demonstrate the validity of area-length estimates of cardiac output by DVSA.

Angiocardiography↗
PubMed1981

The carotid sinus-blood pressure reflex in conscious rabbits: the relative importance of changes in cardiac output and peripheral resistance.

This paper reports experiments to determine the relative roles of changes in cardiac output and systemic vascular resistance in determining the blood pressure response to intermittent step-changes and continuous sinusoidal changes in carotid sinus transmural pressure. Conscious rabbits with a variable-pressure capsule implanted around an innervated carotid sinus were used. After step-change in capsule pressure the approximate proportions of the changes in blood pressure attributable to changes in cardiac output were, during the pressor response, 7% after 2.5 s, 22% after 10 s and 27% at plateau, and during the depressor response 100%, 8% and 17%, respectively. During sinusoidal change in capsule pressure a mean 7% of the change in blood pressure over the full cycle was attributable to change in cardiac output.

Animals↗
PubMed1987

Influence of changes in cardiac output on the acid-base status of arterial and mixed venous blood.

While maintaining the arterial CO2 tension constant near the normal level of the dog (4.3 kPa), we studied the influence of decreasing cardiac output on both the arterial and mixed-venous blood acid-base status in anaesthetized, artificially ventilated dogs. Cardiac output was manipulated by applying positive end-expiratory pressure (PEEP), and by beta-adrenergic blockade to suppress a compensatory heart rate response. The systemic vascular response was attenuated by alpha-adrenergic blockade. Metabolic rate remained virtually unchanged when cardiac output decreased. Under these conditions a fall in cardiac output led to a shift of the arterial acid-base status in the direction of a metabolic acidosis. The changes occurring in the mixed-venous blood resembled those of an in-vivo CO2 bufferline, with the shift being such as if a respiratory acidosis was developing.

Acid-Base Imbalance↗
PubMedDate not supplied

Understanding techniques for measuring cardiac output.

In summary, use of thermodilution as a method to measure cardiac output has attained universal appeal in the clinical environment. Other means of detecting cardiac output (impedance-cardiogram and ballistocardiogram, to name two) have been developed and are being used clinically, but the development of the flow-directed thermodilution catheter has profoundly affected the universal acceptance of the thermodilution method. Thermodilution techniques, when performed properly, are capable of obtaining accurate and reproducible results. Medical and nursing personnel who are educated in proper procedures will be able to make educated choices when faced with difficult decisions. It is likely that they will turn to the biomedical or clinical engineering department for help if those personnel are well informed regarding the techniques and procedures.

Cardiac Output↗
PubMedDate not supplied

Effects of intravenous diltiazem on cardiocirculatory dynamics and cardiac output distribution in conscious spontaneously hypertensive rats.

The effects of the calcium channel blocker, diltiazem hydrochloride (DZ), on conscious, resting spontaneously hypertensive rats (SHR) were evaluated and compared with results from parallel studies on Wistar-Kyoto (WKY) controls. DZ was administered as a continuous, cumulative infusion at rates equal to 0.40, 2.00, and 10.00 mg/kg/h (each dose was administered for 15 min). Parallel volume infusion (saline) controls were simultaneously conducted using volume infusion rates identical to those used in DZ studies (0.015, 0.100, and 0.500 ml/min). Three hours prior to study, animals were instrumented under halothane anesthesia for measurement of left ventricular, arterial, and central venous pressures; heart rate and arterial blood gases; and for injection of radioactive microspheres and subsequent determination of cardiac output, regional blood flows, and cardiac output distribution. All data were collected at control (C) before initiation of infusion, and at the end of each 15-min infusion period in each animal. At C and compared with WKY, SHR had increased heart rate (392 vs. 280 beats/min), mean arterial pressure (155 vs. 100 mm Hg), left ventricular peak systolic pressure (200 vs. 132 mm Hg), and systemic vascular resistance (0.3 vs. 0.2 mm Hg/ml/min/kg), and reduced stroke volume (1.8 vs. 2.2 ml/beat/kg); but no difference in cardiac output, left ventricular end diastolic pressure, or central venous pressure was found. At C, SHR tended to have increased blood flow and reduced vascular resistance in the coronary circulation and increased vascular resistance in the cutaneous, renal, bronchial arterial, hepatic arterial, testicular, and cerebral circulations. Infusion of DZ increased cardiac output and stroke volume and decreased heart rate, left ventricular and arterial pressures, and systemic vascular resistance in SHR. Similar changes of substantially smaller magnitude were observed in WKY. DZ increased flow and reduced resistance in the coronary and skeletal muscle circulations of SHR to a greater extent than in WKY. DZ also normalized vascular resistance in previously elevated regions. These results suggest that acute intravenous infusion of DZ at doses ranging between 2 and 5 mg/kg is capable of normalizing cardiovascular hemodynamics and regional blood flow distribution in SHR.

Animals↗
PubMed1987

Comparative radionuclide and thermodilution determinations of cardiac output and stroke volume in the baboon (Papio ursinus).

Thermodilution cardiac output determinations and multigated equilibrium blood-pool scintigraphy were performed in ten healthy chacma baboons (Papio ursinus). The correlation was moderately good between both the radionuclide and thermodilution stroke volume (r = 0.58, SEE = 3 ml; SVth = 0.78SVr + 15.6 ml) as well as the cardiac output (r = 0.72, SEE = 0.2 liter/min; COth = 0.56 Cor + 2.1 liter/min). The attenuation depth dr as determined by radionuclide techniques was found to correlate well with the radiologically determined values dx (r = 0.8, SEE = 0.4 cm; dx = 0.87dr + 0.72 cm) which validated the depth values used in the calculations.

Animals↗
PubMed1982

Overestimation of pediatric cardiac output by thermal indicator loss.

The accurate measurement of pediatric cardiac output by thermodilution requires that the quantity of cold indicator introduced into the central circulation be known. This study defines an important source of error in the correction factor for the amount of heat gained by small volumes of cold injectate during passage through pediatric catheter systems. This error may result in significant overestimation of cardiac output (as much as 59%) when blood at body temperature is withdrawn into the injection lumen of the pediatric catheter before the injection.

Age Factors↗