Comparison of transtracheal and extravascular Doppler determinations of stroke volume and cardiac output at various states of volume loading in piglets

The use of live three-dimensional Doppler echocardiography in the measurement of cardiac output

OBJECTIVES

The purpose of this study was to investigate whether cardiac output (CO) could be accurately computed from live three-dimensional (3-D) Doppler echocardiographic data in an acute open-chested animal preparation.

BACKGROUND

The accurate measurement of CO is important in both patient management and research. Current methods use invasive pulmonary artery catheters or two-dimensional (2-D) echocardiography or esophageal aortic Doppler measures, with the inherent risks and inaccuracies of these techniques.

METHODS

Seventeen juvenile, open-chested pigs were studied before undergoing a separate cardiopulmonary bypass procedure. Live 3-D Doppler echocardiography images of the left ventricular outflow tract and aortic valve were obtained by epicardial scanning, using a Philips Medical Systems (Andover, Massachusetts) Sonos 7500 Live 3-D Echo system with a 2.5-MHz probe. Simultaneous CO measurements were obtained from an ultrasonic flow probe placed around the aortic root. Subsequent offline processing using custom software computed the CO from the digital 3-D Doppler DICOM data, and this was compared to the gold standard of the aortic flow probe measurements.

RESULTS

One hundred forty-three individual CO measurements were taken from 16 pigs, one being excluded because of severe aortic regurgitation. There was good correlation between the 3-D Doppler and flow probe methods of CO measurement (y = 1.1x - 9.82, R(2) = 0.93).

CONCLUSIONS

In this acute animal preparation, live 3-D Doppler echocardiographic data allowed for accurate assessment of CO as compared to the ultrasonic flow probe measurement.

Noninvasive monitoring of cardiac output in human neonates and juvenile piglets by inductance cardiography (thoracocardiography)

PURPOSE

Thoracocardiography has been used in adult patients to noninvasively estimate changes in cardiac output (CO) by analysis of ventricular volume curves recorded by an inductive plethysmographic transducer encircling the chest at the level of the heart. The purpose of this study was to investigate the potential of thoracocardiography to monitor cardiac output in human neonates and in a small animal model, the juvenile piglet.

MATERIALS AND METHODS

In 6 human premature neonates weighing 1.0 to 1.6 kg the effect of periodic respiration on CO was studied with thoracocardiography. In 9 piglets weighing 8.5 to 10.2 kg changes in CO were estimated simultaneously by thoracocardiography and thermodilution during fluid loading and rapid atrial pacing.

RESULTS

In human neonates, CO during breathing was 136% to 320% of the corresponding value during apneas. In piglets, CO by thermodilution ranged from 0.25 to 3.26 L/min. The mean difference in 40 paired estimates of relative changes in CO by thoracocardiography and thermodilution was 3%, limits of agreement (bias +/- 2 SD) were +/- 30%.

CONCLUSIONS

In neonates, increases in CO during respiratory phases of periodic breathing are consistent with expected cardiorespiratory interactions. Thoracocardiography monitored changes in CO in piglets with acceptable accuracy. Thoracocardiography holds promise for noninvasive monitoring in human neonates but further validation is required.

Noninvasive whole-body electrical bioimpedance cardiac output and invasive thermodilution cardiac output in high-risk surgical patients

OBJECTIVE

To evaluate the reliability of whole-body impedance cardiography with two electrodes on either both wrists or one wrist and one ankle for the measurement of cardiac output compared with the thermodilution method.

DESIGN

Prospective, clinical investigation

SETTING

Surgical intensive care unit of a university-affiliated community hospital.

PATIENTS

Simultaneous cardiac output measurements by noninvasive whole-body impedance cardiography (nCO) and invasive thermodilution (thCO) in 22 high-risk surgical patients scheduled for extended surgery requiring perioperative pulmonary artery catheter monitoring.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 109 sets of measurements consisting of 455 single comparison measurements between nCO and thCO were included in the analysis. The mean cardiac output difference between the two methods was 1.62 L/min with limits of agreement (2 SD) of +/- 4.64 L/min. The inter-measurement variance was slightly higher for nCO. The correlation coefficient between nCO and thCO was r2 = 0.061 (p < .001) for single measurements and r2 = 0.083 (p < .002) for sets of three to six measurements. The two most predictive factors for between-method differences were the absolute thCO value (r2 = 0.13; p < .001) and whether or not a continuous nitroglycerin infusion was used (p < .05, Student's t-test).

CONCLUSIONS

Agreement between whole-body impedance cardiography and thermodilution in the measurement of cardiac output was unsatisfactory. Factors that can explain these differences are differences between the populations used for calibration of nCO and the study population, the influence of changing peripheral perfusion, and the effect of a supranormal hemodynamic state on the bioimpedance signal. Whole-body impedance cardiography cannot be recommended for assessing the hemodynamic state of high-risk surgical patients as studied in this investigation.