Cardiac output determined by ultrasound-Doppler: clinical applications

Summary. A non-invasive method for cardiac output determination (COD) based on ultrasound-Doppler technique was evaluated in patients with cardiac disease at rest and during exercise, including patients with heart transplants. The aortic blood flow velocity was measured with pulsed Doppler technique from the jugulum, placing the sample volume just above the aortic valve, and the area from a parasternal 2-D echocardiographic measurement of the aortic annulus diameter assuming a circular area. Cardiac output was calculated as the product of the systolic velocity integral, the aortic annulus area and the heart rate. A high correlation was found between this method and a simultaneously performed invasive cardiac output (COF) and stroke volume (SVF) determination by the direct Fick method (COD = 0.3+0.9 x COF, r= 0.96, SD_res= 0.5 1 min^-1 and SVD = 3.9+0.92 × SVF, r= 0.94, SD_res= 6.9 ml). However, looking just at the systolic velocity integral compared to stroke index determined with the Fick method we found a low correlation, especially in patients with heart transplants. We conclude that cardiac output can reliably be measured non-invasively with this method—also in patients with heart transplants. The systolic velocity integral alone can be used for assessing changes in stroke volume but for absolute values of stroke volume and stroke index flow area should also be determined.     

Cardiac output and circulating blood volume analysis by pulse dye-densitometry

Objective. Pulse dye-densitometry (PDD) is a newly developed methodfor monitoring the indocyanine green (ICG) concentration in an artery withwhich cardiac output (CO) and circulating blood volume (CBV) can bedetermined. We evaluated its accuracy for clinical use. Methods. In 7patients under general anesthesia, ICG-sensitive optical probes (805 and 890nm) were attached to a finger. Following injection of ICG, the arterialconcentration of dye was recorded optically by the non-invasive testinstrument and sampled arterial blood ICG concentration was also measuredphotometrically for comparison. In order to validate the PDD analysis, CO wasalso measured by both the dye dilution cuvette method and by thermodilutionin 8 patients scheduled for coronary artery bypass grafting. In 30 otherpatients, CBV assessed by PDD was compared with its value estimated from bodysize. Results. The blood dye concentration correlated well with thevalues obtained by PDD (r = 0.953, p < 0.01). Meanbias for the test PDD CO was +0.15 ± 0.72 minl^–1 (not significant (n.s.)) compared with the cuvette methodwhile the mean bias of the thermodilution method vs thecuvette method was +0.79 ± 0.84 min l^–1 (p < 0.0001.). The average value of CBV obtained by PDD was 3.81± 1.39 L compared with that estimated value, 3.72 ± 0.77 L (n.s.).Conclusions. CO determined by PDD agrees wellwith cuvette densitometry, and somewhat less well with CO by thermodilution.The new method, by not requiring a pulmonary arterial catheter, is lessinvasivethan either older method, and yields in addition a value of CBV.     

Cardiac output and end-tidal carbon dioxide

Previous studies demonstrated selective increases in mixed venous carbon dioxide tension (PvCO2) during CPR in a porcine model of cardiac arrest. This was associated with a decrease in end-tidal carbon dioxide concentration (ETCO2), possibly due to a critical reduction in cardiac output and therefore pulmonary blood flow during CPR. We investigated the relationship between ETco2 and cardiac output before cardiac arrest and during CPR. Observations in 19 minipigs confirmed a high linear correlation between ETco2 and cardiac output. We conclude that the increase in Pvco2 and the concurrent decrease in ETco2 reflect a critical reduction in cardiac output, which reduces alveolar blood flow to the extent that carbon dioxide clearance by the lung fails to keep pace with systemic CO2 production.     

Cardiac output measurement in children: comparison of the Ultrasound Cardiac Output Monitor with thermodilution cardiac output measurement

OBJECTIVE: To compare the assessment of cardiac output (CO) in children using the noninvasive Ultrasound Cardiac Output Monitor (USCOM) with the invasive pulmonary artery catheter (PAC) thermodilution cardiac output measurement. DESIGN AND SETTING: Prospective observational study in a tertiary center for pediatric cardiology of a university children's hospital. PATIENTS: Twenty-four pediatric patients with congenital heart disease without shunt undergoing cardiac catheterization under general anesthesia. MEASUREMENTS AND RESULTS: CO was measured by USCOM using a suprasternal CO Doppler probe in children undergoing cardiac catheterization. USCOM data were compared to CO simultaneously measured by PAC thermodilution technique. Measurements were repeated three times within 5 min in each patient. A mean percentage error not exceeding 30% was defined as indicating clinical useful reliability of the USCOM. CO values measured by PAC ranged from 1.3 to 5.3 l/min (median 3.6 l/min). Bias and precision were -0.13 and 1.34 l/min, respectively. The mean percentage error of CO measurement by the USCOM compared to PAC thermodilution technique was 36.4% for USCOM. CONCLUSIONS: Our preliminary data demonstrate that cardiac output measurement in children using the USCOM does not reliably represent absolute CO values as compared to PAC thermodilution. Further studies must evaluate the impact of incorporating effective aortic valve diameters on CO measurement using the USCOM.     

Cardiac output and its distribution in peritonitis

Cardiac output and its distribution were studied in rats made septic by an i.p. injection of live E. coli bacteria and in controls given an equivalent amount of saline. The E. coli injection was followed by signs of severe shock in eight of 12 rats. Control animals all survived with only minor changes in cardiac output and peripheral hemodynamics. Blood flow in shocked animals was characterized by a reduction of cardiac output, while myocardial and cerebral flows were not reduced. The intact circulation to the brain and to the heart in the shocked rats was at the expense of kidney, spleen, and skin blood flows.     

Cardiac output by Modelflow method from intra-arterial and fingertip pulse pressure profiles

Modelflow, when applied to non-invasive fingertip pulse pressure recordings, is a poor predictor of cardiac output (Q, litre x min(-1)). The use of constants established from the aortic elastic characteristics, which differ from those of finger arteries, may introduce signal distortions, leading to errors in computing Q. We therefore hypothesized that peripheral recording of pulse pressure profiles undermines the measurement of Q with Modelflow, so we compared Modelflow beat-by-beat Q values obtained simultaneously non-invasively from the finger and invasively from the radial artery at rest and during exercise. Seven subjects (age, 24.0 +/- 2.9 years; weight, 81.2 +/- 12.6 kg) rested, then exercised at 50 and 100 W, carrying a catheter with a pressure head in the left radial artery and the photoplethysmographic cuff of a finger pressure device on the third and fourth fingers of the contralateral hand. Pulse pressure from both devices was recorded simultaneously and stored on a PC for subsequent Q computation. The mean values of systolic, diastolic and mean arterial pressure at rest and exercise steady state were significantly ( P < 0.05) lower from the finger than the intra-arterial catheter. The corresponding mean steady-state Q obtained from the finger (Qporta) was significantly ( P < 0.05) higher than that computed from the intra-arterial recordings (Qpia). The line relating beat-by-beat Qporta and Qpia was y =1.55 x -3.02 ( r2 = 0.640). The bias was 1.44 litre x min(-1) and the precision was 2.84 litre x min(-1). The slope of this line was significantly higher than 1, implying a systematic overestimate of Q by Qporta with respect to Qpia. Consistent with the tested hypothesis, these results demonstrate that pulse pressure profiles from the finger provide inaccurate absolute Q values with respect to the radial artery, and therefore cannot be used without correction with a calibration factor calculated previously by measuring Q with an independent method.     

Cardiac output determined by the CO2 rebreathing method during arm exercise

Summary: Since arm exercise affects the respiratory muscles the CO₂ rebreathing method for determining cardiac output (QR) has to be evaluated during arm exercise. The purpose of this study was (1) to compare three different methods of determining arterial CO₂ tension (PaCO₂) during arm exercise, (2) to verify the linearity of the relationship between QR and oxygen uptake (VO₂) during arm exercise, and (3) to investigate whether the CO₂ rebreathing method according to Collier can determine accurately QR during arm exercise. Sixty male subjects performed arm-cranking exercise at 20%, 40% and 60% of their individual maximal load. Carbon dioxide output (V?O₂) was measured by gas exchange measurement, and mixed venous CO₂ tension (Pv?O₂) was determined from the CO₂ rebreathing plateau at each exercise level. PaCO₂ was estimated in three different ways: (A) by the modified Bohr formula for dead space, (B) by an arterialized blood sample from the hyperaemic ear-lobe, and (C) by the end-expiratory CO₂ tension. A, B, and C were used to calculate QRa, Qb and Qc, respectively. The Pearson's correlation coefficient was high (P < 0–01) among the three different ways of estimating PaCO₂. The QR-VO₂ relationship proved to be linear (P < 0–01). The Q-values showed a good agreement with the direct Fick measurements, and were in the same range compared to other results obtained by dye dilution, electrical impedance cardiography and the exponential CO₂ rebreathing method during arm exercise. In conclusion, the CO₂ rebreathing method appeared to be accurate to determine Q during submaximal arm exercise.,     

Cardiac resynchronization therapy optimization by ultrasonic cardiac output monitoring (USCOM) device

OBJECTIVES: We investigated the accuracy and feasibility of a 2D echo-independent ultrasonic continuous wave Doppler cardiac output monitoring device (USCOM) operated by trained nurse for the atrio-ventricular interval (AVI) optimization in cardiac resynchronization therapy (CRT). BACKGROUND: CRT is of proven benefit in patients with advanced chronic heart failure and ventricular conduction delay. Appropriate AVI selection is critical to optimize hemodynamic in CRT. Currently, most non-invasive methods for AVI optimization are often complicated and labor-intensive. Methods: USCOM method, Ritter method, and aortic outflow cardiac output method were used to determine the optima AVI in 20 patients with CRT. The accuracy and time for measurement of each method were determined. RESULTS: The optimal AVI determined by USCOM method had good correlation with Ritter's method and aortic outflow estimated cardiac output method (r2= 0.78, P < 0.01 and r2= 0.73, P < 0.01, respectively). The optimal AVI determined USCOM method showed good agreement (within 10 msec range) with Ritter's method (85% patients) and aortic outflow estimated cardiac output method (80%). The mean time for determining AVI using USCOM method was shorter than that with aortic outflow method (7.1 +/- 0.7 min vs 12.7 +/- 1.1 min, P < 0.01), whereas the mean time was shortest for Ritter method (4.7 +/- 1.6 min vs 7.1 +/- 0.7 min, P < 0.01). CONCLUSION: USCOM device operated by trained nurse can provide a simple, accurate, and fast non-invasive method for the AVI optimization in CRT population.     

Cardiac output: theory, technique, and troubleshooting

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.     

Cardiac resynchronization therapy optimization using noninvasive cardiac output measurement

Aims: Noninvasive cardiac output (CO) measurement (NICOM) is a novel method to assess ventricular function and offers a potential alternative for optimization of cardiac resynchronization therapy (CRT) devices. We compared the effect of NICOM‐based optimization to no optimization (empiric settings) on CRT outcomes. Methods: Two hundred and three patients undergoing CRT were assessed in two consecutive nonrandomized groups; an empiric group (n = 54) was programmed to “out of the box” settings with a fixed AV delay of 120 ms and a VV delay of 0 ms; and the optimization group (n = 149) underwent adjustments of both the AV and VV delays according to the greatest improvement in resting CO. The primary endpoints were improvements in left ventricular (LV) volumes and function from baseline at 6 months. Secondary endpoints were change in New York Heart Association (NYHA) class, quality of life score, and 6‐minute walk test (6 MWT) performance. Results: After 6 months of CRT, the optimization group had a better clinical response with lower NYHA class (2.1±0.8 vs 2.4 ± 0.8, P = 0.048) and quality of life scores (35 ± 18 vs 42 ± 20, P = 0.045) but no differences in 6‐MWT performance (269 ± 110 vs 277 ± 114 m, P = 0.81). Echocardiographic response was also better in the optimization group with lower LV end systolic volume (108 ± 51 vs 126 ± 60 mL, P = 0.048) and higher ejection fraction (30 ± 7 vs 27 ± 8, P = 0.01) compared to empiric settings. Conclusion: Device optimization using noninvasive measures of CO is associated with better clinical and echocardiographic response compared to empiric settings. (PACE 2011; 34:1527–1536)