Relative Changes In Cardiac Output Research Articles

Volumetric and End-Tidal Capnography for the Detection of Cardiac Output Changes in Mechanically Ventilated Patients Early after Open Heart Surgery.

Background Exhaled carbon dioxide (CO2) reflects cardiac output (CO) provided stable ventilation and metabolism. Detecting CO changes may help distinguish hypovolemia or cardiac dysfunction from other causes of haemodynamic instability. We investigated whether CO2 measured as end-tidal concentration (EtCO2) and eliminated volume per breath (VtCO2) reflect sudden changes in cardiac output (CO). Methods We measured changes in CO, VtCO2, and EtCO2 during right ventricular pacing and passive leg raise in 33 ventilated patients after open heart surgery. CO was measured with oesophageal Doppler. Results During right ventricular pacing, CO was reduced by 21% (CI 18–24; p < 0.001), VtCO2 by 11% (CI 7.9–13; p < 0.001), and EtCO2 by 4.9% (CI 3.6–6.1; p < 0.001). During passive leg raise, CO increased by 21% (CI 17–24; p < 0.001), VtCO2 by 10% (CI 7.8–12; p < 0.001), and EtCO2 by 4.2% (CI 3.2–5.1; p < 0.001). Changes in VtCO2 were significantly larger than changes in EtCO2 (ventricular pacing: 11% vs. 4.9% (p < 0.001); passive leg raise: 10% vs. 4.2% (p < 0.001)). Relative changes in CO correlated with changes in VtCO2 (ρ=0.53; p=0.002) and EtCO2 (ρ=0.47; p=0.006) only during reductions in CO. When dichotomising CO changes at 15%, only EtCO2 detected a CO change as judged by area under the receiver operating characteristic curve. Conclusion VtCO2 and EtCO2 reflected reductions in cardiac output, although correlations were modest. The changes in VtCO2 were larger than the changes in EtCO2, but only EtCO2 detected CO reduction as judged by receiver operating characteristic curves. The predictive ability of EtCO2 in this setting was fair. This trial is registered with NCT02070861.

The response of a standardized fluid challenge during cardiac surgery on cerebral oxygen saturation measured with near-infrared spectroscopy

Near infrared spectroscopy (NIRS) has been used to evaluate regional cerebral tissue oxygen saturation (ScO2) during the last decades. Perioperative management algorithms advocate to maintain ScO2, by maintaining or increasing cardiac output (CO), e.g. with fluid infusion. We hypothesized that ScO2 would increase in responders to a standardized fluid challenge (FC) and that the relative changes in CO and ScO2 would correlate. This study is a retrospective substudy of the FLuid Responsiveness Prediction Using Extra Systoles (FLEX) trial. In the FLEX trial, patients were administered two standardized FCs (5 mL/kg ideal body weight each) during cardiac surgery. NIRS monitoring was used during the intraoperative period and CO was monitored continuously. Patients were considered responders if stroke volume increased more than 10% following FC. Datasets from 29 non-responders and 27 responders to FC were available for analysis. Relative changes of ScO2 did not change significantly in non-responders (mean difference − 0.3% ± 2.3%, p = 0.534) or in fluid responders (mean difference 1.6% ± 4.6%, p = 0.088). Relative changes in CO and ScO2 correlated significantly, p = 0.027. Increasing CO by fluid did not change cerebral oxygenation. Despite this, relative changes in CO correlated to relative changes in ScO2. However, the clinical impact of the present observations is unclear, and the results must be interpreted with caution.Trial registration:http://ClinicalTrial.gov identifier for main study (FLuid Responsiveness Prediction Using Extra Systoles—FLEX): NCT03002129.

Wearable ballistocardiogram and seismocardiogram systems for health and performance.

Cardiovascular diseases (CVDs) are prevalent in the US, and many forms of CVD primarily affect the mechanical aspects of heart function. Wearable technologies for monitoring the mechanical health of the heart and vasculature could enable proactive management of CVDs through titration of care based on physiological status as well as preventative wellness monitoring to help promote lifestyle choices that reduce the overall risk of developing CVDs. Additionally, such wearable technologies could be used to optimize human performance in austere environments. This review describes our progress in developing wearable ballistocardiogram (BCG)- and seismocardiogram-based systems for monitoring relative changes in cardiac output, contractility, and blood pressure. Our systems use miniature, low-noise accelerometers to measure the movements of the body in response to the heartbeat and novel machine learning algorithms to provide robustness against motion artifacts and sensor misplacement. Moreover, we have mathematically related wearable BCG signals-representing local, cardiogenic movements of a point on the body-to better understood whole body BCG signals, and thereby improved estimation of key health parameters. We validated these systems with experiments in healthy subjects, studies in patients with heart failure, and measurements in austere environments such as water immersion. The systems can be used in future work as a tool for clinicians and physiologists to measure the mechanical aspects of cardiovascular function outside of clinical settings, and to thereby titrate care for patients with CVDs, provide preventative screening, and optimize performance in austere environments by providing real-time in-depth information regarding performance and risk.

Evaluation of the non-calibrated pulse contour cardiac output monitor FloTrac/Vigileo against thermodilution in standing horses

ObjectiveTo evaluate the non-calibrated, minimally invasive cardiac output (CO) monitor FloTrac/Vigileo (FloTrac) against thermodilution (TD) CO in standing horses. Study designProspective, experimental trial. AnimalsNine adult horses weighing a median (range) of 535 (470–602) kg. MethodsCatheters were placed in the right atrium, pulmonary artery and carotid artery under local anaesthesia. CO was measured 147 times by TD and FloTrac and indexed to body weight. Changes in CO were achieved with romifidine or xylazine and dobutamine constant rate infusions. Bland–Altman analysis, concordance and polar plot analysis were used to assess agreement and ability to track changes in CO. ResultsMean ± standard deviation COTD of 48 ± 16 mL kg−1 minute−1 (range: 19–93 mLkg−1 minute−1) and mean COFloTrac of 9 ± 3 mLkg−1 minute−1 (range: 5–21 mL kg−1 minute−1) were measured. Low agreement with a large mean bias of 39 mL kg−1 minute−1 and wide limits of agreement of 8–70 mL kg−1 minute−1 were found. The percentage error of 108% and precision of TD of ±18% resulted in an estimated precision of FloTrac of ±106%. Comparison of changes in COFloTrac with changes in COTD gave a concordance rate of 52% in the four-quadrant plot, and a mean polar angle of -11° with radial limits of agreement of ±61 ° in the polar plot. Mean arterial pressure (MAP) and COFloTrac were positively correlated (r = 0.5, p < 0.0001). No correlation of MAP with COTD was observed. Conclusions and clinical relevanceThe FloTrac system, originally designed for use in humans, neither measured absolute CO in standing horses accurately nor tracked relative changes in CO measured by TD correctly. The false dependence of COFloTrac on arterial blood pressure further discourages the use of this technique in horses.

Non-invasive estimation of cardiovascular parameters using ballistocardiography.

Ballistocardiography is a non-invasive technique to estimate heart function and relative changes in cardiac output. The goal of this study was to establish the relationship between ballistocardiogram (BCG) parameters and changes in cardiovascular parameters. A group of 20 subjects performed three different exercises on a force plate. In this study, we have characterized the significant differences induced by static and dynamic squats, and controlled respiration exercises on BCG parameters such as IJ-amplitude and RJ-time. The dynamic squat exercise induced the largest changes in IJ-amplitude (107-123% higher) and the RJ-time (21-23% lower). Furthermore, the IJ-amplitude of the BCG signal was found to be positively related to the cardiac output.

Non-Invasive Determination of Cardiac Output in Pre-Capillary Pulmonary Hypertension.

BackgroundCardiac output (CO) is a major diagnostic and prognostic factor in pre-capillary pulmonary hypertension (PH). Reference methods for CO determination, like thermodilution (TD), require invasive procedures and allow only steady-state measurements. The Modelflow (MF) method is an appealing technique for this purpose as it allows non-invasive and beat-by-beat determination of CO.MethodsWe aimed to compare CO values obtained simultaneously from non-invasive pulse wave analysis by MF (COMF) and by TD (COTD) to determine its precision and accuracy in pre-capillary PH. The study was performed on 50 patients with pulmonary arterial hypertension (PAH) or chronic thrombo-embolic PH (CTEPH). CO was determined at rest in all patients (n = 50) and during nitric oxide vasoreactivity test, fluid challenge or exercise (n = 48).ResultsBaseline COMF and COTD were 6.18 ± 1.95 and 5.46 ± 1.95 L·min-1, respectively. Accuracy and precision were 0.72 and 1.04 L·min-1, respectively. Limits of agreement (LoA) ranged from -1.32 to 2.76 L·min-1. Percentage error (PE) was ±35.7%. Overall sensitivity and specificity of COMF for directional change were 95.2% and 82.4%, (n = 48) and 93.3% and 100% for directional changes during exercise (n = 16), respectively. After application of a correction factor (1.17 ± 0.25), neither proportional nor fixed bias was found for subsequent CO determination (n = 48). Accuracy was -0.03 L·min−1 and precision 0.61 L·min−1. LoA ranged from -1.23 to 1.17 L·min−1 and PE was ±19.8%.ConclusionsAfter correction against a reference method, MF is precise and accurate enough to determine absolute values and beat-by-beat relative changes of CO in pre-capillary PH.

Effects of one-lung ventilation on thermodilution-derived assessment of cardiac output

Cardiac output (CO) monitoring can be useful in high-risk patients during one-lung ventilation (OLV), but it is unclear whether thermodilution-derived CO monitoring is valid during OLV. Therefore, we compared pulmonary artery (CO(PATD)) and transcardiopulmonary thermodilution (CO(TPTD)) with an experimental reference in a porcine model. CO(PATD) and CO(TPTD) were measured in 23 pigs during double-lung ventilation (DLV) and 15 min after the onset of OLV, during conditions of normovolaemia and after haemorrhage. An ultrasonic flow probe placed around the pulmonary artery (CO(PAFP)) was used for reference. The range of CO in these experiments was 1.5-3 litre min(-1). Normovolaemia: during DLV and conditions of normovolaemia, the mean (95% limits of agreement) bias for CO(PATD) compared with CO(PAFP) was -0.05 (-0.92 and 0.83) litre min(-1), and 0.58 (-0.40 and 1.55) litre min(-1) for CO(TPTD). During OLV, the bias for CO(PATD) remained unchanged at 0.08 (-0.51 and 0.66) litre min(-1), P=0.15, and the bias for CO(TPTD) increased significantly to 0.85 (0.05 and 1.64) litre min(-1), P=0.047. Hypovolaemia: during DLV, the bias for CO(PATD) compared with CO(PAFP) was 0.22 (-0.20 and 0.66) litre min(-1) and for CO(TPTD) was 0.60 (0.12 and 1.10) litre min(-1). There was no significant change of bias during OLV for CO(PATD) [0.30 (-0.10 and 0.70) (litre min(-1)), P=0.25] or bias CO(TPTD) [0.72 (0.21 and 1.22) (litre min(-1)), P=0.14]. Trending ability during OLV, quantified by the mean of angles θ, showed good values for both CO(PATD) (θ=11.2°) and CO(TPTD) (θ=1.3°). CO(TPTD) is, to some extent, affected by OLV, whereas CO(PATD) is unchanged. Nonetheless, both methods provide an acceptable estimation of CO and particularly of relative changes of CO during OLV.

Non-invasive measurement of cardiac output by Finometer in patients with cirrhosis

The Finometer measures haemodynamic parameters including cardiac output (CO) using non-invasive volume-clamp techniques. The aim of this study was to determine the accuracy of the Finometer in hyperdynamic cirrhotic patients using an invasive indicator dilution technique as control. CO was measured in twenty-three patients referred for invasive measurements of the hepatic venous pressure gradient on suspicion of cirrhosis. Invasive measurements of CO were performed using indicator dilution technique (CO(I)) and simultaneous measurements of CO were recorded with the Finometer (CO(F)). In six patients, measurements of CO were performed with invasive technique and the Finometer both before and after beta-blockade using 80 mg of propranolol and the changes in CO (DeltaCO(I) and DeltaCO(F) respectively) were calculated to evaluate the Finometers ability to detect relative changes in CO. Mean CO(I) was 6.1 +/- 1.6 [3.9;9.7] l min(-1) (mean +/- SD [range]) compared to mean CO(F) of 7.2 +/- 2.3 [3.1;11.9] l min(-1). There was a mean difference between CO(F) and CO(I) of 1.0 +/- 1.8 [-2.1;4.0] l min(-1) and 95% confidence interval of [0.2;1.8], P<0.001. In patients with measurements before and after beta-blockade, mean DeltaCO(I) was 1.6 +/- 1.4 [-0.1;3.3] l min(-1) compared to mean DeltaCO(F) of 1.9 +/- 1.3 [0.4;3.8] l min(-1). Mean difference between DeltaCO(F) and DeltaCO(I) was 0.3 +/- 0.3 [-0.2;0.7] l min(-1) with a 95% confidence interval of [-0.1;0.6], P = 0.11. Compared with invasive measurements, the Finometer can be used to measure changes in CO, whereas absolute measurements are associated with higher variation in patients with cirrhosis. The Finometer seems useful for repeated determinations such as in studies of effect of pharmacotherapy.

Estimation of the Aortic Pressure Waveform and Beat-to-Beat Relative Cardiac Output Changes From Multiple Peripheral Artery Pressure Waveforms

We introduce a patient- and time-specific technique to estimate the clinically more relevant aortic pressure (AP) waveform and beat-to-beat relative changes in cardiac output (CO) from multiple peripheral artery pressure (PAP) waveforms distorted by wave reflections. The basic idea of the technique is to first estimate the AP waveform by applying a new multichannel blind system identification method that we have developed (rather than the conventional generalized transfer function) to the PAP waveforms and then estimate the beat-to-beat proportional CO by fitting a Windkessel model to the estimated waveform in which wave distortion should be attenuated. We present an evaluation of the technique with respect to four swine datasets including simultaneous measurements of two peripheral AP waveforms, a reference AP waveform, and reference aortic flow probe CO during diverse hemodynamic interventions. Our results show an overall AP waveform error of 3.5 mmHg and an overall beat-to-beat CO error of 12.9% (after a single CO calibration in each animal). These estimation errors represent substantial improvements compared to those obtained with several alternative PAP waveform analysis techniques. With further successful testing, the new technique may ultimately be employed for automated and less invasive monitoring of central hemodynamics in various cardiovascular patients.

Continuous blood pressure-derived cardiac output monitoring—should we be thinking long term?

Cardiac output, along with cardiac filling pressure, arterial blood pressure, and heart rate, is one of the most important hemodynamic variables to monitor continuously in patients with compromised cardiovascular performance. This point is illustrated strikingly in [Fig. 1][1], which shows an

Reproducibility of circulatory changes to head-up tilt in healthy elderly subjects.

to assess the reproducibility of the cardiovascular responses to head-up tilt including cardiac output, stroke volume and peripheral resistance, in healthy older subjects using non-invasive methods. twenty-five healthy community-dwelling volunteers with a mean age of 69+/-3 years. the subjects underwent head-up tilt table testing on two occasions at an interval of 6 weeks. Pulse interval and blood pressure data were collected, on a beat-to-beat basis using a non-invasive monitor (Finapres, Ohmeda), during 70 degrees head-up tilt table testing and stored for analysis. the pulse interval and blood pressure data for the group were pooled and the relative changes in cardiac output, stroke volume and peripheral resistance were calculated using pulse contour analysis. the systolic blood pressure, pulse interval, cardiac output and stroke volume fell immediately after tilt with a rise in peripheral resistance. These responses were similar, though the baseline systolic blood pressure levels were lower at the second visit (P=0.06). these non-invasively assessed cardiovascular responses to head-up tilt in healthy older subjects show little variation between visits. The reproducibility of the responses in subjects with syncope and autonomic failure warrants further investigation.

Cardiac Output Estimations by Esophageal Doppler Cannot Replace Estimations by the Thermodilution Method in Off-pump Coronary Artery Bypass Surgery Patients

Background: Esophageal doppler is discribed as a non-invasive alternative to cardiac output (CO) estimation by thermodilution, the current bedside “gold standard”. This study was designed to evaluate the accuracy of CO estimations performed by esophageal doppler (EDCO), compared to those obtained using a continuous CO pulmonary flotation catheter (TDCO). Methods: In 16 patients undergoing off-pump coronary artery bypass surgery, CO was measured simultaneously by the esophageal doppler and the thermodilution method, after induction (A), after sternotomy (B), after coronary revascularization (C), and after sternal closure (D). Agreement between the TDCO and EDCO estimations was assessed by analyzing their mean differences and the distribution of these differences. Relative CO changes (percentages of the previous value) was analyzed by the same method. Results: Both absolute CO values and relative CO changes by esophageal doppler showed a considerable scatter compared to those obtained using the thermodilution method. The bias (EDCO-TDCO) between the two mehtods was -0.8 2.7 L/min for A, -0.9 2.5 L/min for B, -0.9 3.6 L/min for C, and -0.6 2.7 (mean 2 SD) L/min for D. On analyzing changes in CO, no significant method bias was found but 2 SD of the bias were 74% for A to B, 100% for B to C, and 83% for C to D. Conclusions: These results suggest that CO estimations by esophageal doppler cannot replace estimations by the thermodilution method in patients undergoing off-pump coronary artery bypass graft surgery.

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

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. 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. 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%. 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.

Airway oximetry improves monitoring of dopamine effects in pediatric cardiac patients.

Simple, preferably noninvasive measurements of cardiac output are useful in pediatric patients receiving inotropic support. Oxygen saturation in pulmonary artery (Svo(2)) gives information about oxygen delivery and demand. Many inotropic drugs influence oxygen consumption. When effects on Svo(2) are studied, after a change in inotropic drug dosage, a change in oxygen consumption needs to be considered to accurately estimate the change in cardiac output. The aim of this investigation was to study whether information on inspired to end-tidal oxygen concentration difference (Fi-eto(2)) in addition to Svo(2) would improve estimation of changes in cardiac output. Prospective observational study of Fi-eto(2), Svo(2), and oxygen saturation from central vein (Scvco(2)) for measurements of circulatory and metabolic effects of changes in dopamine dosage. Intensive care unit in a children's hospital. Twenty patients (age 4 days to 98 months) were studied after cardiac surgery. Dopamine was administered in doses of 5, 10, 0, and 5 microg x kg(-1) x min(-1), 20 mins on each level. Cardiac output, measured with thermodilution, oxygen saturation from systemic artery (Sao(2)), Svo(2), and Scvco(2) were measured at 15 mins on each dopamine dose. Oxygen consumption was calculated by using the Fick equation. Fi-eto(2) was measured continuously with a paramagnetic oxygen analyzer. Both cardiac output and oxygen consumption were affected by changes in dopamine dosage. Relative changes in cardiac output were poorly correlated to the change in 1/Sa-vo(2) (r(2) =.54). Using Fi-eto(2) improved correlation between changes in cardiac output and changes in Fi-eto(2)/Sa-vo(2) (r(2) =.72). When Svo(2) was replaced by Scvco(2), the correlation between changes in cardiac output and changes in Fi-eto(2)/Sa-cvco(2) was only slightly altered (r(2) =.69). Dopamine affects oxygen consumption as well as cardiac output. The accuracy of Svo(2)-based estimations of changes in cardiac output after dopamine is enhanced if changes in Fi-eto(2) are also considered. The more easily achievable Scvco(2) gave equivalent information as Svo(2).

Abnormal diurnal variation of blood pressure, cardiac output, and vascular resistance in cardiac transplant recipients.

An attenuated or absent nocturnal decline in blood pressure has repeatedly been documented in cardiac transplant recipients. The present study was aimed at investigating the hemodynamic mechanism underlying this abnormality. In 23 cardiac transplant recipients (11 to 36 months after transplantation) and in 23 control subjects matched for age and 24-hour mean arterial pressure, invasive 24-hour ambulatory blood pressure was measured by means of the Oxford technique. Beat-to-beat relative values of stroke volume were determined by means of a pulse-contour method, and relative changes of cardiac output (stroke volume x heart rate) and total peripheral vascular resistance (blood pressure/cardiac output) over the 24-hour period were calculated. The nocturnal decline in blood pressure was 20 +/- 8% (mean +/- SD) in control subjects but only 5 +/- 9% (P < .001) in cardiac transplant recipients. In control subjects, the nocturnal decline in blood pressure was associated with a nocturnal fall in cardiac output of 24 +/- 13%, whereas vascular resistance compared with daytime value did not change. The small nocturnal decline in blood pressure in cardiac transplant recipients was associated with an attenuated nocturnal fall in cardiac output of 14 +/- 12% (P < .05 versus control subjects). In addition, vascular resistance compared with daytime value was increased by 9 +/- 9% (P < .05) during the night. Both in cardiac transplant recipients and in control subjects, the nocturnal changes in blood pressure were correlated with the nocturnal changes in cardiac output but not with the nocturnal changes in total peripheral vascular resistance. This study confirms the attenuated nocturnal fall in blood pressure in cardiac transplant recipients. Hemodynamically, this attenuated blood pressure decline is characterized by a reduced nocturnal fall in cardiac output, and it is associated with a nocturnal increase in vascular resistance.

Reliability of a New Generation Transesophageal Doppler Device for Cardiac Output Monitoring

A new generation continuous-wave transesophageal Doppler (TED) device for cardiac output (CO) monitoring (Accucom 2, Datascope), which displays aortic blood flow velocity in real time, was evaluated by 140 simultaneous comparisons with thermodilution (TD) in 16 patients early after coronary artery bypass surgery. The aim was to determine whether this technologic advancement improves the accuracy of COTED assessment. Absolute COTED values showed a considerable scatter as compared to COTD [COTED = 1.77 + 0.75.COTD (L/min), r = 0.52]. The bias, i.e., the mean of individual CO differences (COTD-COTED) was -0.37 +/- 1.70 L/min (SD). In contrast, relative CO changes (delta CO, % of preceding value) showed a satisfactory agreement between TED and TD [delta COTED = 1.04 + 0.91.delta COTD (%), r = 0.84, n = 124], the bias (delta COTD-delta COTED) being -0.66 +/- 9.72%. In 8 of 124 situations (6.45%), however, significant COTED changes opposite in direction to that of significant COTD changes occurred. This frequency was significantly greater (P < 0.01) than the ideal frequency of 0%. The agreement between delta COTD and delta COTED improved (P < 0.05) when the aortic diameter changes induced by changes in mean arterial pressure were considered [delta COTEDMAPC = 1.10 + 0.95.delta COTD (%), r = 0.87, n = 124]. Compared with previous results, the reliability of the second generation device to monitor relative CO changes was considerably improved. Provided that the aortic blood flow velocity signal was stable and free from any disturbances, the second generation TED device may be regarded acceptable for CO trend monitoring in sedated, paralyzed patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic measurement of cardiac output in man using mitral annulus method.

The mitral inflow method of measuring cardiac output with pulsed Doppler two-dimensional echocardiography was developed and validated against the thermodilution technique in 42 patients. A mitral inflow method combined the velocity of left ventricular inflow at the mitral annulus (apical long-axis view) with the cross-sectional area of the annulus calculated from its diameter (parasternal long-axis view). A good correlation was observed between thermodilution and Doppler measurements of cardiac output (r = 0.93). The ratio of Doppler measurements to thermodilution measurements will be between 0.76 and 1.15 for about 95% of cases. There was a good correlation between percentage change in thermal cardiac output and those in Doppler cardiac output (r = 0.95); the limits of agreement were -11.5% to 10.5%, suggesting that this method can be most useful for assessing relative changes in cardiac output.

Noninvasive versus invasive assessment of cardiac output after cardiac surgery: clinical validation

The accuracy of noninvasive cardiac output (CO) measurement techniques, such as electrical bioimpedance (BIO), suprasternal continuous-wave Doppler (CWD), pulsed-wave Doppler (PWD), and transesophageal continuous-wave Doppler (TED) ultrasound has been variably judged in recent years. In addition, clinical comparisons are hampered by the fact that there is no generally accepted gold standard in CO measurement. After coronary artery bypass surgery in 25 patients, CO was simultaneously determined by invasive standard techniques (thermodilution [TD] and Fick methods) plus BID, CWD, PWD, and TED. There was an excellent agreement found between TD and the Fick method (CO F = 0.13 + 1.01 · CO TD; r = 0.96; n = 99). Thermodilution was thus chosen to be the reference method. Bioimpedance underestimated CO TD (CO BIO = 0.47 + 0.60 · CO TD; r = 0.78; n = 111). Allowing physiological ejection times only led to an improved agreement between BIO and TD (CO BIO = 0.05 + 0.69 · CO TD; r = 0.82; n = 79), but BID still significantly underestimated CO TD ( P < 0.0005). Using physiologic ejection times during COcwO determination reduced the scatter of data as compared with TD; however, CWD still considerably overestimated CO TD, when CO CWD computation was based on the echocardiographic aortic diameter (ECHO) (CO CWD ECHO = 0.79 + 1.40 · CO TD; r = 0.84; n = 52). With the surgical aortic diameter (SURG), the agreement improved (CO CWD SURG = 0.75 + 1.16 · CO TD; r = 0.89; n = 44), but overestimation of COTD remained significant ( P < 0.05). Irrespective of the aortic diameter, CO PWD values showed a considerable scatter of data compared with CO TD (CO PWD ECHO = 1.26 + 0.60 · CO TD; r = 0.62; n = 64 and CO PWD SURG = 1.42 + 0.41 CO TD; r = 0.47; n = 61). Correlation of absolute CO TED values to thermodilution depended on the method used for calibration. All investigated noninvasive CO measurement techniques unreliably measured relative CO changes. Despite its invasiveness, TD remains the method of choice for accurate CO determination in adult patients following cardiac surgery.

Monitoring of cardiac output and cardiac work during anaesthesia by means of pulsed ultrasound Doppler

During anaesthesia haemodynamic measurements were performed with pulsed ultrasound Doppler in six patients with a Swan-Ganz catheter. Cardiac output (CO), heart rate (HR), arterial blood pressure (AP), systemic vascular resistance (SVR) and left cardiac work (LCW) were measured simultaneously with the velocity measurements of the bloodstream in the ascending aorta. Six to fourteen (median 9) simultaneous measurements were done in each patient. Sixty-two measurements were made. The velocity (V) and the product of velocity and heart rate (VHR) were compared with CO in order to establish a non-invasive index of the cardiac output. The product of velocity, the heart rate and the arterial blood pressure (VHRAP) was compared with LCW, showing a good correlation between VHR and CO (V = maximum velocity) (rho = median 0.85), as was the case between VHRAP and LCW (rho = 0.88). Furthermore, a negative correlation between V and SVR was found, illustrating that the velocity of the bloodstream in the aorta obviously depends on the afterload. It is concluded that pulsed ultrasound Doppler in combination with HR and AP can measure relative changes in CO and LCW.

Effects of mechanical ventilation on the measurement of cardiac output by thermodilution.

Phasic variation in cardiac output (CO) of 10-50% during mechanical ventilation was documented in dogs, and in 1 patient by injection of thermal indicator at 1-sec intervals throughout the ventilation cycle. Measured flow variation increased with inflation pressure when other variables were unchanged, and was not influenced to a significant degree by the injection of iced vs room temperature injectate. Such variation can occur in adult patients requiring only minimally increased airway pressure for ventilation. The technique of injecting indicator at a particular moment of the ventilation cycle is not appropriate to monitor absolute or even relative changes in CO because of occasional changes in the phase relation between the ventilation cycle and the flow variation. The mean CO by thermodilution technique is approximately best by the mean of values taken at regularly spaced intervals through the ventilation cycle.