Non-invasive assessment of cardiac output in children.

BACKGROUND: Stroke distance, the systolic velocity integral of aortic blood flow, is a linear analogue of stroke volume; its product with heart rate is minute distance, analogous to cardiac output. OBJECTIVE: To investigate the feasibility of assessing cardiac output in children with a simple non-invasive Doppler ultrasound technique, and to determine the normal range of values. METHODS: Peak aortic blood velocity, stroke distance, and minute distance were measured through the suprasternal window in 166 children (mean age 9.6 years, range 2-14) using a portable non-imaging Doppler ultrasound instrument. RESULTS: The technique was well tolerated by all the children participating. Mean peak aortic blood velocity was 138 cm/s and was independent of age. Mean stroke distance was 31.8 cm and showed a small but significant increase with age; mean minute distance was 2490 cm and fell with age, as did heart rate. CONCLUSIONS: Suprasternal Doppler ultrasound measurement of stroke distance is a convenient, well tolerated, non-invasive technique for the assessment of cardiac output in children. The normal range of values during childhood has been established. The technique has great potential for assessing hypovolaemia in children.     

Non-invasive cardiac output monitoring by aortic blood flow measurement with the Dynemo 3000

The operating principles and methods for the continuous determination of aortic blood flow (ABF) with the Dynemo 3000 system are described in detail. The system uses a novel transesophageal ultrasonic Echo-Doppler probe simultaneously to measure aortic diameter and blood flow velocity at the same anatomic level, in real-time. Non-invasive ABF measurement is combined with vital sign data from standard monitors to provide a composite hemodynamicprofile including volume, after load and contractility data used by the physician to optimize therapy. A review of the clinical validation and comparison to thermo dilution measurements showing a significant positive correlation over a wide range of clinical flow situations is also briefly presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-invasive estimation of cardiac output in critical care patients

Objective.This study was carried out to compare cardiac output measurements determined by thermodilution and by Portapres, a non-invasive system. Design, patients and setting.Eighty-seven non-invasive blood pressure measurements were performed in 46 patients in our critical care unit utilising the new, non-invasive Portapres system. Cardiac output values were obtained from these blood pressure values using an aortic impendance model and compared to cardiac output values estimated by the thermodilution technique.Measurements and main results.Statistically significant (p< 0.01) differences (2.3 l/min; limits of agreement ± 5l/min) were noted between invasive and non-invasive cardiac output measurements. Differences in measured cardiac outputs increased for patients receiving catecholamine therapy, in patients with hemodynamic instability(e.g., sepsis and cardiac insufficiency), in patients with artificial ventilation, in patients with long duration of intensive care, in younger(<60 yr) patients and in women. We found no influence of the body mass index (BMI) on the accuracy of Portapres results. In only one single subgroup,10 patients with pulmonary diseases, Portapres measurements were not statistically significant different from reference results. Conclusions.To date, Portapres measurements cannot replace thermodilution cardiac output estimations. Fluctuations of finger arterial perfusion due to hemodynamic instability, hypothermia and catecholamines may be responsible for problems of Portapres use in critically ill patients. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-invasive ultrasonic cardiac output measurement in intensive care unit

A non-invasive method for measuring cardiac output utilizing M-mode echography and pulsed Doppler ultrasound is described. Measurements were obtained in 26 of 29 randomly selected, mechanically ventilated patients. These values were compared with simultaneously measured cardiac outputs by thermodilution. There was a statistically significant linear relationship between Cardiac Output measured by Doppler (DCO) and Thermodilution (TDCO): DCO = 0.86 TDCO + 0.29 1/min (r = 0.96, N = 26, SEE = 0.45 1/min) over the range of 1.75-8.5 1/ min. DCO had the additional advantage of measuring peak flow velocity and maximal blood flow acceleration during early systole, indices of left ventricular pumping ability. Ultrasonic monitoring of cardiac output may be an important supplement to invasive methods in critical care.     

Semicontinuous cardiac output monitoring using a neural network.

OBJECTIVES: This study compared 2-mL bolus thermodilution cardiac output measurements with standard 10-mL bolus measurements. DESIGN: Cardiac output was measured with the new 2-mL bolus technique and the 10-mL standard thermodilution technique in a perspective series. We describe a system that automatically cools and injects 2-mL boluses of saline into a standard pulmonary artery catheter. It uses a Peltier effect solid-state cooler and pneumatically driven syringe injector to measure cardiac output once per minute. SETTING: Animal laboratory. ANIMALS: Eight adult Duroc swine weighing between 38.0 and 57.5 kg. INTERVENTIONS: Once each minute, 2 mL of cooled 5% dextrose was injected through the pulmonary catheter. Once every 8 mins, four sequential measurements of cardiac output were made using 10-mL injections. MEASUREMENTS AND MAIN RESULTS: A total of 1249 paired waveforms were processed with both a conventional algorithm and with a neural network. For the conventional algorithm, the correlation coefficient was r2 = .92 and the SD of the difference was 1.30 L/min. For the neural network, the correlation coefficient was r2 = .94 and the SD of the difference was 0.88 L/min. Output filtering improved the results in both cases. CONCLUSION: Neural networks accurately derive cardiac output from 2-mL bolus thermodilution injections, allowing cardiac output to be monitored automatically once per minute in many patients. The technique is convenient and uses standard low-cost catheters.     

Less-invasive cardiac output monitoring by earpiece densitometry

Cardiac output was measured by thermodilution and ear densitometry in surgical ICU patients who had pulmonary arterial catheters. Overall comparison based on 56 sets of triplicate measurements revealed a correlation coefficient (r) of 0.76 between the two techniques. Although ear densitometry was more accurate with injection via the antecubital vein (r = 0.88) vs. more distal injection (r = 0.67), these data suggest that this technique lacks the accuracy for clinical application.     

Comparison of an advanced minimally invasive cardiac output monitoring with a continuous invasive cardiac output monitoring during lung transplantation

The aim of this study was to compare a continuous non-calibrated left heart cardiac index (CI) measurement by arterial waveform analysis (FloTrac^®/Vigileo^®) with a continuous calibrated right heart CI measurement by pulmonary artery thermodilution (CCOmbo-PAC^®/Vigilance II^®) for hemodynamic monitoring during lung transplantation. CI was measured simultaneously by both techniques in 13 consecutive lung transplants (n = 4 single-lung transplants, n = 9 sequential double-lung transplants) at distinct time points perioperatively. Linear regression analysis and Bland–Altman analysis with percentage error calculation were used for statistical comparison of CI measurements by both techniques. In this study the FloTrac^® system underestimated the CI in comparison with the continuous pulmonary arterial thermodilution (p < 0.000). For all measurement pairs we calculated a bias of ?0.55 l/min/m² with limits of agreement between ?2.31 and 1.21 l/min/m² and a percentage error of 55 %. The overall correlations before clamping a branch oft the pulmonary artery (percentage error 41 %) and during the clamping periods of a branch oft the pulmonary artery (percentage error 66 %) failed to reached the required percentage error of less than 30 %. We found good agreement of both CI measurements techniques only during the measurement point “15 min after starting the second one-lung ventilation period” (percentage error 30 %). No agreement was found during all other measurement points. This pilot study shows for the first time that the CI of the FloTrac^® system is not comparable with the continuous pulmonary-artery thermodilution during lung transplantation including the time periods without clamping a branch of the pulmonary artery. Arterial waveform and continuous pulmonary artery thermodilution are, therefore, not interchangeable during these complex operations.     

Non-invasive cardiac output and oxygen delivery measurement in an infant with critical anemia

Objective

To assess the combination of a non-invasive blood oxygen content (CaO₂) monitor and a non-invasive cardiac output (CO) monitor to continuously measure oxygen delivery (DO₂; DO₂ = CaO₂ × CO).

Methods

DO₂ was assessed during blood transfusions in an infant with acute hemolytic anemia following admission (~48 h). CaO₂ was measured by Pulse Co-Oximetry, which also provides estimates of hemoglobin (Hgb) concentration and percent oxygen saturation. CO was measured by Electrical Velocimetry, which also provides an estimate of stroke volume (SV). Lactate levels, an indirect measure of adequate DO₂, were assessed during the initial 8 h following admission.

Results

Incremental blood transfusions during the first 36 h increased Hgb from 2.7 to 9.5 g/dL during which time heart rate (HR) normalized from 156 to 115 beats/min. Lactate levels decreased from 20 to 0.8 mmol/L in the first 7 h. Non-invasive Hgb and CaO₂ measurements were well correlated with invasive Hgb and CaO₂ measures (r ² = 0.88; P = 0.019; r ² = 0.86; P = 0.0074, respectively). CO decreased from 2.47 ± 0.06 to 1.28 ± 0.02 L/min and SV decreased from 15.9 ± 0.4 to 11.1 ± 0.2 mL/beat. Mean arterial blood pressure was stable throughout the admission with systemic vascular resistance increasing from 407.6 ± 15.2 to 887.7 ± 30.1 dynes-s/cm⁵. DO₂ was estimated to increase from 120.2 ± 18.9 to 182.4 ± 5.6 mL O₂/min.

Conclusions

Non-invasive contin- uous CO and CaO₂ monitors are shown in this single case to provide continuous DO₂ measurement. The ability to assess DO₂ may improve hemodynamic monitoring during goal directed therapies.     

Continuous cardiac output and mixed venous oxygen saturation monitoring

Continuous assessment of cardiac output and Svo₂ in the critically ill may be helpful in both the monitoring variations in the patient's cardiovascular state and in determining the efficacy of therapy.

Commercially available continuous cardiac output (CCO) monitoring systems are based on the pulsed warm thermodilution technique. In vitro validation studies have demonstrated that this method provides higher accuracy and greater resistance to thermal noise than standard bolus thermodilution techniques. Numerous clinical studies comparing bolus with continuous thermodilution techniques have shown this technique similarly accurate to track each other and to have negligible bias between them. The comparison between continuous thermal and other cardiac output methods also demonstrates good precision of the continuous thermal technique.

Accuracy of continuous oximetry monitoring using reflectance oximetry via fiberoptics has been assessed both in vitro and in vivo. Most of the studies testing agreement between continuous Svo₂ measurements and pulmonary arterial blood samples measured by standard oximetry have shown good correlation. Continuous Svo₂ monitoring is often used in the management of critically ill patients. The most recently designed pulmonary artery catheters are now able to simultaneously measure either Svo₂ and CCO or Svo₂ and right ventricular ejection fraction. This ability to view simultaneous trends of Svo₂ and right ventricular performance parameters will probably allow the clinician to graphically see the impact of volume loading or inotropic therapy over time, as well as the influence of multiple factors, including right ventricular dysfunction, on Svo₂. However, the cost-effectiveness of new pulmonary artery catheters application remains still questionable because no established utility or therapeutic guidelines are available.     

Non-invasive measurement of cardiac output in patients with acute lung injury using the carbon dioxide rebreathing method.

STUDY OBJECTIVE: To compare measurement of cardiac output by the CO2 rebreathing method with the thermodilution cardiac output technique in mechanically ventilated patients with acute lung injury. DESIGN: Prospective study comparing two methods of cardiac output measurement in 22 consecutive patients with acute lung injury. SETTING: Intensive care unit of a university hospital. PATIENTS: Twenty-two mechanically ventilated patients with acute lung injury monitored with systemic and pulmonary artery catheters. MEASUREMENTS AND RESULTS: Cardiac output was determined using both the thermodilution technique and an indirect CO2 Fick method. Veno-arterial CO2 content difference was calculated from an estimated mixed venous CO2 tension obtained by an equilibrium CO2 rebreathing method and measured arterial CO2 tension. Carbon dioxide pressure was converted to content using the equation of the CO2 dissociation curve described by McHardy. A wide range of cardiac index was studied from 2.7-5.7 l/min/m2. There was a significant correlation between thermodilution and CO2 rebreathing methods (r2 = 0.82, p < 0.01). The mean difference between the CO2 rebreathing method and thermodilution was 0.05 l/min/m2, with a standard deviation for the bias of 0.38 l/min/m2. CONCLUSION: Our results suggest that the CO2 rebreathing method may be a reliable non-invasive technique to determine cardiac output in mechanically ventilated patients with acute lung injury.     

Continuous cardiac output monitoring with pulse contour analysis: a comparison with lithium indicator dilution cardiac output measurement

OBJECTIVE: Pulse contour analysis can be used to provide beat-to-beat cardiac output (CO) measurement. The current study sought to evaluate this technique by comparing its results with lithium dilution CO (LiCO) measurements. DESIGN: Prospective, observational study. SETTING: Surgical intensive care unit. PATIENTS: Twenty-two patients after cardiac or major noncardiac surgery. MEASUREMENTS: After initial calibration of the pulse contour CO (PCO) method, CO was measured by PCO and by LiCO methods at 4, 8, 16, and 24 hrs. Recalibration of PCO was performed every 8 hrs. The systemic vascular resistance and dynamic response characteristics of the arterial catheter-transducer system were measured at each time point to determine whether these influenced the agreement between PCO and LiCO methods. MAIN RESULTS: There was an excellent correlation between methods (r = .94). Bias was small (-0.005 L/min), and clinically acceptable limits of agreement were demonstrated between techniques. Although many catheter-transducer systems had poor dynamic response characteristics, this did not influence the level of agreement between the two techniques. An increase in systemic vascular resistance between two time points did tend to cause overestimation of LiCO by the PCO. CONCLUSIONS: PCO measurement compared well with the lithium dilution method and can be considered an accurate technique for measuring beat-to-beat CO with limited risk to the patient.     

神经外科围术期心输出量测定对心功能评估的意义

目的:研究二氧化碳部分重复吸入法测量心输出量(partialCO2re-brethingcardiacoutput,RBCO)与经食管超声多普勒法测量心输出量(transesophagealdopplercardiacoutput,TECO)用于监测神经外科患者围术期心输出量的相关性,比较其应用可靠性。方法:选择2003-03/11首都医科大学附属北京天坛医院麻醉科29例择期颅脑手术患者,麻醉诱导气管内插管后接呼吸机行间歇正压通气。分别于手术开始、颅骨钻孔、开骨瓣、剪开硬膜、取肿瘤、止血及手术结束时各时点采用RBCO和TECO同步监测术中心输出量的变化。采用直线回归方法分析两种测定方法的相关性。结果:RBCO和TECO结果有显著相关性(r=0.78,P<0.01),回归方程为RBCO=0.88TECO+0.63。结论:RBCO方法简便、无创,与TECO测定结果具有良好的相关性。     

Testing the safety of baxter continuous cardiac output monitoring system

The safety of a new continuous cardiac output monitoring system, recently introduced by Baxter Healthcare Corporation's Edwards Critical-Care Division, was evaluated in normal sheep. The study compared the biocompatibility and safety of the Vigilance® CCO Monitoring System, which employs a continuous cardiac output (CCO) catheter with Baxter Edwards' standard Paceport? pulmonary artery catheter. The CCO catheter, which monitors hemodynamic pressures and provides continuons measurement of cardiac output based on the thermodilution principle, contains a thermal filament that is powered and controlled by a unique cardiac output monitor. Parameters were measured periodically in conscious animals and complete necropsies were performed alter each study. Time Control, Paceport?, and four CCO groups were studied. Selected groups were studied for 3 days (acute), 7 days (subacute), and/or 4 weeks after 3 days of continuons use (recovery). Results showed no significant differences between the CCO and Paceport? catheters in any of the parameters studied. On gross pathology, observations were similar. The only difference between catheters were microscopie findings of focal subendothelial or subendocardial changes correlated with areas that could have corne into contact with the CCO catheter. In acute groups, these changes consisted of a localized myofiber degeneration or necrosis, while in subacute and recovery groups, consisted only of fibrosis. None of the changes were clinically significant. Thus, the CCO catheter, used in conjunction with the Vigilance® CCO Monitoring System, appears to pose no additional risk over a standard Paceport? catheter in normal sheep after continuons use for up to 7 days.