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.

Validation of continuous thermodilution cardiac output in critically ill patients with analysis of systematic errors.

PURPOSE: Bolus thermodilution cardiac output (BCO) measurements are affected by variations in injectate volume, rate, and temperature. These variations are eliminated when CO is measured by a continuous automated thermal technique (CCO). Further, CCO eliminates the need for fluid boluses, reduces contamination risk, requires no operator, and provides a continuous CO trend. We prospectively evaluated CCO versus BCO in a population of critically ill adults with low, normal, and high CO states. We sought to discern any systematic effects of temperature fluctuations or signal-to-noise-ratios (SNR) on disparities between BCO and CCO measurements and also sought to assess the relative cost effectiveness of the CCO system. MATERIALS AND METHODS: Pulmonary artery catheterizations were performed in a convenience sample of 20 patients over 6 months. BCO data were obtained using a standardized protocol. Three bolus injections of 5% dextrose were given when each CO was within 10% of the median before averaging; otherwise five boluses were given, with the high and low values eliminated before averaging. Injectates were administered randomly through the respiratory cycle and at 1-minute intervals. CCO measurements were recorded from a Vigilance monitor pre and post BCO measurements, yielding an average CCO value. Also recorded were pre- and post-core temperatures and SNR during the first CCO measurement. Cost data included estimates of operator time for BCO determinations as well as costs of Intellicath (Baxter-Edwards, Irvine, CA) pulmonary artery catheters, Vigilance (Baxter-Edwards, Irvine, CA) monitors, conventional catheters, and injectates. RESULTS: Of the 20 patients, 15 were mechanically ventilated. A total of 306 paired CO values were obtained for analysis. CCO ranged from 2.5 to 14.4 L/min and BCO from 2.4 to 13.3 L/min. Absolute differences between CCO and BCO measurements increased with increasing CO, but percentage differences did not. Of the paired values, 77% were within 1 L/min of one another. Temperature instability and SNR independently had weak correlations with CCO/BCO disparities. The Vigilance system had a slightly higher net cost than conventional BCO, although no economical value was assigned to the clinical usefulness of continuous, as opposed to intermittent, CO monitoring. CONCLUSIONS: Continuous CO is a reliable and cost-effective alternative to bolus thermodilution CO for critically ill patients in low, normal, and high CO states.

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.

Cardiac output measurement in critical care patients: Thoracic Electrical Bioimpedance versus thermodilution.

Thoracic Electrical Bioimpedance (TEB) is a method for measuring cardiac performance which is noninvasive, continuous, has minimal technical requirements, and no patient risk. We used a commercially available TEB device to measure cardiac output in patients with thermodilution catheters in place. We compared the cardiac output measurements for the two modalities. We also compared the average hospital cost for initial cardiac assessment using the two techniques. The mean difference between the two cardiac output measurements was small (0.23 +/- 0.56) and not affected by the magnitude of the cardiac output readings. There was a strong correlation between COTD and COTEB (r = 0.91) and the regression slope was 0.91 with a Y intercept of 0.76. Cost analysis demonstrated that the use of TEB was approximately $600 less than thermodilution. Thoracic electrical bioimpedance measurement of cardiac output may offer a valuable alternative to the invasive measurement of the thermodilution catheter.