Pulsatile flow simulator for comparison of cardiac output measurements by electromagnetic flow meter and thermodilution

Abstract

This study examined a pulsatile flow simulator for the purpose of evaluating two measurement devices, an extracorporeal flow probe with an electromagnetic flow meter and several thermodilution catheters. We measured the performance of these devices in a range of low to high flows. Using either saline or blood as a perfusate, we obtained different results with these fluids (p less than 0.001). Each catheter behaved in a linear manner, although variation occurred among the catheters with both saline (minimum slope 1.090, maximum slope 1.190) and blood (minimum slope 1.107, maximum slope 1.154). An increase in rate and stroke volumes of the simulator did not demonstrate an identifiable trend in error. The thermodilution catheters were most accurate at 5.0 L/min irrespective of rate, stroke volume, or perfusate used. In contrast, the electromagnetic flow meter accurately represented flows across the wide range of outputs examined (2.4 to 10.7 L/min). (Slope with saline 1.091, slope with blood 1.080) Throughout the range of flow, the flow meter gave a calibration line 5% higher with blood than with saline. The results indicate that accurate measurement of pulsatile blood flow can be achieved in vitro with an electromagnetic flow meter using saline as a perfusate, provided a correction factor is determined and applied to convert values for saline to accurate values for blood.

Different dosages of dobutamine in septic shock patients: determining oxygen consumption with a metabolic monitor integrated in a ventilator

“…The phenomenon of increased scatter of data in our study at the low and high values (Fig. 2) could be caused by a greater variability of CO measurements at these levels of CO [9]. The effects of intervention (fluid loading catecholamine support) on DO 2 and VO 2 were studied in critically ill patients.…”

“…The determination of VO 2,Fick contains the potential risk of measurement errors when determining cardiac output (CO), oxygen and hemoglobin concentration and oxygen(O 2 ) saturation of hemoglobin [8]. In hypodynamic and hyperdynamic shock the measurement error using this technique may be above 10 % [9]. Factors like volume and temperature of injectant in the process of obtaining CO may also influence the accuracy of this method [10].…”

Accuracy of the thermodilution method in estimating high flow - an in vitro study

“…In addition, the heat capacity of the tubing and chamber is different than that of cardiac and pulmonary tissues. Finally, the difference in specific heat and specific gravity of the water in the hydraulic model as compared to blood and saline or 5% dextrose used in uivo results in overestimation of cardiac output by a factor of 1.08, a significant factor in some studies (Hosie 1962;Jebson and Karkow 1986).…”

“…Accuracy of thermodilution as a technique for measuring flow has been tested in in uitro models using saline (Jebson and Karkow 1986), distilled water (Pavek et al 1964), tap water (Moodie et al 1978;Norris et al 1986;Powner and Snyder 1978), and blood (Bilfinger, Lin and Anagostopoulos 1982;Jebson and Karkow 1986;MacKenzie et al 1986) as the perfusate under pulsatile (Cropp and Burton 1966;Jebson and Karkow 1986;Powner and Snyder 1978;) or constant (Bilfinger et al 1982;Moodie et al 1978;Norris et al 1986) flow conditions. Thermodilution values were compared to flow measured volumetrically (Cropp and Burton 1966;Forrester et al 1972;MacKenzie et al 1986) or using flow meters (Cropp and Burton 1966;Forrester et al 1972;Jebson and Karkow 1986). The range of flows evaluated in these studies was 0.13-14.2 L/min with injectate volumes of 1-10 ml.…”

“…In some instances thermodilution cardiac output computers are used to estimate magnitude of blood flow substantially greater than the original sphere of investigator interest. Results of previous studies suggest inaccuracy of flow measurement increases with increasing fluid flow (Jebson and Karkow 1986;Powner and Snyder 1978). Few studies have been conducted to characterize blood flow rates in the range produced by exercising humans or in large animals (such as horses) at rest (Dunlop et al 1988;Muir, Skarda and Milne 1976).…”