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PubMed1997

Noninvasive determination of cardiac output in a model of acute lung injury.

OBJECTIVE: To examine the utility of single breath CO2 analysis as a noninvasive measure of cardiac output in a model of acute lung injury. SETTING: An animal laboratory in a university-affiliated medical center. DESIGN: A prospective, animal cohort study comparing 21 parameters derived from single breath CO2 analysis with cardiac output determined by an ultrasonic flow probe. SUBJECTS: Six adult sheep with saline lavage-induced acute lung injury. INTERVENTIONS: Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (PaO2 of < 100 torr [< 13.32 kPa] on an FIO2 of 1.0). Cardiac output was manipulated by successive injections of an hydraulic constrictor placed around the inferior vena cava and measured using an ultrasonic flow probe. Twenty-one derived components of the CO2 expirogram were evaluated as predictors of cardiac output. MEASUREMENTS AND MAIN RESULTS: Thirty-eight measurements of cardiac output were available for comparison with derived variables from the CO2 expirogam. Stepwise linear regression identified four variables for the equation predicting cardiac output: a) PaO2/FIO2 ratio; b) the angle between the slope lines for phases II and III divided by the tidal volume; c) mixed expired CO2 tension; and d) physiologic deadspace to tidal volume ratio. The multivariate equation was highly statistically significant and explained 80% of the variance (adjusted R2 = .80, p < .0001). The blas and precision of the calculated cardiac output were .00 and .38, respectively. The mean percent difference for the cardiac output estimates derived from the single breath CO2 analysis station was -0.01%. CONCLUSIONS: Our results indicate that changes in cardiac output can be determined using components of the CO2 expirogram with a high degree of reliability in animals with induced acute lung injury. Specifically, the use of four parameters derived from a plot of expired CO2 concentration vs. expired volume predict changes in cardiac output in adult sheep with induced lung injury with an adjusted coefficient of determination of .80. Prospective application of this technology in the clinical setting with the rapidly changing physiology that is characteristic of the acutely ill patient will be essential in determining the clinical usefulness of single breath CO2 analysis as a noninvasive measure of cardiac output.

Acute Disease↗
PubMed1989

A comparison of thermodilution and pulsed Doppler cardiac output measurement in critically ill children.

To evaluate the pulsed Doppler cardiac output method as a noninvasive means for determining cardiac output in critically ill children, we performed paired pulsed Doppler and thermodilution cardiac output determinations in 17 critically ill children. Commercially available equipment, specifically designed for this purpose, was employed. Forty paired thermodilution and pulsed Doppler determinations were made. There was a significant correlation between the two measurements (pulsed Doppler = 0.84 thermodilution + 0.39; r = 0.79, p less than 0.01). The ranges of thermodilution measurements (1.02 to 6.26 L/min; median 2.77 L/min) and pulsed Doppler measurements (1.13 to 6.35 L/min; median 2.57 L/min) were not different (p = 0.25). However, differences between individual paired thermodilution and pulsed Doppler measurements were large (-3.13 to 2.03 L/min; median 0.12 L/min), and the percentage difference between individual paired thermodilution and pulsed Doppler measurements ranged from 0.41% to 102.5% (median 12.7%). A discrepancy of 15% or more between thermodilution and pulsed Doppler was encountered in 18 (45%) of 40 of paired measurements (95% confidence interval: 29% to 61%), and one fourth of the paired measurements differed by more than 25%. We conclude that, as employed in this study, pulsed Doppler cardiac output determination is not sufficiently representative of the thermodilution output to be employed for hemodynamic monitoring in critically ill children.

Adolescent↗
PubMed1983

Cardiac output and organ blood flow in young rabbits during intermittent positive-pressure ventilation.

Cardiac output and organ blood flow were measured by a microsphere technique in three groups of healthy young rabbits. In one group, animals were subjected to light sedation and intermittent positive-pressure ventilation. Control animals in a second group were sedated but not ventilated. In a third group, animals were conscious and breathing spontaneously. Cardiac output increased significantly (p less than 0.05) in conscious controls and in one measurement in anesthetized controls. It did not change in ventilated rabbits. Blood flow to the brain increased during study in all three groups and to the eye in both control groups. These elevations in cardiac output and cerebral blood flow were attributed to arousal. Blood flow to the kidney decreased in both anesthetized groups. The blood flow to skin, muscle, ileum and colon decreased significantly in the ventilated animals though not in the anesthetized controls. In both groups, similar reductions were found in the fractional distribution of cardiac output to these areas. It was concluded that ventilation at low pressure had no effect on cardiac output. The occurrence of redistribution of the circulation was deduced from the parallel reductions of regional blood flows and fractions of cardiac output received by some organs together with preservation of cerebral blood flow, though it was obscured in the two control groups by simultaneous increases in cardiac output. The circumstances suggested that this redistribution was due to disturbed homeostasis from arousal. Implications for the newborn were discussed.

Animals↗
PubMed1995

Multiplane transesophageal echocardiographic doppler imaging accurately determines cardiac output measurements in critically ill patients.

OBJECTIVES: To compare cardiac output and stroke volume measured by multiplane transesophageal Doppler echocardiography with that measured by the thermodilution technique. DESIGN: Prospective direct comparison of paired measurements by both techniques in each patient. SETTING: Cardiac surgery and myocardial infarction intensive care units. PATIENTS: Twenty-nine patients, mean age (+/- SD) 67 +/- 8 years. Nineteen had undergone open heart surgery and 10 had suffered acute myocardial infarction. METHODS: Cardiac output and stroke volume were measured simultaneously by the thermodilution technique and multiplane transesophageal Doppler echocardiography via the transgastric view (119 +/- 8 degrees) with the sample volume positioned at the level of the left ventricular outflow tract. RESULTS: Stroke volume and cardiac output measurements were obtained in 29 of 33 patients (88%). Mean values were 50 +/- 13 mL and 4.8 +/- 1.3 L/min by Doppler and 51 +/- 14 mL and 4.9 +/- 1.4 L/min by thermodilution (r = 0.90, r = 0.91, p < 0.001). The mean differences in values obtained with the two techniques were 1 +/- 6 mL (2 +/- 12%) and 0.1 +/- 0.7 L/min (2 +/- 12%). CONCLUSIONS: Multiplane transesophageal echocardiography enhances the ability to estimate accurately cardiac output and stroke volume by providing new access to left ventricular outflow tract in critically ill patients.

Aged↗
PubMed1983

Cardiac output and uteroplacental blood flow in diet-restricted and diet-repleted pregnant rats.

Cardiac output and uteroplacental blood flow were measured with 15 mu radioactive microspheres in anesthetized pregnant rats which were fed: (1) ad libitum throughout gestation; (2) a 50% restricted diet from day 5 of gestation; and (3) a 50% restricted diet from days 5 to 13 of gestation and ad libitum from day 14 of gestation. An additional group of nonpregnant rats fed ad libitum was also used. Dietary restriction caused a net maternal weight loss and a 20% reduction in mean fetal weight and mean placental weight by day 21 of gestation. Restricted dams fed ad libitum during the last week of gestation showed a net maternal weight gain, while mean fetal weight, but not placental weight, was near that of the ad libitum--fed controls. In the diet-restricted rats, total cardiac output was reduced 30% relative to controls by days 20 and 21 of gestation, but cardiac output per unit maternal body weight was not significantly different. Dietary restriction decreased both total uterine and placental blood flow by about 65%. Diet repletion late in gestation did not significantly increase total cardiac output or cardiac output per unit body weight. Total uterine and placental blood flows were near those of controls, primarily because of an increased fraction of cardiac output distributed to the uterus.

Animals↗
PubMed1988

Effects of enalapril on changes in cardiac output and organ vascular resistances induced by alpha 1- and alpha 2-adrenoceptor agonists in pithed normotensive rats.

1. Cardiac output, its distribution and regional vascular resistances were determined with tracer microspheres in pithed rats in the presence of the angiotensin converting enzyme inhibitor enalapril. The effects of enalapril on the cardiovascular responses elicited by either the alpha 1-adrenoceptor agonist phenylephrine or the alpha 2-adrenoceptor agonist xylazine were determined. 2. Enalapril decreased diastolic and mean blood pressure by decreasing cardiac index and total peripheral resistance. It induced vasodilatation in the kidney, epididimides, epididimidal fat and pancreas/mesentery. Vasoconstriction in the lungs, testes and liver was evident following enalapril administration as well as a decrease in the proportion of cardiac output passing to them, whilst the pancreas and mesentery received a greater proportion of the cardiac output. All the above effects of enalapril were reversed by infusion of angiotensin II at a rate of 75 ng kg-1 min-1. 3. Xylazine increased blood pressure by increasing both cardiac output and total peripheral resistance. Enalapril did not affect the increase in cardiac output caused by xylazine but decreased the effect of the alpha 2-agonist on blood pressure by preventing the increase in total peripheral resistance. Inhibition by enalapril of xylazine-induced vasoconstriction in the kidneys, testes, fat and gastrointestinal tract contributed to the decrease in total peripheral resistance. Enalapril also inhibited xylazine-induced changes in cardiac output distribution to the liver, lungs and heart. All the above effects of enalapril were reversed by infusion of angiotensin II. 4. Enalapril decreased the sustained phase of the pressor response to an infusion of phenylephrine whilst having no effect on the initial peak pressor response to a bolus injection of phenylephrine. Phenylephrine increased both cardiac output and total peripheral resistance and enalapril abolished its effect on total peripheral resistance whilst having no effect on the increase in cardiac output. Enalapril inhibited phenylephrine-induced vasoconstriction in the testes, fat, muscle, spleen and gastrointestinal tract. Enalapril also inhibited phenylephrine-induced changes in cardiac output distribution to the lungs and liver. The infusion of angiotensin II did not fully reverse the inhibitory effect of enalapril either on the phenylephrine-induced increases in diastolic blood pressure or on the vasoconstriction in the fat, spleen and gastrointestinal tract, but did reverse all other effects of enalapril.

Adrenergic alpha-Agonists↗
PubMed2005

Precision of bolus thermodilution cardiac output measurements in patients with atrial fibrillation.

BACKGROUND: The precision of bolus thermodilution cardiac output measurements in patients with atrial fibrillation (AF) has not previously been determined. A priori we suspected that the precision would be lower in patients with AF than in patients with sinus rhythm (SR). Consequently, we also determined if the precision could be improved by injecting the thermal indicator into the right ventricle instead of the right atrium. METHODS: Cardiac output was determined as the average result of four injections of 10 ml of iced saline. Replicate measurements were performed with thermal indicator injections into the right atrium and ventricle. The coefficients of variation and the precisions were calculated. RESULTS: In the 25 patients with AF, mean cardiac output was 3.96 l min(-1) (range 2.4-7.4), the coefficient of variation 0.073 (95% CI +/- 0.011), and the precision 0.38 l min(-1) (95% CI +/- 0.14) with injection into the right atrium. In the 25 patients with SR, mean cardiac output was 4.73 l min(-1) (range 2.4-7.3), the coefficient of variation 0.047(95% CI +/- 0.006), and the precision 0.38 l min(-1) (95% CI +/- 0.14). In both groups, an agreement analysis demonstrated that the injection of indicator into the right ventricle resulted in a significantly higher cardiac output [AF+0.25 (95% CI +/- 0.15) l min(-1), SR+0.29 ( +/- 0.20) l min(-1)]. CONCLUSION: The coefficient of variation for cardiac output determinations is 55% higher in patients with AF. Two measurements, separated by time or intervention, must differ by 15% in AF patients and 9% in SR patients before one can be 95% confident that a real change has taken place.

Aged↗
PubMed1989

Cardiac output in women undergoing cesarean section with epidural or general anesthesia.

Cardiac output during cesarean section and for 24 hours after delivery was estimated by using a noninvasive ultrasonic Doppler technique and was compared between term pregnant patients who underwent either epidural or general anesthesia. Cardiac output peaked by 36.7% and 26.3% of baseline values at 15 and 30 minutes after delivery, respectively, with epidural anesthesia and by 28% and 17.2%, respectively, with general anesthesia. From 60 minutes to 24 hours after delivery, cardiac output in both groups remained elevated at preoperative levels. This study demonstrates a similar pattern of increase in cardiac output with epidural and general anesthesia and a return by 60 minutes to preoperative levels, which persisted for up to 24 hours after delivery. The applicability of this noninvasive technique can be extended in various circumstances during pregnancy, labor, delivery, and the postpartum period to further define cardiac output in pregnancy.

Anesthesia, Epidural↗
PubMed1996

Pulsed wave Doppler measurement of cardiac output from the right ventricular outflow tract.

Doppler ultrasound can be used to measure cardiac output (CO). Intraoperative Doppler cardiac output (DCO) by transesophageal echocardiography (TEE) has been studied using blood flow velocity from the left ventricular outflow tract (LVOT), the mitral valve (MV), and the main pulmonary artery (MPA). The purpose of this study was to compare DCO, measured from a relatively new TEE view of the right ventricular outflow tract (RVOT), with thermodilution cardiac output (TDCO). We also compared changes in DCO from the RVOT to changes in TDCO. A 5.0/3.7 MHz multiplane TEE probe was placed in 45 adult cardiac surgical patients undergoing general anesthesia. Patients were excluded if there was greater than mild tricuspid valve insufficiency. From the transgastric view, at approximately 110-140 degrees, the RVOT was imaged. DCO was calculated from 1) the time-velocity integral (TVI) using pulse wave (PW) Doppler, 2) the area of the RVOT (measured in early systole using the diameter (pi(D/2)2) of the RVOT at the level of the PW Doppler sample volume), and 3) the heart rate. Simultaneous TDCO was performed by a separate examiner. The RVOT was imaged satisfactorily in 84% of patients (38/45). The mean bias between DCO and TDCO was -0.01 L/min (2 SD +/- 0.45 L/min; n = 38). There was good correlation between DCO and TDCO (R2 = 0.97). Changes in TDCO and changes in DCO were compared in 15 patients. The mean bias between changes in DCO and changes in TDCO was 0.04 L/min (2 SD +/- 0.66 L/min). Analysis of the changes in DCO and TDCO showed good correlation (R2 = 0.96). We conclude that there is a good correlation between DCO measured from the RVOT and TDCO. This technique permits cardiac output measurement without the necessity of placing a pulmonary artery catheter, and it also provides a method of evaluating RVOT blood flow.

Adult↗
PubMed2006

Noninvasive, automated and continuous cardiac output monitoring by pulmonary capnodynamics: breath-by-breath comparison with ultrasonic flow probe.

BACKGROUND: Cardiac output monitoring is most important where cardiovascular stability is potentially threatened, such as during major surgery and in critically ill patients. However, continuous monitoring of cardiac output is still not performed routinely during anesthesia and critical care, because of invasiveness, expense, and inaccuracy of available technologies. METHODS: A technique termed the capnodynamic method was tested for breath-to-breath measurement of pulmonary blood flow from lung carbon dioxide mass balance, using measured carbon dioxide elimination and end-tidal concentration. A prototype measurement system was constructed for a feasibility study in six anesthetized sheep. Large and rapid fluctuations in cardiac output were generated by repeated dobutamine and esmolol challenge. Measurements were compared with an indwelling ultrasonic flow probe placed on the ascending aorta or pulmonary artery. RESULTS: Cardiac output measured by the flow probe varied between zero and 8.67 l/min, with a mean of 3.50 l/min. Overall mean bias [SD of the difference] between the methods (capnodynamic - flow probe) was -0.25 [0.94] l/min, r = 0.79 (P < 0.001). During periods of stability in cardiac output of 5 min or more, mean bias was -0.20 [0.55] l/min. The method successfully indicated two cardiac arrest events, which were induced in one of the animals. CONCLUSIONS: The method satisfactorily tracked wide fluctuations in cardiac output in real time. The capnodynamic method may have potential for continuous noninvasive cardiac output monitoring in patients undergoing anesthesia for major surgery, and in critical care, on a routine basis.

Animals↗
PubMed1982

Non-invasive determination of the distribution of cardiac output in man at rest and during exercise.

The distribution of cardiac output, as expressed by the regional uptake of thallium-201 following injection, has been studied by whole body scanning with a gamma-camera in six healthy persons and eight patients with aortic valvular disease. In the patients, cardiac output at rest and during exercise was also measured by the dye dilution technique. Combining the values of cardiac output and regional thallium uptake enabled the calculation of organ blood flow. The myocardial uptake of thallium at rest was 3.2 +/- 0.32% in the control group, which is significantly lower than 8.3 +/- 1.52%, found in the patients. The corresponding values measured in the kidneys were 12.5 +/- 1.91% in the healthy subjects and 7.1 +/- 0.50% in the patient material. Myocardial uptake increased and kidney uptake decreased in both groups following injection at peak exercise. Thallium uptake in the legs increased from about 13% at rest to about 39% at exercise in both groups. Distribution of thallium after injection at peak exercise did not, however, vary significantly between the two groups in the kidneys, abdominal area or the legs. Further methodological work is required before it can be ascertained to what extent the regional thallium uptake reflects the distribution of cardiac output. We nevertheless propose that the technique should be explored further, since it appears to be a simple non-invasive means of visualizing the distribution of the cardiac output in man under certain conditions.

Adult↗
PubMed1990

Doppler measurement of cardiac output across prosthetic mitral valves.

In 46 patients with a normal functioning mitral valve prosthesis (15 St. Jude, 19 Medtronic Hall, 12 Hancock) cardiac output was measured by pulsed Doppler echocardiography across the valve prosthesis. Simultaneously cardiac output was determined by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract (2.8 l/min-9.5 l/min). The prosthetic valve area was calculated using the pressure half-time method. Cardiac output was calculated by multiplying time-velocity integrals with the mitral valve area. Cardiac output measurements across the mitral prosthesis correlated significantly with thermodilution (r = 0.96, SEE = 0.400 l/min) and pulsed Doppler echocardiography flow measurements in the left ventricular outflow tract (r = 0.82, SEE = 0.679 l/min). The mean percent error of the Doppler transmitral flow measurement was 10.8%. Doppler transmitral flow underestimated cardiac output valves of more than 6.5 l/min in 6 of 7 patients. Cardiac output measurements across Hancock (SEE = 0.473 l/min) and St. Jude prostheses (SEE = 0.538 l/min) were more accurate than across Medtronic Hall prostheses (SEE = 0.847 l/min). Cardiac output can be calculated by pulsed Doppler echocardiography across normal functioning mitral prostheses. Due to the different flow dynamics the accuracy of cardiac output measurement depends on the prosthetic valve type. Reliable measurements of cardiac output can be performed across Hancock and St. Jude prostheses only. This method is limited in volume flow measurements across Medtronic Hall prostheses.

Adult↗
PubMed1989

Errors in microsphere determination of cardiac output: a computer simulation in fetal sheep.

Through use of a compartmental model, we simulated the measurement of cardiac output and distribution by means of radioactively labeled microspheres in fetal lambs with weights between 0.5 and 3 kg. A systematic error in measured cardiac output caused by artifactual changes in blood volume caused by the injection and withdrawal of fluids during the procedure was less than 5% for fetal weights greater than or equal to 1 kg but increased for fetal weights less than 1 kg and when hypovolemia was simulated at all fetal weights. Sensitivity analysis disclosed no significant effect of changes in vascular resistance. We examined the effects of recirculation of microspheres and found no significant increase in error in the measured value of cardiac output due to 20% recirculation of all spheres entering a single isolated organ system; however, errors between 7 and 14% were observed with simulations of 20% recirculation in more than one compartment simultaneously. Recirculation also introduced significant errors in the measured distribution of cardiac output in certain cases. The effect on the measured cardiac output of a temporary change in the true cardiac output was dampened by the artifactual blood volume changes mentioned above and the fact that the measurement is a time-weighted average. We also evaluated four different experimental designs. We conclude that the microsphere technique provides a remarkably reliable means of quantifying cardiac output and individual organ flow in the fetus. The nonrandom errors inherent in the procedure examined in this study are of the order of 10%, which is likely to be less than the moment-to-moment variation in the true cardiac output.

Algorithms↗
PubMedDate not supplied

[Reliability of cardiac output by thermodilution. Effect of marker temperature].

Classically, the cardiac output is measured by the thermodilution method, employing a standard volume of 5% D/W at 4 degrees C. Recently, however, a room-temperature (17-24 degrees C) measurements have been used, in such a way that a lower gradient between the injectate and the patient temperature is established. This lact could question the sensitivity and reliability of the technique evaluated. We have studied 20 patients undergoing different operations, in whom the cardiac output was measured by injecting a standard volume of 5 ml 5% D/W at room-temperature or at 5 degrees C, randomly assigned, in order to evaluate any difference between the two techniques. Over a total of 100 cardiac output determinations taken in normothermic conditions (19-24 degrees C) the mean was 4.24 +/- 1.13 l/min (means +/- SD). In hypothermic conditions the cardiac output was 4.28 +/- 1.14 l/min (means +/- SD). Results showed no statistical difference between both methods.

Aged↗
PubMed1991

Thermodilution cardiac output: proximal lumen versus right ventricular port.

OBJECTIVE: To assess the accuracy of thermodilution cardiac output measurements from the right ventricular port vs. the central venous port. In addition, waveform patterns were evaluated in 50 right-heart catheters to determine the actual location of the right ventricular port. DESIGN: Central venous port cardiac output measurements were compared with right ventricular port cardiac output measurements using the same right-heart catheter. SETTING: The general ICU of Memorial Sloan-Kettering Cancer Center. PATIENTS: Forty-seven critically ill cancer patients with 60 different right-heart catheters were evaluated. INTERVENTION: Four injections of 10 mL of iced normal saline were made through each port, with the results of the last three injections averaged. Cardiac output determinations from both ports were completed in less than 10 min. The order of port injection was random. RESULTS: No difference was noted between cardiac output determinations from the two ports (paired t-test). Twenty-five of 50 right-heart catheters were in the right ventricle, with the other 25 in the right atrium. A comparison of ports in the 25 catheters that were in the right ventricle showed no difference with a significant (p less than .01, r2 = .94) correlation. CONCLUSION: Thermodilution cardiac output measurements using 10 mL of iced saline can be determined accurately using the right ventricular port if the central venous port becomes nonfunctional.

Adult↗
PubMed2004

Passive regulation of cardiac output during exercise by the elastic characteristics of the peripheral circulation.

A change in cardiac output induced by a change in cardiac performance is accompanied by opposite changes in cardiac filling pressure owing to the resistive and capacitive properties of blood vessels. The inverse relationship between cardiac output and cardiac filling pressure provides a passive (hydraulic) regulatory mechanism that functions to keep cardiac output constant during rest and exercise.

Adaptation, Physiological↗
PubMed1996

Cardiac output in normal pregnancy: a critical review.

OBJECTIVE: To review the literature about the effect of normal pregnancy on cardiac output, with special attention to study design, measurement technique, position of the subject, and parity. DATA SOURCES: For studies from the period 1955-1987, we examined Cumulated Index Medicus (National Library of Medicine Cataloging in Publication. Chicago: American Medical Association). For studies from 1988 to May 1, 1994, we used Medline on Silver Platter (U.S. National Library of Medicine Silver Platter International, 1994). METHODS OF STUDY SELECTION: Thirty-three cross-sectional and 19 longitudinal studies on cardiac output measurement in normal pregnancy were retrieved and reviewed. Thirteen longitudinal studies were excluded from analysis because an unvalidated technique was used or because not all subjects were measured at each study interval. The six remaining studies of genuine longitudinal design with at least two measurements throughout pregnancy were used for the definitive analysis. The results of the cross-sectional studies were included only to demonstrate a trend. DATA EXTRACTION AND SYNTHESIS: By pooling data from cross-sectional studies, a tendency was shown toward a higher cardiac output in the second trimester compared with the first trimester, and a tendency toward lower cardiac output was found in the third trimester compared with the second trimester. After delivery, cardiac output was lower than at any time during pregnancy. Selected longitudinal studies showed that the rise in cardiac output occurred early in the first trimester, and a further rise occurred during the second trimester. During the third trimester, cardiac output rose, fell, or plateaued, irrespective of the method of measurement applied or conditions during measurement. CONCLUSIONS: Cardiac output during the third trimester was widely divergent among the studies and probably dependent on individual factors. The tendency to report cardiac output as averages negated these inter-individual differences.

Cardiac Output↗
PubMed1999

Improved accuracy and precision of thermodilution cardiac output measurement using a dual thermistor catheter system.

OBJECTIVES: To assess whether thermodilution cardiac output determination based on measurement of injectate temperature in vivo leads to more accurate and precise estimates and to study the influence of chilled injectate on test performance. BACKGROUND: Cardiac output measurement via right heart catheterization is used extensively for hemodynamic evaluation in a variety of diagnostic, perioperative and critical care settings. Maximizing accuracy is essential for optimal patient care. METHODS: This prospective study of 960 thermodilution cardiac output measurements was conducted using conventional and dual thermistor techniques. Specialized dual thermistor right heart catheters were constructed using a second thermistor positioned to measure injectate temperature in vivo just prior to entry into the right atrium. To eliminate interinjection variability, a custom set-up was developed that permitted output measurement using both techniques simultaneously. Both ambient temperature injections and cooled injections were investigated. RESULTS: The dual thermistor technique demonstrated significantly less measurement variability than the conventional technique for both ambient temperature (precision = 0.41 vs. 0.55 L/min, p < 0.001) and cooled (precision = 0.35 vs. 0.43 L/min, p = 0.01) injections. Similarly, the average range of cardiac output values obtained during five sequential injections in each patient was less using the dual thermistor approach (1.05 vs. 1.55 L/min, p < 0.001). The use of cooled injectate reduced the mean error of the dual thermistor technique but actually increased the mean error of the conventional technique. Even with ambient temperature injections, injectate warming during catheter transit varied considerably and unpredictably from injection to injection (2 SD range = -0.22 to 5.74 degrees C). Conventional ambient temperature and cooled measurements significantly overestimated Fick cardiac output measurements by 0.32 and 0.50 L/min, respectively (p < 0.001). In contrast, dual thermistor measurements were statistically similar (-0.08 and -0.08 L/min, p = 0.34) to Fick measurements. CONCLUSIONS: This new dual thermistor approach results in a significant improvement in both precision and accuracy of thermodilution cardiac output measurement.

Cardiac Catheterization↗