Mean Cardiac Output Values Research Articles

Hemodynamic effect of pimobendan following intramuscular and intravenous administration in healthy dogs: A pilot study.

BackgroundPimobendan is widely used for the treatment of dogs with heart failure via the oral route. A new injectable form of pimobendan is now available and its potential usefulness via intravenous route has been recently demonstrated in dogs. However, the cardiovascular effects of intramuscular (IM) administration of injectable pimobendan have not been investigated yet.HypothesisIM administration of pimobendan may have the same hemodynamic effect as the IV route.MethodsSix healthy Beagle dogs underwent a placebo-controlled double-blind crossover study. The early cardiovascular effects after a single dose of IM and IV injections of pimobendan (0.2 ml/kg; Pimo IM and Pimo IV, respectively) were compared to the same volume of IM placebo (Saline IM) in anesthetized dogs. Clinical [heart rate (HR) and blood pressure (BP)] and echocardiographic hemodynamic parameters [left ventricular (LV) inflow waveforms of diastolic early wave (eV), atrial systolic wave (aV), diastolic early mitral ring velocity (e′), peak velocity (pV), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR)] were monitored with 15 min intervals for 120 min.ResultsDiastolic BP decreased significantly at 30 min in Pimo IM compared to Saline IM. Mean eV and CO values significantly increased from 75 min, e′ from 60 min, pV from 75 min, and SV from 15 to 120 min, whereas SVR significantly decreased at 30–60 min in Pimo IM compared to those of Saline IM (P < 0.05). Compared with the Pimo IV, eV and pV were significantly lower at 30–60 min (P < 0.05) while SV was significantly higher at 90–105 min in Pimo IM (P < 0.05). Other hemodynamic parameters (BP, HR, SVR, CO, e′, and E/e′) did not significantly change between Pimo IM and IV.ConclusionsThe hemodynamic effect of pimobendan following IM and IV injection was described. Our results suggested that IM administration of pimobendan is equally comparable and possibly interchangeable with IV administration. This warrant further studies to investigate the clinical effectiveness of IM pimobendan in treating dogs with congestive heart failure or in heart failure cases unable to receive IV or oral administration.

Cross-comparisons of trending accuracies of continuous cardiac-output measurements: pulse contour analysis, bioreactance, and pulmonary-artery catheter.

We compared the similarity of cardiac-output (CO) estimates between available bolus thermodilution pulmonary-artery catheters (PAC), arterial pulse-contour analysis (LiDCOplus™, FloTrac™ and PiCCOplus™), and bioreactance (NICOM™). Repetitive simultaneous estimates of CO obtained from the above devices were compared in 21 cardiac-surgery patients during the first 2h post-surgery. Mean and absolute values for CO across the devices were compared by ANOVA, Bland-Altman, Pearson moment, and linear-regression analyses. Twenty-one simultaneous CO measurements were made before and after therapeutic interventions. Mean PAC CO (5.7 ± 1.5L min) was similar to LiDCO™, FloTrac™, PiCCO™, and NICOM™ CO (6.0 ± 1.9, 5.9 ± 1.0, 5.7 ± 1.8, 5.3 ± 1.0L min, respectively). Mean CO bias between each paired method was -0.10 (PAC-LiDCO), 0.18 (PAC-PiCCO), -0.40 (PAC-FloTrac), -0.71 (PAC-NICOM), 0.28 (LiDCO-PiCCO), 0.39 (LiDCO-FloTrac), -0.97 (NICOM-LiDCO), 0.61 (PiCCO-FloTrac), -1.0 (NICOM-FloTrac), -0.73 (NICOM-PiCCO) L/min, with limits of agreement (1.96 SD, ±95% CI) of ± 2.01, ±2.35, ±2.27, ±2.70, ±1.97, ±2.17, ±3.51, ±2.87, ±2.40, and ± 3.14L min, respectively, and the percentage error for each of the paired devices was 35, 41, 40, 47, 33, 36, 59, 50, 42, and 55%, respectively. From Pearson moment analysis, dynamic changes in CO, estimated by each device, showed good cross-correlations. Although all devices studied recorded similar mean CO values, which dynamically changed in similar directions, they have markedly different bias and precision values relative to each other. Thus, results from prior studies that have used one device to estimate CO cannot be used to validate others devices.

Comparing the Rates of Dopamine Hemodynamic Effect Onset after Infusion through Peripheral Veins in Three Regions.

Background Dopamine is an inotropic agent that is often selected for continuous infusion. For hemodynamic stability, the rate of infusion is controlled in the range of 5-15 μg/kg/min. This study aimed to compare the time intervals from the administration of dopamine to the onset of its hemodynamic effects when dopamine was administered through three different peripheral veins (the cephalic vein [CV], the great saphenous vein [GSV], and the external jugular vein [EJV]).Methods Patients in group 1, group 2, and group 3 received dopamine infusions in the CV, GSV, and EJV, respectively. A noninvasive continuous cardiac output monitor (NICCOMO™, Medis, Ilmenau, Germany) was used to assess cardiac output (CO) and systemic vascular resistance (SVR). Six minutes after intubation, baseline heart rate (HR), systolic blood pressure (BP), diastolic BP, mean arterial pressure (MAP), CO, and SVR values were recorded and dopamine infusion was initiated at a dose of 10 μg/kg/min. Hemodynamic changes at 0, 4, 8, 12, and 15 minutes postinfusion were recorded.Results No statistically significant differences were observed among the three groups with respect to the rate of hemodynamic change. In all groups, systolic BP, diastolic BP, MAP, and SVR tended to increase after decreasing for the first 4 minutes; in contrast, HR and CO decreased until 8 minutes, after which they tended to reach a plateau.Conclusions For patients under general anesthesia receiving dopamine at 10 μg/kg/min, there were no clinical differences in the effect of dopamine administered through three different peripheral veins.

Non-invasive Estimation of Cardiac Output in Mechanically Ventilated Patients: A Prolonged Expiration Method

A non-invasive method for the estimation of cardiac output in mechanically ventilated patients is described. The method is based on prolonged expiration, and relies on measurement of gas concentrations and flow rate. A pneumatic system, with an ad hoc designed orifice resistance, has been made and experimentally characterized to adapt the breathing circuit to this application. Cardiac output is calculated using two algorithms and the results are compared with the ones obtained by thermodilution. To this purpose, we prospectively enrolled twenty mechanically ventilated patients, who had undergone cardiac surgery, and both algorithms show good correlation with thermodilution (R > 0.8). The application of the first algorithm gave mean cardiac output values slightly lower than those obtained by thermodilution (-6%), while the application of the second algorithm gave higher values (+30%). Difference standard deviations between paired measurements is 0.72 L min(-1) for the first algorithm and 1.07 L min(-1) for the second one. Standard deviation obtained by the application of the first algorithm is slightly lower than those relative to other minimally invasive techniques. Through prolonged expiration, and standardization and automation of the procedure on mechanically ventilated patients, the proposed system allows to obtain a non-invasive estimation of cardiac output.

Hemodynamic Responses Following High Intensity Isokinetic Exercise

PURPOSE: To compare the influence of exercise velocity and muscle mass, on hemodynamic responses following an isokinetic exercise protocol. METHODS: Fourteen male volunteers aged (26.9± 3.1 yrs; height 181.8±9.6 cm; weight 81.2±9 kg; BMI 24.6±1.8 kg m−2) performed twenty maximal isokinetic arm or leg contractions (eccentric and concentric) at 60 deg·sec−1, 150 deg·sec−1, and 240 deg·sec−1, administered in randomized order. Immediately following these tests, continuous, non-invasive, beat-by-beat recordings were made of Mean Arterial Pressure (MAP), Cardiac Output (CO), Heart Rate (HR), Stroke Volume (SV). RESULTS: Repeated measures 3-way ANOVA (velocity × muscle group × time) indicated no significant differences in recovery arm MAP across the three velocities. The arm MAP values were significantly higher (P<0.05) than the leg values (114.5±22.4; 107.85±17.65 mmHg). Overall, there was a decline in MAP during the first 30 seconds of recovery. The greatest undershoot of the MAP was seen during the 240 deg·sec−1 condition. The mean CO values following the leg tests were higher than arm tests (12.06±1.8 vs. 10.31±1.6 L•min−1). CO following the 60 deg·sec−1 testing velocity (arm) was lower [P<0.05] (9.49±1.32 L•min−1) than those recorded in the other two velocity conditions (10.72±1.73 L•min−1). Heart rates were significantly higher (125.37±17.85; 133.65±20.04; 136.22±19.12 bts•min−1 during the leg tests. Recovery heart rates in the 60 deg·sec−1 condition were lower (111.9±16.22; 119.62±22.64; 122.06±20.70 bts•min−1)] when compared to the 150 deg·sec−1 and 240 deg·sec−1 testing velocities. At the onset of recovery, the SV tended to be significantly below resting baseline values particularly after the arm tests. Within 10 seconds of recovery the SV tended to overshoot the baseline values and then remained elevated throughout the duration of the 110 second analysis period. Following the 150 deg·sec−1 arm test the SV was significantly higher (P<0.05) any of the other tests (91.11±12.06 vs 87.55±10.27 ml·bt−1). CONCLUSIONS: Recovery hemodynamics following high intensity isokinetic exercise exhibited unique characteristics not clearly indicative of a hypotensive state. These changes appear to be influenced partly by muscle mass and the velocity of movement.

Cross-comparison of cardiac output trending accuracy of LiDCO, PiCCO, FloTrac and pulmonary artery catheters

IntroductionAlthough less invasive than pulmonary artery catheters (PACs), arterial pulse pressure analysis techniques for estimating cardiac output (CO) have not been simultaneously compared to PAC bolus thermodilution CO (COtd) or continuous CO (CCO) devices.MethodsWe compared the accuracy, bias and trending ability of LiDCO™, PiCCO™ and FloTrac™ with PACs (COtd, CCO) to simultaneously track CO in a prospective observational study in 17 postoperative cardiac surgery patients for the first 4 hours following intensive care unit admission. Fifty-five paired simultaneous quadruple CO measurements were made before and after therapeutic interventions (volume, vasopressor/dilator, and inotrope).ResultsMean CO values for PAC, LiDCO, PiCCO and FloTrac were similar (5.6 ± 1.5, 5.4 ± 1.6, 5.4 ± 1.5 and 6.1 ± 1.9 L/min, respectively). The mean CO bias by each paired method was -0.18 (PAC-LiDCO), 0.24 (PAC-PiCCO), -0.43 (PAC-FloTrac), 0.06 (LiDCO-PiCCO), -0.63 (LiDCO-FloTrac) and -0.67 L/min (PiCCO-FloTrac), with limits of agreement (1.96 standard deviation, 95% confidence interval) of ± 1.56, ± 2.22, ± 3.37, ± 2.03, ± 2.97 and ± 3.44 L/min, respectively. The instantaneous directional changes between any paired CO measurements displayed 74% (PAC-LiDCO), 72% (PAC-PiCCO), 59% (PAC-FloTrac), 70% (LiDCO-PiCCO), 71% (LiDCO-FloTrac) and 63% (PiCCO-FloTrac) concordance, but poor correlation (r2 = 0.36, 0.11, 0.08, 0.20, 0.23 and 0.11, respectively). For mean CO < 5 L/min measured by each paired devices, the bias decreased slightly.ConclusionsAlthough PAC (COTD/CCO), FloTrac, LiDCO and PiCCO display similar mean CO values, they often trend differently in response to therapy and show different interdevice agreement. In the clinically relevant low CO range (< 5 L/min), agreement improved slightly. Thus, utility and validation studies using only one CO device may potentially not be extrapolated to equivalency of using another similar device.

A fMRI Study of Verbal Working Memory, Cardiac Output, and Ejection Fraction in Elderly Patients with Cardiovascular Disease

Cardiovascular disease (CVD) is associated with cognitive deficits even in the absence of stroke. We examined the relationship between cardiac performance, as measured by cardiac output (CO) and ejection fraction (EF), and brain activity during a verbal working memory (VWM) task in elderly CVD patients who tend to be at increased risk for vascular cognitive impairments. Seventeen patients were recruited from a cohort participating in an ongoing prospective study examining the effects of CVD on cognitive function in the elderly. Participants were diagnosed with CVD (age 68±8) and completed a 2-back VWM task in a 1.5T fMRI paradigm. CO and EF were calculated from echocardiogram measures. Task-related activation was averaged in a priori regions of interest. The relationship between CO, EF, and 2-back-related activity was modeled using partial correlations (two-tailed p<.05) controlling for age and 2-back accuracy. All participants were globally cognitively intact as indicated by Mini-Mental Status Exam and Dementia Rating Scale scores. Mean accuracy on the 2-back was 78±9% while reaction time averaged 1,027±192 ms. Mean CO and EF values showed a large range (CO: 3.55 to 6.31; EF: 0.36 to 0.76) but average values were within the normal range. After controlling for age and 2-back accuracy, lower EF was related to decrease in left insula activity (r=0.61, p=0.03). There were trends for EF to be related to accuracy (r=0.47, p=0.09) and reaction time (r=-0.48, p=0.09). CO was also related to insula activity (r=0.60, p=0.04) and activity in the supplementary motor area activity (r=0.66, p=0.01). Cardiac performance was related to decreased efficiency in task related brain areas and tended to be related to performance on a VWM task in elderly patients with CVD. Results have implications for a line of investigation indicating that cardiac and systemic vascular indices could be used as proxy measures to examine mechanisms of cerebrovascular dysfunction in the elderly.

Evaluation of a noninvasive continuous cardiac output monitoring system based on thoracic bioreactance

Noninvasive cardiac output (CO) measurement can be useful in many clinical settings where invasive monitoring is not desired. Bioimpedance (intrabeat measurement of changes in transthoracic voltage amplitude in response to an injected high-frequency current) has been explored for this purpose but is limited in some clinical settings because of inherently low signal-to-noise ratio. Since changes in fluid content also induce changes in thoracic capacitive and inductive properties, we tested whether a noninvasive CO measurement could be obtained through measurement of the relative phase shift of an injected current (i.e., bioreactance). We constructed a prototype device that applies a 75-kHz current and determines the relative phase shift (dPhi/dt) of the recorded transthoracic voltage. CO was related to the product of peak dPhi/dt, heart rate, and ventricular ejection time. The preclinical study was done in nine open-chest pigs put on right heart bypass so that CO could be varied at known values. This was followed by a feasibility study in 27 postoperative patients who had a Swan-Ganz catheter (SGC). The measurements of noninvasive CO measurement and cardiopulmonary bypass pump correlated to each other (r = 0.84) despite the large variation in CO and temperatures. Similarly, in patients, mean CO values were 5.18 and 5.17 l/min as measured by SGC and the noninvasive CO measurement system, respectively, and were highly correlated over the range of values studied (r = 0.90). Preclinical and clinical data demonstrate the feasibility of using blood flow-related phase shifts of transthoracic electric signals to perform noninvasive continuous CO monitoring.

EFFECTS OF AEROBIC EXERCISE ON CARDIOVASCULAR RESPONSES DURING THE COLD PRESSOR TEST IN AFRICAN AMERICANS

Previous studies have shown that during the cold pressor test (CPT) an increase in systolic blood pressure (SBP) ≥ 25 mm Hg above baseline is associated with an increased risk of developing hypertension(HT). We investigated the effects of aerobic exercise training on cardiovascular reactivity (CR) during the CPT in normotensive college-aged African American (AA) males. Ten aerobically-trained males and ten similar non-trained males served as subjects. The CPT consisted of immersing the foot in ice water (5°C) for two minues. The exercise training protocol consisted of eight weeks of cycling at 70% peak oxygen uptake (VO2peak), three days/week for 30 minutes/session. Oxygen uptake was determined using the open-circuit method. Blood pressure (BP) was assessed noninvasively using the continuous method of tonometry. Cardiac output(CO) and stroke volume (SV) were measured using impedance cardiography. Total peripheral vascular resistance (TPR) was calculated using the mean arterial BP (MABP) and CO values. Cardiac neural activity (CNA) was assessed by time domain and frequency domain analysis of heart rate variability. CR was determined by contrasting differences in resting measures and those recorded during the CPT. After training, VO2peak in the trained group increased 16% (pre-trained = 33.6 ± 2 vs. post-trained = 40.1 ± 1 ml kg−1 min−1) (P < 0.05). No significant change in VO2peak was found in the control group. In the exercise-trained group SBP, diastolic BP, MABP, heart rate, SV, CO, and TPR differences tended to be lower than before training (p > 0.05). We observed that in the exercise-trained group pre and post-trained SBP difference values were 27.4 ± 4 and 21.7 ± 6 mm Hg respectively. This magnitude of decrease in the post-trained SBP difference score is of clinical significance since it is indicative of a reduction in the risk for developing HT. In the control group there were no changes in the measured CR difference scores. Analysis of difference scores for CNA determined by assessing R-R interval (SDNN) and spectral analysis illustrated no difference in the exercise-trained and non-trained groups. In this study exercise training had no significant effect on the CR to behavioral stress. However, our data are of clinical significance since the training program used in this study produced a difference in the SBP response to stress. A change such as this may reduce the risk of HT in AA. Supported by NIH GM-08016.

Comparison of Exercise Cardiac Output by the Fick Principle Using Oxygen and Carbon Dioxide*

Theoretically, cardiac output (CO) calculated by the Fick principle should be the same using O(2) (CO[O2]) or CO2 (CO[CO2]) as the test gas. However, agreement depends on the accuracy of gas exchange and blood gas measurements and the validity of the equations to convert measured variables into blood gas contents. Considering the widespread use of indirect estimates of pulmonary artery blood PCO2 and CO2 content to measure Fick principle CO during exercise, we wished to determine whether CO[O2] and CO[CO2] were equal during exercise and whether CO[CO2] could be accurately and precisely determined using direct measures of pulmonary artery blood. PREPARATION AND METHODS: Five healthy young nonsmoking volunteer men performed incremental exercise from rest to peak exercise on two separate occasions with intervening rest. Catheters were placed in brachial and pulmonary arteries to allow repeated blood sampling every minute during concurrent breath-by-breath gas exchange measurements from rest to peak exercise. CO[O2] was compared with CO[CO2] at multiple levels of exercise. Using standard equations, arterial and mixed venous O2 contents were calculated from hemoglobin concentration (Hb), oxyhemoglobin saturation (SO2), and PO2, whereas CO2 contents were calculated from PCO2, pH, Hb, and SO2. Blood gas analyzers were used for measurement of pH, PCO2, and PO2, and a co-oximeter was used for measurement of Hb and SO2. Initial calculations suggested that exercise CO[CO2] was 14% higher than CO[O2] and helped disclose small systematic measurement errors in PCO(2) for values > 45 mm Hg detected by proficiency testing surveys and documented with blood tonometry in the blood gas analyzer. After correcting PCO2 for the small systematic measurement error found, the measures and equations used to calculate arterial and mixed venous O2 and CO2 contents were adequate to provide mean CO values that are reasonably similar. However CO[CO2] values were more than twice as variable as CO[O2]. The increased variability of Fick principle CO[CO2] compared with CO[O2] is attributable to the much lower extraction ratio for CO2 and the greater complexity in calculation of blood CO2 than O2 contents. These results raise concerns about the accuracy and precision of estimating CO and stroke volume using CO2 as a test gas, even with direct measurement of blood CO2 contents in normal subjects.

The effect of lung injury and excessive lung fluid, on impedance cardiac output measurements, in the critically ill.

To investigate the relationship between the attenuation of impedance cardiac output (IC(co)) measurements and lung fluid content in critically ill patients. Observational study. Intensive Care Unit of a major teaching hospital in Hong Kong. Twenty-four critically ill patients who required a pulmonary artery catheter. Triplicate thermodilution cardiac output (TD(co)) and BoMed NCCOM3 (IC(co)) measurements were made simultaneously on a single occasion in each patient. Lung fluid accumulation was assessed by: (a) thoracic impedance (Zo), (b) radiological assessment of chest X-rays using an alveolar consolidation score (0-4) and (c) scoring the degree of hypoxia and use of positive end-expiratory pressure (PEEP). Offsets (TD(co)-IC(co))/TD(co), expressed as percentage, were compared with these indices of excess lung fluid. Patients were divided into those with sepsis (n = 13), fluid balance problems (n = 5) and cardiothoracic problems (n = 6). Mean cardiac output values were: 6.7 l/min TD(co) (range 3.6-12.9) and 5.2 l/min IC(co) (range 2.7-9.0). Overall the TD(co) and IC(co) values showed great variance, with a bias and limits of agreement of 1.49 +/- 4.16 l/min, or +/- 69%. In septic patients, increasing offset was correlated with decreases in Zo (r = 0.73, P = 0.005) and increases in alveolar consolidation score (r = 0.72, P = 0.005). The BoMed under-estimates cardiac output in critically ill patients. In septic patients the degree of attenuation of IC(co) can be related to the extent of lung injury and fluid accumulation within the thorax.

RELIABILITY OF THE CPX/D NON-INVASIVE CARDIAC OUTPUT BY CO2 REBREATHING APPARATUS 1478

The purpose of this study was to determine the reliability of the CPX/D non-invasive cardiac output by CO2 rebreathing (exponential method) in a healthy population. Six healthy females ranging from 18-45 years of age were recruited. A total of 6 tests were performed by each subject, 3 at rest and 3 while exercising. The resting measurements were taken while the subjects were seated comfortably in a chair. The exercise measurements were taken when the subjects begin walking on a treadmill at a zero incline and a speed of 3 mph. The cardiac output was measured when the subjects reached a steady-state by rebreathing 4% CO2 in a closed-circuit for 20 seconds. A repeated measures ANOVA was performed on the data collected and an intraclass correlation ICC(3,k) formula was used to determine an index of reliability of the trials. The test proved to have ICC's at rest =.84 (F=6.349, p =.022) and while exercising=.85 (F = 7.055, p =.017). The mean cardiac output values in L/min for females at rest: R1 = 5.82 (SD =.084), R2 = 6.04 (SD =.241) & R3 = 5.66 (SD =.207) Females exercising in L/min E1 = 9.50 (SD =.255), E2 = 9.92 (SD =.084) & E3 = 9.80 (SD =.274). The data suggests the CPX/D non-invasive cardiac output by CO2 rebreathing apparatus (Medical Graphics) is a reliable instrument at rest and at low intensity exercise.

Inhibition of platelet GPIIbIa in an ex vivo model of hyperacute xenograft rejection does not prolong cardiac survival time

Abstract: Discordant cardiac xenografts are rapidly rejected in a process characterized by platelet activation with microvascular thrombosis, termed hyperacute rejection (HAR). The fibrinogen receptor GPIIbIIIa is crucial for the formation of platelet aggregates and potentiates platelet adhesion to subendothelial matrix. We have studied the effects of a specific GPIIbIIIa antagonist (GPI 562) in an ex vivo working heart model using discordant porcine hearts perfused with fresh, heparinized human blood. Stable plasma GPI 562 inhibitory levels were confirmed by inhibition of human platelet aggregation in vitro. Biopsies from the left ventricle of rejected hearts were analyzed by immunopathology. Control porcine hearts (n=8) underwent HAR and ceased functioning at around 60 min. Hearts perfused with human blood containing GPI 562 at 0.5 μM (n=5) appeared to show an initial increase in coronary blood flow relative to controls, but neither this difference nor survival times of the hearts reached significance. Mean cardiac output values were 7.3 ml/g (SEM 2.5) in the experimental group and 5 ml/g (SEM 0.6) in the control group following 5 min of working mode and were comparable at other timepoints. Platelet counts in the perfusate were maintained in the presence of GPI 562, unlike the reduction of over 50% in control samples. Immunohistochemistry suggested decreased platelet vascular plugging as determined by P‐selectin staining in the GPI 562 group, with associated reduction in neutrophil adherence and fibrin deposition. The use of GPI 562 in this ex vivo model conferred no marked benefits with respect to cardiac function and explant survival despite some positive differences on histological comparison. Further studies of this agent, in association with modalities of complement inhibition, are warranted in other models of discordant xenograft rejection.

Use of noninvasive bioelectric impedance to predict cardiac output in open heart recovery

Cardiac outputs (CO) measured by bioelectric impedance ( Z) and thermodilution (TD) were compared in ten stable, non-ventilated male coronary artery bypass patients (mean age 59 ± 12 years) in an open heart recovery unit. The measurements were obtained blindly in three sequential body positions (supine, 45°, final supine) using either a calculated value for resistivity ( p) (based upon hematocrit with blood sampled at the time of the study) to estimate CO( Z), or assumed values of p = 135.5 Ω cm and p = 150 Ω cm. The results indicate high correlations between the two measurement methods (range: r = 0.97 to 0.99) in the initial supine position for all resistivity conditions followed by a progressive decline when body position was changed to 45° and supine (range: r = 0.74 to 0.90). The highest overall correlations and closest absolute mean cardiac output values were obtained when p was calculated from actual hematocrit values obtained at the time of the study. Applying a two-way ANOVA to assess the simultaneous effects of method (TD vx. Z) and position change (supine, 45°, supine), no significant main effects or interactions were found when cardiac output values were estimated using the calculated measurement of p. However, significant main effects of method were found when p was assumed to be either 135.5 Ω cm ( p ⩾ 0.005) or 150.0 Ω cm ( p ⩾ 0.0001), with impedance showing a tendency to overestimate cardiac output. In conclusion, our findings suggest that impedance is a valid method to estimate cardiac output in this subpopulation of patients in open heart recovery provided that p is calculated at the time the study is performed.

Thermodilution cardiac output: Comparison between automated and manual injection of indicator

In clinical practice, cardiac output (CO) is usually reported as the average of thermodilution determinations with injection of the thermal indicator performed at end-exhalation. However, an average of multiple determinations with injections equally dispersed throughout the respiratory cycle has been shown to provide the best estimate of mean CO. This study sought to determine the reproducibility of CO determinations obtained with manual injections of indicator solution performed at end-exhalation, compared with those determined by computer-controlled injections equally dispersed throughout the breathing cycle of 27 patients undergoing cardiac operations. Mean CO was calculated by averaging the four determinations obtained with each technique before induction of anesthesia, after induction of anesthesia, after sternotomy, after cardiopulmonary bypass, and after sternal closure. A total of 130 pairs of mean CO estimations were obtained with manual and automated injections. Mean CO values obtained with manual injections were significantly lower than those obtained with the dispersed injection technique (5.0 ± 1.4 L/min vs 5.3 ± 1.6 L/min, P = 0.002). The bias between CO values measured with the manual technique was −0.25 ± 0.47 L/min lower than those obtained with the dispersed technique. The mean relative bias for the group was 7 ± 18% with 95% confidence intervals of ± 26%. During mechanical ventilation, the thermodilution technique with manual injection of indicator solution significantly underestimated CO. Variability in the manual injection technique and inappropriate representation of the mean CO by injections timed to occur at end-exhalation contributed to the disparity. These results indicate that the manual technique of determining CO at end-exhalation may not accurately reflect the average CO.

A new closed-system using partially frozen injectate for thermodilution cardiac output determinations.

The FI (partially frozen injectate) system, a new closed-system devised by the authors for thermodilution cardiac output determinations, has two major features: 1) it needs no ice-filled receptacle to keep injectate cold because it uses partially frozen injectate, and 2) it can go without monitoring the injectate temperatures during the whole process of cardiac output determinations. The author evaluated the accuracy and reproducibility of cardiac output determinations with the FI system in 10 critically ill patients, as compared with another closed-system (which is commercially available) and the standard open method. The injectate temperatures in the FI system were also measured in vitro. The mean injectate temperature in the FI system was 0.71 +/- 0.26 degrees C and 80% of the injectate temperatures were lower than 1.0 degrees C. Even when no monitoring of injectate temperatures was made, the predicated error in the calculated cardiac output resulted as low as 2% with the FI system. The mean cardiac output values were not statistically different between the FI system and the other two systems.

Pulsed Doppler Determinations of Cardiac Output in Neonates: Normal Standards for Clinical Use

Noninvasive monitoring of cardiac output can greatly facilitate the clinical assessment and management of neonates with cardiovascular compromise. To assess normal values of cardiac output in neonates, mean blood flow velocity was measured in the ascending aorta from a suprasternal approach using a range-gated, pulsed Doppler velocity meter, and aortic root diameter was determined from an M-mode echocardiogram. These techniques were combined, and cardiac output was evaluated in 59 healthy premature and 62 term newborn infants during the first week of life. Birth weights ranged from 780 g to 4,740 g and gestational age from 27 to 42 weeks. Cardiac output values increased linearly with advancing birth weight (r = +.94, P less than 0.001) and gestational age (r = +.95, P less than .001). Mean cardiac output values (+/- SD) per kilogram of body weight were 249 +/- 34 mL/min/kg and decreased with advancing birth weight: less than 1,500 g = 265 +/- 32 mL/min/kg; 1,500 to 2,500 g = 253 +/- 34 mL/min/kg; and greater than 2,500 g = 241 +/- 33 mL/min/kg. For clinical use, 325 mL/min/kg and 200 mL/min/kg can be used as upper and lower limits of normal, respectively. Doppler cardiac output estimates compared favorably with studies using invasive techniques.

Patient selection for iced versus room temperature injectate for thermodilution cardiac output determinations

In 42 patients who required hemodynamic monitoring there was no statistically significant difference between mean cardiac output determined with iced vs. room temperature injectate. There was also no statistical difference in mean cardiac output values using iced vs. room temperature injectate when data were grouped according to body temperature, mean arterial pressure, and cardiac output. These results suggest that when cardiac output is measured by the methods described, the use of iced injectate is unnecessary in many critically ill patients.