Evaluation of a continuous cardiac output and mixed venous oxygen saturation catheter in critically ill surgical patients

OBJECTIVE: To evaluate the agreement of continuous cardiac output and mixed venous oxygen saturation measurements, obtained with a modified pulmonary artery catheter, with those values obtained by standard intermittent bolus thermodilution and cooximetry. DESIGN: Prospective, clinical investigation. SETTING: A surgical intensive care unit in a tertiary referral center. PATIENTS: Twenty-one adult critically ill surgical patients, requiring pulmonary artery catheter monitoring. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A modified pulmonary artery catheter capable of continuous monitoring of cardiac output and mixed venous oxygen saturation was used with either an 8.5-Fr or a 9-Fr introducer. At random intervals, the continuous cardiac output measurement was compared with the cardiac output obtained using standard intermittent bolus thermodilution. The system was calibrated every 24 hrs for mixed venous oxygen saturation monitoring. Each saturation obtained by the laboratory cooximeter was compared with that value recorded using the catheter. Data points for 202 pairs of cardiac output (21 patients, 31 catheters) and 65 pairs of mixed venous oxygen saturation (20 patients, 28 catheters) were obtained. The bias and precision of the cardiac output data were 0.49 and 1.01 L/min, respectively. The agreement between the continuous and bolus values decreased as the cardiac output increased. Heart rate did not affect the agreement between the continuous and bolus techniques. The bias and precision of the mixed venous oxygen saturation data were -0.57% and 3.76%, respectively. The hematocrit did not affect the bias or precision of the venous saturation data over the hematocrit range observed (23.2% to 44.6%). Fewer catheter malfunctions were observed when the catheter was used with a 9-Fr introducer than with an 8.5-Fr introducer. CONCLUSIONS: The test catheter adequately measures continuous cardiac output and mixed venous oxygen saturation in the clinical setting. Because intermittent bolus thermodilution is not a true "gold standard" for cardiac output determination, new techniques compared with bolus thermodilution may fail to achieve accuracy expectations. A 9-Fr introducer is recommended, as fiberoptic damage may have occurred when the 8.5-Fr introducer was used.     

Agreement and clinical utility of 2 techniques for measuring cardiac output in patients with low cardiac output

BACKGROUND: The reliability of cardiac output obtained with the bolus technique is a problem. OBJECTIVES: To compare measurements of cardiac output measured with bolus and continuous techniques in patients with low cardiac output and to determine if measurements obtained with the continuous technique increased the number of subsequent clinical decisions. METHODS: In 60 intensive care patients, a nurse recorded a single continuous cardiac output measurement and then obtained the mean of 3 consecutive bolus determinations. The medical records of these 60 patients (experimental group) for the next 48 hours and of 60 other patients with regular or mixed venous oximetry catheters (control group) were reviewed to assess the occurrence of cardiac output events and the frequency of clinical decisions based on the events. RESULTS: Mean cardiac output was 4.46 L/min by the continuous technique and 5.20 L/min by the bolus technique (P = .011) for the experimental group. Median bias between the 2 types of measurements was -0.10 L/min (P = .79). Twenty-three of the pairs (38%) had an absolute percent difference greater than 15%. Of these, 18 (78%) had a higher bolus reading. Treatment decisions per 48 hours were 9.9 for the experimental group and 8.6 for the control group (P = .014). Median length of stay was 2 days less in the experimental group (P = .02), and mean highest cardiac output was 0.81 L/min higher (P = .009). CONCLUSIONS: Measurements of cardiac output determined with the continuous technique may be more precise than measurements determined with the bolus technique. Continuous cardiac output information increases the number of treatment decisions and actions that may shorten hospital length of stay.     

Lithium dilution cardiac output measurement: a comparison with thermodilution

OBJECTIVE: To compare the results of cardiac output measurements obtained by lithium dilution and thermodilution. DESIGN: Case series, observational study. SETTING: High-dependency postoperative unit and intensive care unit of a teaching hospital. PATIENTS: Forty patients were studied. Thirty-four patients had undergoing heart surgery requiring cardiopulmonary bypass within the previous 2 days; the diagnoses in the other patients were myocardial infarct (n = 2), septicemia (n = 2), adult respiratory distress syndrome, and pericardectomy. INTERVENTIONS: Cardiac output was measured five times in each patient, using lithium dilution (single measurement) and bolus thermodilution (series of three to six measurements according to standard clinical practice, taking the average of the closest three). In a subgroup of 14 patients, cardiac output was also measured using "continuous thermodilution." MEASUREMENTS AND MAIN RESULTS: Comparing lithium dilution with bolus thermodilution, the mean of the differences (lithium dilution-thermodilution) was -0.25 +/- 0.46 [SD] L/min. Linear regression analysis gave y = 0.31 + 0.89x (r2 = .94) for lithium dilution vs. thermodilution. CONCLUSIONS: The overall agreement between the two methods was good. The variability of the thermodilution measurements was greater than that of the lithium dilution measurements. The lithium dilution method is at least as accurate as bolus thermodilution and, since pulmonary artery catheterization is not needed, it has the advantages of being safe and quick to perform.     

Effects of iced and room temperature injectate on cardiac output measurements in critically ill patients with low and high cardiac outputs

OBJECTIVE: To determine the effect of injectate temperature (iced or room temperature) on cardiac output values in critically ill adults with low and high cardiac outputs. DESIGN: Quasi-experimental. SETTINGS: Two multidisciplinary intensive care units in two large, metropolitan, private, nonprofit hospitals in Texas. SUBJECTS: A convenience sample of 21 critically ill men and women who averaged 61 years of age (range 31 to 82 years) and whose most recent cardiac output measured with room temperature injectate was low (< or = 3.5 L/min) or high (> or = 8.0 L/min). INTERVENTION: Iced injectate and room temperature injectate (randomly ordered) were used to measure cardiac output in each subject. OUTCOME MEASURES: Cardiac output value with iced injectate versus cardiac output value with room temperature injectate. RESULTS: We found significant differences between cardiac output measurements with room temperature and those with iced injectate in eleven critically ill patients with low cardiac outputs (< or = 3.5 L/min) and in ten critically ill patients with high cardiac outputs (> or = 8.0 L/min). In the low cardiac output group, cardiac outputs using room temperature injectate averaged 0.37 L/min (range 0.1 to 1.10 L/min) higher than cardiac outputs using iced injectate (p = 0.001). In the high cardiac output group, measurements with room temperature injectate averaged 1.17 L/min L/min (range 0.3 to 3.0 L/min) higher than cardiac outputs with iced injectate (p = 0.005). Percent differences between room temperature and iced injectate values averaged 13% (range 3% to 27%) in patients with low cardiac outputs and 11% (range 3% to 29%) in patients with high cardiac outputs. Seven (77%) of the patients in the low cardiac output group and four (40%) of the patients in the high cardiac group had a 10% or greater difference--which many clinicians describe as a clinically significant difference--between room temperature and iced injectate cardiac output values. CONCLUSION: Although research is clearly needed to substantiate these findings, we suggest that nurses use iced injectate in patients with low and high cardiac outputs (< or = 3.5 L/min or > or = 8.0 L/min) to ensure accurate measurement of cardiac output.     

Continuous measurements of cardiac output in the perioperative period

Management of critically ill patients is based on knowledge of fundamental physiological variables. Automatized and continuous measurement of these variables is preferable. A new system based upon the thermodilution method has been developed to measure cardiac output automatically and continuously. We evaluated the system in the potentially unstable perioperative period with possible great and rapid changes in cardiac output. Twenty patients, scheduled for open heart or abdominal aortic aneurysm surgery, were included into the study, which was approved by the local ethical committee. The patients were monitored for up to 30 hours. At random intervals five iced bolus thermodilution cardiac output (BCO) determinations were made and compared to the continuous measurements (CCO). Two hundred and thirty-one pairs of data were obtained. The cardiac outputs ranged from 2.5-14.9 l/min. The absolute bias was 0.31 l/min (95% limits of agreement -1.4 l/min to 2.0 l/min). The mean relative error was 4.7% with a standard deviation of the relative error of 15.4%. The linear regression was represented by: CCO = 11.352 x BCO - 0.36. The correlation coefficient R was 0.90 (p < 0.001). In conclusion, the CCO measurement technique is a promising clinical method. The method is straightforward, requires no calibration, is independent of vascular geometry and measures with its limitations volumetric flow. Finally automatic and continuous patient monitoring provides more information and has potential to reveal previously undetected haemodynamic events.     

Measurement of cardiac output with continuous thermodilution. b1 Clinical experience with the Intellicath-Vigilans system

BACKGROUND: Thermodilution cardiac output measurements are commonly obtained by a manual bolus technique with a pulmonary artery catheter. METHODS: A new thermodilution catheter has been developed which utilizes an integral thermal filament and provides semicontinuous online cardiac output. The response of this new device in 25 patients undergoing coronary artery bypass grafting was examined. A total of 250 data pairs was obtained; the cardiac outputs ranged from 2.2 to 11.9 lts.min. RESULTS: The linear regression is represented by the following equation: continuous thermodilution = 0.7196 bolus thermodilution +1.038. The correlation coefficient was 0.75; the mean bias was 0.493 +/- 1.034. CONCLUSIONS: The new technique provides acceptable accuracy in many clinical situations except when sudden haemodynamic changes occur.     

Continuous measurement of cardiac output by the Fick principle in infants and children: comparison with the thermodilution method

OBJECTIVE: To compare a system that continuously monitors cardiac output by the Fick principle with measurements by the thermodilution technique in pediatric patients. DESIGN: Prospective direct comparison of the above two techniques. SETTING: Pediatric intensive care unit of a university hospital. PATIENTS: 25 infants and children, aged 1 week to 17 years (median 10 months), who had undergone open heart surgery were studied. Only patients without an endotracheal tube leak and without a residual shunt were included. METHODS: The system based on the Fick principle uses measurements of oxygen consumption taken by a metabolic monitor and of arterial and mixed venous oxygen saturation taken by pulse- and fiberoptic oximetry to calculate cardiac output every 20s. INTERVENTIONS: In every patient one pair of measurements was taken. Continuous Fick and thermodilution cardiac output measurements were performed simultaneously, with the examiners remaining ignorant of the results of the other method. RESULTS: Cardiac output measurements ranged from 0.21 to 4.55 l/min. A good correlation coefficient was found: r2 = 0.98; P < 0.001; SEE = 0.41 l/min. The bias is absolute values and in percent of average cardiac output was - 0.05 l/min or - 4.4% with a precision of 0.32 l/min or 21.3% at 2 SD, respectively. The difference was most marked in a neonate with low cardiac output. CONCLUSION: Continuous measurement of cardiac output by the Fick principle offers a convenient method for the hemodynamic monitoring of unstable infants and children.     

Noninvasive assessment of cardiac output in critically ill patients by analysis of the finger blood pressure waveform

OBJECTIVE: To assess whether the measurement of cardiac output by computer-assisted analysis of the finger blood pressure waveform can substitute for the thermodilution method in critically ill patients. DESIGN: Prospective data collection. SETTING: Emergency department in a 2000-bed inner city hospital PATIENTS: Forty-six critically ill patients requiring invasive monitoring for clinical management were prospectively studied. INTERVENTIONS: Under local anesthesia a 7-Fr pulmonary artery catheter was inserted via the central subclavian or jugular vein. Cardiac output was determined by the use of a cardiac output computer and injections of 10 mL ice-cold glucose 5%. Noninvasive cardiac output was calculated from the finger blood pressure waveform by the use of the test software program. MEASUREMENTS AND MAIN RESULTS: Three hundred twenty-three pairs of invasive and noninvasive hemodynamic measurements were collected in intervals of 30 mins from 46 patients (mean age 61.9 +/- 12.4 yrs; 35 male, 11 female). The average cardiac index during the study period was 2.83 L/min/m2 (range 0.97 to 5.56). The overall discrepancy between both measurements was 0.14 L/min/m2 (95% confidence interval: 0.10-.018, p < .001). Seventy-five (23.2%) measurements had an absolute discrepancy > +/- 0.50 L/min/m2. Noninvasive and invasive comparisons of mean differential cardiac output were out of phase for 9.7% of all readings. CONCLUSION: Computer-assisted analysis of finger blood pressure waveform to assess cardiac output is not a substitute for the thermodilution method due to a high percentage (23.2%) of inaccurate readings; however, it may be a useful tool for the detection of relative hemodynamic trends in critically ill patients.     

Hypocapnia does not alter hepatic blood flow or oxygen consumption in patients with head injury

OBJECTIVE: To evaluate the effects of hypocapnia on the systemic and hepatic circulations and oxygenation values in patients with head injury. DESIGN: Open-label, prospective study. SETTING: University hospital, department of anesthesiology and intensive care unit. PATIENTS: Eleven mechanically ventilated patients with isolated head trauma and stable hemodynamic status. INTERVENTIONS: At the beginning of the study, each patient presented with normocapnic ventilation. Mechanical hyperventilation was then adjusted to obtain stable hypocapnia over an interval of 24 hrs. Cardiac output and other systemic hemodynamic parameters were measured, using a pulmonary artery catheter. Hepatic parameters were measured via a catheter inserted into the hepatic vein. Total hepatic blood flow was determined by the Fick principle using a continuous infusion of indocyanine green. Arterial and hepatic venous blood gases were sampled to determine systemic and hepatic-splanchnic oxygenation. Measurements were done at the end of the four phases: a) 30 mins of normocapnia (N); b) 30 mins of hypocapnia (H0); c) 3 hrs of hypocapnia (H3); and d) 24 hrs of hypocapnia (H24). Intracranial pressure and cerebral perfusion pressure were hourly monitored throughout the study. MEASUREMENTS AND MAIN RESULTS: There were no significant changes in systemic hemodynamic parameters. The hepatic blood flow index did not differ from normocapnia (N 1.8 +/- 0.4 L/min/m2) to hypocapnia (H0 1.6 +/- 0.3 L/min/m2; H3 1.7 +/- 0.4 L/min/m2; H24 1.7 +/- 0.4 L/min/m2). The ratio of hepatic blood flow index to cardiac index remained stable throughout the study. Hypocapnia did not affect hepatic-splanchnic oxygen delivery and consumption. CONCLUSIONS: Hypocapnic hyperventilation does not alter hepatic hemodynamic parameters in patients with head injury. This result may be related to the lack of changes in cardiac output or in the hepatic vasoreactivity. Moreover, hypocapnia does not modify hepatic-splanchnic oxygenation. Thus, in case of intracranial hypertension, hypocapnia might be used without undesirable effect on the hepatic-splanchnic perfusion.     

Value of single oral loading dose of propafenone in converting recent-onset atrial fibrillation. Results of a randomized, double-blind, controlled study

OBJECTIVE: To assess the effects of dobutamine at a rate of 5 micrograms/kg/min on hemodynamics and gastric intramucosal acidosis in patients with hyperdynamic septic shock treated with epinephrine. DESIGN: A prospective, interventional, clinical trial. SETTING: An adult, 16-bed medical/surgical intensive care unit of a university hospital. PATIENTS: Twenty septic shock patients with a mean arterial pressure of > 75 mm Hg and a cardiac index of > 3.5 L/min/m2. INTERVENTIONS: After baseline measurements (H0), each patient received dobutamine at a rate of 5 micrograms/kg/min. Baseline measurements included: hemodynamic parameters, tonometric parameters, arterial and mixed venous gases, and arterial lactate concentrations. These measurements were repeated after 1 (H1), 2 (H2), and 3 (H3) hrs. After H2 measurements, dobutamine was stopped. The patients were separated into two groups according to their PCO2 gap (tonometer PCO2-PaCO2). The increased PCO2 gap group was defined by a PCO2 gap > 8 torr (> 1.1 kPa) (n = 13), and the normal PCO2 gap group by a PCO2 gap < or = 8 torr (< or = 1.1 kPa)(n = 7). MEASUREMENTS AND MAIN RESULTS: Dobutamine at 5 micrograms/kg/min had no significant effects on mean arterial pressure, heart rate, cardiac index, systemic vascular resistance, oxygen delivery, and oxygen consumption in epinephrine-treated septic shock. No patients developed arrhythmia or electrocardiographic signs of myocardial ischemia. During dobutamine infusion, arterial lactate concentration decreased from 5.1 +/- 0.4 in the increased PCO2 gap group and 4.2 +/- 0.4 in the normal PCO2 gap group to 3.9 +/- 0.3 and 3.5 +/- 0.3 mmol/L, respectively (p < .01). The PCO2 gap decreased and gastric intramucosal pH increased in the increased PCO2 gap group from 12 +/- 0.8 (1.6 +/- 0.1 kPa) to 3.5 +/- 0.8 torr (0.5 +/- 0.1 kPa) (p < .01) and from 7.11 +/- 0.03 to 7.18 +/- 0.02 (p < .01), respectively, and did not change in the normal PCO2 gap group. After stopping dobutamine infusion, the PCO2 gap and intramucosal pH returned to baseline values in the increased PCO2 gap group. CONCLUSION: The addition of 5 micrograms/kg/min of dobutamine added to epinephrine in hyperdynamic septic shock selectively improved the adequacy of gastric mucosal perfusion without modification in systemic hemodynamics.     

Clinical, biological, and immunophenotypical characteristics of B-cell chronic lymphocytic leukemia with trisomy 12 by fluorescence in situ hybridization

Intra-aortic balloon pumping is frequently used in patients with cardiogenic shock when oliguria persists despite maximal pharmacologic support. The objective of this study was to measure the effect of intra-aortic balloon pumping on renal blood flow, renal oxygen delivery, and renal oxygen consumption in such patients. Central hemodynamics, renal blood flow, and oxygen transport were measured in 10 patients in low cardiac output states. Measurements were made with and without intra-aortic balloon counterpulsation. Renal blood flow was measured by continuous renal vein thermodilution. Small improvements were observed in cardiac output (3.1 +/- 0.8 vs 3.5 +/- 0.8 L/min, P < .01) and pulmonary capillary wedge pressure (22 +/- 5.6 vs 19 +/- 5.3 mmHg, P < .05), but mean arterial blood pressure was unchanged (69 +/- 11 vs 69 +/- 5 mmHg, not significant). Baseline renal blood flow was reduced to approximately 37%, renal oxygen delivery to 31%, and renal oxygen consumption to 60% of normal values. No significant improvement was seen in single-kidney renal blood flow (184 +/- 108 vs 193 +/- 107 mL/min), renal oxygen delivery (28 +/- 16 vs 30 +/- 16 mL/min), or renal oxygen consumption (4.9 +/- 2.0 vs 4.7 +/- 2.5 mL/min) in response to 1:1 counterpulsation. In comparison with measurements made during short-term suspension of counterpulsation, 1:1 aortic balloon pumping failed to result in an increase in renal blood flow, oxygen delivery, or oxygen consumption from the low levels observed in these patients.     

Beobachtungsstudien im Rahmen eines naturheilkundlichen Klinikverbunds

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.     

Use of modified Ilizarov olive wires as pushing wires

BACKGROUND: Measurements of cardiac output with the thermodilution technique add to data for clinical decision making and therefore must be valid and reliable. However, the results of studies on the accuracy of values obtained with room-temperature and iced injectates, especially in patients with high or low cardiac output, have been conflicting. OBJECTIVE: To determine the effect of the temperature of the injectate (iced or room temperature) on cardiac output values obtained with the thermodilution technique in critically ill adults with known low cardiac output. METHODS: A convenience sample of 50 subjects (41 men and 9 women) who had a cardiac index of less than 2.5 (calculated as cardiac output in liters per minute divided by body surface area in square meters) before the study had cardiac output measured by using a closed system and manual injections of room-temperature and iced injectates. RESULTS: A paired t test indicated no significant difference between iced and room-temperature injectates for cardiac output (iced, 3.62 L/min; room temperature, 3.71 L/min; t = 0.99; P = .327) and cardiac index (iced, 1.95; room temperature, 1.99; t = 0.71; P = .482). CONCLUSION: The findings support the practice of using room-temperature injectate to measure cardiac output in patients with low cardiac output.     

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.     

Static or frictional electricity and the discovery of direct current

OBJECTIVE: To examine the usefulness of preload indices obtained by transoesophageal echocardiography (TOE) for estimating stroke volume at various levels of cardiac index. DESIGN: Prospective clinical study. SETTING: Intensive care unit with surgical patients. PATIENTS: 16 ventilated patients monitored via Swan-Ganz catheterization and TOE. INTERVENTIONS: Echocardiographic images of left ventricular cross-sectional short-axis areas were analysed for the preload indices end-diastolic area (EDA), stroke area and end-diastolic wall stress. The relation between these indices and stroke volume, calculated from thermodilution cardiac output, was analysed in all patients and in nine patient groups discriminated by various ranges in heart rate (< or = 70 to > 110 beats/min), pulmonary artery occlusion pressure (< or = 8 to > 12 mmHg) and cardiac index (< or = 3.0 to > 4.2 l/min per m2). MEASUREMENTS AND RESULTS: Overall stroke volume (n = 155) correlated significantly (p < 0.0001) with EDA (r = 0.89) and stroke area (r = 0.80). The correlation with end-diastolic wall stress was non-significant (r = 0.51). Linearity in the relation between stroke volume and EDA or stroke area was independent of variations in heart rate and pulmonary artery occlusion pressure. Stroke volume correlated well with EDA and stroke area, when cardiac index was normal or high, but the relation slightly deteriorated (r = 0.63 to < or = 0.72) when the cardiac index was low. Changes in EDA and stroke area by more than 1, 2 or 3 cm2 were weak predictors for changes in stroke volume greater than 20%. CONCLUSIONS: Stability of the relation between echocardiographic preload indices and stroke volume emphasize the potential of TOE for continuous preload monitoring in the critically ill.     

Improved oxygen utilization during mild exercise in heart failure

In heart failure with low cardiac output, exercise tolerance is reduced despite modulated regional blood distribution and oxygen extraction. However, low cardiac output does not necessarily lead to reduced exercise tolerance especially during mild exercise. In the present study, in order to understand the mechanisms regulating exercise tolerance in heart failure, we measured oxygen consumption (VO2) and cardiac output (CO) during both mild and intense exercise. Patients with heart failure were divided into 2 groups; group L (n = 8) consists of patients with low anaerobic threshold (AT) < 13 ml/min per kg and group H (n = 7) consisting of patients with AT > 13 ml/min per kg. At rest, VO2 was similar between groups L and H, whereas CO was lower in group L than in group H (3.5 + 0.3 vs 4.8 + 1.4 ml/min, p < 0.01). Increase in VO2 during warm-up exercise was not significant between the 2 groups (7.4 +/- 0.5 (group L) vs 6.2 +/- 0.3 ml/min per kg (group H), ns), but increase in CO was lower in group L than in group H (2.5 +/- 0.6 vs 3.4 +/- 0.4 ml/min, p < 0.01). After warm-up to the AT point, however, the increase in not only VO2 but also CO was markedly reduced in group L than in group H (VO2: 0.5 +/- 0.4 vs 3.7 +/- 0.8 ml/min per kg, p < 0.01, CO: 0.2 +/- 0.3 vs 1.1 +/- 0.3 L/min, p < 0.01). Based on these measurements, we calculated the arteriovenous oxygen difference (c(A-V)O2 difference) during exercise in individual patients using Fick's equation. The c(A-V)O2 difference was markedly increased in severe heart failure during the warm-up stage, but between the end of warm-up and the AT point, it remained at the same level as that of group H. These results suggest the presence of a unique mechanism regulating the c(A-V)O2 difference in severe heart failure patients, activation of which may, at least during mild exercise, contribute to efficient oxygen delivery to the peripheral tissues thus compensating for the jeopardized exercise tolerance in those patients.     

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.     

Atrial natriuretic peptide is not degraded by the lungs in humans

In an attempt to identify and quantify the sites of atrial natriuretic peptide (ANP) degradation, particularly the lungs, a new tracer method to study ANP metabolism in vivo in humans was developed and applied to patients with left ventricular dysfunction. Thirteen male, normotensive, cardiac patients with different degrees of left ventricular myocardial involvement were enrolled in the study. The study protocol required constant infusion (3 patients) or bolus injection (10 patients) of 125I-labeled ANP just upstream of the right atrium and blood sampling from different sites (pulmonary artery, aorta, inferior vena cava, and femoral vein) during the hemodynamic study. Data analysis was based on a kinetic model consisting of three blocks in series (right heart, lungs and left heart, and periphery) supplied by the same plasma flow (plasma cardiac output). Plasma levels of native ANP were measured with a sensitive and specific immunoradiometric assay method. ANP values measured in the aorta (163.9 +/- 144.8 pg/mL, n = 80) were superimposable on those measured in the pulmonary artery (161.8 +/- 136.5 pg/mL, n = 80). Negligible extraction of 125I-labeled ANP was found in the lungs and left heart block (on average 0.08 +/- 3.92%), whereas the peripheral block extraction (46.2 +/- 7.8%) accounted for almost total hormone removal from the blood (whole body extraction was 46.4 +/- 6.6%). ANP metabolic clearance rate (3.11 +/- 1.48, range 1.4-6.8 L/min) declined with the progression of left ventricular dysfunction (plasma cardiac output 3.46 +/- 1.08, range 1.2-5.7 L/min), and a close correlation between metabolic clearance rate and cardiac output was evident. Our data suggest that lungs do not extract, or extract only very small amounts, of labeled ANP administered iv to patients with different degrees of left ventricular myocardial involvement, and whole body extraction of labeled ANP remains relatively stable with the progression of disease, and the large reductions in clearance values observed in our patients can be ascribed mainly to the reductions in cardiac output.     

Temperature-dependent cardioprotection of exogenous substrates in long-term heart preservation with continuous perfusion: twenty-four-hour preservation of isolated rat heart with St. Thomas' Hospital solution containing glucose, insulin, and aspartate

BACKGROUND AND METHODS: Using an isolated working rat heart model, we determined the effects of glucose, insulin, and aspartate on recovery of cardiac function when used as components of preservation solution at different temperatures. After measurement of baseline cardiac function, hearts (n = 6 per group) were perfused with oxygenated St. Thomas' Hospital solution containing (1) vehicle, glucose (9 mmol/L) or aspartate (20 mmol/L) for 12 hours at either 20 degrees or 4 degrees C; (2) glucose or glucose + insulin (10 U/L) at 20 degrees C for 20 hours; and (3) glucose + insulin at 20 degrees C or glucose + insulin + aspartate at either 20 degrees or 4 degrees C for 24 hours. Cardiac function was measured after preservation and expressed as a percentage of baseline values. RESULTS: At 20 degrees C, both glucose and aspartate increased recovery of cardiac output (vehicle, 57.7% +/- 3.8%; glucose, 76.5% +/- 2.4% [p < 0.05 versus vehicle]; aspartate, 79.9% +/- 1.4% [p < 0.05 versus vehicle]). At 4 degrees C, glucose decreased recovery of cardiac output, whereas aspartate did not change the value (vehicle, 74.4% +/- 2.2%; glucose, 61.4% +/- 2.8% [p < 0.05 versus vehicle]; aspartate, 80.5% +/- 1.7%). The addition of insulin to glucose increased recovery of cardiac output (glucose, 24.6% +/- 4.0%; insulin + glucose, 69.2% +/- 2.0%: p < 0.05). The combined use of these three agents showed an additive effect in improvement of recovery of cardiac output at 20 degrees C (glucose + insulin, 64.2% +/- 2.2%; glucose + insulin + aspartate, 76.0% +/- 1.1%; p < 0.05), but the recovery at 4 degrees C (63.1% +/- 1.8%) was significantly lower than at 20 degrees C. CONCLUSIONS: These results suggest that glucose and aspartate afford differential cardioprotective effects depending on the temperature of the preservation solution and that combined use of glucose, insulin, and aspartate at the optimal temperature may extend graft preservation time.     

Hemodynamic effects of the implantation of an intracaval oxygenator

Treatment of severe respiratory failure by extracorporeal membrane oxygenation (ECMO) is complex. However, there is now an intravascular gas exchanger (IVOX) available that provides extrapulmonary gas transfer without requiring an extracorporeal blood path. The present study was performed to determine the hemodynamic effects resulting from the intracaval placement of the intravascular device. A bovine model (n = 6; body-weight = 72 +/- 5 kg) was selected for temporary lung support with the intravascular device. The latter was placed in the caval axis under fluoroscopic control after full instrumentation of the animal for hemodynamic measurements including a pulmonary artery catheter for determination of cardiac output by thermodilution and continuous readout of mixed venous oxygen saturation. All measurements were taken after a stabilization period of 15 min. The heart rate moved from 65 +/- 8 before to 72 +/- 10 after implantation and 68 +/- 9 after onset of intravascular gas exchange (NS). Right atrial pressure was 13 +/- 3 mm Hg before, 12 +/- 3 mm Hg after implantation and 10 +/- 3 mm Hg after onset (NS) whereas femoral venous pressure moved from 14 +/- 3 mm Hg to 17 +/- 4 mm Hg (p < 0.05) and remained at 17 +/- 4 mm Hg after onset. Cardiac output was 5.3 +/- 0.7 l/min before, 5.4 +/- 0.7 l/min after implantation and 5.3 +/- 1.1 l/min after onset (NS) while mixed venous oxygen saturation dropped from 60 +/- 7% to 54 +/- 11% and moved to 57 +/- 11 after onset of the device (NS).(ABSTRACT TRUNCATED AT 250 WORDS)