Effects of induction of anaesthesia with sufentanil and positive-pressure ventilation on the intra- to extrathoracic volume distribution.

BACKGROUND AND OBJECTIVE: Induction of general anaesthesia in combination with positive-pressure ventilation is often associated with a significant decrease of arterial pressure. A decreased preload may contribute to this phenomenon. The aim was to investigate whether a change in cardiac filling occurs following the induction of general anaesthesia with sufentanil under typical clinical conditions. METHODS: Fifteen patients scheduled for elective coronary bypass grafting were studied immediately before surgery. In addition to standard monitors, a transpulmonary double-indicator dilution technique measured in vivo intrathoracic blood volume, global end-diastolic volume and total circulating blood volume. For induction of anaesthesia 2 microg kg(-1) sufentanil was given. Measurements were performed awake and after the induction of anaesthesia, intubation and mechanical ventilation of the lungs. RESULTS: To maintain arterial pressure during the induction period within -20% of baseline pressure, on average 22 +/- 6mLkg(-1) crystalloids and 8 +/- 6mLkg(-1) colloids were given. Despite these amounts of fluid, cardiac filling was decreased, whereas circulating blood volume increased significantly. Both central venous pressure and pulmonary capillary wedge pressure increased. CONCLUSIONS: Induction of general anaesthesia with positive-pressure ventilation is regularly associated with a blood volume shift from intra- to extrathoracic compartments. Even in low-dose opioid monoanaesthesia with sufentanil--often regarded as relatively inert in haemodynamic terms--the phenomenon could be demonstrated as the primary cause of the often-observed decrease of arterial pressure. It seems, therefore, rationally justified to restore cardiac filling by generous administration of intravenous fluids, at least in patients with unaffected cardiac pump function. During induction of anaesthesia, central venous pressure and pulmonary capillary wedge pressure do not reliably indicate cardiac filling.

Perioperative monitoring of indocyanine green clearance and plasma disappearance rate in patients undergoing liver transplantation.

INTRODUCTION: Indocyanine green (ICG) elimination tests have been repeatedly suggested as an early predictor of graft function in patients with liver transplantation. Conventionally, ICG clearance (ClICG) is measured by a series of blood samples with subsequent laboratory analysis. More recently bedside techniques have become available to measure ICG concentrations in vivo and in addition to ClICG, the plasma disappearance rate of ICG (PDRICG) is increasingly being used. The aim of this study was to assess and to compare the normal time courses of ClICG and PDRICG in liver transplant recipients. METHODS: ClICG and PDRICG were measured perioperatively and at various times up to 24 h after liver transplantation. The bedside transpulmonary indicator dilution technique with an arterial fiberoptic-thermistor catheter was used to assess the ICG concentration time curve together with total circulating blood volume (Vd circ). RESULTS: Similar patterns of the time courses of ClICG and PDRICG with a fast recovery of ICG elimination in the early reperfusion period were observed. Compared to healthy subjects, ClICG was supranormal and PDRICG was slightly subnormal. In this study, Vd circ was increased at baseline and remained increased during surgery. CONCLUSIONS: PDRICG and ClICG are well suited to monitor onset and maintenance of graft function in patients undergoing liver transplantation. The PDRICG values measured tend to be relatively lower than ClICG because of an increased blood volume in these patients. By knowing these differences it is justified to monitor liver function in a very simple manner with PDRICG.

Reliability of cerebral blood flow measurements by transcerebral double-indicator dilution technique.

BACKGROUND AND OBJECTIVE: The recently developed transcerebral double-indicator dilution technique has proven to be a feasible monitoring alternative to measure global cerebral blood flow at the bedside. However, the short-term repeatability of transcerebral double-indicator dilution measurements has not yet been investigated. The present study was designed to investigate the accuracy in terms of reliability for repeated transcerebral double-indicator dilution measurements to assess global cerebral blood flow during a definite carbon dioxide challenge in a clinical trial. METHODS: The investigation was performed in 10 patients scheduled for elective coronary artery bypass grafting. After induction of anaesthesia, repeated cerebral blood flow measurements using transcerebral double-indicator dilution were performed during target normocapnia, hypocapnia and hypercapnia. For transcerebral double-indicator dilution measurements, a bolus injection of ice-cold indocyanine green was administered into a central vein. The resulting thermal dye dilution curves were recorded simultaneously in the aorta and the jugular bulb using combined fibreoptic thermistor catheters. Cerebral blood flow was calculated from the mean transit times of the indicators through the brain. Additionally, transcranial Doppler sonography was simultaneously performed to measure transient changes in the cerebral blood flow velocity. RESULTS: Transcerebral double-indicator dilution measurements revealed a reasonable coefficient of repeatability with 9.1, 9.7 and 20.2 mL min-1 100 g-1 during normo-, hypo- and hypercapnic conditions, respectively. However, a total of 20% of the administered measurements had to be rejected for methodological reasons. CONCLUSIONS: Repeated measurements with the transcerebral double-indicator dilution method show a reasonable repeatability. With consideration to the limitations of the transcerebral double-indicator dilution technique, this new method proves to be a reliable monitoring tool to measure global cerebral blood flow at the bedside.

Determination of total blood volume by indicator dilution: a comparison of mean transit time and mass conservation principle.

OBJECTIVE: Using indocyanine green (ICG), blood volume can be determined within minutes according to the mass conservation principle by back-extrapolation of the concentration/time curve to the time of injection (BVTinj) or by the transit time approach (BVMTT) as the product of cardiac output and mean transit time (MTT) of ICG through the circulation. To see which factor accounts for the difference between the two methods we measured cardiac output and MTT independently and compared the volumes with those obtained by dilution of Evans blue (BVEB). DESIGN: Prospective animal study. SETTINGS: University department of experimental anaesthesiology. ANIMALS: Six anaesthetised, spontaneously breathing dogs with chronically implanted ultrasound flow probes around the pulmonary artery. MEASUREMENTS AND RESULTS: BVMTT and BVTinj agreed closely (48 +/- 2 ml.kg-1 and 49 +/- 2 ml.kg-1), but underestimated blood volume by about 40% compared with BVEB (75 +/- 1 ml.kg-1). Transit times measured were 33 +/- 1 s and should be about 50 s as calculated from the quotient of BVEB and cardiac output. CONCLUSIONS: Both methods underestimate blood volume by about the same extent compared with BVEB, probably because slowly perfused compartments are not detected during the short measurement period of 4 min. In the case of the transit time approach, rather short transit times result and in the case of the mass conservation principle, back-extra-polation yields rather high plasma concentrations of ICG at the time of injection. Accordingly, the two methods seem to be equivalent for measuring blood volume rapidly, although the absolute volume is underestimated by about 40%.

Are microbubbles free flowing tracers through the Myocardium? Comparison of indicator-dilution curves obtained from dye dilution and echo contrast using harmonic power Doppler imaging.

BACKGROUND: Harmonic power Doppler imaging (H-PDI) has been introduced into the field of contrast echocardiography as a contrast-specific imaging modality. However, there has been considerable skepticism as to whether H-PDI would be quantifiable, because it depends on the destruction of microbubbles and has more complex signal processing than gray scale imaging. The aim of the present study was to evaluate the relationship between the concentration of microbubbles and the resulting H-PDI signals even under conditions where bubble destruction is most likely. Furthermore, we evaluated whether microbubbles of Levovist freely pass the microcirculation, which is a prerequisite for the assessment of myocardial blood flow. METHODS AND RESULTS: A strong positive correlation was found between the H-PDI signals and the amount of microbubbles up to the onset of acoustic shadowing (r = 0. 968, P<0.001). Time-intensity curves for H-PDI of air-filled microbubbles were compared with time-concentration curves of indocyanine green (ICG) in both a flow phantom and a working heart setup. The mean transit times (MTTs) through the myocardium of both agents were compared after a bolus injection into the left coronary artery. A close correlation was observed between 1/MTT and flow in both setups (r>0.98, P<0.0001). However, at high flow rates, the MTTs of the microbubbles were slightly, albeit not significantly, faster than those of indocyanine green. CONCLUSIONS: We conclude that microbubbles fulfill the prerequisites of free flowing tracers through the myocardium. Furthermore, H-PDI technology allows a reliable assessment of time-concentration curves of air-filled microbubbles up to the onset of acoustic shadowing.

Bedside monitoring of cerebral blood flow in patients with acute hemispheric stroke.

OBJECTIVE: To test the practicability of a new double indicator dilution method for bedside monitoring of cerebral blood flow (CBF) and to assess the clinical value of CBF monitoring as a prognostic tool for outcome and in therapy of elevated intracranial pressure (ICP) in patients with acute hemispheric stroke. DESIGN: Prospective study. Clinical evaluation of a new method. SETTING: Neurological intensive care unit of a university hospital. PATIENTS: Ten patients with acute complete middle cerebral artery territory- or hemispheric infarctions. INTERVENTIONS: Two combined fiberoptic thermistor catheters were placed in the right jugular bulb and in the thoracic aorta. Central venous injections of ice-cold indocyanine green dye were performed. CBF was estimated by calculating the mean transit times of the cold bolus and dye. MEASUREMENTS AND MAIN RESULTS: A total of 104 reproducible CBF measurements were obtained. No complications associated with the method were observed. Twelve pairs of measurements were performed within 30 mins with unchanged clinical conditions. The standard deviation of repeated measurements was 2.7 mL/100 g/min; the interrater reliability was between 0.95 and 0.99. The median CBF in patients who died (n = 4) was lower (27 mL/100g/min) than in those who survived (n = 6) (45 mL/100g/ min). Patients who died more frequently had low CBF values of <30 mL/100g/min (22 of 38; 58%) than patients who survived (10 of 54; 19%). A total of 37 CBF measurements were done during ICP elevation of >20 mm Hg. In patients who survived, ICP elevations were only associated with low CBF values in 5 of 26 events; whereas in patients who died, ICP elevations were associated with low CBF values in 8 of 11 events. CONCLUSIONS: The new double indicator dilution technique may be suitable for serial bedside CBF measurement. It is easy to perform and can be rapidly repeated in the ICU environment. Validation of the method by comparison with standard methods is needed. The preliminary data indicate that bedside monitoring of CBF may give prognostic information for outcome and may guide therapy of elevated ICP in patients with malignant hemispheric infarction.

Bedside assessment of cerebral blood flow by double-indicator dilution technique.

BACKGROUND: Currently, quantitative measurement of global cerebral blood flow (CBF) at bedside is not widely performed. The aim of the present study was to evaluate a newly developed method for bedside measurement of CBF based on thermodilution in a clinical setting. METHODS: The investigation was performed in 14 anesthetized patients before coronary bypass surgery. CBF was altered by hypocapnia, normocapnia, and hypercapnia. CBF was measured simultaneously by the Kety-Schmidt inert-gas technique with argon and a newly developed transcerebral double-indicator dilution technique (TCID). For TCID, bolus injections of ice-cold indocyanine green were performed via a central venous line, and the resulting thermo-dye dilution curves were recorded simultaneously in the aorta and the jugular bulb using combined fiberoptic thermistor catheters. CBF was calculated from the mean transit times of the indicators through the brain. RESULTS: Both methods of measurement of CBF indicate a decrease during hypocapnia and an increase during hypercapnia, whereas cerebral metabolic rate remained unchanged. Bias between CBF(TCID) and CBFargon was -7.1+/-2.2 (SEM) ml x min(-1) x 100 g(-1); precision (+/- 2 x SD of differences) between methods was 26.6 ml x min(-1) x 100 g(-1). CONCLUSIONS: In the clinical setting, TCID was feasible and less time-consuming than alternative methods. The authors conclude that TCID is an alternative method to measure global CBF at bedside and offers a new opportunity to monitor cerebral perfusion of patients.

Basics of myocardial pump function.

Myocardial pump function and the performance of the entire cardiovascular system are determined by preload, afterload and contractility. The best clinical measure of preload is the end-diastolic volume of the heart, which can be assessed by ventriculography, echocardiography or by indicator dilution techniques. Afterload is basically the wall tension during the ejection phase. For clinical purposes afterload can be reasonably monitored by arterial blood pressure. The most difficult parameter to assess under clinical conditions is contractility, since exact measurement of contractility requires instantaneous measurements of left-ventricular pressure-volume loops and an artificial afterload or preload challenge. However, most recent theoretical analysis of ventricular-arterial coupling by various models revealed that the ejection fraction seems to be an appropriate parameter to evaluate, whether the prevailing contractility matches preload and afterload conditions. An ejection fraction of approximately 60% under almost any clinical circumstances is associated with an optimal performance of the heart in terms of myocardial oxygen utilisation.

[Cardiac output determination with transpulmonary thermodilution. An alternative to pulmonary catheterization?]. / HZV-Bestimmung mittels transpulmonaler Thermodilution. Eine Alternative zum Pulmonaliskatheter?

UNLABELLED: Cardiac output measurements are often helpful in the management of critically ill patients and high risk-patients. In this study an alternative technique for measurement of cardiac output by the transpulmonary indicator dilution technique (TPID) was evaluated in comparison to conventional thermodilution using a pulmonary artery catheter. With TPID, a thermistor-tipped catheter (the smallest available is 1.3 F) is placed in the aorta via a femoral artery introducer. Thus, TPID can also be used in very small children in whom placement of a pulmonary artery catheter may be difficult or even impossible. In principle, TPID is less invasive since the possible complications of the pulmonary catheters are avoided. We investigated the accuracy and reproducibility of transpulmonary thermodilution in patients over a broad range in age and body surface. METHODS: Following approval by the ethics committee and written consent, the data were obtained from 21 patients without a circulatory shunt undergoing diagnostic heart catheterization. The patients were between 0.5 and 25.2 years old, their body surface between 0.35 and 1.89 m2. Measurements were performed in duplicate with bolus injections of ice-cold normal saline (0.15 ml/kg), randomly spread over the respiratory cycle. In total 48 thermodilution curves were measured simultaneously in the pulmonary artery and in the aorta. Thermodilution curves were monoexponentially extrapolated for elimination of recirculation and cardiac output was calculated with a standard Stewart Hamilton procedure. RESULTS: The amplitude of the typical arterial thermodilution curve shows a smaller and more delayed course than the pulmonary artery thermodilution curve. There was a very good correlation between the values found by pulmonary and TPID cardiac output measurements (R = 0.968). There was a slightly smaller cardiac output value measured by the TPID (Bias = -4.7 +/- 1.5% sem) The reproducibility of duplicate measurements with the two methods were nearly the same, the standard deviation of the difference was 10.9% for the pulmonary thermodilution method and 11.7% for TPID. DISCUSSION. TPID gives an alternative technique for measurement of cardiac output. We showed over a broad range in age and body surface a very good correlation with thermodilution measurements in the pulmonary artery. The slightly smaller values for TPID are explained by early recirculation, for clinical purposes the difference is negligible. However, the reproducibility of a method is clinically very important. Both methods showed in duplicate measurements basically the same reproducibility. The disadvantage of TPID in being more sensitive to baseline alteration is counterbalanced by less respiratory variability in comparison to the conventional thermodilution technique. However, by increasing the amount of injected indicator (i.e., 0.2 ml/kg approximately equal to 15 ml in an adult) it is possible to reduce the effect of baseline alteration. By using fiberoptic catheters it is even possible to use TPID as double-indicator dilution technique to measure intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). We conclude that in many patients TPID might be an attractive, less invasive and reliable alternative to conventional cardiac output measurement by pulmonary artery catheter.

[The effect of an intracardiac left-right shunt on thermodilution measurements of cardiac output. An extracorporeal circulation model]. / Einfluss eines intrakardialen Links-Rechts-Shunts auf pulmonal-arterielle Thermodilutionsmessungen des Herzzeitvolumens. Untersuchungen in einem extrakorporalen Kreislaufmodell.

Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extra-corporeal flow model. METHODS. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a mono-exponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. RESULTS. At moderate left-to-right shunts (Qp:Qs < 2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs > or = 2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. DISCUSSION AND CONCLUSION. Under varying levels of left-to-right shunt, both the response time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be

Application of a transpulmonary double indicator dilution method for postoperative assessment of cardiac index, pulmonary vascular resistance index, and extravascular lung water in children undergoing total cavo-pulmonary anastomosis: preliminary results in six patients.

Total cavo-pulmonary anastomosis (TCPA) is used for the functional correction of an increasing spectrum of congenital heart diseases. The passive pulmonary perfusion after surgical exclusion of the right ventricle has significant implications for the postoperative hemodynamic management of these patients. Because conventional pulmonary artery thermodilution catheters present methodologic problems in patients after TCPA, important cardiovascular variables such as cardiac index (CI) and pulmonary and systemic vascular resistance indices (PVRI, SVRI) usually cannot be assessed directly. In a preliminary series of six patients undergoing TCPA (age 6-22 years), the applicability of a transpulmonary double indicator dilution technique for postoperative determinations of CI, PVRI, SVRI, and extravascular lung water (EVLW) was investigated. After central venous injection of ice-cold indocyanine green (5 mg), thermal and dye dilution curves were recorded in the abdominal aorta using a combined 4F fiberoptic thermistor catheter. Qualitative assessment of the tracer curves did not show major differences in measurements in patients with pulsatile perfusion of the lungs. CI, SVRI, and EVLW could be determined by use of standard algorithms. Pulmonary perfusion pressure for the calculation of PVRI was based on the gradient between central venous and left atrial pressure. The quality of indicator dilution curves allowed determination of flow-related variables in 33 of a total of 34 sets of measurements. No catheter-related problems occurred during or after the period of investigation. Postoperative EVLW was within the range that is commonly accepted as normal for adults. Mean PVRI initially decreased during the postoperative course but showed a significant increase after extubation.(ABSTRACT TRUNCATED AT 250 WORDS)