W. Buhre

Comparison of cardiac output assessed by pulse-contour analysis and thermodilution in patients undergoing minimally invasive direct coronary artery bypass grafting

OBJECTIVEnTo investigate the precision and accuracy of continuous pulse contour cardiac output (PCCO) compared with intermittent transcardiopulmonary (TCPCO) and pulmonary artery thermodilution (TDCO) measurements in patients undergoing minimally invasive coronary bypass surgery (MIDCAB).nnnDESIGNnProspective, controlled, clinical study.nnnSETTINGnUniversity hospital.nnnPARTICIPANTSnTwelve patients undergoing MIDCAB.nnnINTERVENTIONSnThirty-six measurements of PCCO and thermodilution cardiac output (CO) were simultaneously performed after the start of surgery, during bypass grafting, and at the end of surgery. TCPCO and TDCO were simultaneously assessed by three injections of ice-cold saline randomly spread over the respiratory cycle. The pulse contour device was initially calibrated with an additional set of aortic thermodilution measurements.nnnMEASUREMENTS AND MAIN RESULTSnAbsolute values of CO ranged between 1.6 and 9.2 L/min. A close agreement among the three techniques was observed at all measurements. Mean bias between PCCO and TDCO and TCPCO was 0.003 L/min (2 SD of differences between methods = 1.26 L/min) and 0.27 L/min (2 SD of differences between methods = 1.16 L/min), respectively. The correlation coefficients were r2 = 0.90 for TCPCO versus PCCO and r2 = 0.88 for TDCO versus PCCO.nnnCONCLUSIONnThe results of the present study show that compared with thermodilution CO, pulse contour analysis enables accurate measurement of continuous CO in patients undergoing MIDCAB.

Changes in cardiac output and intrathoracic blood volume: a mathematical coupling of data?

Background: Measurements of intrathoracic blood volume (ITBV) provide volumetric information about cardiac preload and are used to investigate the cause of alterations in cardiac output (CO). On the other hand, CO is required to calculate ITBV. Thus, concerns have been raised with respect to a mathematical coupling of data. The aim of this prospective, clinical study was to investigate whether a variation in CO induced by high‐dose beta‐blockade influences thermodilution measurements of ITBV in the absence of changes in intravascular volume in patients undergoing minimally invasive coronary artery bypass grafting.

Assessment of intrathoracic blood volume Thermo-dye dilution technique vs single- thermodilution technique

ZusammenfassungEine vereinfachte Thermodilutionstechnik zur Bestimmung des intrathorakalen Blutvolumens (ITBVTD) wurde hinsichtlich ihrer Genauigkeit mit der etablierten Doppelindikatordilutionstechnik unter Verwendung der Indikatoren Kälte und Indozyaningrün (ITBVDD) verglichen. Es wurden 10 Patienten, die sich einem neurochirurgischen Eingriff in sitzender Position unterziehen mußten, in die Untersuchung einbezogen. Das intrathorakale Blutvolumen wurde vor und nach Narkoseeinleitung sowie nach Umlagerung in die sitzende Position bestimmt. Das ITBVTD war im Vergleich zum ITBVDD im Mittel um 32±45u2005ml m–2 erhöht. Der mit der Doppelindikatordilutionstechnik bestimmte Abfall des ITBVDD nach Narkoseeinleitung sowie nach Umlagerung der Patienten in die sitzende Position ging jedoch mit vergleichbaren Änderungen des ITBVTD einher. Die Reproduzierbarkeit der Methoden war vergleichbar. Die vorliegenden Ergebnisse zeigen, daß mit der Thermodilutionstechnik trotz einer geringen systematischen Überschätzung relative Änderungen des intrathorakalen Blutvolumens verläßlich wiedergegeben werden. Für die Bestimmung von Absolutwerten sind jedoch intermittierende Bestimmungen des ITBV mit der etablierten Doppelindikatordilutionstechnik zu empfehlen.

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)

Influence of intra-aortic balloon pumping on cerebral blood flow pattern in patients after cardiac surgery.

Background and objective: The effects of intra‐aortic balloon pumping (IABP) on cerebral perfusion are still a matter of debate. End‐diastolic reversal of blood flow in cerebral arteries has been observed in a small number of patients. We prospectively investigated the incidence and the amount of transient cerebral artery blood flow reversal during balloon pumping in patients recovering from cardiac surgery. Methods: In 23 patients receiving IABP support, blood flow velocities in the right middle cerebral artery were assessed by transcranial Doppler‐sonography. Additionally, systemic haemodynamics were monitored. In each patient, measurements were performed at three different pump settings: without support, assist ratio 1 : 1 and assist ratio 1 : 2. Results: In 8 of 23 patients, balloon pumping caused a transient diastolic reversal of blood flow in the middle cerebral artery during balloon deflation. Antegrade mean flow velocity in the middle cerebral artery significantly increased from 57 ± 27 to 61 ± 26 (assist ratio 1 : 1) and 61 ± 29 cm s−1 (assist ratio 1 : 2) (P < 0.05). Taking transient blood flow reversal into account, net mean flow velocity did not increase with balloon pump support. Systemic haemodynamic parameters remained unchanged. Conclusion: Left ventricular support with IABP significantly changed flow patterns in basal cerebral arteries of our patients. In 35% of patients, support resulted in a transient reversal of intracranial blood flow which counterbalanced a slight increase in mean antegrade flow.

Pathogenetic mechanisms of venous congestion after the Fontan procedure.

BACKGROUNDnThe hemodynamic status after a Fontan type procedure for definitive palliation of functionally univentricular hearts is dominated by a high central venous pressure, which seems to be one of several factors responsible for venous congestion appearing as a frequent complication in the early and late postoperative course. The purpose of our study was to find other hemodynamic parameters correlating with the presence of venous congestion and effusions in these patients.nnnMETHODSnWe compared the hemodynamic data of 18 patients who had an uneventful long-term course after a Fontan type procedure with the respective data of 10 patients who developed symptoms of venous congestion in the immediate postoperative period. Based on a theoretical model, we developed an algorithm to calculate mean hydrostatic capillary pressure from mean arterial pressure, systemic vascular resistance index and central venous pressure.nnnRESULTSnPulmonary vascular resistance index (2.1 +/- 1.0 mmHg L-1 min m2), mean left atrial pressure (9.7+/-4.0 mmHg) and cardiac index (3.6+/-0.6 l/min/m2) are mainly normal in patients with venous congestion in the immediate postoperative period, but mean hydrostatic capillary pressure is significantly higher compared to patients without venous congestion (24.3+/-3.1 vs 18.3+/-4.0 mmHg). Lower mean hydrostatic capillary pressures in these patients are due to a highly significant increase of systemic vascular resistance index (18.6+/-4.2 versus 33.6+/-6.6 mmHg L-1 min m2) and a concomitant decrease of cardiac index to 2.4+/-0.3 l/min/m2.nnnCONCLUSIONSnThe increase of mean hydrostatic capillary pressure, caused by high central venous pressures but also by relatively low systemic vascular resistance indexes, seems to be the hemodynamic key parameter responsible for venous congestion and effusions in patients after a Fontan type procedure in the immediate postoperative period.

[The effect of nitroglycerin on cerebrovascular circulation, cerebrovascular CO2-reactivity and blood flow rate in basal cerebral arteries].

ZusammenfassungZiel dieser prospektiven kontrollierten Studie war es, 1.) den Einfluß von Nitroglyzerin (NTG) auf den globalen zerebralen Blutfluß (CBF) und die zerebrovaskuläre CO2-Reaktivität zu untersuchen, und 2.) den Einfluß von NTG auf den Zusammenhang zwischen CBF und der Flußgeschwindigkeit in der A. cerebri media (VMCA) zu bestimmen. Bei 10 kardiochirurgischen Patienten wurde zunächst während einer Kontrollphase in randomisierter Reihenfolge eine Hypo- und Hyperkapnie (paCO2≈30 bzw. 50u2005mmHg) induziert. Anschließend wurden alle Messungen unter einer Infusion von 1,5·μg·kg−1·min−1 NTG bei identischen paCO2-Niveaus wiederholt. Die Bestimmung des CBF erfolgte mittels der Kety-Schmidt-Technik. Simultan wurde jeweils die VMCA mittels eines 2-MHz-Dopplersystems aufgezeichnet. Unter NTG-Infusion nahm der zerebrale Perfusionsdruck um 15–17% ab, dennoch zeigte sich aufgrund einer Reduktion des zerebrovaskulären Widerstands eine erhebliche Zunahme des CBF um 96 bzw. 69%, während die VMCA geringfügig abfiel. Die CO2-Reaktivität des CBF zeigte keine signifikante Änderung. Die Ergebnisse der vorliegenden Untersuchung zeigen zum einen, daß NTG zu einer ausgeprägten Zunahme der globalen Hirndurchblutung führt, sofern kein kritischer Abfall des zerebralen Perfusionsdrucks eintritt. Zum anderen legen die Ergebnisse des durchgeführten Methodenvergleichs nahe, daß auch die proximalen Segmente der A. cerebri media (MCA) unter dem Einfluß von NTG eine Vasodilatation aufweisen, die zu einer methodisch relevanten Diskrepanz zwischen relativen Änderungen der Hirndurchblutung und der MCA-Strömungsgeschwindigkeit führt.AbstractThe cerebral haemodynamic effects of vasodilators are of clinical interest because a decrease in mean arterial pressure (MAP) might alter global cerebral blood flow (CBF). Luxury perfusion of the brain, in contrast, might be unfavourable in patients with reduced intracranial compliance. Despite the widespread use of nitroglycerine (NTG), little is known about the cerebral haemodynamic consequences of NTG infusions in humans. This prospective, controlled study was designed: (1) to investigate the effects of NTG on CBF and cerebrovascular CO2 reactivity and (2) to compare reference measurements o

Peroperative cardiovascular stability during brainstem surgery. The use of high-dose methylprednisolone compared to dexamethasone. A retrospective analysis.

Background: In neurosurgical procedures within brainstem structures, corticosteroids are routinely administered to prevent oedema and to reduce intraoperative trauma. After replacing the routine administration of dexamethasone (DX) by high‐dose methylprednisolone (MP) during surgery for tumours within brainstem structures, a decreased incidence of intraoperative haemodynamic instability events was observed. To test this hypothesis, a retrospective analysis was performed.

Combined approach for internal carotid artery stenosis and cardiovascular disease in septuagenarians – a comparative study

OBJECTIVEnThe best surgical approach for concomitant carotid artery and cardiac disease remains controversial. Many studies proved the safety and efficiency of simultaneous surgery. We aimed to demonstrate the same benefits for patients > or = 70 years.nnnMETHODSnWe retrospectively evaluated 205 patients simultaneously operated upon between 1988 and 1998. Group A comprised patients < 70 years (n = 110), group B > or = 70 years, (n = 95). Risk factors, neurologic and cardiac history, angiographic findings, operative data, morbidity and mortality (30-day-postoperatively) were analysed. The mean age was 62 years in group A and 75 years in group B. All patients with symptomatic carotid artery disease, stenosis > 70% or ulcerative carotid disease had simultaneous surgery. Always, the carotid artery was addressed first.nnnRESULTSnPatients in group B had a higher prevalence of peripheral vascular disease (P = 0.0005), renal insufficiency (P = 0.0011) and COPD (P = 0.03). Urgent operation was indicated in 19% of group A patients vs. 37% in group B. In group A 70% were asymptomatic regarding the carotid vs. 48% in group B. Left ventricular dysfunction was present in 45% (group A) and 58% (group B). In the present study 4% in group A and 7% in group B suffered a perioperative myocardial infarction. Pathologic changes of the contralateral carotid were found in 42 vs. 57% (A vs. B). Mortality due to cardiac causes was 1 and 5%, respectively. The combination of persistent neurologic deficit and neurologic death occurred in 3% in group A (n = 3) and 5% in group B (n = 5). Postoperative neuro-cognitive dysfunction was more common in group B (35 vs. 16%; P = 0.01).nnnCONCLUSIONSnThe incidence of persistent neurologic deficits and neurologic mortality in patients > or = 70 years is acceptable, and low in patients < 70 years. Preoperative risk factors are increasing with age and are related to the higher mortality in elderly patients. Due to our results we will conclude that the combined approach for carotid stenosis and cardiovascular disease is the method of choice in this high-risk population.

Einflu eines intrakardialen Links-Rechts-Shunts auf pulmonal-arterielle Thermodilutionsmessungen des Herzzeitvolumens@@@Influence of intracardiac left-to-right shunts on thermodilution measurements of cardiac output

Zusammenfassung. Thermodilutionsmessungen des HZV mittels pulmonal-arterieller Einschwemmkatheter repräsentieren im engeren Sinne den pulmonalen Blutfluß (Qp). Bei Vorliegen eines Vorhof- oder Ventrikelseptumdefekts können jedoch unphysiologisch frühe Rezirkulationen des injizierten Indikators zu methodischen Problemen führen. In der vorliegenden Untersuchung wurde daher in einem Kreislaufmodell der Einfluß eines Links-Rechts-Shunts auf 2 unterschiedliche HZV-Meßsysteme überprüft. Die Flußmessungen erfolgten bei 37u2009°C in zirkulierendem Blut unter Variation des Qp:Qs-Verhältnisses von 1:1 bis 2,5:1, eine Zentrifugalpumpe diente als Flußgenerator und als Mischkammer für den injizierten Indikator. Referenzmessungen des pulmonalen und des systemischen Stromzeitvolumens (Qs) wurden mittels elektromagnetischer Flowmeter durchgeführt. Hohe Shuntvolumina führten aufgrund einer mangelhaften Diskriminierung der Shunt-bedingten Kälterezirkulation zu einer erheblichen Unterschätzung des aktuellen Qp. Abweichungen von den Referenzflußmessungen fanden sich insbesondere bei einer vergleichsweise hohen Zeitkonstante des verwendeten Thermistors sowie bei Verwendung konventioneller Auswertungsalgorithmen, die eine monoexponentielle Extrapolation auf der Basis eines schematisch definierten Kurvenintervalls beinhalten. Die mangelnde Abgrenzung rezirkulierender Indikatoranteile führte zur Ermittlung eines Stromzeitvolumens, das an Stelle von Qp näherungsweise Qs repräsentierte. Eine bessere Übereinstimmung mit Qp-Referenzmessungen konnte durch ein dem Einzelfall angepaßtes Extrapolationsverfahren erzielt werden, das mittels Regressionsanalysen denjenigen Kurvenabschnitt ermittelt, der einem monoexponentiellen Abfall tatsächlich am nächsten kommt.Abstract. 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 extracorporeal 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.u20051). 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 monoexponentially 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≥2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig.u20052). This was particularly true when a slow-response thermistor catheter was used (Fig.u20053). 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.u20054). 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 reponse 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.u20055). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig.u20056). 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 included in the area under curve.