G. Wietasch

HZV-Bestimmung mittels transpulmonaler Thermodilution Eine Alternative zum Pulmonaliskatheter?

ZusammenfassungDie Messung des Herzzeitvolumens (HZV) ist zur Überwachung und Therapiesteuerung von Risikopatienten und Schwerstkranken häufig hilfreich. Die vorliegende Untersuchung beschreibt die HZV-Bestimmung mittels transpulmonaler Thermodilution (TPID) und vergleicht sie mit der herkömmlichen pulmonalarteriellen Thermodilution, wie sie unter Verwendung eines Pulmonaliskatheters klinisch breit angewendet wird. Bei sehr guter Übereinstimmung zwischen pulmonalarteriellem und transpulmonalem HZV (Bias=−4,7%±1,5% sem) über den gesamten untersuchten Altersbereich (0,5 bis 25,2 Jahre), besteht bei Doppelbestimmung auch eine vergleichbare Reproduzierbarkeit für die beiden Verfahren (SD=10.9% vs. 11,7%). Der geringeren Beeinflussung der HZV-Messung mittels TPID vom respiratorischen Zyklus steht die etwas größere Anfälligkeit gegenüber spontanen Temperaturschwankungen des Patienten entgegen. Im Gegensatz zur respiratorischen Abhängigkeit der pulmonalarteriellen Thermodilution kann die Anfälligkeit der TPID gegenüber diesen Temperaturschwankungen jedoch durch eine höhere Indikatordosierung weiter reduziert werden. Die zusätzlichen Einsatzmöglichkeiten in der pädiatrischen Anästhesie und Intensivmedizin, die prinzipiell geringere Invasivität und niedrigere Kosten sind Vorteile dieser Methode. Sie kann aber nicht bei allen klinischen Fragestellungen den Pulmonaliskatheter ersetzen.AbstractCardiac 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 reproduciblity. 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≅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.

Clinical review : use of venous oxygen saturations as a goal - a yet unfinished puzzle

Shock is defined as global tissue hypoxia secondary to an imbalance between systemic oxygen delivery and oxygen demand. Venous oxygen saturations represent this relationship between oxygen delivery and oxygen demand and can therefore be used as an additional parameter to detect an impaired cardiorespiratory reserve. Before appropriate use of venous oxygen saturations, however, one should be aware of the physiology. Although venous oxygen saturation has been the subject of research for many years, increasing interest arose especially in the past decade for its use as a therapeutic goal in critically ill patients and during the perioperative period. Also, there has been debate on differnces between mixed and central venous oxygen saturation and their interchangeability. Both mixed and central venous oxygen saturation are clinically useful but both variables should be used with insightful knowledge and caution. In general, low values warn the clinician about cardiocirculatory or metabolic impairment and should urge further diagnostics and appropriate action, whereas normal or high values do not rule out persistent tissue hypoxia. The use of venous oxygen saturations seems especially useful in the early phase of disease or injury. Whether venous oxygen saturations should be measured continuously remains unclear. Especially, continuous measurement of central venous oxygen saturation as part of the treatment protocol has been shown a valuable strategy in the emergency department and in cardiac surgery. In clinical practice, venous oxygen saturations should always be used in combination with vital signs and other relevant endpoints.

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 translt 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/100g/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.

Effects of dexamethasone on intravascular and extravascular fluid balance in patients undergoing coronary bypass surgery with cardiopulmonary bypass.

Background Cardiac surgery with cardiopulmonary bypass is often associated with postoperative hemodynamic instability. In this regard beneficial effects of corticosteroids are known. The purpose of this study was to investigate whether these effects are due mainly to a modification of the intravascular and extravascular volume status or whether a more direct improvement of cardiovascular performance by corticosteroids is the underlying mechanism. Methods Twenty patients undergoing elective coronary bypass grafting were included in this randomized double-blind study. Patients of the treatment group received 1 mg/kg−1 dexamethasone after induction of anesthesia. In addition to the use of standard monitors and detailed fluid balance assessments, the transpulmonary double-indicator technique was used to measure extravascular lung water, total blood volume, and intrathoracic blood volume. Measurements were done after induction of anesthesia and 1 h, 6 h, and 20 h after the end of surgery. Results After cardiopulmonary bypass, no relevant increase in extravascular lung water was observed, despite highly positive fluid balances in all patients. A significantly smaller increase in extravascular fluid content was observed in the dexamethasone group. Total blood volume and intrathoracic blood volume did not differ in the two groups. Patients pretreated with dexamethasone had a decreased requirement for vasoactive substances and, in contrast with the control group, no increase in pulmonary artery pressure. Conclusions Extravascular fluid but not extravascular lung water is increased in patients after surgery with cardiopulmonary bypass. Pretreatment of adult patients with 1 mg/kg−1 dexamethasone before coronary bypass grafting decreases extravascular fluid gain and seems to improve postoperative cardiovascular performance. This effect is not caused by a better intravascular volume status.

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 CBFTCID and CBFargon was −7.1 ± 2.2 (SEM) ml · min−1 · 100 g−1; precision (± 2 · SD of differences) between methods was 26.6 ml · min−1 · 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.

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

AbstractIntroduction. 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.ZusammenfassungEinleitung. Indozyaningrün (ICG)-Eliminationstests wurden verschiedentlich als Frühindikator der Funktion des Spenderorgans nach einer Lebertransplantation empfohlen. Konventionell wird die ICG-Clearance (ClICG) aus einer Reihe von Blutproben in nachfolgenden Laboruntersuchungen bestimmt. Inzwischen sind aber auch Methoden verfügbar, die die Messung von ICG-Konzentrationen in vivo erlauben, sodass zunehmend die Plasmaverschwinderate von ICG (PDRICG) bestimmt wird. Ziel der vorliegenden Untersuchung war die Messung und der Vergleich der Zeitverläufe von ClICG und PDRICG bei Lebertransplantierten. Methodik. ClICG und PDRICG wurden perioperativ und bis 24 h postoperativ zu vorgegebenen Zeitpunkten bestimmt. Mit der Doppelindikator-Verdünnungstechnik und unter Verwendung eines arteriellen Fiberoptik-Thermistor-Katheters wurden die ICG-Konzentration-Zeit-Verläufe und das totale zirkulierende Blutvolumen (Vd circ) berechnet. Ergebnisse. Die Zeitverläufe der ClICG und der PDRICG– mit einer raschen Aufnahme der ICG-Elimination in der frühen Reperfusionsphase – waren ähnlich. Im Vergleich zu gesunden Probanden war die ClICG supranormal, die PDRICG jedoch leicht erniedrigt. Vd circ war bereits präoperativ erhöht und blieb auch intraoperativ supranormal. Schlussfolgerung. PDRICG und ClICG sind gut geeignet, um die Aufnahme und den Verlauf der Funktion einer Transplantatleber zu beurteilen. Die gemessene PDRICG ist wegen des erhöhten Blutvolumens dieser Patienten relativ gesehen niedriger als die ClICG. Bei Kenntnis dieser Unterschiede ist es gerechtfertigt, die Leberfunktion nach einer Transplantation mit der wenig aufwendigen Messung der PDRICG zu überwachen.

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.

Determinants of renal potassium excretion in critically ill patients : The role of insulin therapy

Objectives:Insulin administration lowers plasma potassium concentration by augmenting intracellular uptake of potassium. The effect of insulin administration on renal potassium excretion is unclear. Some studies suggest that insulin has an antikaliuretic effect although plasma potassium levels were poorly controlled. Since the introduction of glycemic control in the intensive care unit, insulin use has increased. We examined the relation between administered insulin and renal potassium excretion in critically ill patients under computer-assisted glucose and potassium regulation. Design:Prospective observational study. Setting:Twelve-bed surgical intensive care unit of a university teaching hospital. Patients:Consecutive intensive care unit patients. Interventions:Potassium and glucose levels were regulated by a computer-assisted decision support system. Both potassium and insulin were continuously administered by syringe pump. Measurements and Main Results:Renal potassium excretion was measured daily in the 24-hr urine collections. The 24-hr urinary samples of patients with kidney failure or on renal replacement therapy were excluded. Multivariate analysis with potassium excretion as the dependent variable was performed. In 178 consecutive patients, 1,456 24-hr urinary samples, were analyzed. Mean ± SD plasma potassium was 4.2 ± 0.3 mmol/L, with 79 ± 46 mmol/d of potassium administered and a mean insulin dose of 53 ± 38 U/day. Renal potassium excretion was 126 ± 51 mmol/day. After multivariate analysis correcting for relevant variables (including diuretics, pH, potassium levels and renal sodium excretion), insulin administration was independently and positively associated with renal potassium excretion. Other significant variables were potassium levels, potassium administration, renal sodium and chloride excretion, creatinine clearance, diuretic therapy, pH, known diabetes and intensive care unit admission day (R2 = .52; p <. 001). Conclusion:Insulin administration is associated with an increase in the renal potassium excretion in critically ill patients.

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 37 °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. 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 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. 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 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. 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 included in the area under curve.

Outcome predictors of uncomplicated sepsis.

BackgroundThe development of sepsis risk prediction models and treatment guidelines has largely been based on patients presenting in the emergency department (ED) with severe sepsis or septic shock. Therefore, in this study we investigated which patient characteristics might identify patients with an adverse outcome in a heterogeneous group of patients presenting with uncomplicated sepsis to the emergency department (ED).FindingsWe performed a retrospective cohort analysis of all ED patients presenting with uncomplicated sepsis in a large teaching hospital during a 3-month period. During this period, 70 patients fulfilled the criteria of uncomplicated sepsis. Eight died in the hospital. Non-survivors were characterized by a higher abbreviated Mortality in Emergency Department Sepsis (MEDS) score (7.2 ± 3.4 vs. 4.8 ± 2.9, p = 0.03) and a lower Hb (6.6 ± 1.2 vs. 7.7 ± 1.4, p = 0.03), and they used beta-blockers more often (75% vs. 19%, p < 0.01).ConclusionsNon-survivors of uncomplicated sepsis had on average a higher abbreviated MEDS score, a lower hemoglobin (Hb) and more often used β-blockers compared to survivors. Early identification of these factors might contribute to optimization of sepsis treatment for this patient category and thereby prevent disease progression to severe sepsis or septic shock.