S. Kazmaier

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

OBJECTIVE To 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). DESIGN Prospective, controlled, clinical study. SETTING University hospital. PARTICIPANTS Twelve patients undergoing MIDCAB. INTERVENTIONS Thirty-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. MEASUREMENTS AND MAIN RESULTS Absolute 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. CONCLUSION The results of the present study show that compared with thermodilution CO, pulse contour analysis enables accurate measurement of continuous CO in patients undergoing MIDCAB.

Cerebrovascular tone rather than intracranial pressure determines the effective downstream pressure of the cerebral circulation in the absence of intracranial hypertension.

Cerebral perfusion pressure is commonly calculated from the difference between mean arterial pressure and intracranial pressure because intracranial pressure is known to represent the effective downstream pressure of the cerebral circulation. Studies of other organs, however, have shown that effective downstream pressure is determined by a critical closing pressure located at the arteriolar level. This study was designed to investigate the effects of PCO2-induced variations in cerebrovascular tone on the effective downstream pressure of the cerebral circulation. Sixteen patients recovering from head injury were studied. Intracranial pressure was assessed by epidural pressure transducers. Blood flow velocity in the middle cerebral artery was monitored by transcranial Doppler sonography. Effective downstream pressure was derived from the zero flow pressure as extrapolated by regression analysis of instantaneous arterial pressure/middle cerebral artery flow velocity relationships. PaCO2 was varied between 30 and 47 mm Hg in randomized sequence. Intracranial pressure decreased from 18.5 ± 5.2 mm Hg during hypercapnia to 9.9 ± 3.1 mm Hg during hypocapnia. In contrast, effective downstream pressure increased from 13.7 ± 9.6 mm Hg to 23.4 ± 8.6 mm Hg and exceeded intracranial pressure at hypocapnic PaCO2 levels. Our results demonstrate that, in the absence of intracranial hypertension, intracranial pressure does not necessarily represent the effective downstream pressure of the cerebral circulation. Instead, the tone of cerebral resistance vessels seems to determine effective downstream pressure. This suggests a modified model of the cerebral circulation based on the existence of two Starling resistors in a series connection.

Prospective Clinical and Fiberoptic Evaluation of the Supreme Laryngeal Mask Airway

Background:In March 2007, a new disposable laryngeal mask airway (LMA) became available. The LMA Supreme™ (The Laryngeal Mask Company Limited, St. Helier, Jersey, Channel Islands) aims to combine the LMA Fastrach™ feature of easy insertion with the gastric access and high oropharyngeal leak pressures of the LMA ProSeal™. Methods:The authors performed an evaluative study with the LMA Supreme™, size 4, on 100 women to measure the ease of insertion, determinate the laryngeal fit by fiberoptic classification, evaluate the oropharyngeal leak pressure, and report adverse events. Results:Insertion of the LMA Supreme™ was possible in 94 patients (94%) during the first attempt, and in 5 patients (5%) during the second attempt. In one small patient, the LMA Supreme™ could not be inserted because of limited pharyngeal space. This patient was excluded from further analysis. Insertion of a gastric tube was possible in all patients at the first attempt. The median time for LMA Supreme™ insertion was 10.0 s (±4.7 s; range, 8–30 s). Laryngeal fit, evaluated by fiberscopic view, was rated as optimal in all patients, both immediately after insertion of the LMA Supreme™ and at the end of surgery. After equalization to room pressure, the mean cuff volume needed to achieve 60 cm H2O cuff pressure was 18.4 ml (±3.8 ml; range, 8–31 ml). The mean oropharyngeal leak pressure at the level of 60 cm H2O cuff pressure was 28.1 cm H2O (±3.8 cm H2O, range, 21–35 cm H2O). Eight patients (8.1%) complained of a mild sore throat. No patient reported dysphagia or dysphonia. Conclusions:Clinical evaluation of the LMA Supreme™ showed easy insertion, optimal laryngeal fit, and low airway morbidity. Oropharyngeal leak pressure results were comparable to earlier data from the LMA ProSeal™.

Flow velocity measurements as an index of cerebral blood flow. Validity of transcranial Doppler sonographic monitoring during cardiac surgery.

Background:Transcranial Doppler sonography is increasingly used to monitor changes in cerebral perfusion intraoperatively. However, little information is available about the validity of velocity measurements as an index of cerebral blood flow (CBF). The purpose of this study was to compare invasive and Doppler-derived measurements of cerebral hemodynamic variables during coronary artery bypass graft surgery. Methods:In 15 male patients, measurements of CBF and middle cerebral artery flow velocity (VMCA) were performed before and after induction of fentanyl-midazolam anesthesia, during hypothermic cardiopulmonary bypass (CPB), and at the end of the surgical procedure. Transcranial Doppler sonography recordings of systolic, diastolic, and mean VMCA, and derived parameters such as pulsatility (PI) and resistance (RI) indexes were recorded from the proximal segment of the right middle cerebral artery. CBF was measured by the Kety-Schmidt inert gas saturation method with argon as a tracer. To facilitate comparisons of CBF and VMCA measurements, changes between consecutive measurements were expressed as percentage values. Calculations of cerebral perfusion pressure and cerebral vascular resistance (CVR) were based on jugular bulb pressure. The cerebral metabolic rate for oxygen was calculated from CBF and the arterial — cerebral venous oxygen content difference. Results:Changes In mean VMCA paralleled changes in mean CBF except for hemodynamic changes associated with hypothermic CPB. At this stage of surgery, mean VMCA increased while actual CBF decreased. Separate analysis of the periods before and after CPB revealed a poor association between percentage changes In CBF and VMCA (r=0.26, P=0.36; r=0.51, P=0.06, respectively). Mean values of CVR, PI, and RI showed consistent changes after induction of anesthesia. After termination of CPB, mean CVR significantly decreased, whereas mean PI and RI remained virtually unchanged. Neither before nor after CPB was a clinically useful correlation found between percentage changes in PI, RI, and CVR (PI r=0.28, P=0.34; r=-0.47, P=0.09, respectively; RI r=0.16, P=0.59; r=-0.53, P=0.06, respectively). Conclusions:Hypothermic CPB seems to alter the relation between global CBF and flow velocity in basal cerebral arteries. Inconsistency in directional changes in CBF and VMCA at this stage of surgery might be attributable to changes in middle cerebral artery diameter, red blood cell velocity spectra, and regional flow distribution. Although changes in mean VMCA before and after CPB appear to parallel changes In mean CBF, individual responses of VMCA cannot reliably predict percentage changes in CBF. Furthermore, Doppler sonographic PI and RI cannot provide an approximation of changes in CVR during cardiac surgery.

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.

A RATIONAL BASIS FOR THE MEASUREMENT OF FREE PHENYTOIN CONCENTRATION IN CRITICALLY ILL TRAUMA PATIENTS

Phenytoin binding to serum proteins and factors influencing protein binding were investigated in 38 critically ill trauma patients. In 24% of these patients, the free fraction of phenytoin was ≤10%, whereas in 76%, the free phenytoin fraction was increased >10%—up to 24%. Nonantiepileptic co-medication, sex, or age had no influence on phenytoin binding in any of the 38 patients. Elevated free phenytoin fraction was found in those with hypoalbuminemia and hepatic and renal impairments. In these patients, the free phenytoin fraction should be measured routinely.

Effects of respiratory alkalosis and acidosis on myocardial blood flow and metabolism in patients with coronary artery disease

Background Variation of the arterial carbon dioxide partial pressure (PaCO2) is not uncommon in anesthetic practice. However, little is known about the myocardial consequences of respiratory alkalosis and acidosis, particularly in patients with coronary artery disease. The aim of the current study was to investigate the effects of variation in PaCO (2) on myocardial blood flow (MBF), metabolism, and systemic hemodynamics in patients before elective coronary artery bypass graft surgery. Methods In 10 male anesthetized patients, measurements of MBF, myocardial contractility, metabolism, and systemic hemodynamics were made in a randomized sequence at PaCO2 levels of 30, 40, and 50 mmHg, respectively. The MBF was measured using the Kety‐Schmidt technique with argon as a tracer. End‐diastolic left ventricular pressure and the maximal increase of left ventricular pressure were assessed using a manometer‐tipped catheter. Results The cardiac index significantly changed with varying PaCO (2) levels (hypocapnia, ‐ 9%; hypercapnia, 13%). This reaction was associated with inverse changes in systemic vascular resistance index levels. The MBF significantly increased by 15% during hypercapnia, whereas no change was found during hypocapnia. Myocardial oxygen and glucose uptake and the maximal increase of left ventricular pressure were not affected by varying Pa (CO)2 levels. Conclusions In anesthetized patients with coronary artery disease, short‐term variations in PaCO2 have significant effects on MBF but do not influence global myocardial oxygen and glucose uptake. Changes in systemic hemodynamics associated with respiratory alkalosis and acidosis are caused by changes in systemic vascular resistance rather than by alterations in myocardial contractility.

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±45 ml 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.

S-(+)-Ketamin und Kreislauf

ZusammenfassungDas Razemat des Ketamin kommt derzeit sowohl bei der Durchführung von Narkosen, im Rahmen einer Langzeitanalgosedierung auf der Intensivstation wie auch in der Notfallmedizin zum Einsatz. Neuere Untersuchungen zeigten eine etwa doppelt so große analgetische Potenz des rechtsdrehenden Isomers im Vergleich zum Ketamin-Razemat. Des weiteren ist aus tierexperimentellen Studien eine vergleichbare dosisabhängige Toxizität beider Substanzen bekannt. Demzufolge bestand berechtigte Hoffnung, daß durch Halbierung der erforderlichen Substanzmenge bei Verwendung von S-(+)-Ketamin eine entsprechende Reduzierung der bekannten unerwünschten Wirkungen möglich ist. In randomisierten, doppelblinden Studien an gesunden Probanden zeigten sich vergleichbare Anstiege von Herzfrequenz und arteriellem Blutdruck nach 2 mg/kg KG Ketamin-Razemat bzw. 1 mg/kg KG S-(+)-Ketamin. Auch die Zunahme der Katecholaminkonzentrationen im Plasma war vergleichbar. Diese Effekte wurden durch eine Prämedikation mit Midazolam stark reduziert. Auch bei niedriger Dosierung von 0,5 mg/kg KG S-(+)-Ketamin bzw. 1 mg/kg KG Ketamin-Razemat intramuskulär kam es bei gesunden Probanden zu vergleichbaren Anstiegen von Herzfrequenz und arteriellem Blutdruck. Gleichermaßen zeigten Untersuchungen an älteren Patienten, die sich einem größeren orthopädischem Eingriff unterziehen mußten, gleiche sympathomimetische Kreislaufeffekte nach 1 mg/kg KG S-(+)- Ketamin oder 2 mg/kg KG Ketamin-Razemat. Die initialen Blutdruckanstiege führten bei drei Patienten der Razematgruppe zum Abbruch der Untersuchung. In beiden Gruppen kam es zu einem signifikanten und vergleichbaren Anstieg der Plasma-Katecholamine. Ähnliche Untersuchungen an älteren Patienten, die sich einem größeren orthopädischen Eingriff unterziehen mußten, zeigten im Vergleich einer TIVA mit Alfentanil bzw. S-(+)-Ketamin positive Effekte des Ketamin durch stabile intraoperative Kreislaufverhältnisse. Dagegen waren die Ergebnisse einer eigenen Untersuchung zu den Kreislaufwirkungen von S-(+)-Ketamin bzw. Ketamin-Razemat bei Patienten, die sich einer aortokoronaren Bypass-Operation unterzogen, von den Folgen der sympathikotonen Stimulation geprägt. Auch nach starker Sedierung mit Midazolam traten bei jeweils drei von sieben Patienten beider Gruppen erhebliche Anstiege des arteriellen Blutdrucks und der Herzfrequenz auf. In einem Fall der S-(+)-Ketamin-Gruppe mußte die Untersuchung abgebrochen werden. Insgesamt sprechen alle vorliegenden Untersuchungsergebnisse dafür, daß die sympathikotonen Kreislaufeffekte des S-(+)-Ketamin auch bei halber Dosierung im Vergleich zum Ketamin-Razemat nicht signifikant reduziert werden.AbstractThe S-(+) isomer of ketamine has about twice the analgesic potency of the clinically used racemic mixture. Therefore, the known side effects may be reduced when one-half of the usual dose is administered. Several prospective, randomised, and double-blinded studies have been performed to assess whether the S-(+) isomer of ketamine is superior to the racemic mixture with respect to circulatory side effects.Studies in young, healthy volunteers showed that heart rate (HR) and arterial blood pressure (ABP) rise significantly after injection of 2 mg/kg ketamine racemate and 1 mg/kg S-(+) isomer without any significant difference between groups. In the study of Doenicke et al. plasma levels of adrenaline (A) were higher in the racemate group, whereas no difference was found in elevated plasma levels of noradrenaline (NA). Premedication with midazolam blunted major haemodynamic changes. The investigation of Adams et al. confirmed that HR and ABP rise significantly after injection of 2 mg/kg ketamine racemate and 1 mg/kg S-(+) isomer without any significant difference between groups. In this study, no differences were found between groups concerning elevated plasma levels of A and NA. A further study in healthy volunteers also showed comparable haemodynamic changes following i.m. injection of 1.0 mg/kg ketamine racemate or 0.5 mg/kg S-(+) isomer without any significant difference between groups.In a previous clinical study including 40 elderly patients undergoing elective orthopaedic surgery, total intravenous anaesthesia (TIVA) was performed with S-(+)-ketamine or ketamine racemate as an analgesic compound. For induction of TIVA, patients received 0.1 mg/kg midazolam and 1 mg/kg S-(+)-ketamine or 2 mg/kg racemic ketamine, respectively. Throughout surgery, a continuous infusion of 2 mg/kg per hour S-(+)-ketamine or 4 mg/kg racemic ketamine was administered. Three patients in the racemate group showed severe arterial hypertension after induction of anaesthesia and were withdrawn from the study. In both groups plasma A and NA levels as well as HR and ABP increased significantly. In our own randomised, double-blinded study, haemodynamic effects of 2 mg/kg S-(+)-ketamine and 4 mg/kg ketamine racemate, respectively, were investigated in 14 patients undergoing elective aorto-coronary bypass surgery. In both groups HR and ABP significantly increased in 3 patients, each although all patients were deeply sedated with midazolam. One patient in the S-(+)-ketamine group showed severe arterial hypertension and tachycardia after induction of anaesthesia and was withdrawn from the study.With respect to haemodynamic changes, the pharmacodynamic effects of ketamine racemate and S-(+)-ketamine are comparable. Therefore, it can be concluded that neither ketamine nor S-(+)-ketamine should be used in patients who suffer, e.g., from arterial hypertension and coronary artery disease.

[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. 50 mmHg) 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