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Biomedical subjects

A Hoeft

Publications and source records attributed to A Hoeft.

At least 55 records · Page 3Linked to original sources
PubMed1999

Endotoxin inhibits heat shock protein 70 (HSP70) expression in peripheral blood mononuclear cells of patients with severe sepsis.

OBJECTIVE: To investigate the ex vivo endotoxin-inducible heat shock protein 70 (HSP70) expression in the peripheral blood mononuclear cells (PBMC) of patients with severe sepsis in order to assess the capacity of this potentially protective response during systemic inflammation. DESIGN: Prospective observational study in consecutive patients with severe sepsis and healthy blood donors. SETTING: Surgical intensive care unit in a university hospital. PATIENTS AND PARTICIPANTS: Eleven patients with the diagnosis of severe sepsis, one patient who had recovered from severe sepsis and 13 healthy blood donors. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: We studied the inducibility of HSP70 expression in the PBMC of patients with severe sepsis and healthy blood donors ex vivo. Human whole blood was incubated with variable lipopolysaccharide (LPS from Salmonella minnesota Re 595) concentrations (0; 0.1; 10; 100 ng/ml) for different periods of time (0.5; 2; 4; 10 h). The PBMC were separated by Ficoll density gradient and then disrupted by hypotonic lysis. HSP70 was measured by means of enzyme-linked immunosorbent assay (ELISA). We found a LPS dose- and time-dependent inhibition of ex vivo HSP70 expression in the PBMC of both patients with severe sepsis and healthy individuals. However, the levels of HSP70 expression in patients were significantly lower compared to those of healthy individuals at all LPS concentrations and incubation times. On average, HSP70 expression in the PBMC of healthy controls was 2.8 (range 1.2-3.9) times higher than in patients. HSP70 expression was inducible by thermal heat shock in the PBMC of both patients and healthy individuals. CONCLUSIONS: Endotoxin inhibits HSP70 expression in PBMC ex vivo. In vivo, the suppression of HSP70 expression induced by endotoxin and high levels of proinflammatory cytokines may contribute to the cellular dysfunction of immunocompetent cells concerning antigen presentation, phagocytosis and antibody production associated with decreased resistance to infectious insults during severe sepsis.

Adult↗
PubMed1999

Isoflurane, nitrous oxide, and fentanyl pharmacodynamic interactions in surgical patients as measured by effects on median power frequency.

STUDY OBJECTIVE: To identify and quantify the simultaneous interactions of isoflurane, nitrous oxide (N2O), and fentanyl during surgical procedures. The slowing of the EEG to a median power frequency of 2 Hz to 3 Hz was chosen as the measure of pharmacodynamic drug effect. DESIGN: Prospective, randomized, open label. SETTING: Operating room of a university hospital. PATIENTS: 65 ASA physical status I and II patients undergoing gynecological laparatomies. INTERVENTIONS: 25 patients received no fentanyl. 20 patients received a loading dose of 100 micrograms fentanyl and a continuous infusion of 70 micrograms.h-1 fentanyl. Calculated effect compartment concentrations were 0.7 ng.ml-1 between the first and second hours after induction of anesthesia. Another 20 patients received a loading dose of 200 micrograms fentanyl and a continuous infusion of 150 micrograms.h-1 fentanyl; the respective effect compartment concentrations were 1.5 ng.ml-1. N2O was randomly administered in concentrations of 0, 20, 40, and 60 vol%; in the group that did not receive fentanyl, we additionally investigated 75 vol% N2O. Each patient received two different N2O concentrations, with each combination of N2O and fentanyl finally applied to ten patients. Isoflurane vaporizer settings were chosen so that the median power frequency was held between 2 Hz and 3 Hz. The type and degree of interaction among the three anesthetic drugs was analyzed based on a generalized isobole approach. MEASUREMENTS AND MAIN RESULTS: The interaction of isoflurane, N2O, and fentanyl is compatible with additivity. A model with regard to the relative potencies and age dependency is given by: [formula: see text] with C0,iso = 1.30 vol%, C0,N2O = 177 vol%, C0,fen = 10.6 ng.ml-1, and a = -0.0031 yr-1. where conc. = end-tidal or effect compartment concentrations. CONCLUSION: The potency of N2O and fentanyl to substitute isoflurane in maintaining a median power frequency of 2 Hz to 3 Hz during surgery is less than anticipated from minimum alveolar concentration studies.

Adult↗
PubMed1999

Ergonomic evaluation of an ecological interface and a profilogram display for hemodynamic monitoring.

OBJECTIVE: Comprehensive monitoring of the patient state and subsequent decision making is an essential part of the task of an anaesthetist. The physicians' decision making process is based upon a concept of partly abstract physiologic parameters such as depth of anaesthesia or contractility. This concept is derived from the measured parameters given on todays' trend displays in addition to context information available for the anaesthetist. We investigated two alternative approaches of display design for hemodynamic monitoring: 1) integrated displays based on ecological interface design, and 2) profilogram displays based on intelligent alarms. METHOD: To evaluate differences in decision making, the two displays and a trend display were compared in an experimental set-up with computer simulated vital parameter curves. From a start state with random parameter deviations from the ideal state, subjects had to achieve the ideal circulatory performance as fast as possible by manipulating vasomotor tone, heart rate, blood volume and contractility. To analyse subjects' decision making process, eye-tracking, event-logging, and the method of think aloud protocols were used. Twenty anaesthesiologists performed 113 experiments (approximately 2 with each display). RESULTS: The anaesthetists failed to achieve the task in 37% using the trend display, in 19% using the profilogram display, and in 13% using the ecological interface. Hence, a safer task solution was possible with the ecological interface and the profilogram display but at the expense of various performance parameters such as higher trial time, more interactions with the simulated system, and more frequent eye movements. In contrast to the trend display and the profilogram display, where anaesthetists were mainly focussed on controlling the left atrial pressure, such an behaviour was less observed with the ecological interface. CONCLUSION: Our results have shown that subjects came to more effective solutions with the traditional trend display. The main reason for this result may be their years of experience with this kind of display type. Regarding safe and goal-intended decision finding, the results are encouraging for further experiments with redesigned ecological displays. But these displays ought to have smoother changes with respect to the traditional trend displays. Furthermore, new experiments have to be performed under real or fairly real (e.g. together with an anaesthesia simulator) conditions to underline the positive results for ecological interfaces.

Adult↗
PubMed1999

Changes in central venous pressure and pulmonary capillary wedge pressure do not indicate changes in right and left heart volume in patients undergoing coronary artery bypass surgery.

The value of pulmonary artery catheterization is a matter for discussion. Previous studies suggest that direct measurements of intravascular volume distribution and cardiac volume indices may be of greater relevance than central venous and pulmonary capillary wedge pressure. We therefore used a thermo-dye dilution technique for the quantification of central blood volume, right ventricular end-diastolic volume and left heart volume in patients undergoing coronary artery bypass surgery. Measurements were performed after the induction of anaesthesia as well as 1, 6 and 24 h after surgery. Central venous pressure was significantly increased at 1 and 6 h, whereas right ventricular end-diastolic volume was increased only at 6 h post-operatively. Pulmonary capillary wedge pressure showed a tendency to increase whereas left heart and central blood volume decreased significantly after surgery. The results of the present study suggest that changes in cardiac filling pressure do not indicate changes in indices of cardiac volume in patients after coronary bypass surgery.

Blood Volume↗
PubMed1999

Practice of epidural analgesia for labour pain: a German survey.

Epidural analgesia is one of the preferred methods of analgesia for labour. The aim of the present survey was to evaluate current practice in obstetric analgesia in departments of anaesthesia and to make a comparison with former surveys from Germany and other countries. Questionnaires on the practice of pain relief, especially epidural analgesia, during labour and delivery were sent to 1178 anaesthetic departments in Germany in the second half of 1996. Five hundred and thirty-two completed replies were received, which represent 46.9% of all German obstetric units. The majority of the departments of anaesthesia practising epidural analgesia have an epidural rate of less than 10% and 10.2% of the departments do not offer this method to their parturients. In 86.8% of all units performing epidural analgesia, the epidural catheter is placed by an anaesthetist. Only 6.5% of the units provide a 24-h epidural service which is exclusively assigned to labour and delivery. In 77.8% of the units, this service is not exclusively assigned to obstetrics, but also to other duties. Of the obstetric units offering epidural analgesia, 14.7% have no epidural service at night. Plain local anaesthetics for epidural analgesia are used by 55.9% of the departments, a combination of local anaesthetics with epidural opioids by 28.7%. Epidural analgesia is predominantly (82.2%) maintained by intermittent bolus administration. Although the rate of epidural analgesia increased during recent decades, this method is not offered to all parturients. Further improvements in the use of epidural analgesia for labour seem to be necessary.

Analgesia, Epidural↗
PubMed1999

Population pharmacokinetics of piritramide in surgical patients.

BACKGROUND: Piritramide is a synthetic opioid used for postoperative analgesia in several European countries. The authors present a mixed-effects model of its population pharmacokinetics in patients undergoing surgery. METHODS: After institutional approval and informed patient consent was obtained, 29 patients who were classified as American Society of Anesthesiologists physical status I or II and aged 21-82 yr were enrolled in the study. They received 0.2 mg/kg piritramide as an intravenous bolus before anesthesia was induced. Central venous blood samples were drawn for as long as 48 h after administration of the drug. The plasma concentration of piritramide was determined by gas chromatography. The concentration-time data were analyzed by mixed-effects modeling. Target-controlled infusions and intermittent bolus regimens were simulated to identify a regimen suitable for patient-controlled analgesia based on population pharmacokinetics and published pharmacodynamic data. RESULTS: The pharmacokinetics of piritramide were described adequately by a linear three-compartment model. Patient age and weight were significant covariates. The values of the pharmacokinetic parameters are: V1 = 50.5 [1], V2 = 150 x (1 + 9.32 x 10(-3) x (age - 47 yr)) [l], V3 = 212 x (1 + 6.37 x 10(-3) x (age - 47 yr)) [l], Cl1 = 0.56 x (1 - 6.14 x 10(-3) x (age - 47 yr)) [l/min], Cl2 = 8.25 x (1 + 2.02 x 10(-2) x (Wt - 74 kg)) [l/min], Cl3 = 0.80 [l/min]. The age of 47 yr and the weight of 74 kg refer to the median values for these factors in the patients studied. Rapid distribution, slow distribution, and elimination half-lives for the median patient are 0.05, 1.34, and 10.43 h, respectively. The context-sensitive half-time after a 24-h infusion is predicted at 10.5 h in a 75-yr-old patient compared with 7 h for the median patient. CONCLUSIONS: Piritramide is distributed extensively and eliminated slowly. The pharmacokinetic profile of the drug allows for intermittent bolus administration even when constant effect compartment concentrations are desirable, e.g., for PLA.

Adult↗
PubMed1999

Pharmacokinetic-pharmacodynamic modeling of the respiratory depressant effect of alfentanil.

BACKGROUND: Although respiratory depression is the most well-known and dangerous side effect of opioids, no pharmacokinetic-pharmacodynamic model exists for its quantitative analysis. The development of such a model was the aim of this study. METHODS: After institutional approval approval and informed consent were obtained, 14 men (American Society of Anesthesiologists physical status I or II; median age, 42 yr [range, 20-71 yr]; median weight, 82.5 kg [range, 68-108 kg]) were studied before they underwent major urologic surgery. An intravenous infusion of alfentanil (2.3 microg x kg(-1) x min(-1)) was started while the patients were breathing oxygen-enriched air (fraction of inspired oxygen [FIO2 = 0.5) over a tightly fitting continuous positive airway pressure mask. The infusion was discontinued when a cumulative dose of 70 microg/kg had been administered, the end-expiratory partial pressure of carbon dioxide (PE(CO2) exceeded 65 mmHg, or apneic periods lasting more than 60 s occurred During and after the infusion, frequent arterial blood samples were drawn and analyzed for the concentration of alfentanil and the arterial carbon dioxide pressure (PaCO2). A mamillary two-compartment model was fitted to the pharmacokinetic data. The PaCO2 data were described by an indirect response model The model accounted for the respiratory stimulation resulting from increasing PaCO2. The model parameters were estimated using NONMEM. Simulations were performed to define the respiratory response at steady state to different alfentanil concentrations. RESULTS: The indirect response model adequately described the time course of the PaCO2. The following pharmacodynamic parameters were estimated (population means and interindividual variability): EC50, 60.3 microg/l (32%); the elimination rate constant of carbon dioxide (Kel), 0.088 min(-1) (44%); and the gain in the carbon dioxide response, 4(28%) (fixed according to literature values). Simulations revealed the pronounced role of PaCO2 in maintaining alveolar ventilation in the presence of opioid. CONCLUSIONS: The model described the data for the entire opioid-PaCo2 response surface examined. Indirect response models appear to be a promising tool for the quantitative evaluation of drug-induced respiratory depression.

Adult↗
PubMed1999

Comparative pharmacodynamic modeling of the electroencephalography-slowing effect of isoflurane, sevoflurane, and desflurane.

BACKGROUND: The most common measure to compare potencies of volatile anesthetics is minimum alveolar concentration (MAC), although this value describes only a single point on a quantal concentration-response curve and most likely reflects more the effects on the spinal cord rather than on the brain. To obtain more complete concentration-response curves for the cerebral effects of isoflurane, sevoflurane, and desflurane, the authors used the spectral edge frequency at the 95th percentile of the power spectrum (SEF95) as a measure of cerebral effect. METHODS: Thirty-nine patients were randomized to isoflurane, sevoflurane, or desflurane groups. After induction with propofol, intubation, and a waiting period, end-tidal anesthetic concentrations were randomly varied between 0.6 and 1.3 MAC, and the EEG was recorded continuously. Population pharmacodynamic modeling was performed using the software package NONMEM. RESULTS: The population mean EC50 values of the final model for SEF95 suppression were 0.66+/-0.08 (+/- SE of estimate) vol% for isoflurane, 1.18+/-0.10 vol% for sevoflurane, and 3.48+/-0.66 vol% for desflurane. The slopes of the concentration-response curves were not significantly different; the common value was lambda = 0.86+/-0.06. The Ke0 value was significantly higher for desflurane (0.61+/-0.11 min(-1)), whereas separate values for isoflurane and sevoflurane yielded no better fit than the common value of 0.29+/-0.04 min(-1). When concentration data were converted into fractions of the respective MAC values, no significant difference of the C50 values for the three anesthetic agents was found. CONCLUSIONS: This study demonstrated that (1) the concentration-response curves for spectral edge frequency slowing have the same slope, and (2) the ratio C50(SEF95)/MAC is the same for all three anesthetic agents. The authors conclude that MAC and MAC multiples, for the three volatile anesthetics studied, are valid representations of the concentration-response curve for anesthetic suppression of SEF95.

Adult↗
PubMed1999

Impaired inducibility of heat shock protein 70 in peripheral blood lymphocytes of patients with severe sepsis.

OBJECTIVE: To determine the extent of the potentially protective heat shock protein 70 response in peripheral blood lymphocytes of patients with severe sepsis after ex vivo lipopolysaccharide stimulation. DESIGN: Entry study of consecutive patients with severe sepsis, those who were critically ill or nonseptic after major surgery, and healthy blood donors. SETTING: Surgical intensive care unit in a university hospital. PATIENTS: Ten patients with diagnoses of severe sepsis; ten critically ill, nonseptic patients after major surgery; and ten healthy blood donors. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We investigated the ex vivo endotoxin-inducible expression of heat shock protein 70 in peripheral blood lymphocytes of patients with severe sepsis by means of flow cytometry. Only negligible amounts of inducible intracellular heat shock protein 70 accumulation (<4.2% of lymphocytes) could be detected in peripheral blood lymphocytes without lipopolysaccharide stimulation. The proportion of cells accumulating heat shock protein 70 after treatment with lipopolysaccharide was distinctly lower in patients with severe sepsis (p < .05) than in critically ill, nonseptic patients after major surgery and healthy blood donors (38.3+/-3.3%, 82.2+/-4.5%, and 70.9+/-3.9%, respectively; mean +/- SEM; n = 10). Patients with clinical signs of recovery from severe sepsis showed an increase in heat shock protein 70 expression. CONCLUSIONS: Inducibility of ex vivo heat shock protein 70 was impaired in peripheral blood lymphocytes of patients with severe sepsis. The impaired expression of the potentially protective heat shock protein 70 may contribute in vivo to immune dysfunction, because intact functioning of T and B lymphocyte responses is of central importance in resisting infection in severe sepsis. Monitoring of inducible heat shock protein 70 in peripheral blood lymphocytes may contribute to the evaluation of the immune consequences of severe sepsis.

APACHE↗
PubMed1999

Analysis of two human leukocyte antigen-linked polymorphic heat shock protein 70 genes in patients with severe sepsis.

OBJECTIVE: To determine whether the genotype and allelic frequencies of two human leukocyte antigen-linked bi-allelic 70-kilodalton heat shock protein (HSP70) gene polymorphisms are associated with susceptibility to and outcome of severe sepsis. Furthermore, we investigated a possible linkage between HSP70 gene polymorphisms and the previously reported and mortality-related tumor necrosis factor-beta (TNF-beta) NcoI gene polymorphism. DESIGN: Consecutive entry study of patients with severe sepsis. SETTING: Surgical intensive care unit in a university hospital. PATIENTS: Eighty-seven patients with a diagnosis of severe sepsis. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We studied two bi-allelic polymorphisms within the coding region of the constitutively expressed HSP70-HOM C/T, and the stress-inducible HSP70-2 G/A in patients with severe sepsis. The HSP70-HOM Ncol, HSP70-2 Pstl, and TNF-beta NcoI polymorphisms were identified by means of the polymerase chain reaction followed by restriction analysis of the polymerase chain reaction product. No significant differences in genotype and allelic frequencies were observed for both HSP70 gene polymorphisms between the 87 patients and the 110 healthy Caucasians serving as the control group. In addition, no differences in genotype and allelic frequencies between surviving and nonsurviving patients were detected. The allelic frequencies in the group of nonsurvivors were 0.8 for the HSP70-HOM C allele and 0.2 for the HSP70-HOM T allele vs. 0.87 and 0.13 for the survivors (p > .05). The frequency for the HSP70-2 G allele was 0.36 and 0.64 for the HSP70-2 A allele in the group of nonsurvivors vs. 0.41 and 0.59 for the survivors (p > .05). Analysis of a possible linkage between HSP70 and TNF-beta genotypes resulted in a significant association (odds ratio, 4.15; p < .01) of the HSP70-2 A/A homozygous genotype and the TNFB2/B2 homozygous genotype, which is reported to be a genomic marker for a poor prognosis in severe sepsis. CONCLUSIONS: Our data show that the bi-allelic NcoI and PstI polymorphisms within the HSP70-HOM and HSP70-2 locus, respectively, are associated with neither susceptibility to nor outcome of severe sepsis. Moreover, we found a linkage between HSP70-2 A homozygotes and the previously reported and mortality-related homozygous genotype, TNFB2/B2, in patients suffering from severe sepsis.

Case-Control Studies↗
PubMed1999

Comparison of two polymorphisms of the interleukin-1 gene family: interleukin-1 receptor antagonist polymorphism contributes to susceptibility to severe sepsis.

OBJECTIVES: To determine whether the allele frequencies and genotype distribution of an interleukin (IL)-1beta TaqI polymorphism and an interleukin-1 receptor antagonist polymorphism are associated with susceptibility to and outcome of severe sepsis. In addition, we analyze a possible linkage disequilibrium between a previously described NcoI polymorphism within the tumor necrosis factor (TNF) locus and the two IL-1 gene family polymorphisms. DESIGN: Prospective, consecutive entry study of patients with diagnosis of severe sepsis. SETTING: Intensive care unit (ICU) of a university hospital. PATIENTS: Ninety-three patients with diagnosis of severe sepsis admitted to the ICU between June 1993 and June 1996. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The polymorphic region within intron 2 of the IL-1ra gene containing variable numbers of a tandem repeat of 86 base pairs was amplified by means of the polymerase chain reaction. Alleles A1-5 are identified according to the size of the amplified DNA product. The region that contains the biallelic TaqI site within exon 5 of the IL-1beta gene was analyzed by polymerase chain reaction amplification and subsequent digestion using the TaqI restriction enzyme. A NcoI TNF-beta polymorphism was determined. The allele frequency of the allele IL-1raA2 was increased in 93 patients with severe sepsis compared with normal individuals (p < .01). No association with patients' outcome was observed. Allele frequencies or genotype distribution of the IL-1beta TaqI polymorphism did not differ between patients and controls. In addition, the allele TNFB2 of the NcoI TNF-beta polymorphism was associated with nonsurvival. Occurrence of the TNFB1 and TNFB2 alleles and genotypes was unrelated to alleles and genotypes of the two IL-1 gene family polymorphisms. CONCLUSION: In contrast to the TNF-beta NcoI polymorphism, which has been associated with patients' nonsurvival, the allele IL-1raA2 of the polymorphism within the intron 2 of IL-1ra may contribute to susceptibility to sepsis.

Case-Control Studies↗
PubMed1999

Influence of fentanyl, alfentanil, and sufentanil on motor evoked potentials.

The effects of the opioids fentanyl, alfentanil, and sufentanil on motor pathways were studied in a total of 30 rabbits. Compound muscle action potentials (CMAP) were recorded from the extensor muscles of the upper extremity as well as evoked spinal cord potentials (ESCP) from the thoracic epidural space in response to electrical stimulation of the motor cortex. After establishing stable baseline values, an equipotent intravenous bolus of one of the three opioids was applied that abolished reflex motor response to noxious stimulation. Motor evoked potentials (MEP) were recorded from the time of bolus administration until recovery of MEP amplitudes and latencies. Afterwards, the opioids were administered continuously with cumulative dosage up to total absence of motor evoked response. Our results show a dose-dependent suppression of the CMAP: When reflex movement to noxious stimulation was extinguished, we found a significant (P < .001) reduction of the amplitudes to 34+/-18% (mean +/- SD) in the fentanyl group, to 43+/-24% in the alfentanil group, and to 53+/-20% of baseline values in the sufentanil group. Increasing opioid plasma levels were associated with complete extinction of the CMAP. We hypothesize that the descending volleys within motor pathways are mainly inhibited at a spinal level, because ESCP, particularly the number of spinal I-waves, are not severely affected even when CMAP are completely suppressed. In conclusion, intraoperative monitoring of descending pathways by means of MEP during anesthesia with opioids is feasible at anesthetic plasma concentrations maintaining a surgical level of analgesia. Even with high opioid plasma levels, a valid MEP monitoring could be performed evaluating neural activity of spinal MEP.

Action Potentials↗
PubMed1998

[Transpulmonary indicator methods in intensive medicine].

The management of critically ill patients often requires an advanced hemodynamic monitoring. Beside pulmonary artery catheter (PAC) and transesophageal echocardiography (TEE) the transpulmonary indicator dilution technique (TPID) with arterial registration of the indicator dilution curves is a possible approach to get additional hemodynamic information. Being less invasive, measurements of cardiac output by transpulmonary thermodilution are as reliable as the thermodilution using a PAC. Transpulmonary thermodilution can be used even in small children. In addition, intrathoracic blood volume (ITBV) and extravascular lung water (EVLW) can be estimated. ITBV seems to be a better surrogate of cardiac filling than central venous pressure and pulmonary capillary wedge pressure. EVLW can be of special value in the fluid-management of patients with systemic inflammatory response syndrome or acute respiratory failure. By using the dye indocyanine green (ICG) as a second indicator TPID can be performed as transpulmonary double indicator dilution technique. The resulting thermodilution and dye curves are measured with a combined fiberoptic-thermistor catheter. This allows the more accurate measurement of ITBV and EVLW and in addition the assessment of total circulating blood volume and ICG-clearance. ICG-clearance serves clinically as a rapidly reacting indirect measure of liver function. As with the other methods of advanced hemodynamic monitoring the data available at present do not show a positive effect on the incidence of organ failure and mortality by monitoring critically ill patients with TPID. Before applying an advanced hemodynamic monitoring it should be asked critically which parameter is needed for the therapy-management of the individual patient. Based on this a differentiated monitoring decision has to be made.

Critical Care↗
PubMed1998

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.

Animals↗
PubMed1998

[Concentration-dependent changes in the latency and amplitude of somatosensory-evoked potentials by desflurane, isoflurane and sevoflurane].

PURPOSE: Comparison of the influence of desflurane, isoflurane, and sevoflurane on the parameters of cortical somatosensory evoked potentials (SEP). METHODS: A total of 41 patients were randomly allocated to either the isoflurane, desflurane or sevoflurane group. Following induction with propofol and intubation, concentration of the volatile anaesthetic was kept constant at 1.3, 1.0, and 0.7 MAC for 15 minutes each in randomised sequences. No opioids or N2O were used. Cortical somatosensory evoked potentials were recorded following median nerve stimulation at the wrist with 1.5 times motor threshold current. SEP were evaluated for latencies of peak N20 and P25 as well as peak-to-peak amplitude N20P25. Measurements at the end of the 15 minute equilibration intervals were compared by analysis of variance for repeated measurements. Latencies and the logarithm of the amplitudes were assumed to be normally distributed. RESULTS: SEP could be recorded in all patients and at all concentrations. Latency of cortical SEP increased with anaesthetic concentration in a linear manner. No differences in latency increase were found between the three anaesthetics (ANOVA). In contrast, the decrease in amplitude with increasing anaesthetic concentration was non-linear. It was large from control to 0.7 MAC, but small in the range between 0.7 and 1.3 MAC. Amplitude reduction was larger with isoflurane than with sevoflurane or desflurane. CONCLUSION: 1) Sevoflurane and desflurane are better suited for anaesthetic management during intraoperative electrophysiological monitoring than isoflurane, because SEP amplitudes are better preserved. 2) SEP amplitude is less altered by changing anaesthetic concentrations in the concentration range from 0.7 to 1.3 MAC than SEP latency.

Adult↗