Xenon and isoflurane improved biventricular function during right ventricular ischemia and reperfusion.

BACKGROUND: Although anesthetics have some cardioprotective properties, these benefits are often counterbalanced by their negative inotropic effects. Xenon, on the other hand, does not influence myocardial contractility. Thus, xenon may be a superior treatment for the maintenance of global hemodynamics, especially during right ventricular ischemia, which is generally characterized by a high acute complication rate. METHODS: The effects of 70 vol% xenon and 0.9 vol% isoflurane on biventricular function were assessed in a porcine model (n=36) using the conductance catheter technique, and the expression of the type B natriuretic peptide (BNP) gene was measured. The animals underwent 90 min of right ventricular ischemia followed by 120 min of reperfusion. A barbiturate-anesthetized group was included as a control. RESULTS: Cardiac output was compromised in unprotected animals during ischemia by 33+/-18% and during reperfusion by 53+/-17%. This was mainly due to impaired contractility in the left ventricle (LV) and increased stiffness. Isoflurane attenuated the increase in stiffness and resulted in a higher preload. In contrast, xenon increased the right ventricular afterload, which was compensated by an increase in contractility. Its effects on diastolic function were less pronounced. Upregulation of BNP mRNA expression was impeded in the remote area of the LV by both isoflurane and xenon. CONCLUSIONS: Xenon and isoflurane demonstrated equipotent effects in preventing the hemodynamic compromise that is induced by right ventricular ischemia and reperfusion, although they acted through somewhat differential inotropic and vasodilatory effects.

Anti-ischemic effects of inotropic agents in experimental right ventricular infarction.

BACKGROUND: Right ventricular (RV) function is an important determinant of survival after myocardial infarction. The efficacy of reperfusion therapy might be increased by the cardioprotective action of inotropic agents, which are used for symptomatic therapy in situations with compromised hemodynamics. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of milrinone, levosimendan and dobutamine on the extent and degree of myocardial injury. METHODS: IR injury was induced by temporary ligation of the distal right coronary artery for 90 min, followed by 120 min of reperfusion. Treatment was initiated 30 min after coronary artery occlusion. A bolus of milrinone (n=12; 50 microg/kg) and levosimendan (n=10; 24 microg/kg) was applied in different groups, followed by continuous infusion of the drugs at 0.5 and 0.2 microg/kg/min, respectively. The effects on myocardial injury and inflammation were compared with a control (n=12) and a dobutamine group (n=10), where treatment was started with an infusion of 5 microg/kg/min. RESULTS: Milrinone and levosimendan reduced the resulting infarct size with respect to the area at risk (41.7+/-10.2%, 45.7+/-8.1%) when compared with the control group (58.3+/-6.1%). In contrast, dobutamine had no effect (55.8+/-7.7%). All drugs reduced the number of neutrophils infiltrating into the different myocardial regions and the circulating levels of interleukin-6. Increased levels of tumor necrosis factor alpha during reperfusion were only abated by milrinone and levosimendan. CONCLUSIONS: Cardioprotective properties of milrinone and levosimendan were demonstrated for the first time in a clinically relevant model of RV infarction.

Xenon alters right ventricular function.

BACKGROUND: In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo. Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload. METHODS: Right ventricular function was monitored with a volumetric pulmonary artery catheter in 11 pigs during general anesthesia with thiopental. Six animals received additional 70% (volume) xenon (equivalent to 0.55 MAC minimum alveolar concentration). Parameters for systolic function, afterload, and preload were calculated at baseline and during 50 min of xenon application, and in a corresponding control group. Significant differences were detected by multivariate analyses of variance for repeated measures. RESULTS: Xenon reduced CO on average by 30% and increased pulmonary arterial elastance by 60%, which led to a reduction of the right ventricular ejection fraction by 25%. Whereas right ventricular preload remained stable, maximal slope of pulmonary artery pressure and the right ventricular elastance increased. No effect on the ratio of stroke work and end-diastolic volume was found. CONCLUSION: The reduction in CO during xenon anesthesia was partly due to an impairment of the right ventricular function, mainly caused by an increased afterload, without an impairment of systolic ventricular function.

Establishment of a porcine right ventricular infarction model for cardioprotective actions of xenon and isoflurane.

BACKGROUND: Right ventricular (RV) function is an important determinant of post-operative outcome. Consequences of RV infarction might be limited by pre-conditioning with volatile anesthetic drugs. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of isoflurane and xenon on the extent and degree of myocardial injury. METHODS: IR injury was induced by a 90-min ligation of the distal right coronary artery and 120-min reperfusion in thiopental anesthetized pigs. A control group (n=12) was compared with two groups, which received either 0.55 minimum alveolar concentration (MAC) isoflurane (n=10) or xenon (n=12) starting 60 min before ischemia. Myocardial injury was described by three criteria: the infarct size related to area at risk (IS/AAR), the infiltration of neutrophils as determined by myeloperoxidase (MPO) activity, and the plasma levels of tumor necrosis factor alpha (TNFalpha), interleukin 6 (IL-6), myoglobin and troponin-T (TnT). RESULTS: IS/AAR was reduced from 58.3+/-6.2% in the control group to 41.8+/-7.8% after isoflurane and 42.7+/-8.5% after xenon pre-treatment, which equals an absolute reduction of 16.5% [95% confidence interval (CI): 10.9-22.1] and 15.5% (95% CI: 10.1-20.9). The maximum increase of TnT could be observed within the xenon group. Both treatment groups were characterized by lower MPO activity, in the infarct and periinfarct region and lower plasma concentrations of TNFalpha and IL-6. CONCLUSIONS: It could be demonstrated for the first time in a model of RV infarction that the continuous application of isoflurane or xenon before, during and after ischemia reduced the extent (size) and severity (inflammation) of myocardial injury.

A comparison of waste gas concentrations during xenon or nitrous oxide anaesthesia.

BACKGROUND AND OBJECTIVE: The aim of this study was to compare waste gas concentrations during xenon or nitrous oxide anaesthesia. METHODS: A total of 64 patients were included in this study. Gas concentrations were measured with a mass spectrometer during anaesthesia. The probes were taken beside the patient's head and thorax and at a height of 180 cm above and at the floor level. RESULTS: In both groups, waste gas concentrations peak after intubation and extubation. Waste gas levels during xenon anaesthesia are low compared with nitrous oxide. CONCLUSIONS: The low waste gas levels of xenon seem to be beneficial compared to nitrous oxide.

Positron emission tomography study of regional cerebral blood flow and flow-metabolism coupling during general anaesthesia with xenon in humans.

BACKGROUND: The effects of xenon on regional cerebral blood flow (rCBF) are controversial. Moreover, the precise sites of action at which xenon exerts its effects in the human brain remain to be established. METHODS: rCBF was sequentially assessed by H(2)(15)O positron emission tomography in six volunteers. rCBF was determined at baseline and during general anaesthesia induced with propofol and maintained with one minimum alveolar concentration xenon. rCBF measurements were started after the calculated plasma concentration of propofol had decreased to subanaesthetic levels (<1.0 microg ml(-1)). Changes in rCBF were calculated for 13 cerebral volumes of interest by measurement of a semi-quantitative perfusion index (PI). In addition, voxel-wise changes in rCBF were analysed using statistical parametric mapping. RESULTS: Xenon had only minor effects on PI in grey matter volumes of interest. In contrast, PI was increased in white matter [from 1.01 (0.11) to 1.24 (0.15) kcnt ml(-1) MBq(-1), P=0.05, mean (SD)]. Voxel-based analysis showed an increase of rCBF in white matter and a relative decrease of rCBF during xenon anaesthesia in distinct grey matter regions, particularly the orbito- and mesiofrontal cortex, cingulate gyrus, thalamus, hippocampus and bilateral cerebellum (P<0.05 corrected). When correlating PI with cerebral metabolic rate of glucose (previously obtained in another group of six volunteers using (18)F-fluorodeoxyglucose as tracer), the flow-metabolism coupling was preserved during xenon anaesthesia. CONCLUSIONS: Xenon exerted distinct regional effects on CBF: relative decreases in several cortical, subcortical, and cerebellar areas were accompanied by an increase in white matter. Flow-metabolism coupling was not impaired during xenon anaesthesia.

Xenon or propofol anaesthesia for patients at cardiovascular risk in non-cardiac surgery.

BACKGROUND: The results of two European multi-centre trials on xenon anaesthesia led to the hypothesis that a xenon-based anaesthetic would keep left ventricular (LV) and circulatory function more stable than a propofol-based anaesthetic, in patients with coronary artery disease (CAD). METHODS: In a prospective, randomized design, 40 patients of ASA classes III and IV with known CAD were anaesthetized for elective non-cardiac surgery with either xenon (n=20) or propofol (n=20), each combined with remifentanil. Target criteria were intraoperative LV function as evaluated by transoesophageal echocardiography (TOE: Tei index, circumferential fibre shortening), arterial pressure, and heart rate (HR). RESULTS: Mean arterial pressure was decreased with propofol but was stable at pre-anaesthetic level with xenon (P<0.02) and HR was lower with xenon (P<0.01). The Tei index (also known as myocardial performance index) improved from 0.53 (0.14) to 0.45 (0.10) after 1 h with xenon and changed from 0.50 (0.14) to 0.55 (0.20) with propofol anaesthesia [means (SD); P=0.01 between the groups]. Deviation of circumferential fibre shortening from expected value after 1 h was -2 (14)% with xenon and -14 (18)% with propofol [means (SD); P=0.03]. There were no perioperative signs of acute myocardial ischaemia (TOE, ECG, and troponin T release). CONCLUSIONS: Xenon anaesthesia provided a higher arterial pressure level than propofol, with no signs of cardiovascular compromise, in patients with CAD. Echocardiographic indices showed better LV function with xenon.

Autonomic cardiac control with xenon anaesthesia in patients at cardiovascular risk.

BACKGROUND: The cardiovascular stability found with xenon anaesthesia may be caused by absence of circulatory depression. Xenon may also act directly on autonomic cardiovascular control. METHODS: In a prospective, randomized design, 26 patients (ASA class III and IV) with increased cardiac risk were anaesthetized for elective non-cardiac surgery with either xenon (n = 13) or propofol (n = 13), each combined with remifentanil. From intraoperative Holter ECG, 5-min intervals of stable sinus rhythm were analysed at baseline anaesthesia with etomidate/remifentanil, and after 30 and 60 min of propofol or xenon anaesthesia. Target criteria were total power and ratio of low to high frequency power of the heart rate (HR) power spectrum between 0.003 and 0.4 Hz, indicating global activity and sympatho-vagal balance of autonomic modulation of HR. RESULTS: When compared with baseline, total power decreased with propofol from 8.6 (1.6) to 7.1 (0.5) and to 7.8 (1.1) ms(2) at 30 and 60 min, respectively, [mean (sd) of logarithmic transform] and was unchanged with xenon (P = 0.02; anova). The low/high frequency power ratio changed from 3.0 (3.5) to 4.3 (4.3) and 4.1 (6.2), respectively, with xenon and from 3.9 (3.6) to 1.8 (1.5) and 1.8 (0.8) with propofol (P = 0.04; generalized linear model test). Mean arterial pressure was significantly higher with xenon throughout (P < 0.001; anova). CONCLUSIONS: Propofol caused a decrease in arterial pressure as well as autonomic HR modulation, but xenon did not. The higher arterial pressure with xenon anaesthesia may be explained by less suppression of sympatho-vagal balance.

Emergence and early cognitive function in the elderly after xenon or desflurane anaesthesia: a double-blinded randomized controlled trial.

BACKGROUND: Postoperative cognitive impairment after general anaesthesia, especially in the elderly, is a well-recognized problem. Xenon, known to be an N-methyl-d-aspartate antagonist, may be advantageous. In this study, the early cognitive function in the elderly after general anaesthesia with xenon was compared with that after desflurane. METHODS: After approval by the local ethical committee and after obtaining written informed consent, patients were enrolled in this randomized, double-blinded, controlled study. Thirty-eight patients (65-75 yr old, ASA status I-III) undergoing an elective surgery with a planned duration of 60-180 min were allocated to either the xenon (n = 18) or the desflurane (n = 20) anaesthesia group. The primary outcome was the cognitive Test for Attentional Performance (TAP) with its subtests Alertness, Divided Attention, and Working Memory. After baseline assessment 12-24 h before operation, patients were followed-up 6-12 and 66-72 h after operation. Secondary outcomes were emergence times from anaesthesia and the modified Aldrete score. RESULTS: No difference was found between the groups in the TAP at 6-12 and 66-72 h after operation. In the xenon group, emergence time was significantly faster for the following parameters: time to open eyes (P = 0.001), to react on demand (P = 0.001), to extubation (P = 0.001), and for time and spatial orientation (P = 0.007). The modified Aldrete score was significantly higher after 30, 45 and 60 min in the xenon group. CONCLUSIONS: There was no difference in the postoperative cognitive testing at 6-12 and 66-72 h. Xenon was associated in the elderly with a faster emergence from general anaesthesia than desflurane.

Influence of a 30-min break on divided attention and working memory in resident anaesthetists on daily routine.

BACKGROUND: The aim of this study is to test the hypothesis that a standard 30-min break in a routine 7.5 h period of work makes a difference in cognitive function. METHODS: In a double-blinded, cross-over trial 30 residents in anaesthesia were randomized to receive or not to receive a 30-min break between the assessment times of 07:30 and 14:00. in a normal working day. After at least 28 days the test was repeated with each resident in the opposite group. Primary outcome measure was the Test for Attentional Performance with the subtest of working memory and divided attention. Secondary outcomes are the Stanford Sleepiness Scale and the State-Trait Anxiety Inventory test. RESULTS: The sleep, caffeine and nicotine habits in both groups were comparable. There was no difference between the two groups in the Test for Attentional Performance, Stanford Sleepiness Scale and the State-Trait Anxiety Inventory. The correlation between recovery through sleep and sleep disturbance in the night before investigation to the Stanford Sleepiness Scale (P<0.001 and P=0.003) and State-Trait Anxiety Inventory (P<0.001 and P=0.001) at the 07:30 assessment is significant. For the 14:00 assessment the only significant correlation is between the recovery through sleep with the Stanford Sleepiness Scale (P=0.04) and the State-Trait Anxiety Inventory (P=0.05). CONCLUSION: A 30-min break during a 7.5 h daily routine did not influence cognitive function tests.

Patients' self-evaluation after 4-12 weeks following xenon or propofol anaesthesia: a comparison.

BACKGROUND AND OBJECTIVE: The aim of this study was to assess postoperative patients' self-evaluation after xenon anaesthesia compared to total intravenous anaesthesia with propofol. METHODS: 160 patients aged 18-60 yr, ASA I-II undergoing elective surgery took part in this randomised-controlled trial. After approval by the local Ethics Committee and as soon as the patients had given their written informed consent, they were randomly allocated to either the xenon (n = 80) or propofol (n = 80) group. In both groups remifentanil was used as opioid. The postoperative patients' self-evaluation was assessed with a double-blind telephone poll. Early spatial orientation, patients' self-evaluation of anaesthesia, choice of the same anaesthesia for future operations and recall of uncomfortable feelings after anaesthesia were determined. RESULTS: 116 Patients were analysed, 63 in the xenon and 53 in the propofol group. The two study groups were comparable with respect to age, weight, height, gender and ASA classification. The two groups indicated similar values in the early spatial orientation at the onset of recovery and thereafter. Patients' self-evaluation of anaesthesia with main emphasis at high marks and repetition of the same anaesthesia if necessary were similar in both groups. Recalls of uncomfortable feelings were comparable but not for postoperative pain and appetite/thirst which appeared with a significantly higher incidence in the xenon group. CONCLUSIONS: Patients' self-evaluation and memory of early spatial orientation following xenon anaesthesia are comparable to propofol.

Xenon anaesthesia may preserve cardiovascular function in patients with heart failure.

BACKGROUND: The hypothesis that xenon anaesthesia provided haemodynamic stability was tested in patients with heart failure in a prospective, randomized, single-blind design. METHODS: Twenty-six patients scheduled for implantation of a cardioverter-defibrillator (ICD) received xenon 60-65% in oxygen (xenon group, n = 12) or propofol 3 mg/kg/h (propofol group, n = 14), both combined with remifentanil 0.2 microg/kg/min. After induction of anaesthesia with etomidate and remifentanil, heart rate (HR), mean arterial pressure (MAP) and left ventricular ejection fraction (LVEF) were recorded. After 60 min of propofol or xenon anaesthesia, the same parameters were recorded. RESULTS: While HR decreased in both groups, MAP was unchanged with xenon (73 vs. 76 mmHg) and decreased with propofol (from 78 to 64 mmHg, P < 0.02). LVEF was stable in both groups [32% vs. 37%, xenon (NS), and 30% vs. 34%, propofol (NS)]. Preload, as measured by end-diastolic volume (EDV), did not change (66 vs. 63 ml with xenon; 79 vs. 81 ml with propofol, both NS). Afterload, as determined by end-systolic pressure-volume product (ESPV), decreased with propofol (6760 vs. 4920 ml mmHg) but not with xenon (4060 vs. 3780 ml mmHg, P < 0.01 between groups). CONCLUSION: With propofol, MAP is reduced and LVEF is not increased in spite of reduced afterload. In contrast, MAP and LVEF are maintained with xenon.

Effects of xenon anaesthesia on the circulatory response to hypoventilation.

BACKGROUND: Circulatory response to hypoventilation is aimed at eliminating carbon dioxide and maintaining oxygen delivery (DO(2)) by increasing cardiac output (CO). The hypothesis that this increase is more pronounced with xenon than with isoflurane anaesthesia was tested in pigs. METHODS: Twenty pigs received anaesthesia with xenon 0.55 MAC/remifentanil 0.5 microg kg(-1) min(-1) (group X, n=10) or isoflurane 0.55 MAC/remifentanil 0.5 microg kg(-1)min(-1) (group I, n=10). CO, heart rate (HR), mean arterial pressure (MAP) and left ventricular fractional area change (FAC) were measured at baseline, after 5 and 15 min of hypoventilation and after 5, 15 and 30 min of restored ventilation. RESULTS: CO increased by 10-20% with both anaesthetics, with an equivalent rise in HR, maintaining DO(2) in spite of a 20% reduction in arterial oxygen content. Decreased left ventricular (LV) afterload during hypoventilation increased FAC, and this was more marked with xenon (0.60-0.66, P<0.05 compared with baseline and isoflurane). This difference is attributed to negative inotropic effects of isoflurane. Increased pulmonary vascular resistance during hypoventilation was found with both anaesthetics. CONCLUSION: The cardiovascular effects observed in this model of moderate hypoventilation were sufficient to maintain DO(2). Although the haemodynamic response appeared more pronounced with xenon, differences were not clinically relevant. An increase in FAC with xenon is attributed to its lack of negative inotropic effects.

Haemodynamic effects of haemorrhage during xenon anaesthesia in pigs.

BACKGROUND: It was hypothesized that xenon would stabilize mean arterial pressure (MAP) in haemorrhagic shock, recovery, and volume resuscitation, because a higher MAP has been observed with xenon, when compared with isoflurane anaesthesia. The responses to haemorrhage and subsequent volume replacement were therefore compared between xenon and isoflurane anaesthesia, in pigs. METHODS: Pigs were randomized to anaesthesia with xenon 0.55 MAC (group Xe, n=9) or isoflurane 0.55 MAC (group Iso, n=9), each with remifentanil 0.5 microg kg(-1) min(-1). MAP, heart rate, cardiac output (CO), and left ventricular fractional area change (FAC) were collected at control (1), after haemorrhage (20 ml kg(-1)) (2), after 10 min of recovery (3), after volume replacement (4), and 30 min later (5). Data were analysed by two-way repeated measures anova. RESULTS: Blood loss decreased MAP (Xe: 103 [21] to 53 [24] mm Hg; Iso: 92 [18] to 55 [14] mm Hg) and CO (Xe: 4.1 [0.8] to 2.6 [0.5] litre min(-1); Iso: 5.1 [1.1] to 3.8 [1.2] litre min(-1)), in spite of significant tachycardia. MAP and CO recovered to about 75% of control, and subsequent volume replacement completely reversed symptoms in both groups, but increased FAC only with xenon. CONCLUSION: Haemodynamic response to acute haemorrhage appeared faster with xenon/remifentanil than with isoflurane/remifentanil anaesthesia. In particular MAP decrease and short-term recovery were more marked with xenon (P<0.02). In the xenon group, volume replacement increased FAC compared with control and isoflurane (P<0.02).

Randomized controlled trial of the haemodynamic and recovery effects of xenon or propofol anaesthesia.

BACKGROUND: There is limited clinical experience with xenon in a large number of patients. We present intra- and postoperative haemodynamic and recovery data comparing xenon and total intravenous anaesthesia with propofol. METHODS: A total of 160 patients aged 18-60 years (ASA I and II) undergoing elective surgery took part in this prospective non-blinded randomized controlled trial. After local ethics committee approval and written informed consent, patients were allocated randomly to either the xenon or the propofol group. Anaesthesia was induced with propofol and remifentanil and was maintained with xenon at 60% (minimal alveolar concentration 0.95) or with propofol 0.1-0.12 mg kg(-1) min(-1). Remifentanil was titrated to clinical need in both groups. RESULTS: The two study groups were comparable with respect to age, weight, height, gender and ASA classification. Baseline in heart rate and systolic arterial pressure (SAP) were comparable in both groups. Following induction, SAP initially decreased but returned to baseline values over 15 min in the xenon group and differed significantly from the propofol group. Heart rate decreased significantly only in the xenon group and remained at stable values. Occurrence and duration of hypertension, hypotension and bradycardia showed no significant difference between groups. Patient recovery time in the post-anaesthetic care unit and recovery from anaesthesia was similar in the two groups. CONCLUSIONS: After induction the xenon/opioid regimen maintains systolic blood pressure at baseline levels and a low heart rate. No differences between groups were found in haemodynamic stability during anaesthesia. Recovery from xenon anaesthesia was similar to that observed in the propofol group.

Xenon, a modern anaesthesia gas.

Xenon is an interesting anesthetic as it appears to lack negative inotropicy and vasodilatation, giving great advantages to both patients with limited cardiovascular reserve or those who require hemodynamic stability. It has low toxicity and is not teratogenic. Xenon gives rapid induction and recovery, due to its low blood/gas partition coefficient (0.15), and has a MAC of 63%. Several vitro studies showed that Xenon may protect neural cells against ischaemic injury. Its low blood solubility can take to diffusion hypoxia if Xenon is not substituted by 100% oxygen at the end of anesthesia. It has been shown that, compared to other anesthetic regimens, Xenon anesthesia produces the highest regional blood flow in the brain, liver, kidney and intestine. In conclusion, the most important positive effects of Xenon are cardiovascular stability, cerebral protection and favourable pharmacokinetics. Negative points are high cost and the limited number of ventilators supplying Xenon.

Minimum alveolar concentration (MAC) of xenon in intubated swine.

BACKGROUND: The minimum alveolar concentration (MAC) is a traditional index of the hypnotic potency of an inhalational anaesthetic. To investigate the anaesthetic as well as the unwanted effects of xenon (Xe) in a swine model, it is useful to know MAC(Xe). METHODS: The study was performed using ten swine (weight 27.8-35.4 kg) anaesthetized with halothane and Xe 0, 15, 30, 40, 50 and 65% in oxygen. With each Xe concentration, various concentrations of halothane were administered in a step-by-step design. For each combination, a supramaximal pain stimulus (claw clamp) was applied and the appearance of a withdrawal reaction was recorded. The MAC(Xe) with halothane was calculated using a logistic regression model. RESULTS: During stable ventilation, haemodynamics and temperature, MAC(Xe) value was determined as 119 vol. % (95% confidence limits 103-135). CONCLUSION: MAC(Xe) in swine was calculated by extrapolation of a logistic regression model. Its theoretical value is 119 vol. %.

Influence of differences in body weight and volume management on experimental results in porcine models.

BACKGROUND: In contrast to humans, young pigs naturally have a low COPpl (12-16 mmHg versus 22-26 mmHg in young humans). Thus, behavior occurring when volume management is performed similar to human medicine might be different. Potentially underestimated intra- to extravascular fluid and solute shifts could influence time course of variables investigated. That is why we studied whether differences in the basic protocol for infusion therapy and different levels of COP according to age or body weight, respectively - impair reproducibility and reliability of experimental results. METHODS: Group A [n=6, lower body weight (LBW < 22 kg)] was treated with unrestricted infusion rates (UIR) adjusted to maintain a constant blood pressure; group B [n=6, higher body weight (HBW > 28 kg)] was treated with a restricted continuous infusion rate for fluid balance (RIR); group C (n=6) combined HBW and UIR protocol. Blood pressure, plasma solutes, diuresis, and peritoneal fluid were analysed. Statistical analysis was performed using Kruskal-Wallis test and Wilcoxon test. RESULTS: UIR-treated pigs with LBW (group A) developed ascites and demonstrated time dependent decreases of plasma solute concentrations whereas in pigs of group C mainly diuresis was increased and subcutaneous edema occurred. None of the protocols enabled constant blood pressure. DISCUSSION: In young pigs (LBW), an adaptive volume substitution using crystalloids to standardize blood pressure may induce fluid extravasation; in turn data may not show statistical significance, stable hemodynamics may not be achieved and changes in plasma solute concentrations may lead to false interpretations. RIR-strategy provided reproducible, plausible results and thus should be recommended in combination with pigs >29 kg BW for the use of porcine models.

Measurement of motor evoked potentials following repetitive magnetic motor cortex stimulation during isoflurane or propofol anaesthesia.

BACKGROUND: Isoflurane and propofol reduce the recordability of compound muscle action potentials (CMAP) following single transcranial magnetic stimulation of the motor cortex (sTCMS). Repetition of the magnetic stimulus (repetitive transcranial magnetic stimulation, rTCMS) might allow the inhibition caused by anaesthesia with isoflurane or propofol to be overcome. METHODS: We applied rTCMS (four stimuli; inter-stimulus intervals of 3, 4, 5 ms (333, 250, 200 Hz), output 2.5 Tesla) in 27 patients and recorded CMAP from the hypothenar and anterior tibial muscle. Anaesthesia was maintained with fentanyl 0.5-1 microg kg(-1) x h(-1) and either isoflurane 1.2% (10 patients) or propofol 5 mg kg(-1) x h(-1) with nitrous oxide 60% in oxygen (17 patients). RESULTS: No CMAP were detected during isoflurane anaesthesia. During propofol anaesthesia 333 Hz, four-pulse magnetic stimulation evoked CMAP in the hypothenar muscle in 75%, and in the anterior tibial muscle in 65% of the patients. Less response was obtained with 250 and 200 Hz stimulation. CONCLUSIONS: In most patients, rTCMS can overcome suppression of CMAP during propofol/nitrous oxide anaesthesia, but not during isoflurane anaesthesia. A train of four magnetic stimuli at a frequency of 333 Hz is most effective in evoking potentials from the upper and lower limb muscles. The authors conclude that rTCMS can be used for evaluation of the descending motor pathways during anaesthesia.

Increased airway resistance during xenon anaesthesia in pigs is attributed to physical properties of the gas.

BACKGROUND: In this study we investigated the effects of the physical properties of xenon on respiratory mechanisms in pigs. METHODS: With institutional approval, 10 female pigs (mean 25.2 (SD 2.5) kg) were anaesthetized with thiopental, remifentanil, and pancuronium. Gas flow and pressure were recorded continuously at the proximal end of the tracheal tube during constant flow ventilation for control, with 100% oxygen (control), followed by 1.5% isoflurane in 70/30% nitrogen/oxygen, 1.0% isoflurane in 70/30% nitrous oxide/oxygen, and 70/30% xenon/oxygen in random order. Compliance (C) and resistance (R) were calculated using a single compartment model. Resistance was corrected for gas viscosities eta and also for densities pho and viscosities eta as (pho*eta)(1/2) to compare assumptions of laminar and mixed flow in the airways. RESULTS: With constant flow ventilation, xenon increases inspiratory pressure compared with other gas mixtures. There were no significant differences in resistance, corrected for laminar or mixed flow, between the gas mixtures. Xenon anaesthesia did not affect compliance. CONCLUSIONS: The increase in airway pressure observed with xenon anaesthesia is attributed completely to its higher density and viscosity. Therefore, determination of airway resistance must take into account the physical properties of the gas. Xenon does not exert any major effect on airway diameter.