The effects of electromyographic activity on the accuracy of the Narcotrend monitor compared with the Bispectral Index during combined anaesthesia.

The Narcotrend is a monitor system for the assessment of depth of anaesthesia. The objective of this trial was to investigate the susceptibility of the Narcotrend to electromyographic (EMG) activity when compared with the Bispectral Index (BIS). We enrolled 33 patients undergoing major urological procedures under combined anaesthesia (thoracic epidural analgesia and general anaesthesia). Anaesthetic depth was assessed simultaneously by the BIS XP and Narcotrend. The intended anaesthetic depth ranged between 40 and 55 in the BIS and between D2 and D0 in the Narcotrend. BIS, but not Narcotrend, values correlated significantly (p < 0.0001) with EMG. BIS values between 70 and 80 occurred intermittently above an EMG activity of 35 dB, whereas the Narcotrend and the clinical signs remained unchanged during the period of elevated BIS values. None of the patients reported intra-operative awareness. Increased electromyographic activity does not affect Narcotrend values. Under combined anaesthesia, the Narcotrend monitor is more reliable when compared with the BIS regarding susceptibility to increased EMG activity.

Spatial pulmonary flow distribution in rabbit isolated lungs is a poor representation of the situation in vivo.

1. Isolated lung preparations are established to investigate effects on pulmonary vascular tone and spatial pulmonary flow (Q (rel)) distribution. In the present study, we hypothesized that Q (rel) distribution in isolated lungs is only poorly correlated with the in vivo situation. 2. Fourteen rabbits were anaesthetized and mechanically ventilated with room air. Animals were held in an upright position for 15 min and Q (rel) was assessed using fluorescent microspheres (Q (rel-in vivo)). A second injection of microspheres was made after isolation of the lungs (Q (rel-ex vivo)). Lungs were dried, cut into 1 cm(3) cubes and spatial Q (rel) distributions were analysed. 3. The mean correlation of Q (rel-in vivo) and Q (rel-ex vivo) was 0.592 +/- 0.188 (95% confidence interval 0.493-0.690). The Q (rel) was redistributed to more ventral (the mean slope of Q (rel) vs the dorsal-ventral axis changed from -0.289 +/- 0.227 to -0.147 +/- 0.114; P = 0.03), cranial (mean slope of Q (rel) vs the caudal-cranial axis changed from -0.386 +/- 0.193 to -0.176 +/- 0.142; P < 0.001) and central (mean slope of Q (rel) vs the hilus-peripheral axis changed from 0.436 +/- 0.133 to -0.236 +/- 0.159; P = 0.003) lung areas. 4. The results obtained from studies investigating Q (rel) distributions in isolated lung models must be interpreted cautiously because the isolated lung set-up significantly affects the spatial distribution of pulmonary flow.

[Reduction in the aggressiveness of ventilation by inhalation of perfluorohexane after therapy of oleic acid-induced respiratory failure]. / Reduktion der Aggressivität der Beatmung nach Therapie eines Olsäure-induzierten Lungenversagens durch Inhalation von Perfluorhexan.

INTRODUCTION: The application of perfluorohexane (PFH) vapor led to an improvement of oxygenation and mechanical lung function in a model of oleic acid-induced ARDS in sheep. The aim of this study was to investigate the effects of PFH on gas exchange over an extended time period and to reduce the invasiveness of ventilation. METHOD: ARDS was induced in sheep ( n=12) by injecting 0.1 ml/kg body weight oleic acid intravenously. Six sheep were treated for 30 min with 18 vol.% PFH (PFH-Tx) and followed up over a time period of 240 min while untreated sheep ( n=6) served as controls. Subsequently the F(I)O(2) was reduced to generate a p(a)O(2) between 100-140 mmHg. Gas exchange, respiratory and hemodynamic data were collected at regular intervals. Data were analysed using covariance analysis. RESULTS: PFH treatment led to an improvement in oxygenation ( p<0.01) and in mechanical lung function ( p<0.01). Furthermore, mean pulmonary artery pressure ( p<0.01) and shunt ( p<0.01) were lower in PFH-Tx. F(I)O(2) could be reduced in all PFH-treated animals ( p<0.01). CONCLUSION: Treatment of oleic acid-induced lung injury with PFH vapor improved oxygenation and mechanical lung function over a extended time period allowing a reduction in the invasiveness of ventilation.

[From isoflurane to perfluorohexane? Perfluorocarbons--therapeutic strategies in acute lung failure]. / Vom Isofluran zum Perfluorhexan? Perfluorkarbone--Therapiemöglichkeiten beim akuten Lungenversagen.

The introduction of Perfluorochemicals into medicine and especially into the treatment of severe lung injury is a fascinating scientific task. Many recall the famous experiments from Clark et al. in 1966 when he demonstrated "liquidventilation with perfluorocarbons" in the mammal species for the first time. After this hallmark, perfluorocarbons were subsequently introduced in research of acute lung injury by the techniques of Total- and Partial-Liquid-Ventilation (TLV; PLV). Perfluorocarbons (saturated organofluorids) have unique chemical and physical properties which made them attractive substances for intraalveolar application. The strong C-F bindings in the perfluorocarbon molecules are responsible for their chemical stability, biochemical inertness, high capacity to dissolve respiratory gases, low surface tension and high vapor pressures. Furthermore, the high density of the PFC lead to radio-opacity and their distribution to dependent lung areas. The efficacy of PFC liquid, applied by TLV/PLV has been demonstrated in numerous animal studies using different models of acute lung injury. Currently, several mechanisms of action of perfluorocarbon fluids in acute lung injury are discussed: recruitment of atelectatic alveoli, prevention of endexpiratory collapse of alveoli ("liquid PEEP"), redistribution of perfusion, oxygen transport, surfactant like effects and decrease of inflammation. Since total liquid ventilation has been used only in experimental models of lung injury, partial liquid ventilation has been introduced successfully into clinical trials (phase I-II). However, the results of the first randomised, controlled study of PLV in 90 adult patients suffering from severe respiratory failure (ALI/ARDS) showed no differences between PLV and conventional treatment. Furthermore, the instillation of relatively large amounts of liquid into the lungs poses several technical challenges and may be associated with complications such as liquithoraces, pneumothoraces and hypoxia. Since mammal lungs are evolutionary specialised to gas exchange using atmospheric oxygen, the application of liquids, even if they transport respiratory gases very well is not physiologic. To overcome these unwanted side effects, we developed a technique of perfluorocarbon vaporisation in analogy to the application of inhalation anaesthetic agents. After resolving some technical issues, this application technique was used successfully in an animal model of acute lung injury. Vaporisation of perfluorohexane in a concentration of 18 Vol.% of inspired gas improved significantly oxygenation and lung compliance. Though these results are promising, mechanisms of action, dose-efficacy relation, surfactant-perfluorocarbon interaction or anti-inflammatory effects of vaporised perfluorohexane are still unclear. These questions need to be clarified before this technique can be applied clinically. However, the inhalation of vapor, a technique already familiar to anaesthesiologists should avoid risks of large amounts of fluids in the bronchoalveolar space. Furthermore, this technique can be administered by established anaesthetic equipment with the advantage of exact dosing, continuous monitoring, and demand application in a way near to clinical routine.

Hemodynamic effects of hypertonic hydroxyethyl starch 6% solution and isotonic hydroxyethyl starch 6% solution after declamping during abdominal aortic aneurysm repair.

Fluid resuscitation with hypertonic hydroxyethyl starch solutions (HES) is effective in haemorrhagic shock due to the rapid mobilisation of fluids into the intravascular compartment. Declamping of the abdominal aorta with acute redistribution of blood into the vessels of the lower body half causes declamping-induced hypotension. Usually large amount of fluids or vasopressors are necessary to restore hemodynamic stability. Therefore, infusion of a hypertonic colloid solution may be an attractive option to achieve hemodynamic stability. This study was conducted to determine the amount of fluid of either hypertonic HES (HES 6%;7.2% NaCl) or isotonic HES (HES 6%;0.9% NaCl) needed to attain best wedge pressure (PCWP) cardiac index (CI) relation after declamping. Thirty-two high-risk patients undergoing elective abdominal aneurysm resection were enrolled in a prospective, randomised, double blinded study. The individual optimised PCWP/CI relation was determined after induction of anaesthesia. After declamping, both solutions were titrated in small boluses of 100 mL until the previously determined best wedge was reached. The amount of fluid after declamping was significantly reduced in the hypertonic HES- group 162 mL vs. 265 mL in the control group (P < 0.05). Resuscitation time was shortened, and cardiac index was slightly higher in the treatment group. The use of hypertonic HES-solution after aortic declamping led to a significant reduction of fluids necessary to attain optimised PCWP/CI relation. In this clinical trial with moderate blood loss in high-risk patients, hypertonic HES applied in a titrated fashion restored hemodynamic stability faster and without volume overload.

Vaporized perfluorocarbon improves oxygenation and pulmonary function in an ovine model of acute respiratory distress syndrome.

BACKGROUND: Perfluorocarbon liquids are being used experimentally and in clinical trials for the treatment of acute lung injury. Their resemblance to inhaled anesthetic agents suggests the possibility of application by vaporization. The authors' aim was to develop the technical means for perfluorocarbon vaporization and to investigate its effects on gas exchange and lung function in an ovine model of oleic acid-induced lung injury. METHODS: Two vaporizers were calibrated for perfluorohexane and connected sequentially in the inspiratory limb of a conventional anesthetic machine. Twenty sheep were ventilated in a volume controlled mode at an inspired oxygen fraction of 1.0. Lung injury was induced by intravenous injection of 0.1 ml oleic acid per kilogram body weight. Ten sheep were treated with vaporized perfluorohexane for 30 min and followed for 2 h; 10 sheep served as controls. Measurements of blood gases and respiratory and hemodynamic parameters were obtained at regular intervals. RESULTS: Vaporization of perfluorohexane significantly increased arterial oxygen tension 30 min after the end of treatment (P < 0.01). At 2 h after treatment the oxygen tension was 376+/-182 mmHg (mean +/- SD). Peak inspiratory pressures (P < 0.01) and compliance (P < 0.01) were significantly reduced from the end of the treatment interval onward. CONCLUSION: Vaporization is a new application technique for perfluorocarbon that significantly improved oxygenation and pulmonary function in oleic acid-induced lung injury.

[Combined anesthesia procedures]. / Kombinierte Anästhesieverfahren.

The additive properties of general and regional anesthetic techniques are brought together in combined anesthesia to minimise side effects of the individual techniques. Despite a wide experience with both used as single anesthetic techniques, no definite recommendations regarding indications, general contraindications and procedure exist for their combination. Beneficial effects on haemodynamics, respiratory function, intestinal motility and postoperative stress response have been demonstrated for a combination of general anesthesia and thoracic epidural anesthesia (TEA). In addition TEA is favourable in the management of postoperative pain, which has advantageous effects on convalescence especially in a high risk patient group. Nevertheless, until now no reduction of perioperative morbidity and mortality has been demonstrated. Since the combination of two anesthesia techniques theoretically increases the rate of complication, the expected benefit for the patient must predominate. To estimate the risks and benefits of combined anesthesia, the anesthesiologist must be familiar with each single method, as well as with the synergistic effects of both techniques in order to evaluate the individual indication.

Oxygenation of dog liver transplants as an early indicator of graft failure.

This study examines the potential value of liver oxygenation as a predictor of early graft function. pO2 measurements were performed on 10 pairs of beagle (donor) and foxhound (recipient) dogs during pentobarbital anesthesis. Two different explantation techniques were used: complete preparation and dissection before perfusion and explantation (group A) or rapid perfusion and explantation with detailed preparation of the liver and dissection of vessels ex situ after explantation (group B). In both groups, the technique of liver perfusion with 1,000 ml arterial and 500 ml portovenous application of ice-cold UW solution was equal. Local oxygen partial pressure values were obtained polarographically with miniaturized needle electrodes. The liver oxygenation directly after laparotomy was comparable in both groups (median values around 54 mm Hg). Prior to the infusion of UW solution, a reduction of the tissue oxygenation values to 24 mm Hg was observed in group A (p < 0.01 compared to postlaparotomy values). In group B, limited preexplantation surgical dissection resulted in a reduced pO2 decline to 42 mm Hg (n.s.). After transplantation, the reduced tissue oxygenation persisted in the livers of the dogs which were completely dissected in situ (group B) as compared to the preexplantation recipient and the donor liver before instrumentation (p < 0.01). In contrast, rapidly perfused livers again exhibited only an insignificant reduction of tissue oxygenation following transplantation. Survival correlated linearly with the liver oxygenation within the observation time after transplantation (p < 0.01). A significant survival advantage was found for the rapid perfusion technique (p < 0.05). We conclude that the tissue oxygenation might provide valuable information on early graft function.