Multicomponent diffusion in ionic crystals: theoretical model and application to combined tracer- and interdiffusion in alkali feldspar.

We present a model for multicomponent diffusion in ionic crystals. The model accounts for vacancy-mediated diffusion on a sub-lattice and for diffusion due to binary exchange of different ionic species without involvement of vacancies on the same sub-lattice. The diffusive flux of a specific ionic species depends on the self-diffusion coefficients, on the diffusion coefficients related to the binary exchanges, and on the site fractions of all ionic species. The model delivers explicit expressions for these dependencies, which lead to a set of coupled non-linear diffusion equations. We applied the model to diffusion of 23 Na, 39 K, and 41 K in alkali feldspar. To this end, gem-quality crystals of alkali feldspar were used together with 41 K doped KCl salt as diffusion couples, which were annealed at temperatures between 800 ∘ and 950 ∘ C. Concentration-distance data for 23 Na, 39 K, and 41 K were obtained by Time of Flight Secondary Ion Mass Spectrometry. Over the entire investigated temperature range the Na self-diffusion coefficient is by a factor of ≥ 500 higher than the K self-diffusion coefficient. Diffusion mediated by binary 39 K- 41 K exchange is required for obtaining satisfactory fits of the model curves to the experimental data, and the respective kinetic coefficient is well constrained.

[Ultrasound-guided perivascular axillary brachial plexus block. A simple, effective and efficient procedure]. / Ultraschallgesteuerte perivaskuläre axilläre Plexusanästhesie. Eine einfache, effektive und effiziente Methode.

BACKGROUND: The perivascular axillary plexus block is an easily applicable procedure with a low risk of complications but with a high failure rate. To improve this, the standard procedure was combined with transpectoral sonography to benefit from the advantages of ultrasound, while using a nearly unchanged puncture technique. METHOD: The technique developed by the authors is described in this article and the success rate and the time factor were determined in a sample of 86 patients. The success rates were compared to previous rates without ultrasound and to those in the literature. RESULTS AND CONCLUSIONS: The rate of complete blocks without the use of transpectoral sonography in our clinic and in the literature was approximately 72%, whereas using transpectoral ultrasound it was 96.5%. None of the 86 patients with transpectoral sonography required general anaesthesia. The onset time using transpectoral sonography was approximately 6 min. The perivascular axillary plexus block, combined with transpectoral sonography, is an effective and efficient procedure.

[The effects of active and passive humidification on ventilation-associated nosocomial pneumonia]. / Einfluss von aktiver und passiver Befeuchtung auf die beatmungsassoziierte nosokomiale Pneumonie.

STUDY OBJECTIVE: Airway humidification of ventilated patients in an intensive care unit may be established by heated humidifying systems (active) or by the means of a (passive) heat and moisture exchange filter (HMEF). There is a controversial discussion about the influence of the type of humidification on the rate of ventilator-associated pneumonia (VAP). Among 3,585 patients both methods were tested over a period of 21 months in an open, non-randomized cohort study. The aim of the investigation was to compare the incidence of VAP caused by a change of humidification strategy. METHOD: All patients in a 16-bed surgical intensive care unit who required mechanical ventilation, were included. In the first period (period AB) 1,887 cases were handled with a heated humidifier. During the second period (period PB) 1,698 patients were treated using a HMEF. Infection control was established according to the national Infection Surveillance Program (KISS) based on the CDC criteria for VAP. RESULTS: During the period of 42 months, 99 cases of VAP were reported. The incidence for VAP was found to be 13.5 (AB) and 9.6 (PB) per 1,000 ventilator days, a rate of 32.3 and 22.4 VAP per 1,000 patients, respectively. The rate of VAP among the groups ( p=0.068) and the incidence of VAP per 1,000 ventilator days ( p=0.089) only just failed to reach a significant level, but in the group of patients requiring mechanical ventilation for more than 2 days, the difference did reach statistical significance ( p=0.012). CONCLUSION: Our results showed that the rate of VAP could be significantly reduced by changing the strategy from active to passive humidification devices, especially concerning patients requiring long-term respirator therapy. A more physiological humidification and a reduced number of airway manipulations are discussed as a possible explanation.

[A comparison of the Proseal laryngeal mask to the standard laryngeal mask on anesthesized, non-relaxed patients]. / Ein Vergleich der Larynxmaske (LMA) vom Typ Proseal gegen die Standard-LMA bei anästhesierten, nicht relaxierten Patienten. Ergebnisse einer deutschen Multizenterstudie.

It was our goal to compare the Proseal-laryngeal mask airway (PLMA) with the classical laryngeal mask airway (LMA) in a german multicenter trial. Handling of the instruments and application criteria were to be tested. 7 anaesthesia departments were able to take part in this study. 280 patients could be investigated after approval of the ethics committee of the medical faculty of the university of Goettingen. 145 patients received the PLMA and 135 the LMA. The surgical interventions were small to moderate procedures with a duration of at least 20 minutes in the sections general surgery, trauma/orthopedic surgery, urology, vascular surgery, gynecology, ENT-surgery and ophthalmology. There was equivalence of the two instruments PLMA and LMA concerning duration and ease of insertion, endoscopic position check, observations on emergence, potential for injury and some postoperative complaints. This equivalence could be confirmed statistically. Laryngospasm was observed in three, Bronchospasm in two patients with the PLMA, in no one with the LMA. In one case of laryngospasm and another of bronchospasm a mechanism of supraglottic laryngeal stenosis has been involved which may occur in rare instances with the PLMA. This mechanism is due to the double cuff of the PLMA with the instruments proximity to the laryngeal inlet. The seal pressure in both groups differs significantly (p = 0.001). The mean value for the seal pressure was 29,3 +/- 0,21 mbar for the PLMA and 20,9 +/- 0,21 mbar for the LMA. In the PLMA the gastric tube could be positioned with the first attempt in 118 patients, with the second attempt in 17 cases. In 10 patients the gastric tube could not be placed. Contrary to the LMA the tip of the PLMA cuff may be bent in some cases with loss of airway safety and positioning of the gastric tube. The symptoms sore throat and painful swallowing on the first postoperative day were more frequent with LMA application. These differences could be confirmed statistically (sore throat p = 0.01, painful swallowing p = 0.04). They may be explained by the more rigid LMA compared to the PLMA and by the fact that the LMA in this study was older than the PLMA, loosing plasticizer. The drainage tube within the PLMA offers safety from aspiration in patients with no primary aspiration risk, additional reassurance for a correct position and a better stability of the airway. Our data may support a wider indication range for the PLMA compared with the LMA. The PLMA may be applied in laparoscopies and lower abdominal surgical interventions. Careful clinical observation will show, if the minimal invasiveness of the PLMA offers an advantage for these patients. The PLMA should not be applied in patients with increased aspiration risk.

Treatment of severe Candida infections in high-risk patients in Germany: consensus formed by a panel of interdisciplinary investigators.

Now that modern medicine can provide increasing chances of cure to patients with formerly incurable disorders, therapy-related complications play the key role in outcome. Thus, among opportunistic infections, severe candidiasis remains a challenge. A multidisciplinary panel of 20 investigators was formed to find a consensus on antifungal strategies for various underlying conditions in neutropenic and non-neutropenic patients. To record their preferences, the investigators used an anonymous voting system. Among antifungal agents, fluconazole emerged as the major alternative to the classic amphotericin B, being therapeutically at least equivalent but clearly less toxic. Factors that restrict the use of fluconazole include pretreatment with azoles, involvement of resistant species like Candida krusei, and an inability to exclude aspergillosis. Flucytosine can be reasonably combined with both amphotericin B and fluconazole. Within the limited antifungal armamentarium, amphotericin B lipid formulations and itraconazole also appear useful and require further investigation. The general consensus of the group is that antifungal agents should be administered at sufficient dosages, rather early, and often empirically.

[Importance of mycoses in intra-abdominal infections]. / Stellenwert der Mykosen bei intraabdominalen Infektionen.

Although there is a 20% yeast colonization in the gastrointestinal tract of the population, fungal infections appear only rarely in secondary peritonitis. The risk of severe mycosis increases after a major operation and when a patient is taking broad-spectrum antibiotics, is on total parenteral nutrition, is catheterized, and/or is immune-suppressed. In the past years the incidence of nosocomial fungal infections (usually Candida spp.) has risen significantly. Five percent of CAPD-related peritonitis is caused by fungi. In enteral anastomosis breakdown, invasive mycosis occurs more often, with an accompanying lethality of up to 80%. In severe pancreatitis, up to 5% of peripancreatic necrosis is infected with fungi. The clinical course of severe mycosis, like the septic syndrome, is associated with fungemia in up to 50% of cases. As most of the facultative pathogenic fungi are part of the physiological flora, it is difficult to interpret mycological cultures. In order to diagnose invasive fungal infections, histopathological techniques and serologic tests for antigens and antibodies are available. Three antifungal agents (amphotericin B, flucytosine, fluconazole) are available for intravenous administration. Amphotericin B is given at doses of up to 1 mg/kg per day, in liposomal galenism up to 3 mg/kg per day. Combining amphotericin B with flucytosine (150-200 mg/kg per day) a synergistic effect is reached. Fluconazole at a dosage of 200-800 mg per day represents an alternative with similar antifungal activity and lower side effects.

Selective inhibitors of monoamine oxidase. 3. Structure-activity relationship of tricyclics bearing imidazoline, oxadiazole, or tetrazole groups.

Inhibition of monoamine oxidase A (MAO A) is believed to cause antidepressant and possibly antianxiety effects. The previous paper had developed structure-activity relationships (SAR) for in vitro MAO A inhibition by tricyclic N-arylamides. It is shown in this paper that the same in vitro SAR can be carried over to tricyclics whose potentially toxic amide function is replaced by an appropriately substituted imidazoline, a 1,2,4- or 1,3,4-oxadiazole, or an alkylated tetrazole moiety. Dialysis of the inhibitor from the enzyme was used as a measure of reversibility which correlates with a low ability to cause a blood pressure rise with ingested tyramine ("cheese effect").

Variance of cardiorespiratory parameters during gynaecological surgery with CO2-pneumoperitoneum.

Laparoscopic procedures with CO2-pneumoperitoneum are used widely in gynaecology and surgery. The effects of a 15 degrees head-down position, different intra-abdominal pressures (IAP) and CO2-insufflation flows on cardiorespiratory parameters were studied prospectively in 18 gyneacologic patients under general anaesthesia. The 15 degrees head-down position led to significant changes in heart rate (-6%) and in central venous pressure (+53%). Furthermore, significant changes under commonly used conditions for gynaecological laparoscopy (IAP 9mmHg, CO2-insufflation flow 2.41/ min., 15 degrees head-down position) were found in heart rate (+16%), systolic blood pressure (+21%), diastolic blood pressure (+26%), central venous pressure (+57%), peak inspiratory pressure (+26%), end-tidal CO2-concentration (+19%), central venous pCO2 (+21%), and central venous pH (-7%). On examination of variable pressure and insufflation flows (IAP 3, 9, and 15mmHg; CO2-insufflation flows 1.2, 2.4, and 6.0 1/min.), increasing changes in heart rate (7% - 24%), diastolic blood pressure (22% - 33%), central venous pressure (30% - 59%) and peak inspiratory pressure (10% - 43%) correlated with increasing IAP. However, they were independent of CO2-insufflation flows. The results demonstrate that CO2-pneumoperitoneum causes marked changes in cardiorespiratory parameters, but these do not exceed levels commonly regarded as safe in ASA class I and II patients.

Prolonged effects of cholinesterase inhibition with eptastigmine on the cerebral blood flow-metabolism ratio of normal rats.

The cerebrovascular and metabolic effects of the novel cholinesterase inhibitor eptastigmine were tested in conscious rats. The drug was administered by single intravenous injection, and blood flow or glucose utilization were assessed in 38 brain regions by quantitative autoradiographic techniques. A dose-dependent increase in regional cerebral blood flow (rCBF) was obtained for i.v. doses ranging from 0.5 to 3 mg kg-1. Forty minutes after the dose of 1.5 mg kg-1, average rCBF of the 38 regions studied was (mean +/- SD) 2.62 +/- 0.62 ml g-1 min-1, a value significantly higher than that of saline-injected controls (1.46 +/- 0.26; p < 0.005). In contrast, a similar dose of eptastigmine did not significantly alter regional cerebral glucose utilization (rCGU) (0.90 +/- 0.21 mumol g-1 min-1) when compared with saline-injected controls (0.99 +/- 0.08 mumol g-1 min-1). A linear correlation between rCBF and rCGU was observed both in saline (r = 0.871) and eptastigmine (r = 0.873)-injected animals but the slope of the regression line of rCBF on rCGU was significantly higher (p < 0.01) in the eptastigmine group (2.863 +/- 0.266) than in the controls that received saline (1.00 +/- 0.094). The cerebral vasodilatation induced by eptastigmine peaked at 40 min after drug administration. No toxic signs were observed at the doses used. Mean arterial blood pressure decreased after 0.5 mg kg-1 (control = 109.3 +/- 10.56 mm Hg; eptastigmine = 96.6 +/- 8.10 mm Hg) but did not differ from control at the higher doses. It is concluded that eptastigmine induces a long-lasting increase in rCBF and a significant enhancement of the rCBF:rCGU ratio in most regions. The results suggest an important role of endogenous acetylcholine in the control of cerebral perfusion.

Influence of halothane, enflurane, and isoflurane on motor evoked potentials.

The influence of the inhalational anesthetics halothane, enflurane, and isoflurane on motor evoked potentials was studied in a total of 10 rabbits. Motor evoked potentials were recorded from the extremity muscles as well as from the epidural space of the spinal cord and cauda equina in response to electrical stimulation of the motor cortex at baseline conditions and equianesthetic concentrations (0.25 to 1.5 minimal alveolar concentration). Our results show a dose-dependent suppression of the electromyographic responses, which was similar with all anesthetics. Beyond 0.5 minimal alveolar concentration of any of the agents, electromyographic responses were absent. In contrast, spinal evoked responses representing neural activity were only slightly affected by the anesthetics. We hypothesize that the descending impulse elicited by the electrical stimulation of the motor cortex is mainly inhibited at the level of the spinal interneuronal or motoneuronal systems, because 1) electromyographic responses evoked by the stimulation of the cervical and lumbar nerve roots were only minimally affected by 1.5 minimal alveolar concentration halothane; and 2) spinal evoked responses were stable several minutes after cardiac arrest, indicating a subcortical action site of the electrical impulse. In conclusion, intraoperative monitoring of descending pathways by means of motor evoked potentials during anesthesia with the inhalational agents halothane, enflurane and isoflurane is only feasible when neural activity is evaluated.

[A comparative study of the efficacy and tolerance of dipotassium clorazepate and flunitrazepam for oral premedication]. / Vergleichende Untersuchung der Wirksamkeit und Verträglichkeit von Dikaliumchlorazepat und Flunitrazepam zur oralen Prämedikation.

The literature shows that benzodiazepines, in view of their anxiolytic, sedative, amnesic, muscle relaxant and anticonvulsive action, are the most important substances for premedication. Eminent workers regard anxiolysis as the most important aim of premedication. In the present clinical study, oral administration of the two different benzodiazepine derivatives, flunitrazepam (F) and chlorazepate dipotassium (CD) have been explored with a view to side effects, tolerance, quality of sleep during the night, anxiolytic effect and sedation. The study involved 108 women patients aged from 20 to 60 years (ASA class I or II), all scheduled to undergo gynecological surgery in general anesthesia. There were also 20 women who received no premedication. The three groups of patients were further divided into early (operation started before 10:30 a.m.) and late-operation (operation started after 10:30 a.m.) groups. The test drugs were administered as follows: 43 women received 50 mg CD p.o. on the evening before the operation, followed by 25 mg p.o. in the morning; 45 women received 2 mg F p.o. on the evening before the operation, followed by 1 mg p.o. in the morning. All patients took the preoperative premedication at 7 o'clock in the morning. Following this medication, the anxiolytic, sedative, and amnesic effects, side effects, vigilance and O2 saturation (SaO2) were determined at defined points during the day of the operation and the 1st postoperative day. Blood pressure and heart rate were recorded and interpreted as physiological stress parameters. Anxiolysis was determined using the Erlangen Anxiety Scale (EAS) of Galster and Spörl; the degree of sedation was assessed by the anesthesiologist; amnesia was determined by the patients' recognition of picture cards; vigilance and side-effects were assessed by standardized questionnaires. Both active drugs clearly improved the quality of sleep in the night before the operation over that experienced with no premedication. There were no significant differences among the three groups in the physiological stress parameters. The preoperative SaO2 saturation was decreased significantly by oral F, but it was always more than 95%. CD had little influence on the SaO2. Unwanted somatic symptoms were found a little more frequently in the group without any premedication. There were no signs of restricted tolerance for either of the test drugs. In the premedicated groups, pre- and postoperative anxiety decreased significantly.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulmonary artery occlusion-left atrial pressure gradient: an important factor in determining pulmonary venous vascular resistance in acute pulmonary failure.

OBJECTIVE: To determine whether pulmonary artery occlusion pressure (PAOP) accurately reflects left atrial pressure (LAP) in acute pulmonary failure. DESIGN: Sham-controlled laboratory investigation on Goettingen minipigs. INTERVENTIONS: Induction of acute respiratory failure by a 4-hr infusion of live Escherichia coli bacteria in 11 animals; two animals served as the control group. Anesthesia was obtained with methohexital/piritramide and pancuronium bromide. MEASUREMENTS AND MAIN RESULTS: Cardiac output and pressures were measured by means of femoral artery, pulmonary artery, and left atrial catheters. Arterial-alveolar Po2 ratio was calculated to evaluate pulmonary function. Measurements were obtained before and after 1 and 2 hr of the E. coli infusion. Statistical significance was tested with analysis of variance. E. coli infusion caused the hypodynamic shock and respiratory failure. The PAOP-LAP gradient was -0.3 +/- 1.6 mm Hg before bacteremia and increased significantly (p less than .001) to 2.9 +/- 1.8 and 3.4 +/- 2.0 mm Hg after 1 and 2 hr of bacteremia, respectively. No significant changes occurred in the sham group. CONCLUSIONS: A PAOP-LAP gradient may develop during acute respiratory failure. Therefore, pulmonary venous vascular resistance may be underestimated if its determination is based on PAOP. An increase in bronchial to pulmonary blood flow and pulmonary venoconstriction are discussed as hypothetical causes of a PAOP-LAP gradient during acute respiratory failure.

Role of nucleus basalis in cholinergic control of cortical blood flow.

The present investigation was designed to determine the effect of lesions localized to the nucleus basalis/substantia innominata (NB) on resting and cholinergically activated regional cerebral cortical blood flow (rCBF). Ibotenic acid (10 micrograms) was infused locally at 1 mm caudal to bregma, 3 mm lateral to the midline, and 8 mm below the cortical surface. Effectiveness of lesions was demonstrated by histological verification of lesion sites and determination of choline acetyltransferase activity in cerebral cortex homogenates. rCBF was measured with the autoradiographic iodo-14C-antipyrine technique. Resting rCBF was similar in the hemisphere that received the NB lesion and in the contralateral (intact) side in all regions examined. Physostigmine intravenous infusion (3.3 micrograms.kg-1.min-1) enhanced rCBF in frontal, parietal, occipital, and temporal cortex. The increase was symmetrical, however, indicating inability of NB lesion to affect this phenomenon. It is concluded that the cortical cholinergic afferents originating in the NB are not involved in the control of rCBF.

Pulmonary capillary pressure and gas exchange after E. coli bacteremia in pigs.

In 9 Goettingen minipigs we studied the effect of E. coli bacteremia on effective pulmonary capillary pressure and the longitudinal distribution of pulmonary vascular resistance. Precapillary pressure gradient (dPa) was calculated as the difference between mean pulmonary artery pressure (MPP) and effective pulmonary capillary pressure (Pc) (dPa = MPP-Pc), postcapillary pressure gradient (dPv) as the difference between Pc and left atrial pressure (dPv = Pc-LAP). The disturbance of pulmonary gas exchange was quantified by the AaDO2 quotient 1-PaO2/PAO2. Live E. coli infusion resulted in hypodynamic circulatory failure. Cardiac index fell from 3.7 +/- 0.81 . min-1.m-2 to 2.2 +/- 0.71 .min-1.m-2 after bacteremia lasting for 3.5 h. Simultaneously venous pulmonary vascular resistance rose from 25% of total pulmonary vascular resistance before to 32% after 3.5 h bacteremia, thus raising Pc from 11 mmHg to 16 mmHg. The degree of respiratory insufficiency was correlated with changes of MPP, dPa and dPv: 1-PaO2/PAO2 = 0.2 + 0.035.dPv (r = 0.829). Our results show, that the longitudinal distribution of pulmonary vascular resistance changes during septicemia, thus raising Pc. This may be an important factor in the genesis of septic pulmonary failure.

Acute blood pressure increase during the perioperative period.

Hypertensive reactions occur frequently in the perioperative setting. Perioperative blood pressure elevation is generally amenable to treatment in previously normotensive patients. Alterations in cerebral autoregulation and myocardial performance in chronic hypertension limit the compensatory range available to cope with perioperative blood pressure changes. In cardiovascular or cerebrally compromised patients, the pathophysiology of underlying disease must therefore be taken into account. In the cerebrally compromised patient with space-occupying lesions and even merely locally impaired cerebral autoregulation, any blood pressure increase may reduce cerebral perfusion pressure and cause further cerebral impairment. Furthermore, vasodilation of cerebral vessels must be avoided to prevent further increase in intracranial pressure with reduction of cerebral perfusion. In chronically hypertensive patients, sufficient preoperative antihypertensive therapy is essential to avoid acute perioperative blood pressure elevation. Before antihypertensive pharmacologic therapy is begun, it is essential to rule out all correctable secondary causes of hypertension, particularly impairment of ventilation and oxygen supply. When pharmacologic antihypertensive therapy is necessary, vasodilators (e.g., calcium entry blockers) may be administered to chronically hypertensive patients. If elevated intracranial pressure is the underlying cause of hypertension, cerebral vasodilation must be avoided and only centrally acting antihypertensive agents such as urapidil should be used for management.

[Complaints in the postoperative phase related to anesthetics]. / Beschwerden in der postoperativen Phase in Abhängigkeit vom Narkosemittel.

In two prospective, randomized studies the frequency of headache, nausea, vomiting, and analgesic requirement during the first postoperative 24 h was observed in order to study differences between the sexes and the inhalation anesthetics halothane, enflurane, isoflurane, or balanced anesthesia with enflurane/alfentanil. Nausea and vomiting were more frequent after enflurane than after halothane or isoflurane. There was no significant difference between anesthetics and frequency of headache, but there were significant differences in postoperative analgesic requirements which were highest after halothane and lowest after isoflurane. Postoperative complaints were always significantly greater among women than among men. The second study indicated that balanced anesthesia did not reduce the analgesic requirement compared to enflurane without alfentanil, but lead to a higher incidence of vomiting. After premedication with flunitrazepam and atropine and combined with 70% N2O/30% O2, isoflurane was the most favorable anesthetic agent with regard to the parameters studied. Balanced anesthesia with enflurane/alfentanil did not show any advantages for patients in the postoperative phase under the given conditions.