Emergency medical service transport-induced stress? An experimental approach with healthy volunteers

This randomized controlled trial was designed to evaluate the effects of simulated emergency medical service (EMS) transport related stress on hemodynamic variables, and catecholamine plasma levels. A total of 32 healthy male volunteers were randomized to being carried by paramedics from a third-floor apartment through a staircase with subsequent high-speed EMS transport with lights and sirens (stress; n = 16); or sitting on a chair for 5 min, and lying on a stretcher for 15 min (control; n = 16). Blood samples and hemodynamic variables were taken in the apartment before transfer, at the ground floor, and at the end of EMS transport in the stress group, and at corresponding time points in the control group. The stress versus control group had both significantly (P < 0.05) higher mean +/- SEM epinephrine (71 +/- 7 versus 37 +/- 3 pg/ml), and norepinephrine (397 +/- 29 versus 299 +/- 28 pg/ml) plasma levels after transport through the staircase. After EMS transport, the stress versus control group had significantly higher epinephrine (48 +/-6 versus 32 +/- 2 pg/ml), but not norepinephrine (214 +/- 20 versus 264 +/- 31 pg/ml) plasma levels. Heart rate increased significantly from 72 +/- 2 to 84 +/- 3 bpm after staircase transport, but not during and after EMS transport. In conclusion, volunteers being carried by paramedics through a staircase had a significant discharge of both epinephrine and norepinephrine resulting in increased heart rate, but only elevated epinephrine plasma levels during EMS transport. Transport through a staircase may reflect more stress than emergency EMS transport.

Empirical calculation of the relative free energies of peptide binding to the molecular chaperone DnaK

We describe a methodology to calculate the relative free energies of protein-peptide complex formation. The interaction energy was decomposed into nonpolar, electrostatic and entropic contributions. A free energy-surface area relationship served to calculate the nonpolar free energy term. The electrostatic free energy was calculated with the finite difference Poisson-Boltzmann method and the entropic contribution was estimated from the loss in the conformational entropy of the peptide side chains. We applied this methodology to a series of DnaK*peptide complexes. On the basis of the single known crystal structure of the peptide-binding domain of DnaK with a bound heptapeptide, we modeled ten other DnaK*heptapeptide complexes with experimentally measured K(d) values from 0.06 microM to 11 microM, using molecular dynamics to refine the structures of the complexes. Molecular dynamic trajectories, after equilibration, were used for calculating the energies with greater accuracy. The calculated relative binding free energies were compared with the experimentally determined free energies. Linear scaling of the calculated terms was applied to fit them to the experimental values. The calculated binding free energies were between -7.1 kcal/mol and - 9.4 kcal/mol with a correlation coefficient of 0.86. The calculated nonpolar contributions are mainly due to the central hydrophobic binding pocket of DnaK for three amino acid residues. Negative electrostatic fields generated by the protein increase the binding affinity for basic residues flanking the hydrophobic core of the peptide ligand. Analysis of the individual energy contributions indicated that the nonpolar contributions are predominant compared to the other energy terms even for peptides with low affinity and that inclusion of the change in conformational entropy of the peptide side chains does not improve the discriminative power of the calculation. The method seems to be useful for predicting relative binding energies of peptide ligands of DnaK and might be applicable to other protein-peptide systems, particularly if only the structure of one protein-ligand complex is available.

Conversion of aspartate aminotransferase into an L-aspartate beta-decarboxylase by a triple active-site mutation

The conjoint substitution of three active-site residues in aspartate aminotransferase (AspAT) of Escherichia coli (Y225R/R292K/R386A) increases the ratio of L-aspartate beta-decarboxylase activity to transaminase activity >25 million-fold. This result was achieved by combining an arginine shift mutation (Y225R/R386A) with a conservative substitution of a substrate-binding residue (R292K). In the wild-type enzyme, Arg(386) interacts with the alpha-carboxylate group of the substrate and is one of the four residues that are invariant in all aminotransferases; Tyr(225) is in its vicinity, forming a hydrogen bond with O-3' of the cofactor; and Arg(292) interacts with the distal carboxylate group of the substrate. In the triple-mutant enzyme, k(cat)' for beta-decarboxylation of L-aspartate was 0.08 s(-1), whereas k(cat)' for transamination was decreased to 0.01 s(-1). AspAT was thus converted into an L-aspartate beta-decarboxylase that catalyzes transamination as a side reaction. The major pathway of beta-decarboxylation directly produces L-alanine without intermediary formation of pyruvate. The various single- or double-mutant AspATs corresponding to the triple-mutant enzyme showed, with the exception of AspAT Y225R/R386A, no measurable or only very low beta-decarboxylase activity. The arginine shift mutation Y225R/R386A elicits beta-decarboxylase activity, whereas the R292K substitution suppresses transaminase activity. The reaction specificity of the triple-mutant enzyme is thus achieved in the same way as that of wild-type pyridoxal 5'-phosphate-dependent enzymes in general and possibly of many other enzymes, i.e. by accelerating the specific reaction and suppressing potential side reactions.

Irrigation fluid absorption during transurethral resection of the prostate: spinal vs. general anaesthesia

BACKGROUND

The absorption of irrigation fluid during transurethral resection of the prostate (TURP) is determined primarily by hydrostatic pressure in the bladder and prostatic venous pressure. In comparison to spontaneously breathing patients, patients undergoing mechanical ventilation with positive pressure have a raised central venous pressure and a reduced venous return, both of which can influence intravascular absorption. The purpose of the prospective study was to compare the effects of general (GA) and spinal anaesthetic (SA) techniques on the perioperative absorption of irrigating fluid in patients undergoing TURP.

METHODS

Forty patients undergoing TURP were randomised and assigned either to group GA or SA. Irrigating fluid absorption was traced by adding 1.5% (w/v) ethanol to the irrigating fluid. Perioperative blood ethanol concentration (BEC), haemoglobin concentration, haematocrit, serum sodium concentration and central venous pressure (CVP) were measured at 10-min intervals during TURP and at 30-min intervals while patients were recovering. Absorption routes were indexed by the BEC and changes in serum sodium concentrations. Where the BEC was greater than 0.05 mg.mL-1, absorption of irrigating fluid was assumed. For assessing the volume of irrigating fluid absorbed, the maximum BEC, the absorption rate, the area under the BEC curve (AUC), and the volumes calculated according to the Hahn nomogram (Volin) for each patient were taken into consideration.

RESULTS

There were 15 cases of irrigating fluid absorption in patients receiving GA (75%), and 11 in those receiving SA (55%). CVP was significantly lower in spontaneously breathing patients with SA as compared to those with GA (P < 0.05). In patients with irrigating fluid absorption the maximum BEC (P < 0.02), as well as the rate of irrigant fluid absorption (P < 0.01), were significantly higher amongst patients receiving SA. In this group, the calculated area under the curve and the absorbed fluid volumes determined with the nomogram were significantly increased (P < 0.05).

CONCLUSION

The absorption of irrigation fluid during the TURP is significantly more marked amongst spontaneously breathing patients with regional anaesthesia in comparison to patients undergoing general anaesthesia with positive pressure ventilation. The markedly lower central venous pressure before the start of irrigation should be considered as a possible cause of this effect.

Irrigating fluid absorption during percutaneous nephrolithotripsy

BACKGROUND

The most common complication during percutaneous nephrolithotripsy (PNL) is the destruction of organ structures with extravasation of the irrigation fluid into the retroperitoneal space. Consequently, there is an increased risk of a urosepsis and a complicated therapeutic course. In this study we aimed to show that extravascular absorption could be differentiated from intravascular absorption due to their unique absorption characteristics, and that these characteristics enable a prediction of possible post-operative complications.

METHODS

In a prospective study of 31 patients with PNL, ethanol was added to the irrigating fluid and blood ethanol concentration (BEC) was measured by gas chromatography during the endoscopic procedure and in the recovery room. Following the guidelines of Hahn, patients were divided into two groups: group EVA, in whom extravasation had occurred with subsequent absorption; group IVA, those with intravascular absorption. Patients' post-operative progress along with diagnoses of renal perforations or bleeding, or signs of infection or sepsis, were comprehensively listed.

RESULTS

EVA was diagnosed in 19 cases, and IVA in 12 cases. Maximum BEC levels were achieved after 20 min (median) in the IVA group, and 75 min in the EVA group (P < 0.05). Apart from their significantly higher demand for opioids (P < 0.05), EVA patients had been hospitalised for a substantially and significantly longer period of time (P < 0.01). Although without statistical significance, there was a higher rate of peri-operatively confirmed complications and prolonged intensive therapeutic treatment in the extravasation group.

CONCLUSION

Retroperitoneal extravasation can be identified by using ethanol monitoring during and after PNL. Afflicted patients require considerably longer hospitalisation, probably because of the additional injury to surrounding organ structures.

Maturation-induced conformational changes of HIV-1 capsid protein and identification of two high affinity sites for cyclophilins in the C-terminal domain

Viral incorporation of cyclophilin A (CyPA) during the assembly of human immunodeficiency virus type-1 (HIV-1) is crucial for efficient viral replication. CyPA binds to the previously identified Gly-Pro90 site of the capsid protein p24, but its role remained unclear. Here we report two new interaction sites between cyclophilins and p24. Both are located in the C-terminal domain of p24 around Gly-Pro157 and Gly-Pro224. Peptides corresponding to these regions showed higher affinities (Kd approximately 0.3 microM) for both CyPA and cyclophilin B than the best peptide derived from the Gly-Pro90 site ( approximately 8 microM) and thus revealed new sequence motifs flanking Gly-Pro that are important for tight interaction of peptide ligands with cyclophilins. Between CyPA and an immature (unprocessed) form of p24, a Kd of approximately 8 microM was measured, which corresponded with the Kd of the best of the Gly-Pro90 peptides, indicating an association via this site. Processing of immature p24 by the viral protease, yielding mature p24, elicited a conformational change in its C-terminal domain that was signaled by the covalently attached fluorescence label acrylodan. Consequently, CyPA and cyclophilin B bound with much higher affinities ( approximately 0.6 and 0.25 microM) to the new, i.e. maturation-generated sites. Since this domain is essential for p24 oligomerization and capsid cone formation, CyPA bound to the new sites might impair the regularity of the capsid cone and thus facilitate in vivo core disassembly after host infection.

Conversion of tyrosine phenol-lyase to dicarboxylic amino acid beta-lyase, an enzyme not found in nature

Tyrosine phenol-lyase (TPL), which catalyzes the beta-elimination reaction of L-tyrosine, and aspartate aminotransferase (AspAT), which catalyzes the reversible transfer of an amino group from dicarboxylic amino acids to oxo acids, both belong to the alpha-family of vitamin B6-dependent enzymes. To switch the substrate specificity of TPL from L-tyrosine to dicarboxylic amino acids, two amino acid residues of AspAT, thought to be important for the recognition of dicarboxylic substrates, were grafted into the active site of TPL. Homology modeling and molecular dynamics identified Val-283 in TPL to match Arg-292 in AspAT, which binds the distal carboxylate group of substrates and is conserved among all known AspATs. Arg-100 in TPL was found to correspond to Thr-109 in AspAT, which interacts with the phosphate group of the coenzyme. The double mutation R100T/V283R of TPL increased the beta-elimination activity toward dicarboxylic amino acids at least 10(4)-fold. Dicarboxylic amino acids (L-aspartate, L-glutamate, and L-2-aminoadipate) were degraded to pyruvate, ammonia, and the respective monocarboxylic acids, e.g. formate in the case of L-aspartate. The activity toward L-aspartate (kcat = 0.21 s-1) was two times higher than that toward L-tyrosine. beta-Elimination and transamination as a minor side reaction (kcat = 0.001 s-1) were the only reactions observed. Thus, TPL R100T/V283R accepts dicarboxylic amino acids as substrates without significant change in its reaction specificity. Dicarboxylic amino acid beta-lyase is an enzyme not found in nature.

Concept for an intelligent anaesthesia EEG monitor

Considering the fundamental difficulties to define the term 'depth of anaesthesia', a more feasible concept for assessment of 'adequacy of anaesthesia' will be explained. The basic requirements for a monitoring index are definite response, gradual scaling and independence from the anaesthetic technique used. Additionally the index should be predictive for appearance of clinical signs of an inadequate anaesthesia. Different signal-processing methods will be discussed to extract the relevant information from both the spontaneous and the evoked brain electrical activity. In this context well established methods like spectral analysis are investigated in combination with new and more sophisticated methods like bispectral analysis or wavelet decomposition. Since no single-parameter index has been defined for monitoring depth of anaesthesia, a set of EEG parameters may be more useful to take into account intra- and interindividual variability. In parallel to the description of the monitor concept, the investigation of neural nets and fuzzy techniques, in addition to or in substitution of conventional statistical methods, will be introduced. Examples are given for data quality assessment, parameter extraction and re-classification.

Perioperative cytokine release during coronary artery bypass grafting in patients of different ages

Surgical interventions and cardiopulmonary bypass (CPB) induce a systemic inflammatory response with cytokine release. Ageing is perceived as a process of impaired immune functions: IL-1beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) secretion are increased while IL-2 release is reduced in advanced age. At present, little information is available about perioperative immune reactions at different stages of ageing. The aim of the present study was to compare IL-6, IL-1beta, TNF-alpha, IL-10 and soluble IL-2 receptor (sIL-2R) in younger and older patients undergoing cardiac surgery. Male patients (n = 14) undergoing elective coronary artery bypass grafting (CABG) surgery employing CPB with moderate hypothermia were divided into two groups according to their age: group 1 included seven patients < 50 years old, group 2 included seven patients > 65 years old. All patients received general anaesthesia using a balanced technique with sufentanil, isoflurane and midazolam. Blood samples were collected pre-operatively (T1); intra-operatively during CPB (T2); post-operatively on the day of surgery (T3); on the first post-operative day (T4). Blood concentrations of IL-6, IL-1beta, IL-10, TNF-alpha and sIL-2R were measured using commercially available ELISA kits and corrected for plasma cell volume. Statistical analysis was performed by non-parametric analysis of variance and Mann-Whitney U-test. Significance level was set to P<0.05. There were no statistically significant differences in the perioperative release of TNF-alpha, IL-6, IL-1beta, IL-10 and sIL-2R among the two groups. We conclude that the perioperative course of cytokine release in patients undergoing CABG surgery with CPB and comparable perioperative management does not significantly differ in the two age groups.

The V3 loop of human immunodeficiency virus type-1 envelope protein is a high-affinity ligand for immunophilins present in human blood

Human immunodeficiency virus type-1 (HIV-1) infection requires binding of the envelope protein gp120 to host CD4 receptors and the action of the chemokine receptors CXCR4 or CCR5, which define cell tropism. The proline-containing V3 loop of gp120 determines the selection of the chemokine receptor and participates in conformational changes on binding of gp120 to CD4. In this study, we show that macrophage-tropic and T-cell-tropic V3 loop peptides bind specifically to the active site of the immunophilins FK506-binding protein (FKBP12), and cyclophilins A and B. Macrophage-tropic and T-cell-tropic V3 loop peptides inhibited the peptidyl-prolyl cis-trans isomerase (PPIase) activities of the immunophilins. Kd values in the range 0.036-4.1 microM were determined with V3 loop peptides labeled with an environmentally sensitive fluorophore. The observed binding properties of the V3 loop peptides reveal structural motifs of linear water-soluble peptidic substrates for tight interaction with immunophilins. FKBP12, and cyclophilins A and B were found to be present in normal human blood in the ranges 0.8-1.7, 1.4-2.3 and 2.4-3.1 nM, respectively, as demonstrated by PPIase activity measurements and western blot analysis. Cyclophilins A and B levels in serum of HIV-1-infected individuals were increased 3.6-fold and 1.6-fold. Due to the interaction of immunophilins with V3 loop peptides and with the envelope protein gp120, a role of immunophilins in HIV pathogenesis as conformases or docking mediators seems possible, since immunophilin receptors on cell membranes and immunophilin-related virulence factors of pathogens have been identified.

[Measuring breath alcohol concentration during artificial ventilation. Model studies of the effect of temperature and humidity on measurements by various sampling systems]

The present paper examined the question as to the extent to which the taking of gas samples for the purpose of measuring the breath alcohol concentration (BAC) in the expired air of patients on artificial respiration is influenced by temperature and humidity. For this purpose a lung model standardized at different alcohol concentrations was used, in which the temperature (T: 25, 30 and 35 degrees C) and the relative humidity (RH: 50, 75 and 95%) were varied.

Effects of propofol vs isoflurane on respiratory gas exchange during laparoscopic cholecystectomy

BACKGROUND

Respiratory function and pulmonary gas exchange are affected in laparoscopic procedures where a pneumoperitoneum is introduced using CO2. Previous studies have shown differing results concerning pulmonary gas exchange during laparoscopic procedures: Whereas in patients undergoing isoflurane anaesthesia decreases in PaO2 are demonstrated, this factor remains unchanged in patients undergoing propofol anaesthesia. In the present study, the effects of propofol on pulmonary gas exchange were compared with those of isoflurane in patients undergoing elective laparoscopic cholecystectomy in a prospective randomised manner.

METHODS

Twenty ASA patients with physical status I and II were divided randomly between isoflurane (IG) and propofol groups (PG). After induction of anaesthesia patients were moderately hyperventilated. Respirator settings remained unchanged during pneumoperitoneum (PP) until 10 min after deflation of the peritoneal cavity. Blood gas analyses were performed at 5 time points: 15 min after induction of anaesthesia (giving pre-PP values), immediately before carbon dioxide insufflation (0 min PP), after both 30 and 60 min of PP and 10 min post PP. Inspiration plateau pressure (Pplat), compliance of the respiratory system, and both ins- and expiratory gas concentrations were continuously recorded by an Ultima V monitor (Datex Corp., Helsinki, Finland). The difference between arterial and end-tidal CO2 partial pressure (P(a-et)CO2) was calculated so as to allow assessment of physiological dead space by the modified Bohr equation.

RESULTS

Pulmonary gas exchange differed significantly after 30 min of PP between the IG and the PG. At this time, PaO2 was 19.5 +/- 2.9 kPa (mean +/- SD) in the IG and 23.1 +/- 1.8 kPa in the PG (P < 0.01), whereas PaCO2 was 5.5 +/- 0.37 kPa in the IG and 4.9 +/- 0.27 kPa in the PG (P < 0.01). These discrepancies remained until after carbon dioxide desufflation. At 10 min post PP, PaO2 was 18.3 +/- 2.6 kPa in the isoflurane group and 21.9 +/- 2.2 kPa in the propofol group (P < 0.01), whereas PaCO2 was 5.4 +/- 0.46 kPa in the IG and 4.8 +/- 0.22 kPa in the PG (P < 0.01). During carbon dioxide insufflation the P(a-et)CO2 increased significantly in the IG from 0.47 +/- 0.13 kPa to 0.76 +/- 0.37 kPa (P < 0.05), while the values in the PG remained constant.

CONCLUSION

This study demonstrates that pulmonary gas exchange in patients with laparoscopic cholecystectomy is affected by the choice of anaesthetic procedure. During and after laparoscopic cholecystectomy using isoflurane as the anaesthetic, the PaCO2 is significantly higher and the PaO2 significantly lower than they are with propofol.

[The effect of temperature and humidity on breath samples. Measurement of breath ethanol concentration in artificially respirated patients]

When looking for the possible cause of distortions in values measured for the determination of breath ethanol concentration (BEC) in artificially respirated patients, consideration must be given to the humidity and temperature of the gas examined. In the present study, the effects of humidified and warmed and of dry and cold air on the accuracy of a newly developed BEC measuring device, as compared to a reference model and to a conventional system, were examined in a lung model.

METHODS

A temperature-regulated pediatric incubator was used containing a 10 I gas reservoir and a breath humidifier with temperature regulated water bath. This setup provided constant temperature and humidity in the gas examined during measurement period. In the 'expiration' the air was directed from the breath humidifier through a measuring unit via a 'mouthpiece' into the reference system (Alcotest 7110, Dräger Inc., Lübeck) and then out. The measuring unit consisted of sensors for the temperature and relative humidity, and of a connector for the three sample extraction systems (PES). PES I was the conventional system with a 100-cm gas-sample pipe (Alcomed 3010), PES II the newly developed system (AlcoMed 3011, both from Envitec, Wismar) with a 10-cm gas-sample pipe, and PES III with a 20-cm heated gas-sample pipe. During 'inspiration' 2 l of air was fed into the system to rinse the measuring unit and to fill the reservoir. 61 measurements were performed with dry and cold air, and 71 with humidified and warmed air, in the course of which the ethanol concentration was increased from 0 to 1.5/1000. Data were evaluated using regression analysis and the Bland & Altman method.

RESULTS AND CONCLUSIONS

The constancy of the values set for temperature, relative humidity and absolute humidity in the lung model was given for all measurements. In the dry and cold air, the results from all three test systems coincided almost perfectly with the reference values. The measured BEC in the humidified and warmed air using sample-extraction systems II and III corresponded to a high degree with the reference, while in the case of PES I, only a moderate linear correlation was achieved. The temperature and humidity of the expired gas during artificial respiration influence the gas samples extracted for the purposes of BEC measurement. Newly developed sample-extraction systems II and III coincide with the reference system, even under respiration-simulated gas conditions.

[The preparation for elective interventions--the spectrum and dissemination of somatic and psychological measures in Germany]

INTRODUCTION

The positive effects of preoperative preparation on postoperative recovery in patients undergoing elective surgery have been demonstrated. On that account, we surveyed the practice procedures of preoperative preparation for elective surgery patients at German hospitals.

METHODS

During November 1994, we sent 1500 questionnaires to the directors of anaesthesiology departments in Germany. A total of 590 questionnaires (39.3%) were completed and returned. The participating hospitals range in size from 20 to 2600 beds (mean = 364; s = 334,97), totalling together more than 1.7 million surgical operations per year.

RESULTS

The surveyed hospitals used one or more of the following procedures for pre-operative preparation: 573 (98.6%) of the replying hospitals used medical anxiolysis, 415 (71.3%) applied preoperative respiratory therapy. Furthermore, 222 (38.5%) of the studied hospitals trained their patients in postoperative relevant behaviour (respiratory therapy n = 167; physiotherapy n = 63 and patient-controlled analgesia n = 41). 74 (13%) offered psychological counselling, 29 (5%) made use of other psychological techniques (muscle relaxation; autogenic training, biofeedback) and 26 (4%) used other preparatory methods like video tapes (n = 13), music (n = 5), acupuncture (n = 4).

DISCUSSION

Nearly all hospitals prepared their patients for surgery with a pre-op visit and anxiolytic medications. Further preparatory methods in most surveyed hospitals are only used on a case-by-case basis. At present psychological methods of preoperative preparation are not routinely used in clinical practice in Germany.

CONCLUSIONS

Existing possibilities for optimising preoperative preparation in patients undergoing elective surgery are not used regularly. Preoperative preparation needs to be improved, especially in patients undergoing major surgery. Standardisation of management procedures and integration of several professional groups and regular application of known procedures for preoperative preparation may lead to cost-saving optimisation of the duration of hospital stay.

[A new probe holding device for continuous bilateral measurements of blood flow velocity in basal brain vessels]

The clinical relevance of transcranial Doppler sonography for the evaluation of cerebral perfusion and cerebrovascular regulatory mechanisms, as well as for the registration of embolic events, has increased considerably as a technique of non-invasive monitoring. The continuous measurement of blood flow velocities in two different vessel segments, either ipsilateral or contralateral, is limited by intricate probe fixation and positioning for optimal insonation of the vessel on the one hand. On the other hand probes are displaced frequently during anaesthesiological measures, so that continuous registration during induction of anaesthesia is not always guaranteed. In view of these limitations, a new probe-positioning and holding device has been developed and tested in a clinical study of patients undergoing cardiac surgery (n = 22). The newly designed probe-positioning and holding device allowed the unilateral adjustment and continuous measurement of the blood flow velocity in the middle cerebral artery (Vmca) from anaesthesia induction to endotracheal intubation in all patients (n = 9). This was possible in only 61.5% (n = 8) of the patients who were monitored via conventional mode of probe fixation (n = 13). The new method rendered possible the positioning, insonation and measurement in two vessel segments in 77.8% of the patients, in contrast to 53.8% of the patients where the conventional technique was used. The newly designed probe holding device meets all standard requirements from the anaesthesiological viewpoint, and facilitates the perioperative application of transcranial Doppler sonography for non-invasive monitoring.