Creating a model to predict time intervals from induction of labor to induction of anesthesia and delivery to coordinate workload.

BACKGROUND: Induction of labor continues to become more common. We analyzed induction of labor and timing of obstetric and anesthesia work to create a model to predict the induction-anesthesia interval and the induction-delivery interval in order to co-ordinate workload to occur when staff are most available. METHODS: Patients who underwent induction of labor at a single medical center were identified and multivariable linear regression was used to model anesthesia and delivery times. Data were collected on date of birth, race/ethnicity, body mass index, gestational age, gravidity, parity, indication for labor induction, number of prior deliveries, time of induction, induction agent, cervical dilation, effacement, and fetal station on admission, date and time of anesthesia administration, date and time of delivery, and delivery type. RESULTS: A total of 1746 women met inclusion criteria. Associations which significantly influenced time from induction of labor to anesthesia and delivery included maternal age (anesthesia P <0.001, delivery P =0.002), body mass index (both P <0.001), prior vaginal delivery (both P <0.001), gestational age (anesthesia P <0.001, delivery P <0.018), simplified Bishop score (both P <0.001), and first induction agent (both P <0.001). Induction of labor of nulliparous women at 02:00 h and parous women at 04:00 or 05:00 h had the highest estimated probability of the mother having her first anesthesia encounter and delivering during optimally staffed hours when our institution's specialty personnel are most available. CONCLUSIONS: Time to obstetric and anesthesia tasks can be estimated to optimize induction of labor start times, and shift anesthesia and delivery workload to hours when staff are most available.

Bifunctional alloys for the electroreduction of CO2 and CO.

We use density functional theory to study the reduction of CO2 and CO to hydrocarbons through a formyl pathway on (111) and (211) facets of L12 alloys with an A3B composition. We find that several alloys may reduce the thermodynamic overpotential for CO reduction by more than 0.2 V compared to a copper step, however, these alloys are most often rather unstable in aqueous environment or have low alloy formation energies and may be susceptible to segregation destroying the active sites. Strategies to improve alloy stability against corrosion or segregation would likely be needed in order to realize the full potential of these alloys.

Chemical looping of metal nitride catalysts: low-pressure ammonia synthesis for energy storage.

The activity of many heterogeneous catalysts is limited by strong correlations between activation energies and adsorption energies of reaction intermediates. Although the reaction is thermodynamically favourable at ambient temperature and pressure, the catalytic synthesis of ammonia (NH3), a fertilizer and chemical fuel, from N2 and H2 requires some of the most extreme conditions of the chemical industry. We demonstrate how ammonia can be produced at ambient pressure from air, water, and concentrated sunlight as renewable source of process heat via nitrogen reduction with a looped metal nitride, followed by separate hydrogenation of the lattice nitrogen into ammonia. Separating ammonia synthesis into two reaction steps introduces an additional degree of freedom when designing catalysts with desirable activation and adsorption energies. We discuss the hydrogenation of alkali and alkaline earth metal nitrides and the reduction of transition metal nitrides to outline a promoting role of lattice hydrogen in ammonia evolution. This is rationalized via electronic structure calculations with the activity of nitrogen vacancies controlling the redox-intercalation of hydrogen and the formation and hydrogenation of adsorbed nitrogen species. The predicted trends are confirmed experimentally with evolution of 56.3, 80.7, and 128 µmol NH3 per mol metal per min at 1 bar and above 550 °C via reduction of Mn6N2.58 to Mn4N and hydrogenation of Ca3N2 and Sr2N to Ca2NH and SrH2, respectively.

The changing management role: autocratic doer to team facilitator.

The changing health care environment has challenged nurse managers to change their way of "doing business." Traditionally, nurse managers have used autocratic methods to control staff. That approach no longer provides the tools needed to survive the changes that managers are faced with daily. The nurse manager must be able to motivate and involve staff. The characteristics needed in the changing world of management include allowing staff to make decisions and providing them with the support and facilitation to grow. This article describes the evolution of nurse management from autocratic doer to team facilitator.

Decrease of anion selectivity caused by mutation of Thr501 and Gly502 to Glu in the hydrophobic domain of the colicin E1 channel.

Structure-function relations of the colicin E1 ion channel were studied through the effects of mutations in the 35-residue hydrophobic region of the channel polypeptide and neighboring residues in the channel domain. Mutation of neutral residues threonine 501 and glycine 502 to a more polar or charged glutamic acid generated a protein whose channel conductance properties in each case had a decreased selectivity for anions. There was no significant effect on ion selectivity caused by mutations that changed residue charge outside the hydrophobic domain at the neighboring aspartic acid 509 or at glycine 439. The Thr501----Glu and Gly502----Glu mutants possessed lower cytotoxic and in vitro activity. An altered thermolysin cleavage pattern and a greater binding to membrane vesicles at pH greater than 4.5 of the Gly502----Glu mutant indicated greater exposure of its COOH-terminal hydrophobic domain in solution. It is concluded that the hydrophobic nature of threonine 501 and glycine 502 is important in the structure of the channel lumen and the soluble colicin. Altering proline 462, a residue conserved in five sequenced channel-forming colicins, had no significant effect on channel properties. These conclusions are discussed in the context of sequence-structure-function concepts for channel proteins.

Dynamic properties of membrane proteins: reversible insertion into membrane vesicles of a colicin E1 channel-forming peptide.

The binding of colicin E1 and its COOH-terminal channel-forming peptides to artificial membrane vesicles has an optimum at acidic pH values. The Mr 18,000 thermolytic peptide inserted into membrane vesicles at pH 4.0 has a limited accessibility to exogenous protease. It is converted by trypsin cleavage after Lys-381 and Lys-382 to a lower Mr 14,000 peptide. However, when the pH of a vesicle suspension to which peptide has been bound at pH 4.0 is shifted to 6.0, the accessibility to protease increased greatly. This was shown (i) by the large decrease in the amount of Mr 14,000 or Mr 18,000 peptide after the pH 4----6 shift and treatment with trypsin or Pronase, consistent with (ii) a previously observed decrease in membrane-bound radiolabeled peptide after protease treatment. (iii) When a photoactivable nitrene-generating phospholipid probe was used to label the colicin peptide inserted into the bilayer, the extent of labeling decreased by a factor of 3 when the pH was shifted from 4.0 to 6.5. (iv) Colicin peptide added to vesicles at pH 4.0 can "hop" to other vesicles if the pH and ionic strength of donor vesicles are successively increased. It is proposed that deprotonation of acidic residues in contact with the hydrophobic bilayer or the membrane surface destabilizes the inserted channel and causes it to be extruded from the membrane. The pH-dependent extrusion of the inserted colicin channel provides an example of dynamic properties of an intrinsic membrane protein.

Dephosphorylation of the lipid A moiety of Escherichia coli lipopolysaccharide by mouse macrophages.

An Escherichia coli deep rough lipopolysaccharide (LPS), biosynthetically labeled with 32PO4 and [3H]glucosamine, was used to study dephosphorylation of the lipid A moiety by murine macrophages. Over a 48-h incubation period, the macrophages removed approximately two-thirds of the 32P from [3H32P]LPS that was added to the culture medium. The LPS-derived phosphate was incorporated into cell components (e.g., phospholipids), as well as released from the cells. Cell lysates were also able to remove phosphate from [3H32P]LPS. The phosphatase activity was optimal at acidic pH and was greatly reduced by 10 mM sodium fluoride or heating at 80 degrees C. There was no evident difference in the LPS-dephosphorylating ability of macrophages from LPS-responsive and -hyporesponsive mice. The results indicate that murine macrophages dephosphorylate the lipid A moiety of deep rough E. coli LPS and raise the possibility that enzymatic dephosphorylation may modify LPS bioactivity.

Decreased binding of antibiotics to lipopolysaccharides from polymyxin-resistant strains of Escherichia coli and Salmonella typhimurium.

The interactions of polycationic antibiotics with lipopolysaccharide (LPS) isolated from parental and polymyxin-resistant strains of Salmonella typhimurium and Escherichia coli were measured by using a cationic spin probe. Electron spin resonance spectra indicated that increasing concentrations of cations competitively displaced probe from LPS aggregates. Polymyxin B and other cations displaced less probe from LPS of polymyxin-resistant strains than from LPS of the parental strains, whereas the same amount or more probe was displaced from isolates of the mutants by the structurally similar antibiotic, EM 49 (octapeptin). In general, the differential affinities of these antibiotics for LPS correlated with their antibiotic activity in vivo, suggesting that resistance results from a decrease in antibiotic permeability across the outer membrane due to alterations in the LPS which affect antibiotic binding. The alterations in the structure of LPS from the polymyxin-resistant mutants of E. coli were characterized using 31P nuclear magnetic resonance spectroscopy. The results suggested that esterification of the core-lipid A phosphates is responsible for increased resistance to polymyxin B and that this alteration is different from that previously proposed for the S. typhimurium strains. In both cases, however, resistance was the result of modifications that result in a less acidic lipid A.

Voltage-dependent, monomeric channel activity of colicin E1 in artificial membrane vesicles.

The dependence of colicin channel activity on membrane potential and peptide concentration was studied in large unilamellar vesicles using colicin E1, its COOH-terminal thermolytic peptide and other channel-forming colicins. Channel activity was assayed by release of vesicle-entrapped chloride, and could be detected at a peptide: lipid molar ratio as low as 10(-7). The channel activity was dependent on the magnitude of a transnegative potassium diffusion potential, with larger potentials yielding faster rates of solute efflux. For membrane potentials greater than -60 mV (K+in/K+out greater than or equal to 10), addition of valinomycin resulted in a 10-fold increase in the rate of Cl- efflux. A delay in Cl-efflux observed when the peptide was added to vesicles in the presence of a membrane potential implied a potential-independent binding-insertion mechanism. The initial rate of Cl- efflux was about 1% of the single-channel conductance, implying that only a small fraction of channels were initially open, due to the delay or latency of channel formation known to occur in planar bilayers. The amount of Cl- released as a function of added peptide increased monotonically to a concentration of 0.7 ng peptide/ml, corresponding to release of 75% of the entrapped chloride. It was estimated from this high activity and consideration of vesicle number that 50-100% of the peptide molecules were active. The dependence of the initial rate of Cl- efflux on peptide concentration was linear to approximately the same concentration, implying that the active channel consists of a monomeric unit.

Physical properties of short- and long-O-antigen-containing fractions of lipopolysaccharide from Escherichia coli 0111:B4.

Aggregates of short- and long-chain O-antigen-containing fractions of lipopolysaccharide were analyzed by electron spin resonance probing to reveal differences in their physical properties. The fluidities of the lipid regions of the two fractions were quite similar, although the long-chain lipopolysaccharide aggregates appeared to be more hydrated as reflected by the polarity determined with a lipid probe. In contrast, the head-group region of the long-chain fraction was dramatically more mobile than that of the short-chain sample. The binding of polycations (e.g., polymyxin B, spermine) to lipopolysaccharide aggregates was measured by the partitioning of a cationic spin probe. Less probe was displaced from the long-chain fraction and unseparated lipopolysaccharide than from the short-chain fraction by the addition of cations, suggesting that the long O-antigen masks anionic sites on lipopolysaccharide. These results indicate that the aggregate shape and reactivity of lipopolysaccharide are affected by O-antigen length. Thus, the biological activity of lipopolysaccharide may be modulated directly by the presence of O-antigen and indirectly by the effects of O-antigen on the lipopolysaccharide aggregate structure.

A pH titration study on the ionic bridging within lipopolysaccharide aggregates.

The packing of lipopolysaccharide aggregates from rough strains of Escherichia coli was examined at different pH values. Lipopolysaccharide head-group motion, measured with an electron spin resonance probe, was found to be dependent on pH, and indicated the existence of multiple ionizable groups. Lipopolysaccharide from a rough (Ra) and a heptose-less (Re) mutant were more rigid at pH 5 than at pH 10.5. In addition, head-group mobility of the magnesium salt of Ra lipopolysaccharide was substantially less than that of the sodium salt at pH 7.0, whereas at high pH (pH 12) the two salts were equally fluid. Changes in head-group packing were also reflected in pH-dependent changes in the phase transition measured with differential scanning calorimetry. The enthalpy of the transition, delta Ht, for the sodium salt of Re lipopolysaccharide was greatest at pH 7.5 and approached zero in both the acidic and the basic pH ranges. We propose that fixed charges in the core and lipid A regions significantly influence lipopolysaccharide head-group motion and the lipopolysaccharide aggregation state. Furthermore, ionic bridging among phosphate groups dramatically rigidifies head group interactions in the neutral to acidic pH ranges.

Binding of polycationic antibiotics and polyamines to lipopolysaccharides of Pseudomonas aeruginosa.

Polycations, such as aminoglycoside and peptide antibiotics, and naturally occurring polyamines were found to bind to the lipopolysaccharide of Pseudomonas aeruginosa and alter its packing arrangement. Binding of cations was measured by the displacement of a cationic spin probe from lipopolysaccharide into the aqueous environment upon addition of competitive cations. The level of probe displacement was dependent on the concentration and charge of the competing cation, with the more highly charged cations being more effective at displacing probe. The relative affinity of several antibiotics for lipopolysaccharide correlated with their ability to increase outer membrane permeability, while the relative affinity of several polyamines correlated with their ability to stabilize the outer membrane. Probe mobility within the lipopolysaccharide head group was shown to be decreased by cationic antibiotics and unaltered or increased by polyamines. We propose that antibiotic permeability and disruption of outer membrane integrity by polycationic antibiotics results from binding of the antibiotic to anionic groups on lipopolysaccharide with a consequent change in the conformation of lipopolysaccharide aggregate structure.

High-molecular-weight components in lipopolysaccharides of Salmonella typhimurium, Salmonella minnesota, and Escherichia coli.

Lipopolysaccharide from smooth strains of Salmonella typhimurium, Salmonella minnesota, and Escherichia coli O111:B4, O55:B5, and O127:B8 was fractionated by gel filtration chromatography. All lipopolysaccharide samples separated into three major populations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the fractions from S. typhimurium and S. minnesota indicated that the three peaks were made up of molecules with average O-antigen lengths of (i) 70 or more repeat units, (ii) 30 and 20 repeats units in the samples from S. typhimurium and S. minnesota, respectively, and (iii) 1 repeat unit. In contrast to the Salmonella samples, peak 1 from the E. coli samples was not detected on polyacrylamide gels and lacked detectable phosphate. This high-molecular-weight material had a sugar composition similar to that of O-antigen and was tentatively identified as capsular polysaccharide. Peaks 2 and 3 of the E. coli samples were analogous to those of the Salmonella isolates, containing lipopolysaccharide molecules with averages of 18 and 1 O-antigen repeat units, respectively. These lipopolysaccharide molecules did not completely dissociate during electrophoresis, and multimers were detected as distinct, anomalous, slow-migrating bands. Increasing the concentration of sodium dodecyl sulfate in the gels resulted in the dissociation of these multimers.

Na+-Ca2+ exchange in the axolemma-rich membrane vesicle preparations from the walking-leg nerves of the American lobster.

An axolemma-rich membrane vesicle fraction was prepared from the leg nerve of the lobster, Homerus americanus. In this preparation Ca2+ transport across the membrane was shown to require a Na+ gradient (Na+-Ca2+ exchange), and external K+ was found to facilitate this Na+-Ca2+ exchange activity. In addition, at high Ca2+ concentrations (20 mM) a Ca2+-Ca2+ exchange system was shown to operate, which is stimulated by Li+. The Na+-Ca2+ exchange system is capable of operating in the reverse direction, with Ca2+ uptake coupled with Na+ efflux. Such a vesicular preparation has the potential for providing useful experimental approaches to study the mechanism of this important Ca2+ extrusion system in the nervous system.