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Abstract: Introduction: An important fact when facing new technologies is their cost for the Health Publishes. The purpose of this paper is to compare the costs of performing TEM with harmonic scalpel and classic monopolar scalpel and to analyze complications. Methods: Operation time, blood loss, and hospital stay were recorded to determine the cost of the TEM procedure. We also recorded early and late complications. Patients were divided in two groups: harmonic scalpel group (UC) and monopolar scalpel group (MS). Results: TEM for curative intention was used in 330 rectal tumors from January 1997 to January 2010. A total of 229 patients met the criteria for this study: UC group (n = 87) and MS group (n = 142). Patients from the UC group developed fewer complications (16%) than patients from the MS group (23%). The difference of mean stay between groups was 1.5 days (95% confidence interval, 0.7; 2.2 days; P < 0.001) in favor of the UC group. Conclusions: Harmonic scalpel provides a safer, easier, and more precise surgical section through clean, bloodless, and better visualized operative field. The additional cost of UC was compensated with the decrease in the health resources (mainly hospital stay).

Abstract: Recently developed nanometer-sized synthetic pores display several properties so far believed to be distinctive features of a large variety of biological wide ion channels. Thus conductance in the pS-nS range, pH-dependent ion selectivity, fluctuations of current between open and closed states, flux inhibition caused by protons or divalent cations, current rectification, and the ability to perform selective macromolecule sizing and counting are found in synthetic and biological channels alike. Despite other differences such as pore size and geometry, the similarities open a new field for exploring specific technological applications via the chemical modification of synthetic pores with biological molecules. This article reviews some of the basis concepts and theories relevant to ion transport in nanopores with titratable charges stressing the analogies between synthetic pores and biological ion channels. The ultimate goal is to show that continuum theories may account for the essential features of these systems. A simple electrodiffusion model and its comparison with experimental results are chosen as a case study.

A theory for the reversal potential Vr in a wide, charged ion channel (i.e., with radius comparable to channel length and Debye's length) embedded in a planar membrane is developed. We analyze the influence of a nonuniform channel charge distribution along the channel axis on Vr. The analysis is performed in the framework of the space charge model, which is generalized for axial nonuniform charge distributions. Two kinds of nonhomogeneity are considered:  (1) a symmetrical nonhomogeneous distribution when channel charge is uniformly smeared over the inner surface of channel wall, but it does not extend over the whole surface, and (2) an asymmetrical nonhomogeneous distribution corresponding to some part of the total charge uniformly smeared over the channel wall and some other located on one of the channel entrances. For the first distribution it is shown that even a small deviation from a uniform distribution leads to a significant change in the reversal potential. In particular, the experimentally observed nonmonotonic behavior of Vr for the voltage-dependent anion channel from mitochondria (VDAC) as a function of concentration gradient [Zambrowicz, E. B.; Colombini, M.; Biophys. J. 1993, 65, 1093.] is explained by invoking the axial nonhomogeneity of channel charge. For the second kind of distribution (which resembles that in VDAC closed states) it is shown that the sign and value of the reversal potential depends on the location of the mobile part of the channel charge. Theoretical results are compared with previously reported experimental data for VDAC but they are valid for any charged multiionic channel where the Nernst−Planck formalism can be applied.

The Gibbs model for the boundary between two phases consists of replacing the finite interfacial region, where the properties of the system change gradually, by a dividing surface which acts as a third phase of zero volume in which some magnitudes change abruptly. This thermodynamic concept was recently applied to a planar interface between a fixed charge membrane and an electrolyte solution.¹ The continuous decrease of counterions with the distance from the charged surface is replaced by a step function, so that the diffuse double layer is ideally represented by a charged region depleted of all co-ions. Here the cylindrical geometry is analyzed, and the planar case is revisited by proposing a slightly different step function for ion concentration. By starting from Boltzmann distributions of ions in solution, simple formulas are obtained for the distance between the charged interface and the dividing surface in both geometries. For the purpose of applying this model to charged, microporous membranes, expressions are given for some of the coefficients Lij of the Onsager phenomenological relations in a model membrane composed of identical, parallel, and cylindrical pores. A comparison is made between the values for conductance and streaming potential in a homogeneously charged pore predicted by the Gibbs model and the classical space charge model. Despite the obvious simplifications inherent to the model, good agreement is found for conductivity, while only qualitative agreement is found between streaming potential predictions.

We have considered the ion transport across a membrane with extended soft permeable interfaces (polar zones), placed in an aqueous solution, under short-circuit conditions. The existence of fixed charges and dipoles in these membrane interfaces has been taken into account. The membrane has been modeled as composed of three layers:  an inner hydrophobic layer and two polar zones. Nernst−Planck's equation has been used for describing the ion transport. This paper continues our previous study, where we introduced the general model and analyzed the limit case of the internal hydrophobic layer as the rate-controlling step for ion transport (Langmuir 1996, 12, 4817). Here we have examined another limit case with the polar zones as the rate-controlling step for ion transport. The influence of the electrolyte concentration, the surface dipole density, and thickness of the polar zone on the total ion flux and permselectivity has been analyzed. It is shown that there are two significant differences with respect to the earlier considered limit case. On one hand, the steady-state condition leads to the build up of an additional space charge inside the polar zones, which influences considerably the ion transport. On the other hand, the membrane permselectivity exhibits a different variation with the electrolyte concentration. It is concluded that the analysis of permselectivity can help to find the rate-determining step in specific membrane systems.

We have considered the ion transport across a membrane with extended soft permeable interfaces (polar zones), placed in an aqueous solution, under short-circuit conditions. We have taken into account the existence of fixed charges and dipoles in these membrane interphases. The membrane has been modeled as composed of three layers:  an inner hydrophobic layer and two polar zones. Nernst−Planck's equation has been used for describing the ion transport, and Goldman's approximation has been assumed to be valid for the hydrophobic layer. In this paper the limiting case of the internal hydrophobic layer as the rate-controlling step for ion transport has been studied. The influence of the electrolyte concentration, the surface dipole density, and the thickness of the polar zone on the total ion flux and permselectivity has been analyzed. It has been shown that the permselectivity of such a system depends significantly on all these parameters. Particularly, the permselectivity of the same membrane changes with bulk electrolyte concentration. A general expression for cation selectivity has been obtained. The connection of the developed theory with experimental results has been discussed.