Origin of non-Nernstian anion response slopes of metalloporphyrin-based liquid/polymer membrane electrodes.

The origin of the non-Nernstian potentiometric anion response behavior exhibited by several metalloporphyrin-based liquid/polymeric membrane electrodes is examined. UV-visible spectrophotometry of organic-phase solutions and thin plasticized PVC films containing In(III) and Ga(III) octaethylporphyrins suggests that, in the absence of preferred axial coordination anions, the metalloporphyrins form hydroxide ion bridged dimers within the organic phases, as indicated by a significant blue shift of the Soret band in the visible spectrum. As increasing levels of the preferred anions are added, the degree of dimerization decreases and the intensity of the Soret band corresponding to the monomer species increases. Observation of Nernstian responses with membranes doped with picket fence-type In(III) and Ga(III) porphyrins not capable of forming hydroxide bridged structures (as determined by UV-visible spectroscopy) confirms that dimerization is likely responsible for the super-Nernstian slopes of membrane electrodes formulated with the non-picket fence species. A phase boundary model based on simultaneous binding equilibria of hydroxide ions with two metalloporphyrins to form the dimeric species, while the target anions bind with metalloporphyrins to form neutral 1:1 complexes, is shown to fully predict the observed non-Nernstian behavior. The prospect of utilizing this anion-dependent dimer-monomer metalloporphyrin equilibrium to fabricate anion-selective optical sensors using thin films of metalloporphyrin-doped polymers is also discussed.

Cystic fibrosis transmembrane conductance regulator. Physical basis for lyotropic anion selectivity patterns.

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel exhibits lyotropic anion selectivity. Anions that are more readily dehydrated than Cl exhibit permeability ratios (P(S)/P(Cl)) greater than unity and also bind more tightly in the channel. We compared the selectivity of CFTR to that of a synthetic anion-selective membrane [poly(vinyl chloride)-tridodecylmethylammonium chloride; PVC-TDMAC] for which the nature of the physical process that governs the anion-selective response is more readily apparent. The permeability and binding selectivity patterns of CFTR differed only by a multiplicative constant from that of the PVC-TDMAC membrane; and a continuum electrostatic model suggested that both patterns could be understood in terms of the differences in the relative stabilization of anions by water and the polarizable interior of the channel or synthetic membrane. The calculated energies of anion-channel interaction, derived from measurements of either permeability or binding, varied as a linear function of inverse ionic radius (1/r), as expected from a Born-type model of ion charging in a medium characterized by an effective dielectric constant of 19. The model predicts that large anions, like SCN, although they experience weaker interactions (relative to Cl) with water and also with the channel, are more permeant than Cl because anion-water energy is a steeper function of 1/r than is the anion-channel energy. These large anions also bind more tightly for the same reason: the reduced energy of hydration allows the net transfer energy (the well depth) to be more negative. This simple selectivity mechanism that governs permeability and binding acts to optimize the function of CFTR as a Cl filter. Anions that are smaller (more difficult to dehydrate) than Cl are energetically retarded from entering the channel, while the larger (more readily dehydrated) anions are retarded in their passage by "sticking" within the channel.

Impact of laparoscopic cholecystectomy on indications for surgical treatment of gallstones.

BACKGROUND: The objective of this study was to compare the histology of gallbladders removed prior to the introduction of laparoscopic cholecystectomy with that found after the introduction of the laparoscopic technique to determine if there has been a change in the indications for surgical treatment of gallbladder disease. METHODS: A retrospective review of all patients undergoing cholecystectomy during 1989, 1992, and 1993 was completed at two large community teaching hospitals in two different geographic regions of the United States. Patients who underwent cholecystectomy as the primary procedure were studied. A total of 1,815 cases met the criteria for analysis. Histological diagnoses were categorized as acute cholecystitis with or without cholelithiasis, or chronic cholecystitis with cholelithiasis. RESULTS: The number of cholecystectomies performed increased by 58% from 1989 to 1993 (p < 0.05). The number of cholecystectomies for acute cholecystitis did not change. CONCLUSIONS: With the advent of laparoscopic cholecystectomy, the number of cholecystectomies significantly increased and the proportion of cholecystectomies performed for chronic disease also increased. There has been a significant change in the surgical management of gallbladder disease with increased willingness to recommend elective cholecystectomy. Further study is needed to determine if there is real benefit from earlier elective cholecystectomy.

Short-stay outpatient tonsillectomy.

OBJECTIVE: To determine the risk of complications after discharge in outpatient adenotonsillectomy after a short (< 6 hours) period of postoperative observation. DESIGN: Retrospective chart review. SETTING: Outpatient surgery center at a university hospital. PATIENTS: All patients 18 years of age or less who were scheduled for adenotonsillectomy or tonsillectomy from January 1988 through December 1991. Two hundred fifty-five patient records were reviewed. Twenty-two patients were excluded from the study because of various complicating medical conditions that required planned overnight hospitalization leaving a study population of 233 patients. MAIN OUTCOME MEASURES: (1) Rate and type of complications; (2) duration of postoperative observation. RESULTS: Complication rates of bleeding, emesis, dehydration, and readmission were compared with rates deemed acceptable in the literature (< or = 10%). Power analysis demonstrated that the patient number was sufficient to establish a 95% confidence interval for a complication rate of 0% to 10%. The mean duration of postoperative observation was 136 +/- 48 minutes. Complications included bleeding, emesis, dehydration, and nonscheduled admissions. The total complication rate was 9% (95% confidence interval, 5.5% to 12.7%). The rate of primary bleeding was 1.4%, and all primary bleeding occurred within 75 minutes of arrival in the recovery room; no primary bleeding occurred after discharge from day surgery. This complication rate is comparable with rates previously described in the literature for patients who were observed for a 6- to 12-hour period. CONCLUSION: The findings in this study suggest that short periods of observation are safe for outpatient pediatric patients undergoing adenotonsillectomy after discharge criteria are met.

Effectiveness and tolerance to highly concentrated vs conventional TPN formulas.

Conventional total parenteral nutrition regimens (TPN-C) involve concentrations of dextrose/protein which necessitate administration of 2.5-4 liters/day to meet target nutritional needs. Although this is frequently acceptable, certain clinical settings mandate a volume-restricted (VR) approach. This study compares a VR TPN regimen (TPN-VR) involving the use of 25% dextrose and 9.5% amino acid with D17.5 AA 5.0 (TPN-C). The two groups were compared for adequacy of nutritional delivery, balance, and tolerance. Twenty patients received the TPN-VR (Group 1) and 20 patients received TPN-C (Group 2). The groups were comparable in age, sex, injury severity, and APACHE 2 scores. Harris-Benedict (BEE) x 2 and 2 g/protein/kg of ideal body weight were delivered by the second day of TPN. A 27% reduction in administered fluid was achieved in Group 1 (P < 0.001). Metabolic cart data in both groups demonstrated that delivered calories exceeded REE. The average RQ in Group 1 was 0.84 and in Group 2 was 0.90 (P > 0.1). There was no significant difference between the two groups in nitrogen balance, mean serum bilirubin levels, PT and PTT, serum albumin levels, and triglycerides (P > 0.20). SGPT and alkaline phosphatase levels were significantly higher in Group 2 (P < 0.001). Group 2 received an average of 22% more carbohydrate than Group 1 and 45% required insulin compared to 25% in Group 1 (P < 0.01). In summary, TPN-VR is comparable to TPN-C in terms of effectiveness of delivery, nutritional balance, and tolerance.