Synthesis of size-monodisperse spherical Ag@SiO2 nanoparticles and 3-D assembly assisted by microfluidics

This article reports a one-step approach for the fabrication of highly uniform, spherical Ag particles with tailored dimensions ranging from 10 to 30 nm. Coated with silica shell, the high uniformity of the particles allows their spontaneous assembly into millimeter-long extended 3-D arrays with transverse dimensions of tens of micrometers, using a microfluidic evaporation-based process.

Comparison of commonly used clinical indicators of hypovolaemia with gastrointestinal tonometry

OBJECTIVE

The gastrointestinal tonometer, which allows measurement of gastrointestinal mucosal CO2 and subsequent derivation of gut intramucosal pH (pHi), has been demonstrated to be a sensitive predictor of outcome following major surgery. Current theory suggests that the origin of the low pH may be hypovolaemia. This study was designed to compare the temporal sequence of changes in tonometric readings with invasive blood pressure, stroke volume, heart rate, lactate and arterial blood gas measurements during progressive haemorrhage.

DESIGN

Observational healthy volunteer study.

SETTING

Intensive care unit at University College London Hospitals.

SUBJECTS

Six healthy, medically qualified volunteers.

INTERVENTIONS

After obtaining baseline measurements, the subjects were progressively bled 25% (range = 21-31%) of their blood volume over a period of 1 h in two approximately equal aliquots. Equilibration was allowed for 30 min following the bleed, after which further measurements were made and the blood was then retransfused over 30 min.

MEASUREMENTS AND MAIN RESULTS

There was no consistent change in any of the haemodynamic variables other than gastric intramucosal CO2:arterial CO2 gap (PiCO2-PaCO2) after removal of the first aliquot of blood, although five of the six subjects also demonstrated a fall in pHi. After removal of the second aliquot of blood, PiCO2-PaCO2 gap and pHi continued to indicate a worsening gastric intramucosal acidosis; stroke volume, as measured by suprasternal Doppler, demonstrated a marked fall, while all other variables measured had not altered consistently or to such a degree as to elicit a clinical response or cause suspicion of a hypovolaemic state. On retransfusion, all variables returned towards baseline.

CONCLUSIONS

This study demonstrates the value of tonometry as an early monitor of hypovolaemia and highlights the shortcomings of other more commonly measured clinical variables.

The rational administration of colloids

The safe administration of i.v. fluids is one of the most significant advances in the care of critically ill patients this century. However, despite advances in the monitoring of cardiovascular variables, the questions of what? when? and how much? remain areas of enormous controversy. Ironically as the choice of i.v. fluids becomes greater and the monitoring more sophisticated the controversy grows. This article will concentrate on the diagnosis of hypovolaemia, the consequences of hypovolaemia and the rational use of i.v. fluids, particularly colloids, to treat it.

Pharmacology and physiology of colloids

The importance of an adequate circulating volume in the critically ill is well established. Plasma, albumin, synthetic colloids and crystalloids may all be used for volume expansion but the first two are expensive and crystalloids have to be given in much larger volumes than colloids to achieve the same effect. Synthetic colloids provide a cheaper, safe, effective alternative. There are three classes of synthetic colloid; dextrans, gelatins and hydroxyethyl starches; each is available in several formulations with different properties which affect their initial plasma expanding effects, retention in the circulation and side-effects. There is no ideal colloid but those with low molecular weights such as gelatins are more suitable for rapid, short term volume expansion whilst in states of capillary leak where longer term effects are required hydroxyethyl starches are more effective. Dextrans are as effective as the alternatives but produce more side-effects and the need to pre-treat with hapten-dextran renders them unwieldy in use. Albumin is as persistent as hydroxyethyl starch in the healthy circulation but is retained less well in states of capillary leak. It has no significant advantages over starches and is much more expensive.

Mapping the spread of epidural phenol in cancer pain patients by radionuclide admixture and epidural scintigraphy

This study used a radionuclide imaging technique to map the spread and density contours of phenol in glycerin injected into the epidural space of cancer patients. Correlations were made between phenol injectate volume, sequence of injection, position of patient, and resultant epidural spread and analgesic outcome. Fifteen patients with cancer pain (average age of 61 years) were treated with serial epidural phenol in glycerin injections. Phenol in glycerin is miscible with [99mTc]sulfur colloid. An assumption was made that the admixture injected epidurally was inseparable prior to absorption and the spread was recorded by continuous gamma camera observations with computer collection for 30 min postinjection. The spread of injectate volumes of 2, 3, and 4 ml were compared and further correlations made between observed spread and sequence of injections (first to fifth in series within each patient) and position of patient. Small volumes of phenol may spread extensively in the epidural space (3 ml spreads a mean 13.6 segments) with wide variation among patients. Initial phenol injections spread further than subsequent injections. Maximum spread is achieved by 15 min postinjection and epidural distribution is mostly uniform, independent of patient position. Good analgesia was obtained in 14 patients (93%). Epidural neurolysis using serial injections of small volumes of phenol in glycerin is an effective, safe technique for cancer pain relief. Injectate volumes larger than 3 ml may be unnecessary and potentially dangerous.

Thalamic pain--the effect of electroconvulsive therapy (ECT)

An open study of the effect of a standard course of unilateral ECT applied to 4 patients with intractable thalamic pain. There was no significant change in pain, personality or affective profiles after treatment. Venous plasma endorphins were measured during the ECT course and there were no significant correlations with treatment.

Crystallization and subunit structure of histidine decarboxylase from Lactobacillus 30a

Histidine decarboxylase from Lactobacillus 30a has been crystallized in a variety of forms which together indicate a revised subunit structure for the native particle. Octahedral crystals of the wild type enzyme obtained at room temperature from ammonium sulfate solutions in microdiffusion cells belong to tetragonal space group I4122 with a = b = 222 A and c = 107.5 A. Trigonal and hexagonal plates of prohistidine decarboxylase and activated proenzyme obtained at 4 degrees C from polyethyleneglycol solutions by vapor equilibration using the hanging drop technique belong to the trigonal space group P321 with a = b = 100 A and c = 164 A. The space group symmetries and unit cell contents of these crystals indicate 32 point group symmetry for the subunit structure of these enzymes. Sedimentation coefficients of wild type enzyme measured as a function of ionic strength at pH 7.0 indicate a rapid equilibrium between species varying from 6.9 S to 9.4 S. Sedimentation equilibrium analysis demonstrated the existence of a nearly homogeneous particle with Mr congruent to 208,000 at ionic strengths above I = 0.20, while an additional species of approximately one-half that molecular weight is observed at very ionic strengths (I = 0.2). At the pH optimum of the enzyme (pH 4.8), te larger species is dominant at all ionic strengths tested. Electron micrographs of native wild type enzyme show a dominant tetrahedral particle approximately 60 A on an edge while similar micrographs of enzyme cross-linked with glutaraldehyde show a dumbbell-shaped particle approximately 60 A in width and 120 A in length. These results establish that: (a) the native enzyme has a Mr congruent to 208,000 and a subunit composition (alpha beta)6; (b) the proenzyme has a subunit composition (pi)6; and (c) stable (alpha beta)3 and (pi) 3 particles exist under certain conditions.