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G R Neufeld

Publications and source records attributed to G R Neufeld.

At least 37 records · Page 2Linked to original sources
PubMed1987

Fluorometric quantification of low-dose fluorescein delivery to predict amputation site healing.

This retrospective study evaluated quantification of skin fluorescein delivery by fiberoptic fluorometry as a means of predicting the healing potential of an amputation site. Fluorometry uses a dual-channel fiberoptic light guide--one channel transmits blue light to excite the fluorescein in the skin under study, and the other transmits emitted fluorescence from the skin to a photomultiplier tube where it is measured. Ten minutes after intravenous administration of sodium fluorescein (4 to 8 mg/kg), fluorometric readings were obtained at more than 100 reading sites. In the 86 cases without preoperative cellulitis at the site of amputation, preoperative fluorometry clearly distinguished between healing and nonhealing sites. Healing sites averaged 79% of the fluorescence of a healthy reference area (dye fluorescence index [DFI] = 79), while failing sites averaged only 27% (p less than 0.01 by ANOVA). In all but one case where the DFI was greater than 42, the amputation healed. In all cases where the DFI was less than 38, the amputation failed. In general, uncertainty was limited to sites with values between these limits. The technique maintained its high accuracy in patients with diabetes and for distal amputations. However, it was not accurate at sites of active cellulitis (12 cases). There were no significant adverse effects from the slow injection of the low dose of fluorescein used for this technique. We conclude that fluorometry is an effective means of predicting healing in patients undergoing amputation.

Amputation, Surgical↗
PubMed1985

Errors in measurement of oxygen uptake due to anesthetic gases.

Errors in measurement of exhaled gas volume, mixed expired oxygen and carbon dioxide concentrations, and inspired oxygen concentration and the presence of exhaled anesthetic agents cause errors in on-line calculated oxygen uptake that increase geometrically with increasing inspired oxygen concentration. No one has quantified the decrease in the magnitude of the error that might be realized if directly measured nitrogen concentration were included in the calculation. We used a computer model to evaluate this improvement, assuming an oxygen uptake of 200 ml/min and normal ventilatory parameters. Using a Monte Carlo technique, we generated 100 sets of data points, with random errors averaging 0.5% around the expected gas concentrations, and compared the accuracy of oxygen uptake calculated with and without inclusion of directly measured inspired and expired nitrogen concentrations. When the inspired oxygen fractions were 0.2, 0.5, and 0.8, the calculated oxygen uptakes +/- % standard deviation were 200 +/- 4.3, 200 +/- 12, and 196 +/- 21 when directly measured nitrogen was included versus 200 +/- 3.5, 196 +/- 16, and 205 +/- 71 when it was not. The procedure was repeated, assuming 50 ml/min of anesthetic excretion and the calculated oxygen uptakes were 200 +/- 4.6, 202 +/- 12, and 195 +/- 17 versus 212 +/- 3.8, 251 +/- 17, and 398 +/- 64. Including direct measurement of inhaled and exhaled concentrations of nitrogen or another insoluble inert tracer gas allows accurate measurement of oxygen uptake, even in the presence of exhaled anesthetic gases. It also decreases the error in oxygen uptake determination by a factor of nearly six when the inhaled oxygen fraction is 0.8.

Anesthetics↗
PubMed1985

Gas flux through human skin: effect of temperature, stripping, and inspired tension.

The flux of He and O2 through intact adult human skin was measured at various inspired concentrations and skin temperatures. The skin surface was then stripped with cellophane tape to alter the diffusional conductance of the stratum corneum. He flux for stripped skin was used to estimate skin perfusion as a function of local temperature, and diffusional conductance for O2 was estimated from O2 flux and perfusion. The flux of He or O2 at constant skin temperature can be related to inspired concentration by a simple linear model. Increasing surface temperature in the range 33-43 degrees C produced a much larger increase in O2 flux than in He flux for intact skin. Skin stripping greatly increased skin O2 flux. Estimated skin conductance for O2 showed a more marked temperature dependence than estimated skin perfusion. The results suggest that raising skin temperature in the range 38-43 degrees C has only a modest effect on skin perfusion and that stratum corneum conductance may have a major role in the large increase of O2 flux with temperature.

Biological Transport↗
PubMed1978

An evaluation of the Bentley PFF-100 transfusion filter.

The effects of a new transfusion filter (Bentley PFF-100) on stored whole blood have been examined. Six filters were preloaded by passage of two units of outdated type-specific bank blood and the effects of filtration on a third unit of 21-day-old blood flowing under 19.95 kPa (150 mm Hg) pressure were measured. Filtration did not significantly alter erythrocyte or leukocyte count, total or plasma haemoglobin, red cell fragility, plasma sodium, potassium, albumin, or globulin. Platelet counts were reduced by 31%. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen protein, wet and dry weight of material retained and scanning electron microscopy, was shown to be effective over the entire range of particle size. In comparison with other transfusion filters previously examined in this laboratory, the Bentley PFF-100 filter combines the feature of moderately efficient microaggregate removal with rapid blood flow rate. Compared to its predecessor, the Bentley PF-127, this new filter design has improved flow characteristics without loss of efficiency of microaggregate removal.

Blood Preservation↗
PubMed1978

Inert gas a-A differences: a direct reflection of V/Q distribution.

A computer model was developed to study the relationship between ventilation-to-perfusion (V/Q) mismatch and the development of inert gas arterial-to-alveolar partial pressure differences (a-A differences). Increasing inhomogeneity of V/Q ratio is revealed directly as an increase in the a-A difference of each gas. The quantitative relationships between the Q vs. V/Q distribution and the fractional a-A difference solubility plot (a-A difference plot) were studied and described. These studies demonstrated that for log normally distributed V/Q ratios, the area under the a-A difference plot is linearly related to the log variance of the V/Q distribution and can be estimated directly from the values obtained from six gases. The maximum a-A difference occurs for a gas whose solubility is numerically equal to the mean V/Q. The effects of departure from log normality and multimodality are discussed. We conclude from these studies that quantitative information regarding the degree of inhomogeneity of V/Q for log normal distribution is available from direct calculations of inert gas retention and excretion data. Qualitative information is also available indicating the departure from log normality and the region toward which the distribution is skewed.

Biophysical Phenomena↗
PubMed1978

Principles and hazards of electrosurgery including laparoscopy.

The understanding of the basic principles governing current flow through the body is necessary for the safe application of electrosurgical technique. They also may provide a guide to the design of laboratory studies which are needed to understand completely the ubiquitous nature of radiofrequency current distribution in surgical procedures.

Burns, Electric↗
PubMed1976

Effects of Intersept micropore filtration of blood on microaggregates and other constituents.

Micropore filtration (Intersept) of whole, stored blood was examined in two studies. In Study A, 1 unit of 14-day-old blood flowed by gravity across the filter. In Study B, the filter was preloaded by passage of 2 units of blood, and the effects on a third, consisting of 21-day-old blood, flowing under 150 mm Hg pressure, were examined. Filtration did not significantly alter erythrocyte count, total hemoglobin, plasma hemoglobin, erythrocyte fragility, plasma sodium, potassium, albumin, or globulin in either study, although some platelets and leukocytes were removed. Microaggregates, assessed by Coulter counting, screen filtration pressure, total screen proteins, wet and dry weights of material retained, and scanning electron microscopy, were satisfactorily removed over the whole range of particle sizes. Comparison with the Bentley PFS-127, Fenwal 4C2417, Pall Ultipore, and Swank IL200 filters led to the conclusion that the Intersept is the most efficient filter available at the present time for removing microaggregates during massive blood transfusion.

Blood↗
PubMed1975

Trace anesthetic exposure. Consequences and control.

Epidemiologic and animal studies indicate that chronic exposure to anesthetic gases may consitute a potential health hazard. This is suggested by a higher incidence of spontaneous abortion among female operating room personnel, congenital anomalies in the offspring of operating room personnel, and neoplasia of the reticuloendothelial system. Human data show that performance can be compromised during exposure to anesthetic traces. A direct cause and effect relationship between anesthetic exposure and the alleged hazards will require further prospective studies. Such a study is being planned by the Ad Hoc Committee of the American Society of Anesthesiologists. In the interim, monitoring programs should be established to define adequate clearances of the anesthetic agents. Minimum standards and recommended procedures should be established regarding operating room ventilation and design. The use of effective scavengers and anesthetic techniques not requiring the use of inhalational agents should be encouraged. In this way a clear distinction may be defined by the prosepective study planned by the American Society of Anesthesiologists in 1978.

Abnormalities, Drug-Induced↗
PubMed1975

Lung water volume at rest and exercise in dogs.

Lung water volume was measured in dogs killed at rest and during maximal exercise. There was no significant difference between them. It is concluded that pulmonary interstitial edema does not occur during exercise.

Animals↗