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Biomedical subjects

W W Mapleson

Publications and source records attributed to W W Mapleson.

At least 73 records · Page 4Linked to original sources
PubMed1985

The effect of Fluosol-DA on induction of inhalation anesthesia.

The liquid/gas partition coefficients of three inhalation anesthetics in Fluosol-DA 20% (Fluosol), a perfluorocarbon blood substitute, were determined in vitro. The high values found (6.68 for halothane, 7.54 for enflurane, and 7.20 for isoflurane) suggested that induction with these agents would be prolonged in patients treated with Fluosol. Induction of isoflurane anesthesia (as a representative agent) at constant inspired concentration was studied in five mongrel dogs before and after replacement of about 25% of each animal's blood volume with Fluosol. Inspired and end-tidal isoflurane and carbon dioxide concentrations were recorded breath by breath, together with cardiac output. There was a significant delay in rise of end-tidal isoflurane concentration after Fluosol infusion. However, because cardiac output could not be held constant during each experiment, and because cardiac output also affects the rate of rise of alveolar anesthetic concentration, a physiological computer model was used to compare the isoflurane blood/gas partition coefficients that must have existed to account for the observed end-tidal levels before and after Fluosol infusion, while taking cardiac output variation into account. Post-Fluosol blood/gas partition coefficients calculated in this way (2.59 +/- 0.51 SD) were significantly different (P less than 0.001) from pre-Fluosol levels (1.45 +/- 0.15 SD) and were not significantly different from post-Fluosol partition coefficients calculated by volume-weighted averaging (2.91 +/- 0.36 SD). This indicates that the delay observed was attributable in large part to increased solubility of isoflurane in blood after addition of Fluosol. Based on their similar liquid/gas partition coefficients in Fluosol, similar delays should occur with halothane and enflurane.

Anesthesia, Inhalation↗
PubMed1984

Sore throat after intubation of the trachea.

Eighty female patients were allocated randomly to groups, divided in three ways, to investigate the effects of using cuffed p.v.c. v. red rubber tracheal tubes, intermittent adjustment of the cuff volume, and humidification of inspired gases on the incidence and severity of sore throat after tracheal intubation. In addition, the influence of the anaesthetist's participation in the trial was studied by assessing sore throat in a further 60 female patients where the anaesthetists were unaware of the trial. There were no significant differences between any of the groups despite using three sensitive methods of assessment. In terms of the simple discrimination between "sore throat" and "no sore throat" the 95% confidence limits of the differences of incidence were generally +/- 15-20%. If there are any real differences produced by these changes, and if any of them were as large as 15% then, to show with 95% confidence that any difference is at least 10%, would require a trial involving about 1400 patients. Retrospective analysis of the results showed no difference between patients who received suxamethonium and those who did not.

Adult↗
PubMed1984

Computer assistance in the control of depth of anaesthesia.

A control system was used to bring the tension of anaesthetic in the brain to any value specified (in MAC units) by the anaesthetist and then maintain it constant until a new value was specified. The control was applied to a volatile agent but allowance was automatically made for the anaesthetic effect of any nitrous oxide concomitantly administered by the anaesthetist. The inspired concentration required to achieve the desired brain tension was calculated from a model of the patient and set automatically on the vaporizer. The quantification of the model was matched to the patient on the basis mainly of body mass and periodic non-invasive measurements of alveolar ventilation and cardiac output. In order to adapt the model to the patient an arterial blood sample was taken every 30 min to obtain the arterial tension of halothane for use as feedback. The system has been tested on eight Alsatian dogs. After omitting results affected by avoidable errors, the SD of the measured-to-computed arterial tension ratio was less than 10%.

Anesthesia, Inhalation↗
PubMed1982

Educated cheek.

Explore the source record for details and available documents.

Cheek↗
PubMed1981

A new approach to artificial expansion and ventilation of the lung in the severely asphyxiated neonate.

In severe asphyxia, expansion of the newborn lung must precede ventilation by intermittent positive pressure. Inadequate expansion may lead to hypoxia and excessive expansion to rupture of the lung. The only way in which a predetermined pressure can be achieved, and not exceeded in the alveoli, is by applying that pressure at the mouth and waiting until all flow ceases. Applying pressure in this way and increasing it according to a "staircase" pattern, with appropriate steps at suitable intervals, should ensure that the maximum pressure produced in the alveoli is no greater than the minimum necessary for resuscitation in each individual infant. On the basis of published work, ranges of optimum values for the increments and time intervals are suggested. Clinical judgement is still necessary to select from within these ranges, but this "pressure staircase" method should provide a systematic approach to the problem. A suitable apparatus is described.

Asphyxia Neonatorum↗
PubMed1981

Structure and quantification of a physiological model of the distribution of injected agents and inhaled anaesthetics.

Mapleson's (1973) physiological, circulation-time model of the distribution of inhaled anaesthetics has been elaborated to be suitable for modelling agents in which hepatic metabolism and renal excretion are important factors; as well as the obvious improvement of providing separate compartments for liver and kidney, the arterial and portal supplies to the liver are separately represented, as is the portal blood pool. The separate portal pool also leads to a more realistic total circulation time for the majority of the cardiac output. The quantification for a "standard man" is fully documented and makes use of the latest (1975) report of the International Commission on Radiological Protection, Reference Man, and includes data on the water, fat and protein composition of each tissue compartment. Suggestions are included on adapting the quantification to non-standard men and to other species.

Adult↗
PubMed1980

Blood-gas tension measurement in anaesthesia by bubble equilibration and mass spectrometry.

If a small bubble gas is equilibrated with a volume of blood the partial pressures of the components of the bubble after equilibration approximate to the original tensions in the blood. A method is described in which the bubble is analysed by a respiratory mass spectrometer connected to a mini-computer. The normal respiratory monitoring function of the mass spectrometer need be interrupted for only 20 s for each sample and the complete equilibration and analysis procedure takes only 3 min. Theoretical studies, experimental tests and records of experimental usage show that, in a subject anaesthetized with halothane in nitrous and oxygen, tension can be measured with an overall SD of 5% for carbon dioxide and halothane and, certain reservations, an SD of about 3% for nitrous oxide.

Anesthesia, Inhalation↗
PubMed1980

Minimum artificial lung expansion necessary for resuscitation of the newborn lamb.

In a group of seven lambs, pressure-volume relationships were obtained for the initial artificial expansion of the lungs in the intact chest and subsequent re-expansion afer the lungs had been excised and collapsed. In a second group, of 12 severely asphyxiated lambs, the lungs were expanded in steps and circulatory resuscitation was achieved at pressures ranging from 1.75 to 3.5 kPa, geometric mean 2.3 kPa, with estimated corresponding volumes of 3--24 ml kg-1, geometric mean 5.8 ml kg-1. In a third group, of 24 severely asphyxiated lambs (mean pH 6.84), 22 were successfully resuscitated in the same manner and nine of these survived in apparent good health for more than 6 months. Any resuscitation regime for human neonates should take account of the finding that resuscitation occurred at pressures less than those necessary for full expansion and that, after the first sign of an increase in heart rate, there was a delay of 17--45 s before full circulatory improvement and of 3 min before full improvement in PaO2.

Animals↗
PubMed1979

From Clover to computer. Towards programmed anaesthesia?

The control of depth of anaesthesia has been viewed as a control-system problem the solution of which can involve both feedback and feedforward techniques. The nature of the problem in Clover's day and the solutions he found have been examined. A similar analysis has been made in respect of the modern anaesthetist. Finally, the way in which computers may aid the anaesthetist in his task has been illustrated by reference to various attempts reported from around the world and, in particular, by describing the development in Cardiff of a system which should produce, in the brain of the patient, any tension of an inhaled anaesthetic which the anaesthetist chooses to specify.

Anesthesia, Inhalation↗
PubMed1977

Halothane solubility in human blood.

In a study of the influence of nutritional state on halothane anaesthesia, results were obtained which showed how the blood/gas partition coefficient for halothane varied with blood chemistry in 20 patients undergoing elective surgery. For each patient the partition coefficient lambda was measured by equilibration at 37 degrees C of a blood sample with a 1% halothane in 5% carbon dioxide in air mixture, followed by chemical extraction and estimation of the halothane content by gas chromatography. The haematocrit and haemoglobin, serum albumin, total protein, triglyceride and cholesterol concentrations were measured by routine laboratory methods. Regressions were sought of lambda on each of these, and on the globulin concentration and the ratios of albumin: globulin and albumin: total protein, deduced from these determinations. The only statistically significant regression (P = 0.0004) was that of lambda on the serum triglyceride concentration (T) (mmol/litre): lambda = 1.83 + 0.424T. The dependence of lambda on haemoglobin concentration was not statistically significant, but the slope of the regression was consistent with those of previous investigators. The regressions of lambda, corrected to the mean triglyceride concentration, on the ratios of albumin: globulin and albumin: total protein were not statistically significant but were not significantly different from an earlier reported result.

Anesthesia, Inhalation↗
PubMed1977

Urinary excretion and metabolism of pethidine and norpethidine in the newborn.

In seven neonates, whose mothers were given pethidine during labour, urine was collected for the first 24-40 h of life. Urinary volume and pH, and concentrations of pethidine and norpethidine in the urine were measured. Urine flow rate was low for the first 7-22 h, and then high for about 12 h. The rate of excretion of pethidine and norepethidine was approximately parallel to the urine flow rate. However, the ratio of the rate of excretion of norpethidine to that of pethidine increased with time and the concentration of norpethidine in urine decreased first and then, after 18 h, increased significantly. These findings that the neonate can metabolize pethidine, although the rate of metabolism is probably less than in the adult. The total amounts of pethidine and norpethidine excreted in the first 24 h after birth were positively related to the dose-delivery interval in the mother for intervals up to at least 5 h. From the data it is estimated that 95% of the total pethidine transferred from the mother would be eliminated by the baby by the 2nd to 3rd day after birth.

Humans↗
PubMed1977

Adiposity and the pharmacokinetics of halothane. The effect of adiposity on the maintenance of and recovery from halothane anaesthesia.

Thirty fit patients (15-70 years, 46-98 kg) undergoing body-surface operations were selected to include a wide range of adiposity (12-45% of total body weight estimated from measurements of skinfold thickness). They were anaesthetized with halothane and 70% N2O in O2. From measurements of total ventilation (ml min-1 kg-1) and of halothane concentrations in inspired (F1) end-tidal (FE') and 'mixed-spill' (FS) gases, the following parameters were calculated for 5-min intervals from 20 to 40 min after induction; the rate of uptake of halothane per percent inspired concentration (Vha1 ml min-1%-1) and the degree of equilibrium achieved with the inspired concentration, calculated as FE'/F1 expressed as a percentage. Multiple-regression analysis of the results for 19 patients, taking account of the effects of body fat, ventilation, age, and the blood-gas partition coefficient lambda of halothane for the individual patient, showed that Vha1 increased with adiposity (b=0-375, P=0-0019), and with ventilation (b=0-054, P=0-09) but decreased with increasing age (b=-0-258, P=0-006). The time intervals between the end of the anaesthetic and the achievement of four defined levels of recovery (response to painful stimulus obedience to a simple command, response to a question, orientation in time and space), were recorded. Multiple-regression analysis showed that recovery time increased with addiposity, duration of administration and end-tidal concentration at the end of the administration, and decreased with increasing age. All four effects were statistically non-significant at the first levels of recovery but all increased at the later levels and all eventually became significant.

Adolescent↗
PubMed1977

The Cardiff Aldavac anaesthetic-scavenging system.

The Cardiff Aldavac system consists of a reservoir, adsorption canister, flow restrictor and the necessary pipe connections. It enables theatre pollution control without structural alteration or special installation. It utilizes the hospital piped medical vacuum system but protects the system from excessive flows or contamination by volatile anaesthetics and still allows the vacuum to be used for other purposes.

Anesthesiology↗
PubMed1976

Pharmacokinetics of halothane in the dog. Comparison of theory and measurement in individuals.

After surgical preparation under pentobarbitone anaesthesia seven dogs of mean body weight 31 kg were ventilated with 1% halothane for 80 min. At 1, 2, 5, 10, 20, 40 and 80 min after the start of the halothane administration blood samples were taken from the femoral artery and pulmonary artery and from a cerebral, a renal and a femoral vein. At 80 min a biopsy sample of skeletal muscle (psoas) was taken. The halothane tension in all samples was determined by extraction into carbon tetrachloride followed by gas chromatographic analysis using chloroform as an internal standard. The measured tensions were compared with tensions computed from a multi-compartment model of the uptake and distribution of halothane in the body. The model was quantified by measurements, in each individual, of total body mass, the masses of the major organs and the solubility of halothane in the major organs and tissues; by measurements of blood volume and solubility in blood at the start and finish of the halothane administration; and by repeated measurements of alveolar ventilation, cardiac output and body temperature. For the original version of the model, the computed tensions deviated from the measured tensions to an extent greater than could be attributed to experimental error and in a manner which could be attributed to metabolism of halothane and probably to direct diffusion of halothane from well-perfused organs and lean tissues into fat. Direct experimental evidence of diffusion into perirenal fat was obtained in supplementary experiments. With the quantitation of the model distorted to mimic the processes of metabolism and diffusion, measured arterial tensions could be predicted with a mean error of -0.2 mm Hg (SD 0.6 mm Hg). The mean measured arterial tension was 3.5 mm Hg.

Animals↗