Biomedical subjects

D A Thomson

Publications and source records attributed to D A Thomson.

At least 19 recordsLinked to original sources

PubMed1991

Is the end-tidal partial pressure of isoflurane a good predictor of its arterial partial pressure?

End-tidal partial pressure of isoflurane (PE'iso) may be used as a measure of anaesthetic depth. During uptake, an arterial partial pressure (Paiso) which is considerably less than PE'iso (Paiso/PE'iso much less than 1) leads to underestimation of depth of anaesthesia and, during elimination, PE'iso/Paiso much less than 1 will lead to an overestimation of anaesthetic depth. We measured Paiso/PE'iso during a 60-min uptake period of 1% isoflurane and PE'iso/Paiso during the subsequent 60-min elimination period in 26 patients (age 13-88 yr, ASA I-III) undergoing various surgical procedures. After 15 min of isoflurane uptake, Paiso/PE'iso of 26 patients was mean 0.78 (SD 0.10) and this increased only marginally at 60 min (0.79 (0.09)), whereas during elimination, PE'iso/Paiso was in the range 0.79 (0.14)-0.83 (0.11). Predictability of Paiso in a given patient is hindered by the high SD of Paiso/PE'iso and PE'iso/Paiso, but it may be improved by taking into account age, ASA physical status category, vital capacity, inspired minus end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during uptake; and obesity, end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during elimination. However, even with multiple regression analysis (to account for the various possible variables), clinically useful prediction of Paiso/PE'iso and PE'iso/Paiso in a particular patient is not possible (residual SD 0.084 and 0.113, respectively).

Adolescent↗

PubMed1990

Terminal deletion (14)(q32.3): a new case.

A mildly dysmorphic, 2 year old girl with mental retardation was found to have a small de novo terminal deletion of the long arm of chromosome 14, del(14)(q32.3). She was found to have features in common with two previous terminal deletion cases and particularly with the well documented ring 14 syndrome, although seizures, a characteristic feature of ring 14, were notably absent.

Child, Preschool↗

PubMed1989

The measurement of expiratory oxygen as disconnection alarm.

The efficacy of an oxygen-monitoring alarm in the expiratory limb of an anesthetic circuit was evaluated as a method of detecting disconnections of the patient from the anesthetic machine. Oxygen concentrations were determined in the expiratory limb of a semiclosed anesthetic circuit with a ventilator and a 2-1 reservoir bag serving as a simple lung model. Adjustments of ventilation during the different measurements were a PEEP of 5 cmH2O, respiratory rates of 10/min and 5/min, and tidal volumes of 1,000 and 500 ml, respectively. The alarm time measured with a stopwatch was the time that elapsed between disconnection and the acoustical alarm. The circuit was always disconnected at the y-piece when the reservoir bag had been fully expanded after an inspiration. With various fresh flow rates and oxygen concentrations ranging from 33% to 52%, disconnection always was evident within 30 s. Measurement of the oxygen concentration with an alarm time of 30 s after disconnection may be an effective backing system for detecting a disconnection.

Anesthesiology↗

PubMed1989

Pulse oximetry in methaemoglobinaemia. Failure to detect low oxygen saturation.

The results of pulse oximetry saturation in a patient with a high level of methaemoglobinaemia, who subsequently underwent intravenous methylene blue treatment, are presented. The reasons for the erroneously low values after treatment are explained. Pulse oximeters currently available are not helpful in patients treated with methylene blue and should be used with caution in patients who present with cyanosis of unknown origin.

Adult↗

PubMed1989

An unusual case of mosaic Down's syndrome involving two different Robertsonian translocations.

A baby girl with some of the stigmata of Down's syndrome was found to be a mosaic with three different cell lines: 45,XX,-13,-21,+t(13q21q)/(46,XX/46,XX, -21,+t(21q21q). The chromosome rearrangements detected in this patient appear to have arisen de novo. In the normal cell line the terminal end of the p arm of one chromosome 21 is thought to have been damaged. It seems probable that this is related to the other chromosomal anomalies found.

Chromosome Banding↗

PubMed1989

A preliminary investigation into the effect of thyroid hormones on the metamorphic changes in Meckel's cartilage in Xenopus laevis.

The effects of short-term dosage with thyroid powder on the metamorphic changes in Meckel's cartilage in Xenopus laevis are described. The Lag phase of development appears to be by-passed, and the usual sequential arrangement of the Division and Synthesis phases is disrupted, the processes of normal metamorphic changes being considerably accelerated.

Animals↗

PubMed1988

Influence of ventilatory and circulatory changes on the pharmacokinetics of halothane and isoflurane.

In two groups of dogs, uptake and elimination of halothane and isoflurane were studied using a closed-loop anesthesia system which automatically controlled end-tidal halothane or isoflurane partial pressure at minimal alveolar concentration (MAC) equivalent levels. Hemodynamic and respiratory variables were recorded and the anesthetic partial pressure was measured in the inspired and expired air, as well as in the arterial, cerebrovenous and mixed venous blood. Data were recorded during wash-in, hyperventilation, hypercirculation, hypotension and wash-out. For halothane, the controller delivered a higher inspired partial pressure than for isoflurane to compensate for the higher blood/gas partition coefficient. This was especially pronounced during the wash-in and the hypercirculation periods. Smaller differences between halothane and isoflurane partial pressures occurred during hyperventilation, hypotension and the wash-out period and could be explained by the lower solubility of isoflurane. These results show that even under unstable ventilatory and hemodynamic conditions, the inspired concentration of isoflurane has to be adjusted less often and to a smaller degree than that of halothane if end-tidal concentrations are to be maintained constant.

Animals↗

PubMed1988

Anaesthetic uptake and elimination: is there a difference between halothane and isoflurane in the dog?

In two groups of dogs, the uptake and elimination of halothane and isoflurane were studied using a closed-loop anaesthetic system which automatically controlled end-tidal halothane and isoflurane partial pressures at equi-MAC concentrations. Haemodynamic and respiratory variables were recorded and the anaesthetic partial pressures were measured in the inspired and expired air, as well as in the arterial, cerebrovenous and mixed venous blood. The controller delivered a higher inspired partial pressure of halothane than of isoflurane to compensate for the higher blood/gas partition coefficient. The partial pressures of halothane in the arterial, cerebrovenous and mixed venous blood increased at rates similar to those of isoflurane. During 160 min of uptake, the cerebral venous partial pressures remained significantly lower than the arterial partial pressures for both agents. On discontinuation of the anaesthetic, the partial pressures of halothane and isoflurane decreased at equal rates in arterial, cerebrovenous and mixed venous blood, and in end-tidal gas. It was concluded that the rate of uptake of isoflurane is more rapid than that of halothane from the alveolar space to the blood, but not from the blood to brain tissue. The rates of elimination from brain tissue and from blood were found to be similar for both agents.

Anesthesia, Inhalation↗

PubMed1988

Are double translocations double trouble?

Double translocation heterozygotes are rare, but need not necessarily pose more of a counselling problem than single reciprocal translocation heterozygotes. Nine cases of double translocation are presented, together with a review of the few reports published to date. An attempt is made to provide simple counselling guidelines in the assessment of the risk of producing a liveborn abnormal child. This is not based on theoretical considerations of segregation patterns, but extrapolated from what is known empirically about the viable segregation patterns in carriers of single reciprocal translocations. It assumes that there is no interference with the independent assortment of the two separate exchanges, unless a common participating chromosome is involved. The possibility of an interchromosomal effect has not been taken into consideration.

Congenital Abnormalities↗

PubMed1988

Midazolam in plasma from hospitalized patients as measured by gas-liquid chromatography with electron-capture detection.

The present assay was developed for quantifying midazolam in plasma of patients hospitalized in intensive-care units or undergoing anesthesia and receiving many other drugs as well. Plasma samples are alkalinized with NaOH and midazolam is extracted into n-hexane. The organic phase is evaporated and reconstituted in n-butyl acetate, and the midazolam is quantified by gas-liquid chromatography with electron-capture detection. The calibration graph for midazolam was linear in the ranges 5-200 and 200-800 micrograms/L. The CVs for precision and reproducibility of the assay were less than 8%. The method was very specific for midazolam; most of the drugs commonly used in anesthesia and in the intensive-care unit did not interfere with the assay. The lowest detectable concentration was 1 microgram/L. The method is adaptable for use with an automated chromatographic system.

Aged↗

PubMed1987

Population pharmacokinetics of alfentanil: the average dose-plasma concentration relationship and interindividual variability in patients.

The population pharmacokinetic parameters describing the plasma concentration versus time profile of alfentanil in patients undergoing general anesthesia were determined from 614 plasma concentration measurements collected in four previously reported studies with a total of 45 patients. A nonlinear regression analysis evaluating the effect of six concomitant variables revealed a significant influence of body weight on the volume of the central compartment (Vc), and a decrease with age of total body clearance (CL) and of redistribution rate from the deep compartment (k31). A small but significant effect of sex on the Vc was also observed. The duration of anesthesia and the concomitant administration of inhalational anesthetics had no effect on alfentanil pharmacokinetic parameters. The mean CL and Vc for alfentanil in a 70-kg male, aged less than 40 yr, were estimated as 0.356 l/min and 7.77 l, respectively. After correction for age, body weight, and sex, the remaining interindividual variability of alfentanil kinetics (expressed as coefficient of variation) was 48% for CL and 33% for Vc. These population pharmacokinetic parameter estimates should increase the accuracy of predicting concentration-time profiles for intravenous alfentanil infusions. A computer program is presented that allows prediction of the alfentanil plasma concentration and the 68% interval limits of the prediction from the study data analysis.

Adult↗

PubMed1987

A quantitative analysis of cellular and matrix changes in Meckel's cartilage in Xenopus laevis.

The changes in cell population and matrix volume fraction in Meckel's cartilage during metamorphic climax have been assessed using standard stereological techniques. The period of climax has been divided into three phases, a preliminary 'Lag' phase (NF Stages 57-60), a 'Division' phase (NF Stages 60-62) when the cell population rises rapidly and a 'Synthesis' phase (NF Stages 62-66) when the matrix content of the tissue also increases dramatically. These changes along with the membranous ossification occurring at the same time are postulated to be associated with the change in the feeding habit of the larvae from filtration prior to metamorphic climax to active predation in the young frog.

Animals↗

PubMed1987

[Development of an information system for operations].

The report describes a computer system that provides statistical information on the anesthetic and surgical procedures performed by anesthetists and surgeons, reports on the operative activity of the anesthesia and surgical departments, and assists in daily scheduling of the program. Additional programs can be used for billing, displaying the use of (operating room OR) facilities by the various surgical divisions, and showing the actual stage of on-line operations with monitors. The software system MUMPS has been found to be a low-priced yet efficient and versatile multiuser system. The main features of the program are ease of use, prospective data entry (i.e. during the entire stay of the patient), and the possibility of modifying and expanding the system easily. Missing or inaccurate data are automatically brought to the attention of those who have performed the operation or the anesthesia by a program that is run periodically. The system has been found to be a useful tool for the daily scheduling of the OR program. It provides data for better scheduling of personnel and records can also be kept regarding the professional experience of physicians. The major deficiency of the program at this stage is its lack of a hierarchical structure. For example, it is unable to record multiple operations and/or anesthetic procedures for the same patient. This deficiency will be corrected in a newer version of the program.

Anesthesia↗

PubMed1986

A laboratory investigation of two new portable gas analysers.

Two new portable infrared gas analysers, the Irina (Drägerwerke, Lübeck, Germany) and the Normac (Datex Instrumentarium Corporation, Helsinki, Finland), were tested and the results compared to those from such established methods as gaschromatography and the Beckman LB-2 (Beckman, USA) infrared gas analyser using exactly defined gas mixtures from a vaporizer developed in our laboratory. The analysers were evaluated for their accuracy and precision, noise, zero stability, gain stability and the impact of flow, over-pressure, carrier gas and humidity. All three analysers showed good accuracy and precision. The noise level was acceptable except in the older version of the Normac, but this error has now been corrected by the manufacturer. Zero and gain stability are very good; gas flow and over-pressure do not affect the measurement. The influence of carrier gases and humidity is negligible except for the strong N2O effect on the Beckman. We conclude that this new generation of highly sophisticated and reliable but handy analysers will meet the clinical demands.

Anesthesia, Inhalation↗

PubMed1986

Control of end-tidal halothane concentration. Part A: Anaesthesia breathing system and feedback control of gas delivery.

Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient, a circulating pump and feedback controllers for system volume and anaesthetic concentration. Feedback control was implemented to adjust and control automatically the end-tidal anaesthetic concentration and the volume of the system with oxygen supplied through a mass flow controller and with halothane supplied by a titrating syringe. Controller gains, as a function of body weight, were found using a nine-compartment tissue uptake model. Stability was maintained with +/- 50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal halothane concentration and system volume to provide a rapid and optimized induction of anaesthesia.

Anesthesia, Inhalation↗

PubMed1986

Control of end-tidal halothane concentration. Part B: Verification in dogs.

Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). Then followed 60 min of halothane wash-out and a further 120-min period of halothane at 1.74 vol% (2 MAC). Halothane concentrations were measured in the inspired and expired air, and in the arterial, cerebral venous and mixed venous blood. Haemodynamic and respiratory variables were measured. The system reached 95% of the target end-tidal concentration within 6 min without over-shooting. After 2 h of wash-in, significant gradients still persisted between end-tidal, arterial and cerebral venous blood concentrations. Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limits.

Anesthesia, Inhalation↗

PubMed1986

Meckel's cartilage in Xenopus laevis during metamorphosis: a light and electron microscope study.

Meckel's cartilage, in Xenopus laevis prior to metamorphosis, is a tissue exhibiting very large lacunae, separated by thin rims of matrix, presenting a net-like appearance, similar to that of cartilage in invertebrates. The cells on the periphery of the tissue are rather more flattened, and more closely packed. On the lateral aspects of the cartilage distinct columns of apparently dividing cells are evident. During metamorphic climax, the amount of matrix separating the lacunae increases, with an associated decrease in lacunar size, and some of the deeper cells develop cilia, which are not seen either before or after climax. By the end of metamorphic climax there is a considerable increase in the amount of matrix present in the tissue, while many cells at all depths in the cartilage show the presence of lysosome-like structures, possibly associated with the changing shape of the cartilage. Intramembranous ossification is proceeding around Meckel's cartilage, but there is no evidence of endochondral ossification up to the end of metamorphosis.

Animals↗

PubMed1985

Determination of the partial pressure of halothane (or isoflurane) in blood.

A gas chromatographic method is described for the direct quantitative determination of the partial pressure of halothane (or isoflurane) in blood as well as the blood-gas partition coefficient. A head space technique and a flame ionization detector were used. Standard blood was obtained by equilibrating patients' blood with known gas concentrations in a tonometer. Using an infra-red analyser to measure the halothane gas concentration in the tonometer and within the anaesthetic system allowed for the direct comparison of the partial pressure in blood to the partial pressure in the inspired gas. Technical problems associated with this procedure, and with comparable methods, are discussed.

Chromatography, Gas↗