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Biomedical subjects

W B Runciman

Publications and source records attributed to W B Runciman.

At least 127 records · Page 7Linked to original sources
PubMed1987

An assessment of six different pulmonary artery catheters.

The performance of three samples each of six brands of flow-directed pulmonary artery (PA) catheters was evaluated. In vivo studies determined the reproducibility of PA waveforms over a range of controlled heart rates when compared to those obtained from a transducer-tipped catheter. In vitro studies determined their frequency response, thermistor accuracy, balloon characteristics, and the maximum infusion rates possible through their proximal lumens. All catheters performed similarly in vivo, with mean errors in systolic and diastolic pressures ranging, respectively, from +9% to -12%, at a HR of 80 beat/min, to +23% and -30% at a HR of 160 beat/min. The resonant frequencies of all catheters in vitro were similar at 12 Hz or less; we were unable to obtain the frequency responses (17 to 32 Hz) claimed by the manufacturers. All thermistors were accurate for clinical use when tested over the temperature range 32 degrees to 42 degrees C. Balloon characteristics and infusion rates varied with some catheter brands. Maximum infusion rates varied from 164 to 383 ml/h when infusing 20% dextrose, and from 95 to 213 ml/h when infusing 35% dextrose.

Animals↗
PubMed1987

The influence of drug sorption on pharmacokinetic studies of chlormethiazole and lignocaine.

The influence of drug sorption on the measurement of dose and blood concentrations during pharmacokinetic studies of chlormethiazole and lignocaine in a chronically catheterized sheep preparation has been examined. There was no sorption to soda glass tubes, borosilicate glass volumetric flasks or soda glass microlitre syringes but minor sorption to polypropylene syringes, polypropylene pipette tips and rubber bottle stoppers after 240 min contact. During infusions through administration sets including either polyvinyl chloride or polyethylene catheters, no significant loss of lignocaine occurred, but only 41.7-63.9% of the chlormethiazole dose was delivered. No significant decreases in either drug occurred from blood sampled through an intravascular catheter and stopcock system. There was negligible degradation of the samples over 4 h. Sorption of chlormethiazole or lignocaine to the laboratory equipment used was not a significant source of error but polyvinyl chloride infusion catheters could result in significant reductions in chlormethiazole dose.

Absorption↗
PubMed1987

An evaluation of five carbon dioxide analysers for use in the operating theatre and intensive care unit.

Five commercially available carbon dioxide analysers were assessed with respect to accuracy, response time, stability, the effect of water vapour and the effect of rebreathing. Two side-stream sampling analysers (Datex Normocap and Engstrom Eliza) and one main-stream sampling analyser (Hewlett-Packard Capnoshot) were found to be satisfactory for use both in the operating theatre and intensive care unit. The Instrumentation Laboratory (IL) 200, a side-stream monitor, performed satisfactorily but neither it nor the Siemens Sirecust 404, a main-stream monitor, has the facility to compensate for the presence of nitrous oxide. The Siemens analyser, in the form tested, could not be recommended for clinical use, as it was less accurate than the other monitors, could not detect rebreathing, and was subject to fluctuations when used with gas mixtures saturated with water vapour.

Anesthesiology↗
PubMed1987

An evaluation of intravenous infusion pumps and controllers.

The accuracy, safety, reliability and cost of use of 35 intravenous infusion pumps and 3 flow controllers were assessed. When infusing saline 11 out of 17 syringe pumps, 3 out of 5 peristaltic pumps, 1 out of 2 roller pumps and all 14 cassette pumps tested were accurate to within 5% over their full ranges of operation. There was no significant change in the performance of any of the pumps tested when saline was infused through a standard resistance, except in the cases of the 3 flow controllers which were unable to infuse at all against the resistance. When 50% dextrose was infused, delivery by two peristaltic pumps was reduced by 23 and 38%. No pump cut out or alarmed at pressures of up to 200 mmHg and 21 pumps continued to infuse against pressures of 750 mmHg or greater. Surges of up to 0.5 ml occurred after release of an outlet obstruction. One device was fitted with a variable high pressure alarm. This device could also measure pressure in the infused vessel and was found to be accurate for measurements of central venous pressure. The cost of consumables for a single use for syringe pumps ranges from A$2 to $5, for peristaltic and roller pumps from A$1 to $10, and for cassette pumps from A$7 to $12, with an additional A$2 for a burette. Accurate delivery of intravenous fluids and drugs is available but is expensive and requires the operator to be specially trained. No simple, cheap, accurate device is yet available.

Evaluation Studies as Topic↗
PubMed1987

An evaluation of six disposable heat and moisture exchangers.

Six disposable heat and moisture exchangers were tested on patients undergoing anaesthesia requiring mechanical ventilation. Inspiratory humidity and temperature were monitored to find the steady-state values reached with each device together with the times taken for these to be achieved. The exchangers were tested in a non-rebreathing T-piece circuit and in a conventional circle system with a fresh gas flow of 6 l/min: the Siemens 150 provided 28 and 32 mg of water/litre of inspired gas (at about 30 degrees C) in 10 and 5 min respectively, but is rather heavy and bulky. The Portex Humidvent provided 25 and 30 mg/l, and although taking longer to reach steady state (27 and 15 min respectively) is small, light and cheap. The Siemens 151 provided 25 and 27 mg/l in 18 and 10 min respectively, but is heavier than the Portex exchanger. The performances of these three devices were not significantly different from each other in either study (P less than 0.05). For the T-piece system the Pall and Engstrom exchangers were the next most efficient. The Pall device provided 18 and 23 mg/l (in 18 and 8 min respectively) and the Engstrom provided 20 and 23 mg/l (in 19 and 10 min respectively). In the circle system, there were no significant differences between the performances of the Portex, Siemens 151, Pall and Engstrom exchangers. The Pall is also a very effective bacterial filter and has been found to be satisfactory in the intensive care setting. The Terumo appeared to perform no better than a circle system with catheter mount (13 mg/l at 27 degrees C). It would seem that more complex humidification equipment is not necessary during anaesthesia if an efficient heat and moisture exchanger is used.

Anesthesia, General↗
PubMed1987

Do cardiorespiratory frequencies show entrainment with hopping in the tammar wallaby?

Breathing, heart and gait frequencies, tidal volume, cardiac output, and rates of oxygen consumption were measured in tammar wallabies (Macropus eugenii Desmarest) hopping on a treadmill. At speeds greater than 1.6 ms-1 the rate of metabolic power consumption was independent of hopping speeds. Blood lactate levels within the speed range where VO2 was independent of speed showed a mean increase of 4.8 mmol l-1. During bipedal hopping, the frequencies of breathing and limb movement are phase-locked in the ratio of 1:1. Inspiration begins as the animal leaves the ground and may be a passive process driven by a visceral piston. A relatively large central tendon in the diaphragm may correlate this function. Unlike breathing frequencies, cardiac frequencies show no entrainment with hopping. The site of dissipation of the presumed large arterial pressure excursion is unknown.

Animals↗
PubMed1987

The effects of general anaesthesia on tocainide clearance in the sheep.

The haemodynamic effects and regional clearances of tocainide were investigated in sheep with chronic intravascular cannulae to measure blood flow through, and drug extraction by, lungs, kidneys, liver and gut. 2. Tocainide, at arterial blood concentrations in the therapeutic range, caused no haemodynamic effects and was significantly extracted only by the liver. 3. In the presence of general anaesthesia with halothane, the mean hepatic blood flow and tocainide extraction ratio were each reduced by approximately 25% so that the mean hepatic clearance and intrinsic clearance of tocainide each were reduced by approximately 50%. Thus arterial blood tocainide concentrations were increased by 50%. 4. While the clinical implications of this interaction are unclear because of insufficient information about the margin of safety of tocainide, the pharmacological implications are plain. Because general anaesthesia may alter the relationship between dose and blood drug concentrations, pharmacokinetic and pharmacodynamic data should not be interchanged between awake and anaesthetized subjects.

Anesthesia, General↗
PubMed1987

The influence of acidosis on the distribution of lidocaine and bupivacaine into the myocardium and brain of the sheep.

To test the hypothesis that acidosis can increase the toxicity of bupivacaine more than that of lidocaine by increasing the distribution into the brain, myocardium, or both, studies were performed to measure the in vivo tissue:blood partition coefficients during continuous steady state intravenous infusions of these agents in anesthetized sheep during normal acid-base status and during combined respiratory-metabolic acidosis. Acidosis decreased the partition coefficient of both agents into the myocardium and that of bupivacaine into the brain but did not systematically change that of either agent into skeletal muscle or fat. Total body and hepatic drug clearances were not affected systematically, but plasma binding of both agents was decreased. Thus predictions based on the pH partition hypothesis about the effects of acidosis on myocardial:blood partition coefficients being a basis for explaining the relative toxicity of these agents were not supported.

Acidosis↗
PubMed1986

A sheep preparation for studying interactions between blood flow and drug disposition. VI: Effects of general or subarachnoid anaesthesia on blood flow and chlormethiazole disposition.

Blood flow through and chlormethiazole extraction ratios across lungs, liver, kidneys and gut were measured in awake unrestrained sheep (controls) and with the same animals anaesthetized with 1.5% halothane or whilst undergoing high thoracic subarachnoid blockade with amethocaine. In the control-drug studies, chlormethiazole infused to sub-sedative blood concentrations produced no significant changes in haemodynamics or in the kinetics of iodohippurate (renal and hepatic blood flows). Chlormethiazole was eliminated predominantly by the liver (mean extraction ratio and clearance, respectively, 0.90 and 1.3 litre min-1) and lungs (0.15; 0.6 litre min-1). Renal clearance was absent or negligible (greater than 0.1 litre min-1). Because of pulmonary clearance, mean total body clearance was derived from analysis of pulmonary arterial concentrations. Under general anaesthesia, there were significant reductions in mean cardiac output, hepatic and renal blood flow (to 54%, 63% and 43% of control); chlormethiazole mean hepatic extraction ratios and clearance were reduced, respectively, to 82% and 56% of control, and its pulmonary and renal clearances were abolished. With subarachnoid anaesthesia there were no significant changes in haemodynamics or in chlormethiazole extraction ratios or clearances.

Anesthesia, General↗
PubMed1986

A sheep preparation for studying interactions between blood flow and drug disposition. V: The effects of general and subarachnoid anaesthesia on blood flow and pethidine disposition.

Blood flow through and pethidine extraction ratios across lungs, liver, kidneys and the gastrointestinal tract were measured in awake unrestrained sheep (controls) and with the animals anaesthetized with 1.5% halothane or whilst undergoing high thoracic subarachnoid block with amethocaine. In the control studies, pethidine infused to several times the blood concentrations required for postoperative analgesia in man produced no significant changes in haemodynamics or in the kinetics of iodohippurate (renal and hepatic blood flow); pethidine hepatic extraction ratios were consistently greater than 0.97; renal extraction ratios ranged from negligible to 0.30; and there was negligible extraction across the lungs and the gastrointestinal tract. Under general anaesthesia there were significant reductions in mean cardiac output (46%), mean hepatic blood flow (46%), mean renal blood flow (55%), mean arterial pressure (30%) and mean iodohippurate clearance (17%); but mean arterial blood concentrations of pethidine were doubled, mean hepatic clearance of pethidine was reduced to 60% of control and renal clearance was virtually abolished. With subarachnoid anaesthesia there were no significant changes in haemodynamics or in pethidine or iodohippurate extraction ratios or clearances. Summed measured regional clearances accounted for only one- to two-thirds of the total body clearance of pethidine; the rest was by extravisceral clearance or high affinity tissue binding.

Anesthesia, General↗
PubMed1986

A comparative study of the measurement of mean arterial blood pressure using automatic oscillometers, arterial cannulation and auscultation.

Mean brachial artery pressures determined by five different non-invasive automatic oscillometric and one auscultatory preferred (oscillometric back-up) blood pressure (BP) monitors were compared with mean arterial pressures (MAP) obtained by cannulation of the radial artery of the same arm. The devices tested all performed similarly, showing a wide range of variation (+40% to -29%) compared with the directly measured MAP, and all tended to over-read at low values and under-read at high values. Trend information was generally acceptable, but occasionally was misleading. In addition, using one of the devices, systolic and diastolic blood pressure measurements were compared with those obtained by auscultation. This gives a range of differences from +22 to -25 mmHg for systolic and +20 to -12 mmHg for diastolic BP measurements. (The average fell within 1.0 mmHg of the auscultatory measurement, with a standard deviation of 10 mmHg.) Thus, the automatic oscillometric BP monitors tested were comparable in accuracy to auscultatory BP measurement, and are satisfactory for routine use in the appropriate clinical context. However, in settings where significance is to be attached to individual BP readings rather than to trends, or where a high degree of accuracy is required, automatic oscillometric machines cannot be regarded as satisfactory alternatives to arterial cannulation.

Analysis of Variance↗
PubMed1986

An evaluation of ventilator monitoring alarms.

Thirteen commercially available ventilator monitoring alarms supplied by the distributors were evaluated. It was decided that devices with no power failure precautions or unprotected variable controls could not be recommended for general use. By these criteria only two devices could be recommended for general use as ventilator alarms and a further three as disconnect alarms; in each instance these recommendations are subject to certain reservations and suggested modifications. A ventilator alarm should be regularly serviced and checked before use and should be not used by anyone unfamiliar with the applications or limitations of that particular device.

Equipment Design↗
PubMed1986

An evaluation of fourteen oxygen analysers for use in patient breathing circuits.

Fourteen in-line oxygen monitors designed for use in patient breathing circuits were assessed to determine the lifespans of their sensors when exposed to oxygen, their response times to a sudden change in oxygen concentration from 30% to 0%, the effects of exposure to nitrous oxide, and the effects of some agents and conditions commonly encountered in anaesthetic breathing systems by exposing the sensors repeatedly for three two-hour periods to 1% halothane, 2% enflurane, saturated water vapour at 37 degrees C, 5% carbon dioxide, or a continuous pressure of 40 mmHg. Under the conditions of this study all sensors but one exceeded the manufacturers' claimed lifespans, and all had clinically adequate response times to sudden hypoxic changes. None had significantly altered responses when repeatedly exposed to nitrous oxide. Water vapour was the most common cause of error for both polarographic and galvanic cell sensors, although some errors occurred with each of the test conditions; errors from all causes occurred evenly throughout the lifespans of both types of sensor. The incidence of over-read errors was approximately equal to that of under-read errors. However, clinically potentially dangerous over-read errors of greater than 6% oxygen did not occur in any of the sensors, with the exception, on some occasions, of the Datex Oxygen Analyser when exposed to saturated water vapour at 37 degrees C.

Anesthesia, Inhalation↗
PubMed1986

An evaluation of three volatile anaesthetic agent monitors.

Three volatile anaesthetic agent monitors (Datex Normac Anesthetic Agent Monitor, Engstrom Emma Multigas Monitor and Penlon Halothane Meter) were evaluated for the effects of nitrous oxide or water vapour, and for their linearity, stability, and rate of response to a change in concentration of various anaesthetic agents under simulated working conditions. None was affected by nitrous oxide, and only the Engstrom Emma was affected by water vapour. Linearity was satisfactory for all three devices but stability, with respect to zero and gain drift, was satisfactory only for the Datex Normac and Penlon Meter. Rates of response for 10% to 90% of source signal ranged from 0.8 seconds for the Datex Normac to about three seconds for the Penlon Meter.

Anesthesia, Inhalation↗
PubMed1986

Perturbation of methionine metabolism in sheep with nitrous-oxide-induced inactivation of cobalamin.

Exposure of sheep to 36% nitrous oxide for 8 days (2-hr per day) led to 90%, 82% and 74% inhibition of 5-methyltetrahydrofolate-homocysteine methyltransferase in the liver, heart and brain, respectively, while there was no significant decrease in the activity of methylmalonyl-CoA mutase. There was also no change of betaine-homocysteine methyltransferase activity. The level of plasma methionine in nitrous-oxide-exposed sheep fell to 30% of its initial value. S-Adenosylmethionine level was reduced to 50% of the control value in the liver, and was also significantly decreased in the heart, but not in the brain. Excretion of formiminoglutamic acid and homocystine was also observed in the urine of sheep exposed to nitrous oxide. These results demonstrate that inhibition of 5-methyltetrahydrofolate-homocysteine methyltransferase causes a pronounced perturbation of methionine metabolism in sheep, suggesting that dietary methionine plus methionine synthesized from the methyl groups of betaine are not sufficient to meet the methyl needs for biological methylation reactions in this species and, in turn, emphasizing the role of 5-methyltetrahydrofolate-homocysteine methyltransferase in methionine synthesis in the sheep.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1986

Hepatic and renal clearances of lidocaine in conscious and anesthetized sheep.

Sheep were implanted with cannulae to study blood flow through, and drug extraction by, the lungs, kidneys, liver, and gut. Lidocaine, infused to a steady state in conscious sheep, caused no significant changes in cardiac output or regional blood flow, and was cleared principally by the liver, where the extraction ratio usually exceeded 0.9, and by the kidneys, where the extraction ratio was 0.1-0.2. There was no detectable clearance by lungs or gut. Under general anesthesia with 1.5% halothane, the cardiac output and renal and hepatic blood flows were decreased to means of 77, 44, and 79% of mean control values, respectively, but hepatic and renal extraction ratios of lidocaine were not systematically altered, so that regional clearances of lidocaine were not significantly different from those in conscious animals. There was evidence that the total body clearance of lidocaine exceeded the sum of the directly measured regional clearances in both control and general anesthesia studies. These equivocal findings of the effects of general anesthesia on lidocaine clearance are at variance with unequivocal findings of reduced regional clearances of other drugs tested in this preparation.

Anesthesia, General↗
PubMed1985

A sheep preparation for studying interactions between blood flow and drug disposition. IV: The effects of general and spinal anaesthesia on blood flow and cefoxitin disposition.

Control measurements of blood flow through and cefoxitin extraction ratios across heart and lungs, liver, kidneys and gut were made under steady-state conditions in awake unrestrained sheep. The studies then were repeated with the same animals anaesthetized with 1.5% halothane or whilst undergoing high thoracic (to approximately T4) subarachnoid blockade with amethocaine. In the control-drug studies, it was shown that cefoxitin was cleared by the kidneys and that the cefoxitin infusion produced no significant changes in haemodynamics or in the kinetics of iodohippurate (the marker substance used for determining renal blood flow). Under general anaesthesia, there were significant reductions in renal blood flow (to 61% of the mean control value), in iodohippurate renal extraction ratio and clearance (to, respectively, 64 and 38% of the mean control values) and in cefoxitin renal extraction ratio and clearance (to, respectively, 48 and 23% of the mean control values). Under spinal anaesthesia there were no significant changes in haemodynamics or in cefoxitin or iodohippurate extraction ratios or clearances.

Anesthesia, General↗