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Biomedical subjects

W B Runciman

Publications and source records attributed to W B Runciman.

At least 91 records · Page 5Linked to original sources
PubMed1991

Pulse oximeter probes. A comparison between finger, nose, ear and forehead probes under conditions of poor perfusion.

The performances of 10 pulse oximeters using finger probes were compared with the same pulse oximeters using alternative probes (eight finger probes, two nose probes and a forehead probe) in poorly perfused patients. All readings were then compared with directly measured arterial blood oxygen saturations. The mean difference (bias, 'accuracy'), standard deviation (precision) and 'drop out' rate for each pulse oximeter combination was determined. An overall ranking of performance of each pulse oximeter was calculated using five criteria (accuracy, precision, number of readings within 3% of standard, percentage of readings given within 3% of standard, expected overread limit in 95% of cases). Nose and forehead probes performed poorly. Some ear probes performed well compared to some finger probes, but the overall performance of probes in other sites compared to finger probes was worse, (p = 0.05). Two of eight ear probes and no nose or forehead probes would be expected to be within 4% of the reference value in 95% of readings. The use of finger probes rather than probes in other sites is recommended in the patient with poor peripheral perfusion.

Adult↗
PubMed1991

Potential errors in pulse oximetry. III: Effects of interferences, dyes, dyshaemoglobins and other pigments.

Electrosurgery, patient motion and some types of lighting can cause errors in saturation readout; it is recommended that probes should be shielded from ambient lighting. Intravenous dyes can introduce gross but transient errors, which may also be present in in vitro measurements. Carboxyhaemoglobin causes overestimation of fractional saturation by an amount less than, but possibly close to, the percent of carboxyhaemoglobin present. Methaemoglobin causes the pulse oximeter readout to tend towards 85%. Fetal haemoglobin and bilirubin introduce no significant error, although they may interfere with in vitro measurements. Skin pigmentation can result in a slight decrease in accuracy. Nail polish may cause up to 6% underestimation of saturation; it is recommended that probes should be mounted sideways on fingers with nail polish or long nails. Adhesive tape or a vinyl glove across the probe has no demonstrable effect on accuracy. A blood sample should be analysed by a multiwavelength in vitro oximeter when an erroneous pulse oximeter reading is suspected, although errors may be introduced in the in vitro reading by fetal haemoglobin, bilirubin and intravenous dyes.

Coloring Agents↗
PubMed1991

Failure of the Kety-Schmidt nitrous oxide method for determination of myocardial blood flow.

1. The reliability of the Kety-Schmidt nitrous oxide (N2O) blood-tissue equilibration method was examined in 50 studies of myocardial blood flow in seven conscious, unrestrained sheep using a newly developed carefully validated gas chromatographic assay for N2O. 2. In 10 studies the arterial and coronary sinus N2O blood concentration-time curves converged as expected at the end of the 10 min sampling period. In 14 studies they crossed over, and in 26 studies, the curves failed to converge. 3. A survey of the literature revealed that such results have been encountered previously but have not been accorded particular significance. An ultimate matching equilibrium between arterial and venous blood N2O concentration-time curves is, however, fundamental to the validity of the method. 4. The results indicate that the use of the Kety-Schmidt method with N2O as the indicator gas is invalid as applied to the measurement of myocardial blood flow in this preparation.

Animals↗
PubMed1991

Carbon monoxide poisoning.

Carbon monoxide is a common domestic and industrial poison which may be lethal. Survivors can develop permanent neuropsychiatric disability. The mechanisms of toxicity are poorly understood and the traditional criteria used to determine the severity of the poisoning have low predictability. Oxygen is the recommended antidote to carbon monoxide, but it appears that oxygen under hyperbaric conditions repeated either daily or as indicated by the patient's condition may be required to provide an effective dose. A reliable marker of the severity of carbon monoxide poisoning is urgently needed so that trials of alternative regimens can proceed.

Carbon Monoxide Poisoning↗
PubMed1991

The in vitro uptake and metabolism of lignocaine, procainamide and pethidine by tissues of the hindquarters of sheep.

1. In vitro studies using tissue slices or tissue homogenates of liver, skeletal muscle, fat skin and blood were conducted to determine whether the uptake of procainamide, lignocaine and pethidine into the hindquarters of sheep was due to distribution or metabolism. Both homogenates and slice preparations of liver showed significant metabolism or uptake, confirming the viability of the preparations. 2. None of the drugs was metabolized in blood and there was minimal uptake of the drugs into the skin. 3. There was metabolism of pethidine in skeletal muscle and substantial uptake of pethidine into fat, indicating that the rapid rate of uptake and prolonged elution of pethidine in the hindquarters was due to both distribution and metabolism. 4. No metabolism of lignocaine in muscle was found, but there was substantial uptake into fat, indicating that the rapid rate of uptake and prolonged elution of lignocaine in the hindquarters was due to its distribution into fat. 5. There was negligible uptake of procainamide into either muscle or fat, presumably due to its relatively low lipophilicity.

Adipose Tissue↗
PubMed1991

The in vivo blood, fat and muscle concentrations of lignocaine and bupivacaine in the hindquarters of sheep.

1. A method was developed for sampling muscle and fat from the hindquarters of sheep undergoing spinal anaesthesia. The method was used to measure the concentrations of lignocaine and bupivacaine in the blood, muscle and fat of the hindquarters of sheep during and after 180 min constant-rate infusions of the drugs. 2. For both drugs the muscle drug concentrations were a relatively constant ratio of the simultaneous arterial blood drug concentrations during and after the infusion. 3. There was uptake of both lignocaine and bupivacaine into subcutaneous fat during the infusions. At the end of the infusion the ratio of the fat: arterial blood drug concentrations were 1.54 (SD = 0.57, n = 4) and 3.1 (SD = 1.4, n = 4) for lignocaine and bupivacaine, respectively. 4. The drug concentrations in fat declined relatively slowly after the infusion. The ratio of the fat: arterial blood drug concentrations 180 min after the end of the infusion was 21.5 (SD 4.0, n = 3) and for lignocaine, and 120 min after the end of the infusion was 9.54 (SD 5.2, n = 3) for bupivacaine. 5. It was concluded that the concentrations of lignocaine and bupivacaine in muscle were essentially in equilibrium with the arterial concentrations during and after the infusion. However, the concentrations of lignocaine and bupivacaine in fat were not in equilibrium with the arterial concentrations in the post-infusion period.

Adipose Tissue↗
PubMed1991

Insight into interstitial drug disposition: lymph concentrations of lidocaine, procainamide and meperidine in the hindquarters of unanesthetized and anesthetized sheep.

Drug concentrations in the lymph of the hindquarters of sheep were used to gain insight into drug disposition within the interstitial space. Lidocaine, procainamide and meperidine were each infused into the right atrium of adult merino ewes for 220 min. The time courses of drug concentrations in arterial and inferior vena caval (IVC, draining the hindquarters) blood and hindquarter lymph were determined. It was found that in unanesthetized sheep the mean (+/- S.D., n = 3) lidocaine, procainamide and meperidine concentrations in the hindquarter lymph, were 74 +/- 11, 107 +/- 25 and 94 +/- 17%, respectively, of the arterial and 92 +/- 15, 113 +/- 27 and 134 +/- 28%, respectively, of the IVC blood drug concentrations. Drug binding in lymph, determined by equilibrium dialysis, was not significantly higher than that in blood, except for lidocaine at an initial buffer concentration of 5 micrograms/ml. When the studies were repeated with different animals under halothane anesthesia, the lymph/arterial and lymph/IVC blood drug concentration ratios of the three drugs decreased to 66 +/- 9, 73 +/- 13 and 71 +/- 13% and 77 +/- 8, 88 +/- 19 and 85 +/- 10%, respectively. These values were all significantly lower than those in unanesthetized animals. The results suggest that drug protein binding in interstitial fluid and the status of the microcirculation are important determinants of drug distribution in the interstitial and intracellular spaces. The data also confirm the assumption made in pharmacokinetic studies based upon mass balance principles that the rate of drug removal from organs by lymph is negligible.

Anesthesia↗
PubMed1990

An acute pain service in an Australian teaching hospital: the first year.

The Acute Pain Service began at the Royal Adelaide Hospital in April 1989. Funding, education programmes, policies, procedures, protocols, techniques (particularly patient-controlled analgesia, epidural opioid analgesia and subcutaneous morphine therapy) and daily organisation of the service are described in this article, and the experience with the 1053 patients referred to the Service during the first year of operation is reported. The occurrence of major complications was small. Mild-to-moderate respiratory depression occurred in four (0.5%) of the 747 patients who received patient-controlled analgesia and in none of the 177 who received epidural opioids. Five patients receiving patient-controlled analgesia had persistent nausea/vomiting; 320 (35%) of all patients receiving patient-controlled analgesia or epidural opioids suffered nausea/vomiting that required no treatment or was alleviated by treatment with an antiemetic. Around 13% of patients reported mild-to-moderate itching. In our experience, the combination of appropriately trained nursing and medical staff, standardised orders and procedures, and proper supervision can lead to safe, more effective management of acute pain.

Acute Disease↗
PubMed1990

Regional pharmacokinetics. II. Experimental methods.

Regional pharmacokinetics is the study of the drug concentrations in specific regions of the body. It allows greater insight into the mechanisms of drug disposition than the study of systemic blood concentrations. Experimental methods in regional pharmacokinetics and their applications and limitations are reviewed. Post-mortem tissue biopsies give the drug concentrations in highly specific regions of the body, but require a large number of animals. Serial tissue biopsies yield the time-course of drug concentrations in individual animals, but have limited applications. Regional blood sampling in vivo requires catheterization of blood vessels and a measure of regional blood flow, but allows repeated measurements of the time-course of regional drug concentrations in an individual. In contrast, artificially perfused regions allow greater control of perfusate flow and composition, but are less representative of the in vivo situation. These factors can be retained in some animals by surgically transplanting organs to another location to increase access. Tissues slices and cell cultures can examine drug uptake in the absence of perfusion, and tissue homogenates can be used to study the in vitro rates of drug metabolism and tissue drug binding.

Autoradiography↗
PubMed1990

Cardiovascular effects of propofol and of thiopentone anaesthesia in the sheep.

We have examined the effects on the cardiovascular system and on regional blood flow of propofol and thiopentone when administered with IPPV (FIO2 0.4). A longitudinal study design was used in which 16 studies were performed in eight sheep for 30 min before, during the last 30 min of 70 min anaesthesia, and for 6 h after anaesthesia. During anaesthesia with propofol and thiopentone, mean total body oxygen consumption decreased, respectively, by 47% (P less than 0.001) and 24% (P less than 0.01) of pre-anaesthesia baseline values, mean heart rate increased by approximately 50% (P less than 0.05) with both agents, mean arterial pressures increased by approximately 50% (P less than 0.05) with both agents and the mean cardiac output was unaltered with propofol anaesthesia but was decreased by 20% (P less than 0.05) with thiopentone anaesthesia. The changes in arterial pressure and heart rate were unexpected and may have been a result of a species-specific effect. Mean hepatic blood flow decreased consistently by a mean of 17% (P less than 0.01) during propofol anaesthesia, and inconsistently during thiopentone anaesthesia so that it was not significantly different from baseline values. Mean renal blood flow decreased during propofol anaesthesia by 7% (P less than 0.05) and by 27% (P less than 0.001) during thiopentone anaesthesia. Whereas most variables returned to baseline values within 2 h after propofol anaesthesia, this took 5 h after thiopentone anaesthesia.

Anesthesia, Intravenous↗
PubMed1990

Effects of propofol and of thiopentone anaesthesia on the renal clearance of cefoxitin in the sheep.

We have examined the renal extraction ratios and clearances of cefoxitin in three groups of adult merino ewes. One group (n = 3) was studied for 12 h without perturbation; these were designated control studies. The other two groups (n = 4 each) were studied before (baseline values), during and after the induction and 70-min maintenance of anaesthesia with propofol or thiopentone. In the control studies, mean renal extraction ratio and clearance for cefoxitin were, respectively, 0.67-0.92 and 0.66-0.91 litre min-1 and were consistent throughout the entire study period in individual animals. Comparable values were obtained as baseline values in the anaesthesia groups. Compared with individual baseline values, blood concentrations of cefoxitin doubled during anaesthesia with each agent. At the same time, renal extraction ratio and clearance for cefoxitin each decreased significantly to about 50-60% of their control values. Recovery to control values of arterial blood concentrations and renal extraction ratio of cefoxitin took at least 5 h, but recovery of renal clearance was more rapid. The results indicate that renal elimination of an organic anion such as cefoxitin may be affected by changes in renal blood flow and in renal function produced by propofol and thiopentone; these effects may last for several hours after recovery of renal blood flow.

Anesthesia, Intravenous↗
PubMed1990

Effects of propofol and of thiopentone anaesthesia on the regional kinetics of pethidine in the sheep.

We have examined the extraction ratios, net fluxes and clearances of pethidine by the liver, kidneys and hindquarters in sheep before, during and after continuous anaesthesia (70 min) with propofol or thiopentone. Before anaesthesia, the overall mean respective regional pethidine extraction ratios were 0.98 (SD 0.01), 0.20 (0.06) and 0.44 (0.13), the corresponding net fluxes were 47 (7), 5 (2) and 20 (10)% dose min-1 and the clearances 1.44 (0.22), 0.17 (0.07) and 0.80 (0.39) litre min-1. During propofol anaesthesia, arterial blood concentrations of pethidine approximately doubled (P less than 0.05), mean pethidine hepatic extraction ratio was unchanged, flux was increased to 145 (20)% and clearance decreased to 79 (10)% (P less than 0.05) of baseline values; mean pethidine renal extraction ratio, flux and clearance were 73 (34), 112 (43) and 69 (31)% of baseline values; mean hindquarter pethidine extraction ratio decreased to 65 (25)% (P less than 0.05) of baseline values. During thiopentone anaesthesia, arterial blood concentrations of pethidine approximately doubled (P less than 0.01), mean pethidine hepatic extraction ratio was 97 (2)% of baseline values and flux and clearance were unchanged, mean pethidine renal extraction ratios, flux and clearance decreased to 37 (21), 54 (18) and 27 (19)% (all P less than 0.05) of baseline values and mean pethidine hindquarter extraction ratio was 81 (20)% of baseline values. In spite of only modest changes in hepatic and renal blood flow during anaesthesia, blood concentrations of pethidine doubled and pethidine kinetics were disturbed for several hours after anaesthesia. Overall, however, the changes were of smaller magnitude and shorter duration than those that have been described for anaesthesia with the volatile anaesthetic agents.

Anesthesia, Intravenous↗
PubMed1990

Physiological and biochemical consequences of electroimobilisation in conscious sheep.

An electroimmobilisation device has been developed to facilitate the automated shearing of sheep, but there is little information on its effects on the body. We have studied its effects on the cardiovascular system and on intermediary metabolism in sheep. Electroimmobilisation caused statistically significant increases in mean arterial pressure, heart rate, cardiac output, renal and hepatic and hindquarter glucose and lactate flux, organ and whole body oxygen flux, hindquarter blood flow and core temperature and decreases in arterial and posterior vena cava blood pH, renal and hepatic blood flow and PaCO2. Notably, no change occurred in PaO2. The metabolic changes demonstrated the capacity of sheep to respond to the increased muscular and cardiovascular work induced by electroimmobilisation. Pulmonary function was not compromised during electroimmobilisation as judged from blood gas changes, and the acid/base changes were rapidly reversed after electroimmobilisation. The recovery to control conditions for all perturbations generally took no longer than 30 min, consistent with a rapid and physiologically adequate reversal by the animal's homeostatic mechanisms.

Acid-Base Equilibrium↗
PubMed1989

Monitoring in emergency medicine.

Clinical observation is the most valuable monitoring technique we have. Complexity and invasiveness of monitoring increases from prehospital care to Emergency Department, to Anaesthesia and Intensive Care. Many methods of monitoring have specific applications. Non-invasive blood pressure monitoring has no advantages over conventional cuff methods, other than freeing the hands of the operator. Non-invasive cardiac output measurement, transcutaneous oxygen and carbon dioxide measurement are unlikely to play a major role in the foreseeable future in the emergency setting. The most exciting development in recent years has been the widespread availability of pulse oximetry, which allows beat by beat analysis of haemoglobin oxygen saturation.

Emergency Medical Services↗
PubMed1989

An animal model of systemic carnitine deficiency produced by haemodialysis of sheep.

1. Sheep, which had previously been surgically prepared with cannulae in various vessels to monitor substrate and metabolite exchanges across all the major organs, were connected to a haemodialysis machine and their blood was dialysed at an average rate of 6.23 ml/min/kg body weight. 2. Dialysis for 4 hr reduced the blood free carnitine concentrations to approx. 50% of the initial values and the concentrations returned to the initial values after 18 hr recovery. 3. Carnitine balance studies showed that approx. twice the amount of carnitine lost from the blood during dialysis passed into the dialysate indicating that carnitine was also lost from the extracellular fluid. 4. The average blood concentration of short-chain acylcarnitines did not vary significantly during dialysis or during the recovery phase. However, an output of short-chain acylcarnitines by the liver at 3 and 18 hr recovery and an uptake by the hind-body at 18 hr recovery was observed. 5. These results suggest that haemodialysis of sheep provides a useful model of systemic carnitine deficiency and suggest that treatment with acetylcarnitine or propionylcarnitine could be an efficient means of supplying carnitine in carnitine replacement therapy.

Animals↗
PubMed1989

Experimental analysis of catheter-manometer systems in vitro and in vivo.

The static and dynamic responses of two combinations of transducer amplifiers, pressure transducers, resonance elimination devices, extension tubing, and transcutaneous cannulae were tested in vitro using a sine-wave pressure generator, and in vivo by square-wave pressures generated by a "fast-flush" device. In addition, carotid arterial blood pressure waveforms recorded by these systems in sheep, at two different heart rates, were compared with those simultaneously recorded with a catheter-tip pressure transducer. A new term, "Working Heart Rate" is defined and allows for the prediction of the maximum heart rate up to which a system of given frequency response and damping coefficient should be accurate. When tested in vitro, all the monitoring systems were underdamped and resonated. The performance of all systems was improved by inclusion of an adjustable resonance elimination device but impaired by a nonadjustable resonance eliminator or by recording with an electronically filtered amplifier. When tested in vivo, the accuracy of mean and diastolic blood pressure measurement was not affected by any combination of heart rate, amplifier, length of extension tubing, or use of resonance eliminators. Both resonance elimination devices improved the performance of all systems. In contrast to predictions based on frequency response and damping, the smallest errors in systolic blood pressure were recorded using the electronic filter or the nonadjustable resonance eliminator. There were considerable and misleading differences between the frequency responses and damping coefficients calculated in vitro and those, for the same systems, derived from the in vivo fast-flush tests. It is concluded that the most accurate and consistent readings of systolic blood pressure will be achieved with the use of either an electronic filter or a nonadjustable resonance eliminator.

Amplifiers, Electronic↗