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Biomedical subjects

R J Telford

Publications and source records attributed to R J Telford.

14 recordsLinked to original sources
PubMed2003

Myocardial ischaemia precipitated by acute normovolaemic haemodilution.

Acute normovolaemic haemodilution (ANH) is widely used as part of a blood conservation strategy to minimize the use of allogenic blood in the peri-operative period. Its role has not been proven in a prospective randomized trial. The potential benefits must not blind clinicians to the possible hazards. We report a life-threatening complication of ANH prior to induction of anaesthesia for aortic aneurysm repair.

Aged↗
PubMed2001

A 14,000-year oxygen isotope record from diatom silica in two alpine lakes on Mt. Kenya.

Oxygen isotopes are sensitive tracers of climate change in tropical regions. Abrupt shifts of up to 18 per mil in the oxygen isotope ratio of diatom silica have been found in a 14,000-year record from two alpine lakes on Mt. Kenya. Interpretation of tropical-montane isotope records is controversial, especially concerning the relative roles of precipitation and temperature. Here, we argue that Holocene variations in delta(18)O are better explained by lake moisture balance than by temperature-induced fractionation. Episodes of heavy convective precipitation dated approximately 11,100 to 8600, 6700 to 5600, 2900 to 1900, and <1300 years before the present were linked to enhanced soil erosion, neoglacial ice advances, and forest expansion on Mt. Kenya.

Diatoms↗
PubMed1994

Use of a guide wire and a ureteral dilator as an aid to awake fibreoptic intubation.

We describe the successful use of a guide wire and ureteral dilator to pass a tracheal tube into the trachea through the mouth in an awake, sedated patient when attempts to pass a larger tube over an Olympus LF1 fibreoptic bronchoscope were unsuccessful. Since the ureteral and renal dilators are available in a variety of sizes, if too large a tube is inadvertently mounted on the instrument this technique allows an appropriate sized tube to be inserted without the need to re-endoscope the patient.

Adult↗
PubMed1992

Fentanyl does not alter the "sleep" plasma concentration of thiopental.

Thiopental and fentanyl are commonly combined for induction of anesthesia. The effect of an analgesic concentration of fentanyl on the plasma concentration of thiopental to induce sleep was studied in 46 unpremedicated patients. As a measure of drug effect, sleep (the lack of response to open eyes to a verbal command) was used. Forty-six patients were randomized to receive thiopental infused to one of several predetermined plasma concentrations. Twenty-two of these patients also received a fentanyl infusion to a desired analgesic concentration of 1 ng/mL. Thiopental and fentanyl were infused by means of a pharmacokinetic model-driven infusion device (computer-assisted continuous infusion, CACI). Venous blood samples were taken from the contralateral antecubital fossa at 5 and 10 min after the start of the infusion. At 10 min, the patients' names were firmly spoken, and they were instructed to open their eyes. If they did not respond to this command, they were considered to be asleep. Only patients in whom the 5- and 10-min measured plasma concentrations of thiopental and fentanyl, respectively, were within +/- 30% of each other were used for the determination of the Cp50(asleep), the plasma concentration at which 50% of the patients were asleep. The Cp50(asleep) with and without fentanyl was calculated by logistic regression. The Cp50(asleep) for patients in whom concentrations were maintained within +/- 30% for thiopental alone (n = 17) was 7.32 micrograms/mL (95% confidence interval, 5.53-10.95); for thiopental in the presence of fentanyl (n = 18 with a measured fentanyl concentration of 1.27 +/- 0.5 ng/mL), this was 7.22 micrograms/mL (95% confidence interval, 4.83-10.15).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Ventilatory responsiveness to carbon dioxide below the normal control point in conscious normoxic humans.

A recently developed CO2 pulse technique was used to test for ventilatory sensitivity to CO2 in four normal men following 2 min voluntary hyperventilation down to an end-tidal CO2 tension (PETCO2) of 20 mmHg (2.7 kPa). Pure CO2 was injected into the inspiratory limb of a breathing circuit at 0.4 l.min-1 for 30 s and any small ventilatory response was detected against background noise by ensemble-averaging of multiple runs. Following hyperventilation, ventilation was initially often above control and apnoea was not seen. In one subject, the ventilatory response to the CO2 pulse was barely detectable either before or after hyperventilation. In another subject, there was a response to pulses given before hyperventilation and 3 and 5.5 min after hyperventilation but not 30 s after hyperventilation when PETCO2 was about 25 mmHg (3.3 kPa) and rising. In the two remaining subjects ventilatory responses were seen to CO2 pulses started 30 s after hyperventilation, although PETCO2 following the pulse remained some 5 mmHg (0.7 kPa) below baseline. We conclude that in some subjects the PETCO2 threshold lies well below the normal PETCO2. The technique is tedious for the experimental subject because of the large number of repetitions required and, therefore, unsuitable for a study on a large number of subjects.

Adult↗
PubMed1991

Hypoxia following voluntary hyperventilation during exercise in man.

The importance of carbon dioxide in the control of ventilation during exercise was tested by emptying CO2 stores by voluntary hyperventilation. Healthy subjects were studied after 3 min hyperventilation down to an end-tidal PCO2 of about 20 mmHg on a background of steady exercise at 75 W. Control runs were performed when the hyperventilation was made isocapnic by the addition of CO2. Following hypocapnic hyperventilation, there was a period when ventilation fell below control and this was accompanied by a fall in end-tidal PO2 (minimum 48 mmHg) and oximeter reading (minimum 73%). Ventilation rapidly returned to baseline following isocapnic hyperventilation and hypoxia was not seen. A mathematical simulation suggested that brain PCO2 recovered more slowly than arterial PCO2 and that at the times that ventilation was depressed central chemoreceptor PCO2 would have been low. We conclude that CO2 provides a crucial drive for maintaining adequate ventilation during steady exercise and that the central chemoreceptor may be involved.

Adolescent↗
PubMed1991

Observations on deliberate dural puncture with a Tuohy needle: depth measurements.

Observations were made during the use of a Tuohy needle to perform deliberate dural puncture for the insertion of lumbar drains to improve operating conditions for intracranial aneurysm surgery. The most striking finding was the distance from identification of the epidural space to penetration of the dura. We postulate that this was because of tenting of the dura by the blunt Tuohy needle. This was facilitated by the absence of a negative epidural space pressure because an open system was used, which allowed time for pressure equilibration. This minimised the reactive forces across the dura. Aspiration and rotation of the Tuohy needle revealed dural puncture in some cases.

Adolescent↗
PubMed1991

Observations on deliberate dural puncture with a Tuohy needle: pressure measurements.

Pressure recordings were made during passage of a Tuohy needle from the interspinous ligament to the subarachnoid space for lumbar drain insertion. Epidural space pressures were always positive. Negative pressures were seen only at the moment of entry into the subarachnoid space. These were artefactual and were caused by tenting of the dura by the blunt Tuohy needle. Use of a closed measurement system such as this facilitates the development of large transdural pressure gradients because of the inability of the epidural space pressure to equilibrate with atmospheric pressure. This may contribute to ease of dural puncture.

Cerebrospinal Fluid Pressure↗
PubMed1990

The myasthenic syndrome: anaesthesia in a patient treated with 3.4 diaminopyridine.

A case of anaesthesia in a patient with myasthenic syndrome treated with 3.4 diaminopyridine is described. Despite symptomatic improvement and an improved electromyogram (EMG) on treatment, extreme sensitivity to neuromuscular block occurred with vecuronium. Antagonism of block was poor with an anticholinesterase, while oral 3.4 diaminopyridine improved neuromuscular transmission further. A combination of anticholinesterase with aminopyridine may be the antagonistic combination of choice in this condition.

4-Aminopyridine↗
PubMed1990

The effect of almitrine on the steady-state ventilatory response to carbon dioxide at rest and during exercise in man.

Almitrine has potential as a tool for testing the physiological role of the peripheral chemoreceptor. The effects of almitrine on CO2 chemosensitivity were studied at rest and during light exercise using a constant inflow technique that avoids the hyperoxia of rebreathing methods. The steady-state ventilatory response to CO2 was measured in two groups of six normal men before and 150 min after 100 mg oral almitrine bismesylate or placebo. One group was studied at rest, the other while pedalling at 50 W. The resting group showed a significant increase in CO2 response slope after almitrine when compared with placebo but there was no significant change in the response intercept. During exercise the individual results were very variable and after almitrine no significant change was seen in either the response slope or intercept. Control ventilation was not affected by almitrine in either group. Even in the absence of marked hyperoxia the effect of almitrine on CO2 sensitivity at rest in small. The lack of effect at 50 W is against any important role for the peripheral chemoreceptor during light exercise but other interpretations are possible.

Adult↗
PubMed1989

Pharmacokinetics of bupivacaine following intraoperative intercostal nerve block in neonates and in infants aged less than 6 months.

Pharmacokinetics and blood concentrations of bupivacaine were studied after intercostal nerve blocks were performed intraoperatively using 1.5 mg.kg-1 in 11 neonates (age 0-28 days) and 11 infants between age 1 and 6 months. The study aimed to provide pharmacokinetic data that are limited in these age groups, and to identify any adverse effects of intercostal nerve block in infancy. Arterial blood samples were taken at 0, 5, 10, 15, 20, 30, 60, 120, 240, and 360 min. Whole blood bupivacaine was assayed by high-performance liquid chromatography. Peak blood concentrations were attained within 10 min in 18 of 22 subjects, and were 087 micrograms.ml-1 [corrected] +/- 0.56 micrograms.ml-1 (mean and SD) and 0.91 +/- 0.27 micrograms.ml-1 in neonates and infants, respectively. Pharmacokinetic variables in the two groups included elimination half-life (t1/2 beta): 132 +/- 59 min and 102 +/- 39 min; steady-state volume of distribution (Vdss): 2.56 +/- 0.76 l.kg-1 and 2.17 +/- 0.17 l.kg-1; and total body clearance (Clt): 16.93 +/- 9.32 ml.min-1.kg-1 and 15.71 +/- 6.99 ml.min-1.kg-1. There was no statistically significant difference between neonates and infants with regard to any of these parameters. Patients were further divided into those with acyanotic and cyanotic disease. Cyanotic infants were significantly heavier than acyanotic infants (P less than 0.05), but no other differences were demonstrated. No adverse effects resulting from the technique were identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Bupivacaine↗