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Biomedical subjects

P Hutton

Publications and source records attributed to P Hutton.

At least 55 records · Page 3Linked to original sources
PubMed1987

On using a self-tuning controller for blood pressure regulation during surgery in man.

The generalized minimum-variance self-tuning controller of Clarke and Gawthrop has been used to adjust the flow rate of a modified Vickers Treonic IP4 syringe pump delivering phenylephrine to 20 patients undergoing lower abdominal surgery during epidural analgesia. This proved to be a very effective method of restoring and maintaining normal arterial pressure. The method has also been used to produce controlled hypotension in 18 patients undergoing plastic or neurosurgical procedures via sodium nitroprusside infusions. Valuable insight into patient responses to surgical stimuli, blood loss, fluid loads, opioids, relaxants and other agents was provided.

Anesthesia, Epidural↗
PubMed1986

Halothane and the liver.

Explore the source record for details and available documents.

Chemical and Drug Induced Liver Injury↗
PubMed1986

Factors affecting delivery of drug through extension tubing.

A theoretical laminar flow model of drug delivery via extension sets (1250 mm long) was developed and tested experimentally by tracer studies. Despite discrepancies between theory and experiment (which are discussed in the text), when the infusion was allowed to run normally it was confirmed that there was a hyperbolic relationship between the flow rate of the infusion and the time of delivery of a given percentage of the injected drug. Even with the drip chamber (15 drops ml-1) running as a continuous stream, it can take up to almost 3 min for 90% of a 1-ml or 3-ml injection to enter the patient's vein. An alternative method of flushing the drug in with a syringe of saline produced a non-laminar flow regimen which was more efficient in terms of both the volume and the time required for a given percentage drug delivery.

Humans↗
PubMed1986

Priming and the onset of neuromuscular blockade with alcuronium.

"Priming" with alcuronium has been studied in 72 female patients. Blockade of single twitch responses of the adductor pollicis by alcuronium 0.15, 0.2 or 0.3 mg kg-1 could be accelerated by priming with a suitable priming portion of the total dose. Giving alcuronium 0.04 mg kg-1 30 s after the induction of anaesthesia, followed by the balance 4 min later, resulted in more rapid neuromuscular blockade than giving the total dose at 4.5 min after induction. There was some suggestion of an increase in maximal twitch depression, but this could not be demonstrated confidently. The effect of increasing the priming portion was tested for the 0.3 mg kg-1 total dose, but any priming effect was attenuated. The mechanism of priming is not obvious. Occupation of "spare receptors" does not explain all of the features of priming.

Adult↗
PubMed1986

Performance of needle valves.

The pressure-flow characteristics of needle valves used on anaesthetic equipment were investigated. It was found that, under normal conditions of use, the valves behaved in a manner similar to convergent nozzles with sonic velocity at the throat. This means that, once the valve has been set, the mass flow rate of gas is effectively independent of the downstream changes in resistance and compliance encountered in normal anaesthetic practice. The error in a preset flow induced by the permissible variations in the upstream pipeline pressure was measured.

Anesthesia, Inhalation↗
PubMed1986

The anaesthetist and the obstetric flying squad. Could complacency creep in?

The demands made upon the Bristol obstetric flying squad over the past 14 years have been analysed. During this period, the number of calls received per year has decreased dramatically. The reasons for this are discussed in the context of current obstetric practice. The management of retained placenta is reviewed. Of importance to anaesthetists is the gross reduction in the number of cases where it is necessary to give anaesthesia 'in the field'. This may lead to complacency and lack of familiarity with the equipment carried by the flying squad.

Anesthesia, Obstetrical↗
PubMed1986

The digital control of anaesthetic gas flow.

The theory and construction of a prototype digital gas flow controller are described. Using eight preset needle valves, it has the ability to deliver any flow from 50 to 12750 ml/minute in steps of 50 ml/minute. Under given conditions, the accuracy of this device is very high and its variation in performance with pipeline supply pressures is quantified. The required flow is requested from a BBC 'B' microcomputer which is interfaced with the equipment via a program written in Basic and the 1MHz bus port. The possible uses and potential of a microcomputer-controlled flow regulator in anaesthesia and intensive care are discussed.

Anesthesia, Inhalation↗
PubMed1985

Auscultatory measurement of arterial pressure during anaesthesia: a reassessment of Korotkoff sounds.

The accuracy of the indirect auscultatory method, using Korotkoff sounds for determination of arterial pressures, was investigated by comparison with direct intra-arterial measurements. Eight hundred and sixty-three comparisons were made in 25 patients aged between 27 and 75 years over blood pressures ranging from 59 to 235 mmHg for systolic and 28 to 145 mmHg for diastolic. The regression equation for all systolic pressure measurements was y = 13.9 + 0.81x, and for all diastolic pressure measurements was y = 21.4 + 0.71x. Although there was a significant (P less than 0.001) correlation coefficient between direct and indirect measurements for both systolic (r = 0.93) and diastolic pressures (r = 0.79), the 95% confidence limits (+/- 22 mmHg for systolic and +/- 19 mmHg for diastolic) were very wide, reflecting the influences of observer variation and other sources of error.

Adult↗
PubMed1984

Venous pressure and arm volume changes during simulated Bier's block.

In investigating the possible causes of an observed complication of intravenous regional anaesthesia, cubital fossa venous pressures were measured distal to an inflated tourniquet as standard 40 ml volumes of normal saline were injected. The maximal pressures obtainable were limited by tourniquet pressure since the veins compressed under the tourniquet acted as 'Starling' spillover resistors. Once the compressing pressures were reached, with continued injection, fluid passed easily into the systemic circulation with little further increase in venous pressure. The rates of rise and maximum values of venous pressures tended to be increased by increased injection rates, and by failure to exsanguinate the arm, but the choice of injection site was paramount. Compared with more distal injections, cubital fossa venous injections are more likely to lead to leakage under the tourniquet and should never be used for intravenous regional anaesthesia.

Anesthesia, Conduction↗
PubMed1984

An assessment of the Dinamap 845.

The accuracy of the Dinamap 845 automatic blood pressure recorder was assessed by comparing its own indirect determinations of blood pressure with direct intra-arterial recordings. It was found that in the majority of cases it was capable of producing reliable trend information during anaesthesia. The instrument may not be able to interpret pressure signals from a patient with a severe dysrhythmia. It is probably an unsuitable monitor for use with very rapidly acting drugs such as sodium nitroprusside.

Anesthesia↗
PubMed1982

The oscillotonometer in theory and practice.

The accuracy of the Scala Alternans Altera oscillotonometer was investigated by comparison with direct intra-arterial pressures. It was found that the traditional criteria for detecting systolic and diastolic pressures were in error. A slow deflation rate was essential for the accurate measurement of systolic pressure, the maximum amplitude of needle oscillation correlated closely with mean pressure, and the determination of diastolic pressure was so inaccurate as to be clinically useless. The response of the oscillotonometer was also found to be dependent upon the individual combination of oscillotonometer and patient.

Blood Pressure Determination↗
PubMed1982

Doxapram and the fractured femur.

In a double-blind trial the effects of a single dose of doxapram (1--1.5 mg/kg) on the postoperative arterial oxygen tension of patients who had undergone surgical fixation of a fractured neck of femur was measured. In contrast to other reports of the effect of a single dose of doxapram, there was no improvement in arterial oxygen tension with respect to the control group. It is reasoned that doxapram may exert its effect by increasing the functional residual capacity in the immediate postoperative period. The central analeptic properties of doxapram may be grossly underestimated. The widely held assumption that patients with a fractured neck of femur are significantly hypoxic pre-operatively is questioned.

Aged↗
PubMed1981

Evaluation of the efficacy of an active scavenger for controlling air contamination in an operating theatre.

Contamination of the air with halothane in a poorly ventilated ENT theatre was found to be very great (median concentration 449 micrograms litre-1, 177 samples), but was reduced significantly (P less than 0.005) by the use of an active scavenger of patients' expired gases (median concentration 159 micrograms litre-1, 168 samples). For about 18% of the time when the theatre was in use, the halothane concentration in the air was greater than 1000 micrograms litre-1, whether or not the patients' expired gases were being scavenged. Although not measured quantitatively, this appeared to correspond approximately to the period of time in theatre when patients were not connected to the anaesthetic circuit.

Air Movements↗