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Biomedical subjects

J G Whitwam

Publications and source records attributed to J G Whitwam.

At least 19 recordsLinked to original sources
PubMed1992

Relative effects of intrathecal administration of fentanyl and midazolam on A delta and C fibre reflexes.

The effects of fentanyl and midazolam, administered intrathecally, on somatosympathetic reflexes evoked by tibial nerve stimulation were investigated in 12 anaesthetized and paralysed dogs. Fentanyl depressed both the C and A delta fibre evoked reflexes in a dose ratio of approx 1:2. In contrast, midazolam had a greater effect on A delta compared with C fibre reflexes; while A delta reflexes were abolished by a total dose of 3 mg midazolam, C fibre reflexes were depressed by only 50%. The effect of fentanyl was reversed by naloxone (2 mg, i.v.) and that of midazolam by flumazenil (1 mg, i.v.). The results suggest that fentanyl and midazolam have different relative effects on A delta and C fibre pathways.

Anesthesia, Spinal↗
PubMed1992

Midazolam sedation reversed with flumazenil for cardioversion.

Midazolam was used for anaesthesia in 20 patients undergoing cardioversion; 10 received flumazenil, which caused immediate rapid reversal of anaesthesia, and these patients maintained SpO2 greater than 95%, breathing air, within 5-10 min. In contrast, patients in the placebo group were still partially sedated and required oxygen therapy for up to 2 h to maintain a normal SpO2. Arterial pressure, but not heart rate, also was greater in the flumazenil group in the recovery period.

Adult↗
PubMed1992

Effect of low and high concentrations of alfentanil administered intrathecally on A delta and C fibre mediated somatosympathetic reflexes.

We have studied the effects of alfentanil administered intrathecally on somatosympathetic reflexes evoked by stimulation of radial and tibial nerves in 10 anaesthetized and paralysed dogs. In five animals, alfentanil was administered in doses of 100, 100, 200 and 400 micrograms in 0.8 ml and 800 micrograms in 1.6 ml prepared from the formulation of 500 micrograms ml-1. Five others received alfentanil (high concentration formulation, 5 mg ml-1) in doses of 500 and 2000 micrograms in 0.5 ml and 5000 micrograms in 1 ml. C fibre tibial nerve reflexes were depressed by 100 micrograms and abolished with doses of 200-400 micrograms, but the A delta response remained unaffected. A delta responses were depressed also and abolished, respectively, by doses of alfentanil 2000 micrograms and 5000 micrograms. At the larger, but not the smaller, concentration there was evidence of baroreflex sensitization probably caused by systemic absorption of the drug.

Alfentanil↗
PubMed1992

Magnetic resonance for the anaesthetist. Part I: Physical principles, applications, safety aspects.

Anaesthetists are being increasingly involved in magnetic resonance (MR) procedures, both in patient care and as a research tool. This paper outlines the physical basis of nuclear magnetic resonance and describes its application in magnetic resonance imaging and spectroscopy. Principles of magnet design and safety relevant to anaesthetic practice in a magnetic resonance environment are discussed and guidelines for anaesthetic practice suggested. Some recent clinical magnetic resonance studies of anaesthetic interest are reviewed.

Anesthesiology↗
PubMed1992

Magnetic resonance for the anaesthetist. Part II: Anaesthesia and monitoring in MR units.

Anaesthetists are increasingly involved in patient care during magnetic resonance imaging and spectroscopy. This paper describes a system which has been developed for the management of critically ill patients and the conduct of anaesthesia in a magnetic resonance unit with a 1.6 tesla whole body magnet. Difficulties which arise from working in a confined space in a high magnetic field are highlighted. Different approaches to anaesthesia, sedation and the modification of equipment for use in this environment are reviewed. The problems associated with patient monitoring within a magnetic field are discussed and some solutions are suggested. A transport system for critically ill patients is described and a protocol for management is outlined.

Anesthesia↗
PubMed1992

Clinical use of a small soda lime canister in a low-flow to-and-fro system.

It may be possible to overcome the classical disadvantages of a to-and-fro system by the use of a small soda lime canister. We report our experience of such a system in a series of 13 adult patients requiring mechanical ventilation of the lungs during surgery. The system was found to be convenient to use and the charge of soda lime had sufficient absorptive capacity to last throughout the great majority of surgical cases. Using a fresh gas flow of 1 l.min-1, the ratio of inspired isoflurane concentration to isoflurane vaporizer setting was found to be approximately one half after 10 min of anaesthesia. This ratio was maintained throughout the procedure, except for a few minutes following each change in vaporizer setting. A to-and-fro system using a small soda lime canister is a convenient alternative to the circle system for low-flow anaesthesia.

Adult↗
PubMed1991

A new optical transducer for arterial pressure measurement.

A new optical pressure transducer system (Viggo) has been assessed and compared with a standard P10 transducer (Spectramed) using a similar 20-gauge cannula, both in vitro in terms of linearity and frequency response and in vivo using an animal model. The linearity of the transducers was comparable; the resonant frequencies were 106 Hz and 75 Hz, respectively. However, the resonant frequency of the complete Spectramed system including 150-cm tubing was 11 Hz. The frequencies at which the output amplitude error exceeded 10% of the initial amplitude for the Viggo and for P10 with and without 150-cm tubing were 32 Hz, 24 Hz and 4 Hz, respectively. The principal advantage of the new transducer is that it is sufficiently compact to be mounted directly in the cannula at the wrist, so obviating the use of connecting tubing between the transducer and the cannula.

Animals↗
PubMed1991

A low-flow to-and-fro system. Laboratory study of mixing of anaesthetic and driving gases during mechanical ventilation.

The insertion of a long deadspace tube between an anaesthetic breathing system and a ventilator produces only imperfect separation of the breathing system gas from the driving gas. This laboratory study has investigated different connecting tubes to establish the maximum tidal volume possible before ventilator gas contaminates the gas in a low-flow to-and-fro system (fresh gas flow 1 litre/minute). A larger volume tube enables the use of larger tidal volumes, and plastic corrugated tubes are slightly better than black rubber corrugated tubes in this respect. The maximum tidal volume possible without contamination decreases as ventilatory rate increases, but the maximum minute volume is increased. A 22 mm plastic corrugated tube of internal volume 1.5 litres should be adequate for clinical use with the to-and-fro system described in this study at a fresh gas flow of 1 litre/minute.

Anesthetics↗
PubMed1991

Evaluation of a small soda lime canister in a to-and-fro system.

The main disadvantages of the to-and-fro system (the bulky canister and the progressive increase in apparatus deadspace) may be overcome by the use of a smaller canister. In this laboratory study, we have evaluated a 160 g canister in a low-flow to-and-fro system (fresh gas flow 1 litre/minute). Two carbon dioxide productions of 150 and 200 ml/minute were simulated. The mean times to exhaustion, defined here as a 0.5 kPa rise in end-tidal PCO2, were 112 and 79 minutes in the 150 and 200 ml/minute carbon dioxide groups respectively. Ventilation to normacapnia or hypocapnia did not affect the times to exhaustion. The soda lime absorbed 16 litres of carbon dioxide before exhaustion, and this was not affected by minute volume or carbon dioxide production. A small soda lime canister is suitable for carbon dioxide absorption in a low-flow to-and-fro system for ventilated adults.

Absorption↗
PubMed1979

Responses in sympathetic nerves of the dog evoked by stimulation of somatic nerves.

Responses in thoracic and renal sympathetic nerves evoked by electrical stimulation of cutaneous and muscle nerves in anaesthetized mongrel dogs were observed. Supramaximal stimulation of cutaneous nerves evoked two responses in both thoracic and renal nerves with latencies in the ranges 58--184 msec and 349--733 msec which are referred to as the early and late responses. It was shown that the early and late responses were evoked by group III and group IV afferent fibres respectively. Stimulation of muscle nerves of the forelimb and the hypoglossal nerve evoked smaller early responses which were considered to be due to activation of group III fibres and which had latencies in the range 92--157 msec. Supramaximal stimulation of muscle nerves in the hind limb failed to evoke any responses in approximately two-thirds of preparations and in the remainder only low level inconsistent early responses were observed. No matter how intense the stimuli applied to muscle nerves there were never any responses which could be related to the activation of group IV fibres.

Afferent Pathways↗
PubMed1979

Potential hazard of methylene blue.

The administration of methylene blue to assist the identification of insulin secreting pancreatic adenomata, during surgery in a patient with normal haemoglobin and red cells, was associated with an increase in the methaemoglobin concentration from 0.6% to 7.1%. In patients with unstable haemoglobins or abnormalities of the hexose monophosphate pathway the administration of large amounts of methylene blue is potentially dangerous.

Adenoma↗
PubMed1977

Evidence of a role for the peripheral chemoreceptors in the ventilatory response to doxapram in man.

In seven normal subjects premedicated with atropine and pethidine and lightly anesthetized with thiopentone, the ventilatory response evoked by doxapram 20 mg i.v. was delayed on average from 15.7 s to 23.0 s when changing from air to oxygen breathing. Mean VE, immediately after the administration of doxapram was increased by 3.3 litre and 1.9 litre when breathing air and oxygen respectively. These findings indicate that doxapram has an effect on the peripheral chemoreceptors and are consistent with drug activity on both peripheral and central respiratory control mechanisms.

Adult↗