D. C. White

Topography of the lumbar epidural space.: A study in cadavers using injected polyester resin

Polyester resin was injected into the epidural space of fresh adult cadavers to study the shape of the lumbar epidural space and the spatial relationship between the dura mater and vertebral canal. In most of the anatomical preparations the shape of the lumbar dural sac was distinctly triangular and in some cases a dorso‐median fold of the dura was apparent. These observations support the explanation suggested by others to account for the midline translucency seen in contrast radiological examination of the lumbar epidural space. Factors which may influence the shape and dimensions of the lumbar epidural space are discussed. It is suggested that these anatomical observations may have clinical significance in the practice of lumbar epidural analgesia.

Evaluation of the Datex ‘Normac’ anaesthetic agent monitor

The Datex ‘Normac’ infrared anaesthetic agent monitor has been evaluated for accuracy of calibration, stability and speed of response. Accuracy was assessed by comparing with a gas chromatograph calibrated using volumetric standards and was found to be very good for isopurane and enflurane but was slightly less accurate for halothane, due to a low signal: noise ratio. The stability of the instrument was found to be exceptionally good. The response time is dependent on the sampling rate and we found that, in practice, the instrument would record the end expired anaesthetic concentration on patients breathing up to 15 breaths/minute. The instrument is compact and convenient for use in operating theatres.

Isoflurane concentrations using uncompensated vaporisers within circle systems

In a series of studies designed to investigate the need for a temperature‐compensated vaporiser for use in a circle system, we first studied temperature changes within and isoflurane concentration delivered by a Komesaroff vaporiser during bench tests using different gas flows. Agent temperature and vapour concentration decreased as predicted by the Antoine equation. Using the vaporiser within a circle system during clinical anaesthesia, we then studied 20 patients breathing spontaneously and a further 10 patients receiving controlled ventilation, measuring the temperature of the agent within the vaporiser and the concentration of agent inspired by the patient. In clinical use with the fresh gas flows of 1–3 l.min−1, the inspired agent concentration did not decrease despite the decrease in temperature of the liquid isoflurane in the vaporiser.

Controlled ventilation using isoflurane with an in-circle vaporiser

We studied 19 patients anaesthetised for routine surgery using isoflurane delivered from a Komesaroff vaporiser mounted within a circle system. Their lungs were ventilated using a Penlon Nuffield ventilator attached to the circle system by a trunk of tubing. Fresh gas flow rates of 1, 2 or 3 l.min−1 were used. The inspired agent concentration was measured using a Datex Ultima multigas analyser and was found to be stable and easily controlled.

Respiratory feedback effects on vaporisers in circle systems

We studied a group of spontaneously breathing patients anaesthetised for routine orthopaedic surgery using a circle system and isoflurane in a Komesaroff vaporiser within the circle. We observed and recorded: (1) the change in inspired isoflurane concentration caused by changing the fresh gas flow, (2) the increased respiration produced by surgical stimulus and the resulting increase in isoflurane concentration, (3) the respiratory depression produced by opioids and the consequent decrease in isoflurane concentration. We consider this regulation of anaesthetic uptake by the patient to be beneficial.

Evaluation of the Lamtec anaesthetic agent monitor.

The Lamtec agent monitor is a compact anaesthetic analyser designed to measure halothane, isoflurane and enflurane. It shows good linearity and stability. The faster model can be used for end‐tidal measurements up to 25 breaths per minute. Calibration using a standard of the gas to be measured is recommended.

A semiquantitative analysis of the dynamics of a Goldman‐type vaporiser

When a turbulent flow of a carrier gas is passed over a liquid anaesthetic agent contained in a vaporiser of Goldman design, evaporation from the cooled surface leads rapidly to a succession of fluid instabilities which set in at characteristic critical conditions. An initially quiescent boundary layer at the surface is sequentially replaced by a thin layer of toroidal (Bénard–Marangoni) convection cells which are driven by surface tension gradients. These are then augmented by Rayleigh–Bénard convection driven by gravity, the whole process terminating in intermittent columnar plunging of cold fluid from a chaotic surface layer of pulsating thickness to the base of the liquid pool. Residual striations from these plunging columns persist throughout the bulk of the liquid so long as evaporation continues. The ultimate state is then one in which turbulence occurs throughout both liquid and vapour phases. In this paper, a semiquantitative analysis of the system dynamics is given with supportive experimental evidence where possible.

Follow‐up of reported awareness

[ I ] KUMAR CM. Lignocaine gel 2% per rectal as an adjunct to general anaesthesia for annal stretch. Anaesthesia 1988; 43: 614. [2] ADRIANI J, ZEPERNICK R. Clinical effectiveness of drugs used for topical anesthesia. Journal of the American Medical Association 1964, 188: 71 1-6. [3] Scorr DB, LITTLEWOOD DG, COVINO BG, DRUMMOND GB. Plasma lignocaine concentrations following endotracheal spraying with an aerosol. British Journal of Anaesthesia 1976;

Vacuum stethoscope for respiratory monitoring

Vacuum stethoscope for respiratory monitoring Comments from my colleagues lead me to believe that I am not alone in finding some clarification from Dr Ginott is needed in connection with the description of his respiration monitor device (Anaesthesia, 1977, 32, 896). A drawing of the stethoscope would be helpful as would an explanation of its modus operand. Is making the tape recording an essential part of the procedure? Or is the anaesthetist listening as the tape is being made, in which case the recorder is simply being used as an amplifier? Is the anaesthetist listening with an ear-piece as the mention of a monitor connection suggests or is he listening to the recorder’s loud speaker as the reference to hearing sounds from a distance of 3-4 m implies?