SummaryBench testing was carried out to establish whether the vapour output from an OMV50 vaporizer, as used in the Triservice apparatus, difers according to whether the carrier gas is either drawn or pushed through the vaporizer. Results show that the diferences in output concentration between the two modes were clinically insign8cant. Key wordsAnaesthetic techniques; drawover, inhalation. Equipment; Triservice anaesthetic apparatus.The Triservice apparatus based on the use of the OMVSO vaporizer (Penlon) [l] was primarily designed to function as a drawover system for spontaneously breathing patients. When used for positive pressure ventilation this principle holds true with the vaporizer upstream of the self-inflating bag or suitable mechanical ventilator. The ventilator is used to suck the gas through the vaporizer instead of the patient's own inspiratory effort.The British Army field anaesthesia kit includes the Cape TC50 ventilator (Penlon) which can be used with the Triservice apparatus [2] (Fig. 1). This is a small, robust and simple ventilator. It works on the principle of a rubber bellows which sucks in fresh gas when it is expanded by a spring. The gas is then expelled from the bellows under the influence of a piston pushed by a cam. This is powered by a 240 v AC electric motor. There is a one-way valve on the gas intake and a Laerdal Resuscitator non-rebreathing valve at the patient end of the system. Both these valves are required to ensure the correct flow of anaesthetic gas. The ventilator is designed so that the two OMV50 vaporizers can be placed on the built-in back-bar. The apparatus is conventionally used as a drawover system, with the ventilator downstream of the supplementary oxygen and the vaporizers. This arrangement works very well [3].Unfortunately, in the field, this configuration of the apparatus is not always convenient. It may become necessary, for a variety of reasons, to have the vaporizer between the ventilator and the patient. These reasons include: (1) The Triservice apparatus was originally designed to use a self-inflating bag as the means of performing intermittent positive pressure ventilation (IPPV). The complete set-up could then be sat easily upon the shelf at the head of the Macvicar operating table. The TC50 ventilator is significantly heavier than a self-inflating bag, therefore in field use it is usually more convenient and practical to position it on the ground. In order to view the agent level window, or @ able to adjust the control lever whilst holding a mask on the patient's face, it is far easier and safer to position the OMV50 vaporizer on the shelf attached to the table rather than attach it to the back-bar of the TCSO. This means that the vaporizer must be between the ventilator and the patient. (2) The length of tubing required for the breathing system in drawover set-up is considerably greater than that required if the vaporizer can be positioned on the shelf between the ventilator and the patient. When lengths of tubing get lost or damaged in the field this ...

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Summary An obstetric epidural performed for analgesia showed a changing pattern of neurological block. The original features suggestive of a subdural block were complicated when aspiration of cerebrospinal fluid from the catheter became possible. Subsequent management as a continuous subarachnoid catheter allowed delivery.

A case is described in which a patient was unable to be weaned from ventilatory support whilst the trachea remained intubated. She was successfully weaned using a laryngeal mask.

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