The other portion passes through the bypass pathway. One stream flows into the VC and gets fully saturated with anaesthetic vapour. Hence two channels are created making the FGF entering the vapouriser divide into two streams. This percentage if inhaled is too high and dangerous to patient and has to be lowered to the safe levels. Hence, the concentration of isoflurane created is 239/760 (Pb - ambient pressure), i.e., approximately 31% V/v in the VC. For example, the Psv of isoflurane is 239 mm Hg. Here inside VC the objective is to create Psv in the space over the liquid anaesthetic agent to deliver known amount of vapour. (a) Generic simple flow over vapouriser: I − Inlet port O − Outlet port vapourising chamber Plain arrow shows fresh gas flow (FGF) Arrow with circle shows FGF carrying vapour (b) Flagg can (c) Boyle's bottle
In the recent advanced versions of the vapouriser a central processing unit in the anaesthetic machine controls the operation by continuously monitoring and adjusting fresh gas flow through the vapouriser to maintain desired concentration of the vapour. Anaesthesia trainees if exposed to draw over techniques get a deeper understanding of equipment and improved skills for disaster situations. The descendant of Oxford Miniature Vapourizer, the Triservice vapouriser is still a part of the military anaesthesia draw over equipment meant for field use whereas the Copper Kettle the first precision device is the fore-runner of the Tec 6 and Aladdin cassette vapouriser. It is fascinating to know how some of the older vapourisers, popularly used in the past, functioned. It is important to review the principles governing the design of the vapouriser to gain insight into their working. The improvements in the design was influenced by the development of potent inhalational anaesthetics, unique properties of some agents, a deeper understanding of their mechanism of action, inherent flaws in the older vapourisers, mechanical problems due to thymol deposition, factors influencing their output such as temperature and pressure variations. Vapourisers have evolved from rudimentary inhalers to the microprocessor controlled, temperature compensated and flow sensing devices, which are universal today.
0 kommentar(er)
