Efficient application of volatile anaesthetics: total rebreathing or specific reflection?

The circle system has been in use for more than a 100 years, whereas the first clinical application of an anaesthetic reflector was reported just 15 years ago. Its functional basis relies on molecular sieves such as zeolite crystals or activated carbon. In a circle system, the breathing gas is rebreathed after carbon dioxide absorption; a reflector on the other hand specifically retains the anaesthetic during expiration and resupplies it during the next inspiration. Reflection systems can be used in conjunction with intensive care ventilators and do not need the permanent presence of trained qualified staff. Because of easy handling and better ventilatory capabilities of intensive care ventilators, reflection systems facilitate the routine use of volatile anaesthetics in intensive care units. Until now, there are three reflection systems commercially available: the established AnaConDa™ (Sedana Medical, Uppsala, Sweden), the new smaller AnaConDa-S™, and the Mirus™ (Pall Medical, Dreieich, Germany). The AnaConDa consists only of a reflector which is connected to a syringe pump for infusion of liquid sevoflurane or isoflurane. The Mirus represents a technical advancement; its control unit includes a gas and ventilation monitor as well as a gas dispensing unit. The functionality, specific features, advantages and disadvantages of both systems are discussed in the text.

The Gillies anaesthetic machine.

The Gillies anaesthetic machine was produced commercially after 1941. It was probably the first British true circle apparatus. Notably it incorporated a vaporiser inside the circle. There were serial modifications culminating in the Mark III apparatus of 1951, which continued in use through the 1960s. From 1955 the superior efficiency in carbon dioxide absorption of a true circle apparatus over the rival Coxeter-Mushin 'circle' absorber became realised.

[Theory and practice of low-flow anaesthesia].

The article depicts the history of inhalation anesthesia and closed system anesthesia. Closed or almost closed anesthesia systems have been in use since 1850. At that time, the anesthetic agent was chloroform. It was administered via a closed system, where potassium hydroxide was utilized as a carbon dioxide scavenger. However, that kind of CO2 absorption method did not gain acceptance. Later, a quick and effective method of carbon dioxide absorption was developed when the first soda-lime absorber was introduced in 1917. In the mid 1950's, when halothane was brought forth, the use of low-flow and closed circle system anesthesia diminished significantly. This was largely due to the inherent problem in the first generation halothane vaporizers, which was the unreliable delivery of vapor at low fresh gas flows. Introduction of isoflurane in the early 1980's, gave way to a renewed interest in low flow and closed circuit anesthesia. It was further enhanced by the fact that anesthetic agents are atmospheric pollutants, especially nitrous oxide, halothane, enflurane, and to some extent isoflurane. The introduction of new low solubility agents, like desflurane and sevoflurane, have initiated a renaissance in the use of low-flow anesthesia, in order to contain costs associated with adapting fresh gas flows to patient demand.

The leech airway or pharyngeal bulb gasway.

Beverley Charles Leech (1898 to 1960) patented the Leech airway or "Pharyngeal Bulb Gasway" in 1937. The Leech airway formed a seal with the pharyngeal tissues, resulting in a closed system during cyclopropane anaesthesia. Two prototypes and four commercially available versions of the airway have been identified.

Closed system anaesthesia--historical aspects and recent developments.

Closed circuit anaesthesia was described decades ago but did not achieve wide popularity among anaesthesiologists mainly because reliable control of inspiratory gas concentrations was not possible. Recent innovations including fast gas analysers, electronically controlled dosage systems and algorithms for feedback control have made possible the development of sophisticated closed circuit ventilators designed for routine clinical practice. The main advantages comprise economic use of medical gases and volatile anaesthetics, reduction of anaesthetic gas loss into the atmosphere, improved airway acclimatization as well as estimations of oxygen consumption. This article reviews historical aspects, recent developments as well as advantages and limitations of closed system anaesthesia.

[John Snow (1813-1858): experimental studies on rebreathing of anesthetic gases in exhaled air]. / John Snow (1813-1858): Experimentelle Untersuchungen zur Rückatmung der in der Ausatemluft enthaltenen Narkosegase.

As early as in 1850 (only 4 years after the first clinical performance of ether anaesthesia by W. T. G. Morton on 16 October 1846) John Snow recognised that ether and chloroform were exhaled unchanged with the expired air. To reuse these unchanged vapours in the following inspiration and thereby prolonging the narcotic effect of a given amount of anaesthetic vapour, he converted his ether inhaler into a To-and-Fro Rebreathing System: The apparatus was equipped with a facemask without an expiratory valve and a large reservoir bag containing pure oxygen; an aqueous solution of caustic potash was used as CO2 absorbent. In several experiments, performed on himself, Snow succeeded to demonstrate that rebreathing of the exhaled vapours was possible following carbon dioxide absorption, and that it resulted in a pronounced prolongation of the narcotic effects of the volatile anaesthetics. Furthermore, Snow performed experiments on animals using a closed system for evaluating the carbon dioxide production during anaesthesia. It is all the more worthwhile to introduce Snow's publications on these topics, as, despite their extraordinary theoretical and practical significance, they remained nearly unnoticed. Even in the fundamental articles by D. Jackson and R. Waters, both being the respected protagonists of the rebreathing technique in anaesthesia, the Snow papers remained uncited.

Closed carbon dioxide filtration revisited.

There are compelling reasons why the closed carbon dioxide filtration method for inhalation anaesthesia deserves serious reconsideration. Use of the closed absorption system today can provide all the benefits recognised by those who introduced it seventy to eighty years ago. A most important benefit is the increased opportunity of learning afforded the user, which leads either neophyte or senior clinician to improvement of both concept and clinical skills. The current resurgence of interest is fully appropriate for all physicians who aspire to be true specialists in the care of patients during clinical anaesthesia.