Meeting Abstracts  |   May 1997
Low Flow Anaesthesia Symposium 1996 of the Association for Low Flow Anaesthesia 
Author Notes
  • Department of Anesthesiology, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Road, UHS-2, Portland, Oregon 97201–3098.
Article Information
Meeting Abstracts   |   May 1997
Low Flow Anaesthesia Symposium 1996 of the Association for Low Flow Anaesthesia 
Anesthesiology 5 1997, Vol.86, 1223. doi:
Anesthesiology 5 1997, Vol.86, 1223. doi:
Low Flow Anaesthesia Symposium 1996 of the Association for Low Flow Anaesthesia. Edinburgh, Scotland, October 31-November 1, 1996.
The first of anticipated annual symposia organized by the Association for Low Flow Anaesthesia (ALFA) was held in Edinburgh, Scotland, on October 31 to November 1, 1996. The new Association hopes to provide a forum for exchange of ideas and to encourage research on any aspect of low flow anesthesia (LFA). Formation of ALFA reflects renewed interest in this approach to inhalation anesthesia.
The initial symposium, a two half-day affair, offered 10 invited presentations. In the first presentation, Professor A. A. Spence (Edinburgh), President of ALFA, suggested reasons for renewed interest in LFA. These included prohibitive cost of new volatile agents when used in anything but a low flow setting and availability of reliable monitors of respired gases. Previous dependence on high gas flows to predict inspired gas concentrations can now be replaced confidently by use of agent-specific monitors.
Four speakers reported on current research on older topics that now are being revisited because they have special relevance in LFA. Dr. D. C. White (Northwick Park) described how agent monitors have mitigated earlier concerns about in-circuit vaporizers. He offered data on the effects of minute ventilation, vaporizer temperature, and fresh gas flow on agent concentration when using these vaporizers. He suggested that with agent monitors in widespread use, there is a role in LFA for these cheap, simple, low-maintenance devices. Dr. J. Murray (Belfast) reviewed the history of carbon dioxide absorption in anesthesia and discussed current research on alternatives to existing chemical methods. These include zeolite molecular sieves and a new chemical (nonregenerative) formulation to be introduced in the near future. Professor G. Rolly (Ghent) also spoke on the role of soda lime in the accumulation of carbon monoxide and degradation products of halothane during LFA. He noted the desire to reduce cost of desflurane anesthesia by use of LFA requires attention to possible interaction of the drug with soda lime and baralyme. Professor Rolly also reviewed data on accumulation of nitrogen, methane, acetone, and ethanol during LFA and warned about the danger of gas monitors interpreting trace gases as being the anesthetic. The anesthesiologist may believe patients are asleep when they are not.
Dr. M. Halsey (Oxford) reminded us that 1996 is the fiftieth anniversary year of the first report of the anesthetic effects of xenon. Xenon, being totally inert, has been useful in studies of the mechanisms and toxicity of anesthetics. Dr. Halsey wonders if its other attributes, low tissue solubility, potency slightly greater than nitrous oxide, and minimal cardiovascular and respiratory depression, warrant attempts to overcome limitations to its use, especially manufacturing cost. He urged clinicians to study whether there is an important niche for the drug.
Use of nitrous oxide and oxygen in closed systems or at near-closed system gas flows is not new. Dr. G. Lockwood (London) has taken a fresh look at factors governing nitrous oxide accumulation and resultant decrease of circuit oxygen concentrations during LFA. He suggested approaches to predict the effect of variations in oxygen and nitrous oxide uptake on the concentration of oxygen, which will develop during the course of anesthesia.
Professor Rolly presented a second paper in which he described quantitative closed system anesthesia via servocontrol of anesthetic agent delivery. It allows rapid increase and decrease of alveolar concentration of the volatile agent, the former by computer-controlled liquid injection, the latter by use of charcoal filters.
Favorable attributes of sevoflurane and desflurane have provoked much interest in LFA to reduce cost of using them, although increased levels of carbon monoxide with desflurane and compound A with sevoflurane in LFA cause alarm. Dr. M. Nathanson (Nottingham) thoroughly reviewed the sevoflurane-compound A-LFA problem. The importance of the finding is not settled, although there is meager clinical evidence for a problem. He suggested facets needing further study.
Dr. M. Logan (Edinburgh) assessed the pharmacoeconomics of LFA. Calculation of true savings, although seeming simple, can be complex. Dr. Logan expressed the savings in terms of how many anesthetics are required with a LFA approach to realize cost savings over a high flow approach.
The final paper was given by a master of the physics of anesthesia, Professor W. Mapleson (Cardiff). Inhaled induction is abetted by initial use of high gas flows. Professor Mapleson presented computer-generated models depicting practical sequences of fresh gas flows and delivered concentrations to allow the advantage of high flows for rapid induction, but economical, low flows for maintenance.
A second symposium is planned for late 1997 in Belfast, Northern Ireland. Those interested in ALFA should contact Dr. M. Logan, Department of Anaesthetics, Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh, EH3 9YW, UK. fax: 0131 536 3672.
Wendell C. Stevens, M.D.
Department of Anesthesiology, Oregon Health Sciences University
3181 S.W. Sam Jackson Park Road, UHS-2
Portland, Oregon 97201–3098