A Reminder to Anesthesiologists: Low-Flow Anesthesia

Abstract

Scientific letterAlthough many modern anesthesia machines are suitable for using minimal/low-flow anesthetic techniques and closed-circuit drug delivery methods, high (4-6 L/min) gas flow anesthesia is generally preferred by the majority of the anesthesiologists in routine clinical practice [1]. The aim of this brief report is to indicate the benefits and potential risks of low-flow anesthetic techniques, and to attract the attention of anesthesiologists on this important issue which is not completely clear for most of those. The classification of gas flow rates described by Baker [2] in 1994 has been well accepted by the anesthesia world (Table 1). According to this classification, gas flows less than 1 L/min are defined as low-flow anesthesia (LFA). The term of LFA is generally used to define the inhalation anesthesia techniques that have a re-breathing rate at least 50% and a semi-closed re-breathing system. Although these low-flow anesthetic techniques have been known for a long while, some reasons such as traditional anesthetic habits, little or no training in the use of these techniques during the residency, and concerns on providing a desirable anesthetic depth limited their widely use.The practical aspects of LFA Premedication, pre-oxygenation and induction of anesthesia are performed in accordance with the routine practice. After endotracheal intubation or insertion of a laryngeal mask, patient is connected to re-breathing system. LFA technique can be divided into three phases; initial high-flow, low-flow and recovery. The initial phase lasts 10 to 20 minutes, and characterized a high fresh gas flow of about 4 L/min (for example 1.4 L/min O2 and 3.0 L/min N2O). During this period, sufficient denitrogenation is obtained, the desired anaesthetic gas composition is established within the breathing system, and an essential concentration of anesthetic agents is obtained in order to ensure adequate anesthetic depth. Denitrogenation is to provide the purification of nitrogen in the blood with ventilation of 100% O2 in a high flow. Nitrogen in the lungs is removed by denitrogenation, and thus takes its place to O2. As a result of this event, functional residual capacity and the oxygen reserves increase. Denitrogenation is completed in about 6-8 min with using a fresh gas