Low-stream anesthesia represents a technique of carrying out inhalation anesthesia (usually as a part of combined) at which the fraction of return of gas mix to a reverse contour makes not less than 50% of initially inhaled volume. In this regard incorrect definitions in which low-stream anesthesia is considered as inhalation anesthesia with a stream of fresh gas less than 2 l/min (on others — less than 1 l/min) as for patients with the low body weight (children of younger age) such stream will not lead to recirculation of respiratory mix are represented, therefore, low-stream such anesthesia cannot be considered.
Along with the aforesaid, for adult patients allocate a concept of minimum and stream anesthesia (a stream of fresh gas of 0.5 l/min) and anesthesia on the closed contour (a stream of oxygen of 250 ml/min.).
As the main prerequisite to distribution of low-stream anesthesia emergence of modern expensive inhalation anesthetics, in particular, of a sevoflyuran served. It is obvious that use of low or minimum flows of gas carrier allows to reduce use of the inhalation agent in tens of times. At the same time such technique has pharmacoeconomic effect only if duration of anesthesia is not less than twenty minutes.
All narcotic and respiratory devices offered by our company (Ather 6, Ather 6D, Ather 7 and Ather 7D/C model) allow to carry out low-stream and minimum and stream inhalation anesthesia.
One of indispensable conditions for carrying out low-stream anesthesia is existence of full gas monitoring. Have to monitorirovatsya the inhaled and exhaled oxygen concentration, carbon dioxide, inhalation anesthetic and nitrous oxide (if it is used). The second condition for carrying out low-stream anesthesia is the tightness of a rebreathing system as in the presence of dumping of respiratory mix (usually at the level a contour patient) carrying out anesthesia with low flows of fresh gas will be impossible. In connection with the last requirement use only of tight devices for ensuring passability of respiratory tracts (an endotracheal tube or a laryngeal mask) is possible.
The technique of low-stream anesthesia without use of nitrous oxide includes the following stages. In the beginning there is a phase of a high stream (4–5 l/min) which can take about 10 minutes, depending on the used anesthetic and data of the patient. Ratio of oxygen concentrations and air at the same time usually 1:3. The evaporator is put at the same time on high (but not maximum) by concentration of anesthetic, before achievement of target value of IAC. After their achievement the stream of fresh gas is reduced to 0.5-1 l/min, increasing at the same time concentration of anesthetic on the evaporator (for isoflurane to 6 about. %, for a sevoflyuran — to 5 about. %). Further are guided by indicators of concentration of anesthetic on an exhalation. After the termination of the main stage of intervention, approximately in 10 minutes prior to the end of operation the evaporator is switched off and support a former stream of fresh gas. The patient is transferred to spontaneous breath in the fair-haired way or by means of the support mode pressure (PSV). In 5 minutes prior to extubation residue of inhalation anesthetic is washed away a high stream of fresh gas (5 l/min and more) then there comes awakening of the patient.
If use nitrous oxide, then the technique changes a little. The initial phase of a high stream is made with use of oxygen and nitrous oxide in the ratio 1:2. The evaporator is installed at the same time on average figures of concentration of the inhalation agent (1.5-2 about. % for isoflurane and 2–3 about. % for a sevoflyuran). Duration of this phase can be about 10 minutes. On reaching necessary value of IAC (or being guided directly by concentration of the inhalation agent on an exhalation) the stream of fresh gas is reduced to 0.5-1 l/min, at the same time the ratio of nitrous oxide and oxygen changes on 1:1. Further anesthesia is conducted, being guided by indicators of concentration of the inhalation agent and nitrous oxide on an exhalation. It is necessary to remember that oxygen concentration on a breath should not fall lower than 50% at a stream of fresh gas of 0.5 l/min. In 20-30 minutes prior to the end of operation switch off the evaporator, leaving at the same time a stream of fresh gas low. The patient is transferred to spontaneous breath, and then wash away the remained anesthesiology gases by means of a high stream (5 l/min and more) in 5–10 minutes prior to extubation.
At a stream of fresh gas of 0.5 l/min it is also less necessary to consider the volume of gas which gets from a contour for the purpose of the subsequent analysis as its average speed of a fence can reach 200 ml/min. when using a gas analyzer of a roundabout stream. Therefore for carrying out minimum and stream anesthesia it is desirable to use the devices possessing function of return of the analyzed gas to a contour. Some models narcotic and respiratory the device independently return the studied gas, others demand accession of the additional line in a contour for return.