In the High and Low Flow Anesthesia, the Relationship Between the Anesthetic Agent Concentration and Time Constant

Abstract

Anesthesia vaporizer is a device that is used to vaporize a liquid anesthetic agent and to deliver a controlled amount
to the patient. The most problems during the anesthesia application are caused from the fault of the personnel. Because of
this, the error of the dose must be guessed. In result, the controlling and the measuring of the concentration of anesthetic
agent causes the application of anesthesia safely. In anesthesia technique, the term that defines the reflection time of the
changes of anesthetic agent concentration in fresh gas to the anesthetic agent concentration in the breath system, is time
constant. The objective of this study, in the high and low flow anesthesia, is to investigate the relationship between the
anesthetic agent concentration and time constant, and to attract attention to this relationship during the delivering of
anesthesia and during the calibration measurements. In this study, the concentrations of the anesthetic agents were measured
from the breath system by using Flow analyser. In high flow anesthesia, the flow was stable at 4L/min during all
measurements. The anesthetic agent (isoflurane, sevoflurane) was adjusted to the 2% of concentration. The measurement
time was 45 min. In the software-Flowlab, the changes of the anesthetic agent were investigated from the graph and the time
point that the agent concentration became to the stable, was recorded. In low flow anesthesia, firstly, flow was 4L/min in
approximately 20 minutes, after, this flow was decreased to the 1L/min and all concentration measurements were repeated.
Thus, in high and low flow anesthesia, it was possible to investigate the relationship between the anesthetic agent
concentration and time constant. By decreasing the current of fresh gas, it was seen that the anesthetic agent concentration
decreased. In low flow anesthesia, the changes in the agent concentration of fresh gas reflected to the concentration of
agents in the breath system in a long time.