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―AA‖ stands for one of such five anesthetic gases as Des, Iso, Enf, Sev, or Hal.
18.4
MAC Value
As a basic index reflecting the depth of inhalation anesthesia, MAC (minimum alveolar concentration) is
defined by the standard ISO21647 as the alveolar concentration of an inhalational anesthetic agent in
balanced state in the absence of any other anesthetic agent, which can prevent the body movements of 50%
patients under a standard surgical stimulation.
Below are the 1MAC values for inhalational anesthetic agents:
Anesthetic
Agent
DES
ISO
ENF
SEV
HAL
N2O
1MAC
7.3%*
1.15%
1.7%
2.1%
0.77%
105%**
*: This figure comes from a 25-year-old patient.
**: This 1MAC value for N2O is only obtained in a high-pressure chamber.
Caution
The above data of a 40-year-old healthy male patient comes from ISO21647 and is published by
FDA.
In practice, such factors as age and weight may influence the effect of inhalational anesthetic
agent.
Below is the formula to calculate the MAC value in the presence of one or more anesthetic agents:
―N‖ stands for the number of all anesthetic agents (including N2O) detected by the AG module;
―EtAgenti‖ stands for the end-tidal concentration of each inhalational anesthetic agent; and ―AgentVoli‖
stands for the 1MAC value of each inhalational anesthetic agent.
For example, if the AG module finds that the end-tidal gas for the patient contains 4% DES, 0.5% HAL
and 50% N2O, the MAC value will be:
Caution
The above formula is applicable to adults.
18.5
Preparations for Measurement
