There are two important partition coefficients that describe solubility of volatile agents in body tissues. One is the blood:gas (B:G) partition coefficient and the other the oil:gas (O:G) partition coefficient.
The value of the oil:gas partition coefficient is determined by the lipid solubility of the anaesthetic agent.
Question: Why might lipid solubility be related to potency of the volatile and gaseous anaesthetic agents?
|
Agent |
MAC (%) |
O:G partition coefficient |
|---|---|---|
|
Isoflurane |
1.2 |
98 |
|
Sevoflurane |
2.0 |
80 |
|
N2O |
103.0 |
1.4 |
Table 1 The MAC values and oil:gas (O:G) solubility of commonly used anaesthetic agents
There are two important partition coefficients that describe solubility of volatile agents in body tissues. One is the blood:gas (B:G) partition coefficient and the other the oil:gas (O:G) partition coefficient.
The value of the oil:gas partition coefficient is determined by the lipid solubility of the anaesthetic agent.
Question: Why might lipid solubility be related to potency of the volatile and gaseous anaesthetic agents?
Answer: Because they must reach the CNS to have their effect and this requires them to cross the blood-brain barrier. Only lipid-soluble drugs can gain access to the brain.
Question: Looking at Table 1, does the order of potency follow the order of O:G solubility?
|
Agent |
MAC (%) |
O:G partition coefficient |
|---|---|---|
|
Isoflurane |
1.2 |
98 |
|
Sevoflurane |
2.0 |
80 |
|
N2O |
103.0 |
1.4 |
Table 1 The MAC values and oil:gas (O:G) solubility of commonly used anaesthetic agents
There are two important partition coefficients that describe solubility of volatile agents in body tissues. One is the blood:gas (B:G) partition coefficient and the other the oil:gas (O:G) partition coefficient.
The value of the oil:gas partition coefficient is determined by the lipid solubility of the anaesthetic agent.
Question: Why might lipid solubility be related to potency of the volatile and gaseous anaesthetic agents?
Answer: Because they must reach the CNS to have their effect and this requires them to cross the blood-brain barrier. Only lipid-soluble drugs can gain access to the brain.
Question: Looking at Table 1, does the order of potency follow the order of O:G solubility?
Answer: Yes. In potency order from most to least potent, we have isoflurane > sevoflurane > N2O and this is the same as for lipid solubility.
|
Agent |
MAC (%) |
O:G partition coefficient |
|---|---|---|
|
Isoflurane |
1.2 |
98 |
|
Sevoflurane |
2.0 |
80 |
|
N2O |
103.0 |
1.4 |
Table 1 The MAC values and oil:gas (O:G) solubility of commonly used anaesthetic agents