Amnesia prevent memory formation eg barbiturates

Amnesia – prevent memory formation
( e.g., Barbiturates )

Attenuation of autonomic responses
( e.g.,anti-cholinergics )
paralytics

General Anesthesia Approaches
Induction

Progressive deepening of anesthesia as concentration  at sites of action

Surgical anesthesia is reached before body water & fat stores reach equil.

Induction w/ inhaled agents, higher conc. than maintenance ;
Maintenance

Keep patient at proper level of anesthesia during surgical procedure

Accomplished w/ inhaled agents; but more likely includes IV agent

Conc. of inhaled agent is lowered from induction phase

Choice of agent(s) depends upon length of procedure being done
Recovery

Recovery is based on the same factors as induction ( reversed )

D/C of low-soluble agent results in rapid  in arterial concentration

With high solubility agents, arterial concentration falls more slowly

Recovery can be accelerated by stimulating respiration

Clearance of anesthetic agent can speed process

Complications
- General Anesthesia
Induction

Overdose

Some patients require more anesthetic

Airway disturbances
Maintenance

Keeping patient asleep & alive for a long procedure

Sudden changes in fluid / blood volume

Acute need for more muscle relaxation
Recovery

Period of irrationality

Pain

Compromised body system(s) function

Restlessness

General Anesthesia:
Inhaled Anesthetics

1. Affect nerve transmission in the brain

Low-doses  Substantia gelatinosa in spinal cord

Higher doses   distribution to other brain regions
2. Mechanism of Action:

Allosteric modulator GABA
A
-receptor

Activation of glycine receptor

Antagonize NMDA-receptor
3. Gases & vapors are soluble in blood, tissue fluids &
tissues
4. Inhaled anesthetics are generally lipophilic
5. Administered & eliminated by respiratory tract
6. Requires continuous administration
Inhaled Anesthetics

Inhaled Anesthetic Agents:
Gases and Volatile Liquids
Nitrous oxide – N
2
O
Diethylether – C
4
H
10
O
Halothane – C
2
ClF
3
HBr
Enflurane – C
3
ClF
5
H
2
O
Isoflurane – C
3
ClF
5
H
2
O
Desflurane – C
3
F
6
H
2
O
Sevoflurane – C
4
F
7
H
3
O

Phyisco-chemical Properties of Inhaled
Anesthetics

Ether ( R -O- R ) hydrocarbons (volatile liquids)

Modern ethers contain 4 or less carbons

Halogenation (F, Cl, Br, I)

Impacts potency, flammability, metabolism, and arrhythmic
properties

Potency

The larger (heavier) the halogen , the more potent the agent

Direct correlation between lipophilicity  potency

Phyisco-chemical Properties of Inhaled
Anesthetics

Flammability

Nitrous oxide (N
2
0) is non-flammable but is combustible
when it breaks down; i.e., oxidizer

Halogenated ethers are much less flammable

Chemical stability

Halogen substitution of H atoms  stability

Metabolism

Desflurane: ~ 0.05% metabolism

Isoflurane: ~ 1% metabolism

Sevoflurane: ~ 2- 5% metabolism

Enflurane: ~ 8% metabolism

Halothane: ~ 40% metabolism

Absorption / solubility of anesthetic gases
Drug is less soluble in blood
Drug is more soluble in blood

Transport of gas via simple diffusion

Series of partial pressure (pp) gradients