GENERAL ANESTHETIC

General anesthesia

Reversible Loss of Consciousness and Insensibility to Painful Stimuli

Amnesia

Unconsciousness

Analgesia

Inhibition of autonomic reflexes

Skeletal muscle relaxation

Neurophysiologic state produced by general anesthetics is characterized by five primary effects

• Rapid and pleasant anesthetic induction and recovery

• Induce anesthesia smoothly and rapidly while allowing for prompt recovery after its administration is discontinued

• Rapid changes in anesthetic depth

• Adequate relaxation of skeletal muscles

• Wide margin of safety

• Absence of toxic effects or other adverse properties in normal doses

Properties of an ideal general anesthetic

Balance anesthesia

Combination of IV and inhaled drugs

Monitored anesthesia care

For minor superficial surgery or for invasive diagnostic procedure

Monitored anesthesia care

This is a Sedative + Local Anesthetic

Neuroleptics and Opioids

Augments the action of GA

1. Preoperative drug: Benzodiazepine

2. Induction: IV agent (Thiopental or Propofol)

3. Maintenance:

combination of inhaled (nitrous oxide, vol liquids) or IV drugs (propofol, opioid)

For extensive procedure of balanced anesthesia

1. Preoperative drug:

2. Induction:

3. Maintenance

Stages of general anesthesia

The guedel’s signs or also known as?

Stage 1 –Analgesia

Stage 2 –Excitement

Stage 3 - Surgicalanesthesia

Stage 4 –Medullarydepression

Stages of anestehsia

Stage 1: Analgesia

This is analgesia without amnesia

Stage 1: Analgesia

Later in this stage both analgesia and amnesia are produced

Stage 2: Excitement

This is now causing delirium

Stage 2: Excitement

Respiration is rapid, and heart rate and blood pressure increase

Stage 3: Surgical anesthesia

Slowing of respiration and heart rate and extends to complete cessation of spontaneous respiration (apnea)

Stage 4: Medullary depression

Severe depression of the CNS without circulatory and respiratory support death would rapidly ensue

Stage 2: Excitement

Respiration is irregular both in volume and rate

retching and vomiting may occur

Retching

movements of vomiting w/o actually doing so.

Stage 2: Excitement

From loss of consciousness to beginning of regular respiration.

Stage 3: Surgical anesthesia

This stage begins with the recurrence of regular respiration and extends to complete cessation of spontaneous respiration.

Stage 3: Surgical anesthesia

Divided into 4 planes

Plane 1: Roving eye ball

Plane 2: Loss of corneal and laryngeal reflexes

Plane 3: Pupil starts dilating and light reflex is lost

Plane 4: Intercostal paralysis, shallow abdominal respiration, dilated pupil.

The 4 planes in stage 3

eyelash reflex

regular respiratory pattern

The most reliable indication that stage III has been achieved is loss of the ____ and establishment of a ___.

Stage IV (medullary depression)

This stage of anesthesia includes severe depression of the vasomotor center in the medulla as well as the respiratory center.

Stage IV (medullary depression)

Cessation of breathing to failure of circulation and death.

Pupil is widely dilated,

muscles are totally flabby

pulse is thready or imperceptible and

BP is very low.

Induction

This level encompasses the administration of preoperative medications, adjunctive drugs to anesthesia, and the anesthetics required for surgery.

Maintenance

This level begins when the patient has achieved a depth of anesthesia sufficient to allow the surgery to begin and ends upon the completion of the surgical procedure.

Recovery

begins with the termination of the surgical procedure and continues throughout the postoperative recovery period until the patient is fully responsive to his or her environment.

1. Inhalational

2. Intravenous

3. Rectal (rare)

TYPES/ROUTES OF ADMINISTRATION OF GENERAL ANESTHETICS

Gaseous

Volatile liquid

2 types of inhalational anesthetic

Volatile anesthetic

have low vapor pressures and high boiling point

Gaseous anesthetic

Have high vapor pressures and lowboiling points

Methoxyflurane,

halothane,

enflurane,

isoflurane,

desflurane,

sevoflurane

Example of Volatile anesthetic

Nitrous oxide

Xenon

Example of Gaseous anesthetic

Depth of anesthesia is dependent upon the concentration of anesthetic in the central nervous system.

Pharmackokinetic of General Anesthetic

blood : gas partitioncoefficient

A useful index of solubility and defines the relative affinity of an anesthetic for the blood compared with that of inspired gas.

halothane >enflurane >sevoflurane >isoflurane > desflurane > nitrousoxide

In terms of the extent of hepaticmetabolism, the rank order for the inhaled anesthetics

blood:gas partition coefficient

inspired air concentrations

breathing rate

Factors to consider in Induction

blood:gas partition co-efficient

low blood:gas partition coefficient

1. low solubility in blood

reaches high arterial tensions rapidly, which in turn results in rapid equilibration with the brain

2. fast onset of action.

3. necessary for quick removal of anaesthetic.

oil:gas partition coefficient

High oil: gas coefficient

cause quick redistribution into adipose tissue

Redistribution into fat causes the recovery of consciousness

Weight and fat ratio of a patient

Considerations for the oil: gas partition coefficient

Fick's law

Increase in the inspired anesthetic concentration

• increase the rate of induction of anesthesia by increasing the rate of transfer into the blood according to ___

lungs

Volatile anaesthetics are eliminated in the terminal phase via the ___.

slow

hangover

When oil:water coefficient is high elimination will be , giving a prolonged _effect.

Ach,

AMPA (amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid),

NMDA (N-methyl-D-aspartate)

MOA of Impaired excitatory transmission

Chloride channels

(GABA and Glycine receptors)

Potassium channels

MOA of Potentiated inhibitory effects

Minimum alveolar concentration

the anesthetic concentration that produces immobility in 50% of patients exposed to a noxious stimulus.

MAC

Anesthetic potency is currently described by the ___.

They increase the sensitivity GABAA receptors. This causes a prolongation of the inhibitory chloride ion current after apulse of GABA release. Postsynaptic neuronal excitability is thusdiminished.

• They block the excitatory postsynaptic current of the nicotinic receptors.

MOA of the Inhaled general anesthetic

ETHER

Slow onset, recovery,explosive

CHLOROFORM

Slow onset, verytoxic

CYCLOPROPANE

Fast onset, but very explosive

Nitrous oxide

Low potency, quickrecovery

–Needs other agents for surgical anesthesia

Weak anesthetic, powerfulanalgesic

Hypoxia

Inhibits vitamin B-12metabolism

Hysterical laughing

Side effect of nitrous oxide

Nitrous oxide

Also known as Laughing gas

30% Nitrous oxide

70% Oxygen

The component of Nitrous oxide in dental surgery

Xenon

An inert gas

Nonflammable andnonexplosive.

A potent analgesic

NMDA receptor

What is the receptor in Xenon?

Methoxyflurane

Diffuses into fattytissue

Fluoride oxalic acid

Methoxyflurane metabolised to?

Penthrox

BN of methoxyflurane

Halothane

Halogen substitutedethane

Halothane

Fast induction of anesthesia and fast recovery potent anesthetic and relatively weak analgesic

Halothane

1st halogenated volatile anesthetic agent

Trifluoroethanol

Halothane is metabolized to

Child: Nonhepatotoxic

Adult: Hepatotoxic and can cause arrthymia

Effect of Halothane in child and adult

Enflurane

Isoflurane

Give an anesthetic that is Rapid, smooth induction and Pungent odor

Enflurane

causes electroencephalographic (EEG) patterns consistent with electrical seizure activity,

Seizure disorder

CI of enflurane

isoflurane

structural isomer ofenflurane

Isoflurane

There have been no reports of seizures

Isoflurane

Effects have Bronchoirritating, laryngospasm

Coronary steal syndrome

Isoflurane causes what syndrome?

Coronary steal syndrome

There is an alteration in the circulatoin pattern

Desflurane

Very fast onset and offset and Very pungent

Desflurane

It can cause breath holding, coughing, and laryngealspasm

Desflurane

Not recommended for induction of anesthesia in children

Sevoflurane

Rapid induction and Low pungency

Sevoflurane

Breakdown by CO2 absorbents generates heat and has resulted in sporadic operating roomfires.

THIOPENTAL

PROPOFOL

ETOMIDATE

KETAMINE

OPIODS

Intravenous anesthetics

Thiopental

Act at GABAreceptors (inhibitory), potentiate endogenous GABA activity at the receptor, direct effect on Cl- channel at higher concentration

Thiopental

Build-up in adiposetissue

1) Hypotension

2) Airway obstruction

3) Apnea

Side effect of thiopental

Nitrous oxide

Gas at RT, liquid under pressure in metal cylinders

Nitrous oxide

This is the least toxic anesthetic also the least potent

Nitrous oxide

intermittent dosing for analgesia during dental procedures and the first stage of laborn

Nitrous oxide

Can cause second gas effect?

Second gas effect

causes an increase in the concentration of the other gases

Second gas effect

Reduce the risk of myocardial depression at a given depth of anesthesia compared to the more potent anesthetic given alone

Weak agent

Hypoxia

Bone marrow depression (megaloblastic anemia)

Disadvantage of nitrous oxide

Propofol

Asedative–hypnotic used for the induction and maintenance of anesthesia or sedation

Propofol

An alkyl phenol

Egg lecithin emulsion

Propofol originally formulated in?

Propofol

For anaphylactoid reaction

1%propofol in 10% soybean oil,

2.25% glycerol, 1.2% egg phosphatide

Current formulation of Propofol

Etomidate

Structure similar toketoconozole

Carboxylic acid

Etomidate is metabolized to?

Etomidate

Insoluble in water, formulated in 35% propylene glycol

1) Myoclonic activity

2) Nausea and vomiting(50%)

3) Cortisol suppression

4) Pain on injection

Side effect of etomidate

Addisons disease

This is a disease where the body doesn’t make enough cortisol