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Sleep induction Loss of pain responses Amnesia Skeletal muscle relaxation Loss of reflexes. General Anesthesia. Stages of Anesthesia Stage I Analgesia Stage II Disinhibition Stage III Surgical anesthesia Stage IV Medullary depression. General Anesthesia. I. Inhalation anesthetics

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general anesthesia
Sleep induction

Loss of pain responses

Amnesia

Skeletal muscle relaxation

Loss of reflexes

General Anesthesia
general anesthesia1
Stages of Anesthesia

Stage I

Analgesia

Stage II

Disinhibition

Stage III

Surgical anesthesia

Stage IV

Medullary depression

General Anesthesia
types of anesthetics
I. Inhalation anesthetics

II. Intravenous anesthetics

III. Local anesthetics

Types of anesthetics
i inhalation anesthetics
Mechanisms of Action

Activate K+ channels

Block Na+ channels

Disrupt membrane lipids

In general, all general anesthetics increase the cellular threshold for firing, thus decreasing neuronal activity.

I. Inhalation anesthetics
i inhalation anesthetics1
Ether (diethyl ether)

Spontaneously explosive

Irritant to respiratory tract

High incidence of nausea and vomiting during induction and post-surgical emergence

I. Inhalation anesthetics
i inhalation anesthetics2
Nitrous Oxide

Rapid onset

Good analgesia

Used for short procedures and in combination with other anesthetics

Supplied in blue cylinders

I. Inhalation anesthetics
i inhalation anesthetics3
Halothane (Fluothane)

Volatile liquid

Narrow margin of safety

Less analgesia and muscle relaxation

Hepatotoxic

Reduced cardiac output leads to decrease in mean arterial pressure

Increased sensitization of myocardium to catecholamines

I. Inhalation anesthetics
i inhalation anesthetics4
Enflurane (Ethrane)

Similar to Halothane

Less toxicities

Isoflurane (Forane)

Volatile liquid

Decrease mean arterial pressure resulting from a decrease in systemic vascular resistance

I. Inhalation anesthetics
i inhalation anesthetics5
Pharmacokinetics

The concentration of a gas in a mixture of gases is proportional to the partial pressure

Inverse relationship between blood:gas solubility and rate of induction

Alveoli

Blood

Brain

Nitrous oxide

(low solubility)

Halothane

(high solubility)

I. Inhalation anesthetics
i inhalation anesthetics6
Pharmacokinetics

Increase in inspired anesthetic concentration will increase rate of induction

Direct relationship between ventilation rate and induction rate

Inverse relationship between blood flow to lungs and rate of onset

MAC=minimum concentration in alveoli needed to eliminate pain response in 50% of patients

Elimination

Redistribution from brain to blood to air

Anesthetics that are relatively insoluble in blood and brain are eliminated faster

I. Inhalation anesthetics
i inhalation anesthetics7
Side Effects

Reduce metabolic rate of the brain

Decrease cerebral vascular resistance thus increasing cerebral blood flow = increase in intracranial pressure

Malignant Hyperthermia

Rare, genetically susceptible

Tachycardia, hypertension, hyperkalemia, muscle rigidity, and hyperthermia

Due to massive release of Ca++

Treat with dantrolene (Dantrium), lower elevated temperature, and restore electrolyte imbalance

I. Inhalation anesthetics
ii intravenous anesthetics
Ketamine (Ketaject, Ketalar)

Block glutamate receptors

Dissociative anesthesia:

Catatonia, analgesia, and amnesia without loss of consciousness

Post-op emergence phenomena:

disorientation, sensory and perceptual illusions, vivid dreams

Cardiac stimulant

II. Intravenous anesthetics
ii intravenous anesthetics1
Etomidate (Amidate)

Non-barbiturate

Rapid onset

Minimal cardiovascular and respiratory toxicities

High incidence of nausea and vomiting

II. Intravenous anesthetics
ii intravenous anesthetics2
Propofol (Diprivan)

Mechanism similar to ethanol

Rapid onset and recovery

Mild hypotension

Antiemetic activity

Short-acting barbiturates

Thiopental (Pentothal)

Benzodiazepines

Midazolam (Versed)

II. Intravenous anesthetics
iii local anesthetics
Blockade of sensory transmission to brain from a localized area

Blockade of voltage-sensitive Na+ channels

Use-dependent block

Administer to site of action

Decrease spread and metabolism by co-administering with a1-adrenergic receptor agonist (exception….cocaine)

III. Local anesthetics

O

C

H

2

5

H

N

C

O

C

H

C

H

N

2

2

2

C

H

2

5

Procaine

iii local anesthetics1
Structure-Activity Relationships

Benzoic acid derivatives (Esters)

Aniline derivatives (Amides)

III. Local anesthetics
iii local anesthetics2
Structure-Activity Relationships

O

C

H

2

5

H

N

C

O

C

H

C

H

N

2

2

2

C

H

2

5

III. Local anesthetics

Procaine (Novocain)

Lidocaine (Xylocaine, etc.)

iii local anesthetics3
Structure-Activity RelationshipsIII. Local anesthetics
  • Direct correlation between lipid solubility AND potency as well as rate of onset
  • Local anesthetics are weak bases (pKa’s ~8.0-9.0)

Why are local anesthetics less effective in infected tissues?

slide19

See Katzung, Page 220

  • Activation gate (m gate) is voltage-dependent
  • Open channel allows access to drug binding site (R) from cytoplasm
  • Inactivation gate (h gate) causes channel to be refractory
  • With inactivaton gate closed, drug can access channel through the membrane
  • Closing of the channel (m gate) is distinct from inactivation and blocks access to drug binding site
  • Thus, local anesthetics bind preferentially to the open/inactivated state
iii local anesthetics4
III. Local anesthetics

Drug

Duration of Action

Esters

Cocaine

Medium

Procaine (Novocain)

Short

Tetracaine (Pontocaine)

Long

Benzocaine

Topical use only

Amides

Lidocaine (Xylocaine)

Medium

Mepivacaine (Carbocaine, Isocaine)

Medium

Bupivacaine (Marcaine)

Long

iii local anesthetics5
Techniques of administration

Topical: benzocaine, lidocaine, tetracaine

Infiltration: lidocaine, procaine, bupivacaine

Nerve block: lidocaine, mepivacaine

Spinal: bupivacaine, tetracaine

Epidural: bupivacaine

Caudal: lidocaine, bupivacaine

III. Local anesthetics
iii local anesthetics6
Toxicities:

CNS-sedation, restlessness, nystagmus, convulsions

Cardiovascular- cardiac block, arrhythmias, vasodilation (except cocaine)

Allergic reactions-more common with esters

III. Local anesthetics