2. Anesthesia
General
Anesthetics
Local Anesthetics
(LA)

3. General Anesthetics

4. Definition
General anesthesia is a
controlled reversible CNS
depression characterized
by:
-Loss of consciousness
-Loss of sensation
-Muscle relaxation
-With hemodynamic
stability

5. General Anesthetics
Stages
• Stages and planes of
anesthesia:
• Stage I: Analgesia and
amnesia.
• Stage II: Loss of
consciousness (may be
excitement).
• Stage III: Surgical
anesthesia.
• Stage IV: Medullary
paralysis and failure of
circulation

7. Mechanism of action
General Anesthetics inhibit
synaptic transmission in CNS
by:
- Stimulate the effect of GABA
(inhibitory neurotransmitter)
on GABA A receptors
OR
- Inhibit the NMDA receptors
which represent subtype of
excitatory glutamate receptors

8. 1-Inhalation anesthetics
Classification:
a- Gases inhalation: Nitrous oxide
b- Volatile liquids inhalation:
- Halothane
- Isoflurane
- Sevoflurane
- Desflurane
- Enflurane

9. Pharmacokinetic properties
Potency
a- Factors affecting minimum alveolar
concentration (MAC):
It is the concentration that prevents 50% of
patients from responding to a painful stimulus
such as a skin incision. It is analogous to ED50.

10. Inhalation anesthetics
Nitrous oxide (N2O) Halothane Isoflurane Sevoflurane
Anesthesia
stages
Good analgesic and
sedative effect
Weak anesthetic
Weak skeletal muscle
relaxation
Weak analgesic.
Weak skeletal
muscle relaxation
good analgesic and
sedative effects
advantages Safe on CVS, respiratory
system and vital organs.
bronchodilatation.
controlled
hypotension.
No hepatotoxicity pleasant odor.
No cardiotoxicity
No hepatotoxicity
Adverse effects diffusion hypoxia
during recovery. So give
oxygen during recovery
 Produces
postoperative nausea
and vomiting.
Megaloblastic anemia
Teratogenic.
Cardiotoxic
Hypotension.
Hepatotoxic
Malignant
hyperthermia
pungent odor
Less acceptance by
children
dose-dependent
depression of
cardiovascular system
 muscle movement
Contraindicated in
Parkinsonism
Nausea and
vomiting
Respiratory
depression
uses dental operations &
labor

11. Neuroleptanalgesia
It is produced by combination of :
Fentanyl and droperidol
- Patient in a state of analgesia without loss of
consciousness
- Used in neurosurgery & for minor diagnostic
and surgical produces in which patients is
cooperative as in bronchoscopy

12. 2- Intravenous Anesthetics
Thiopentone (Ultrashort acting
barbiturate):
Propofol Ketamine
Anaethesia
stages
sedation and hypnosis
no analgesic or muscle relaxant
hypnosis
No analgesia
• hallucinogen
• Has analgesic effect
• Has an amnestic action
• loss of motor activity
onset rapid induction :Has a rapid onset (~ 20
seconds) and a short duration (5-10
minutes) due to redistribution.
Has rapid onset, short
duration
Faster than thiopental
Adverse
effects
respiratory depression; can cause cough,
laryngospasm and bronchospasm
pain at injection site Dreams and terrifying hallucination
advantages minimal postoperative nausea and
vomiting
minimal postoperative
nausea and vomiting.
potent bronchodilator
uses 1- induction of general anesthesia
2- general anesthesia for minor short
operations
3- anticonvulsant
induction and
maintenance of
anesthesia
for minor procedures especially in
infants and children

13. Benzodiazepines
Diazepam, Lorazepam and Midazolam are the
members useful clinically as IV anesthetics
Used preoperatively for sedation and to reduce
anxiety.
Used as anesthetic agents for surgical and
diagnostic procedures e.g. endoscopy and
cardiac catheterization.
Produce amnesia (amnesia for the events that
occur after the drug is administered)

14. When used with opioids, cardiovascular
and respiratory depression may be severe
Has a more rapid onset and produces less
cardiovascular depression

15. General Anesthetics

16. Preanesthetic Medication
Benefits
1-To produce: sedation, amnesia and analgesia
2-To reduce:
Amount of anesthetic
Complications after anesthesia
Parasympathetic effects on salivary glands, lungs and
heart
So: decrease salivary& bronchial secretions,
decrease bronchospasm and decrease reflex vagal
stimulation

17. Drugs used:
1- Nacrotic (opioid) analgesics: Morphine and
meperidine
2- Anxiolytics as benzodiazepines
3- Neuroleptics as phenothiazines
4- Parasympatholytics as atropine and hyoscine
Hyoscine is more depressant on CNS (leads to
sedation, amnesia & potent antiemetic action)
• It is also, more potent antisecretory so, decrease
salivary & bronchial secretions

18. Anesthetic Adjuvants
Drugs used during anesthesia to aid it & ensure
a safer anesthesia as:
A-Neuromuscular blockers to provide skeletal
muscle relaxation
B-Drugs used to produce Controlled
hypotension
as Trimetaphan and sodium nitroprusside
C-Hypothermic agents by a cocktail of
chlorpromazine, promethazine & meperidine)

19. Local Anesthetics (LA)

20. Definition:
The are drugs which produce reversible
loss of sensation in a localized region of
the body without loss of consciousness by
producing reversible block of nerve
conduction.

21. Classification of local anesthetics

22. Routes of administration of local anesthetics:
Surface anesthesia:
• LA is applied locally on skin &
mucous membranes, effective
for mucous membranes such as
in the bronchial tree, and
surfaces such as the cornea.
• A non-crystalline mixture of
lidocaine may be used for skin.

23. Infiltration anesthesia
 LA is injected in the
subcutaneous tissues to
block nerve endings,
effective for many regions.
 may require large doses of
anesthetic.
 Vasoconstrictor agents (e.g.
adrenaline) may be used to
retard absorption.
Nerve block
 LA is injected around nerve
trunks.
 It used in many situations
e.g. brachial plexus block

24. Intravenous regional anesthesia:
It is used in limbs.
LA being injected IV distal to an
arterial cuff to restrict it to
periphery.
Systemic effects can occur when
cuff is removed,

25. Spinal anesthesia
 LA is injected in the
subarachnoid space in the
lumbar region
 It often used for pelvic
surgery.
 Longitudinal spread of LA
may cause hypotension and
sometimes respiratory
paralysis.
Epidural anesthesia
• LA is injected in the
epidural space

26. Local Anesthetics pharmacokinetics
Absorption
 Local anesthetics are absorbed from sites of administration
into the systemic circulation
 The rate and extent of absorption to and from nerves are
important in determining onset and duration of action and
also the potential for systemic adverse effects.
 This rate is correlated with the relative lipid solubility and
is influenced by the dose and the drug's physicochemical
properties, as well as by tissue blood flow and drug binding.
 They reduced pH in inflamed tissues

27. Metabolism
Ester group
.
Amide group
The metabolic rate of these
anesthetics is decreased in
patients with decreased or
genetically atypical cholinesterase
Liver disease & Histidine
methyl ester inhibitors
increase toxicity of amide LA

28. Excretion

29. Local anesthetics have:
A. Local anesthetic action
(loss of sensation as they block sensory nerve fibers)
B. Systemic actions: - CNS – CVS
(if sufficient& large amounts of the LA are absorbed)
)
Stimulation → restlessness, tremors and
convulsions. Central stimulation is
followed by Depression→ respiratory
failure→ death
Heart: direct myocardial depression→
cardiac arrest
Blood Vessels: vasodilatation
BP: hypotension

30. Pharmacodynamics

31. Adverse effects and toxicity of LA
Adverse effects are usually the result of overdose or accidental
injection into the vascular system.
Bradycardia &Hypotension
Stimulation followed by respiratory
depression, coma, and death from
respiratory failure.

32. Local toxicity
Pain or hematoma at site of
injection
Persistent paresthesia
Nerve damage → prolonged
sensory & motor loss
Tissue damage → necrosis &
sloughing of tissue
Mucosal irritation

33. Toxicity of spinal anesthesia
a- Early:
-Hypotension due to veno and arterio
dilatation
b- Late:
-Septic meningitis
-Headache

34. Preanesthetic medication for LA
Benzodiazepine (Antianxiety drug):
e.g. diazepam
1- To counter act central stimulant action of LA
& prevent convulsions
2- To relieve anxiety of the patient

35. Common Local Anesthetic Drugs
Amides
intermediate duration of action
long duration of action
greater cardiotoxicity
The prototype amide
longer than that of lidocaine
not used topically

36. Common Local Anesthetic Drugs
.
Procaine
 short-acting.
 not effective topically
 It is taken by mouth or given as a
shot for arthritis
Benzocaine
It is used topically to treat
sunburn, minor burns, and
pruritus.

37. Cocaine:
 medium-acting.
 naturally occurring alkaloid.
 only for the topical anesthesia of mucous membranes.
 Systemically, cocaine will block the uptake of
catecholamines into nerve terminals and may induce
vasoconstriction.
 Adverse effects : include euphoria, CNS stimulation,
tachycardia, restlessness, tremors, convulsions and
arrhythmias.
 It should be used cautiously for patients with hypertension,
cardiovascular disease, or thyrotoxicosis, and with other
drugs that potentiate catecholamine activity.

38. Tetracaine:
long-acting but has a slow
onset of action (> 10
minutes).
often preferred for
ophthalmological use.
not generally used for
peripheral nerve blocks, or
lumbar epidural nerve
blocks