Anesthetic Agents:local, general,regional and topical

1. Anesthetic Agents
GA/LA
Rabindra Adhikary
ravinems@iom.edu.np
M.Optom, 1st Batch
Tilganga Institute of Ophthalmology
Pokhara University

2. Types
• General
• Regional
• Local
• Topical

3. GA
• Combination of drugs causes generalized loss of
consciousness & muscle movements
– Reversible & doesn’t jeopardize pt health
– Fasting Rule:
• Water/clear fluids: 2 hours
• Solid food: 6 hours
• Breast milk: 4 hours
– Drugs
• Barbiturates
• Ketamine
• Etomidate
• Propofol

4. Stages of GA
• STAGE I: Induction
– Consciousness to unconsciosness
• STAGE II: Excitement
– Excitement of inhibitory neurons of CNS
– Involuntary movement of muscle
– Heart rate, BP and respiration increases
• STAGE III: Surgical Anesthesia
– Loss of muscle tone and reflexes
– Ideal stage for surgery
• STAGE IV: Medullary Paralysis
– Respiratory or cardiovascular failure  death
– Overdose
– Careful monitoring in stage 3.

5. Common General Anesthetics [GAs]
• Nitrous Oxide
– Commonly called laughing gas with a formula N2O
– Colorless, non-inflammable, slightly sweet odor and
taste in room temperature
– Most used gaseous anesthetic in the world
– Other uses: food additive as propellant, fuel additive
for higher combustion, respiratory inhalant for
euphoric pleasures, refrigerant
– Due to its weaker anesthetic and muscle relaxant
properties, it is always supplemented with other
agents to increase the potency

6. Dosage and administration
• For the maintenance of anaesthesia, nitrous
oxide must always be mixed with at least 30%
oxygen. This is usually accomplished using a
compressed-gas anaesthetic machine.
• For analgesia, a concentration of 50% nitrous
oxide with 50% oxygen usually suffices
• Mode of administration: Inhalation

7. • Indication of Nitrous Oxide
– Surgical anesthesia, analgesia, pain
• Renal excretion accounts for >70%
• Side effects:
– Nausea, vomitting
– Paresthesia, lack of concentration
– Peripheral neuropathy, atonia
– Hypoxia [in overdose]

8. Halothane
• volatile inhalational anesthetic agent
• colourless, volatile, non-irritant liquid with a
sweet odour
• In anaesthetic dosage it depresses both cerebral
function and sympathetic activity and produces
little, if any, preliminary excitement
• surgical anaesthesia can be produced in 2-5
minutes.
• The recovery time is rapid and the incidence of
postoperative nausea and vomiting is low.

9. • Side effects
– Cardio-depressant
– Hepatitis
– Respiratory and vasomotor depression
• Administered through specially calibrated vaporizer
• Concentrations of 0.5-1.5% are usually adequate
for adults and children
• Recovery is fast, but also depends upon the
dosage
– Shivering is seen during recovery cover with warm
blankets

10. • Contra-indications
– Raised CSF pressure
– Family h/o malignant hyperthermia
– Jaundice/hepatitis
• Halothane should be stored in tightly closed
amber-glass containers protected from light,
below 25°C. Thymol is added as a stabilizing
agent to commercially produced supplies at a
concentration of 100 micrograms/ml.

11. Ketamine HCL
• Non-barbiturate general anesthetic
administered IM or IV
• 2 –(0-chlorophenyl)-2-(methylamino)
cyclohexanone hydrochloride
• Rapidly acting Gawith profound analgesia
• Best suited for short procedures, used in
conjunction with other drugs for long
procedures

12. • Initial dose administered intravenously may range from
1mg/kg to 4.5mg/kg. The average amount to produce 5-10
minutes of surgical anesthesia has been 2mg/kg
• Intramuscular dose ranges from 6.5 to 13mg/kg. A dose of
10mg/kg produces 12-25 min surgical anesthesia
• Given over a period of 60 secs
• Side effects may include:
– Respiratory depression
– Cardiac decompensation
– Systemic hypertension
– Diplopia and nystagmus
– Slightly Raised IOP

13. Propofol
• 2,6-Bis(1-methylethyl) phenol
• C12H18O
• Vulnerable to microbial contamination
– Strict aseptic technique should be applied
• Mode of administration:
– IV infusion
– IV injection

14. Indication
• Induction and maintenance of GA
• Conscious sedation for diagnostic and surgical
procedures
• Sedation during intensive care
• GA for 3 year or above
• Contraindications
– Who has cardiovascular depression/hypotension
– Not be used for ICU sedation for pt who have fat
metabolism disorder
– Epilepsy: various manifestation of seizures have been
reported, so, not indicated to epileptic pts.
– Pregnancy, labor and delivery

15. Propofol Dose
• Rapid and smooth hypnosiswith in 40 sec
(arm-brain circulation time)
– However, induction > 60 sec

16. RA
• Analgesic effect in specific body parts, eg. Legs,
hands [where procedures are targeted] like
epidural anesthesia
– Reduced risks comparative to GA
– Applicable for resource limited set up
– Pt consciousness retained greater cooperation
• Drug:
– Percutaneous lidocaine
– Bupivacaine
– Livobupivacaine
– Ropivacaine

17. LA
• Local anesthetics are a group of structurally
related compounds which share as principal
mechanism of action the blockade of voltage-
gated sodium channel, resulting in reversible
interruption of nerve signal transduction.
– Used both topically or as injection form
• When used with epinephrine [adrenaline] LA has
– prolonged duration of action
– Reduced systemic absorption
[epinephrine has vasoconstriction effect on alpha
receptors of blood vessels]

18. Chemical structure
• All local anesthetic [except cocaine] contains 3
basic structural components:
Aromatic
Ring
• Usually
substituted
Connecting
Group
• Ester
[novocaine]
• Or, amide
[lidocaine]
Ionizable
amino
Group

21. MOA
• LA receptors are located in the Na+ channel of
axonal membrane
• Receptors consists of 2 gates:
– Activation gate (m gate)
– Inactivation gate (h gate)
• Action of h gate is responsible for blocking
Na+ channels

22. MOA- explanation

23. MoA
• Block the nerve conduction by preventing membrane
permeability to sodium ions that normally leads to nerve
impulse through creating membrane potential

24. • An ideal LAs may have the following
characteristics :
– reversibility
– a rapid onset of action
– a predictable duration of action
– good tolerance at high doses with a low risk of
systemic toxicity.

25. • Next to sodium channel blockade LA also act upon
– Calcium and potassium channels
– G protein coupled receptors  this gives the anti-
inflammatory effect
• Different additives may be used with LA for better
and prolonged effect:
– Buprenorphine [↑ed nausea and vomitting]
– Dexmeditomidine & Clonidine [dose dependent
systemic side effect eg. Bradycardia, hypotension]
– Dexamethasone [least systemic side effect and longest
nerve block duration]

26. • Lidocaine 2% with Bupivacaine 0.75%
• In retrobulbar block, use of epinephrine is
done cautiously as it may cause ciliary or
ophthalmic artery spasm

27. Common LAs
Generic Name Trade Name
Lidocaine Xylocaine
Bupivacaine Sensorcaine, Marcaine
2- chloroprocaine Nesacaine
Etidocaine Duranest
Levobupivacaine Chirocaine
Mepivacaine Carbocaine, Polocaine
Proparacaine Aurocaine
Ropivacaine Naropin
Tetracaine Pontocaine
Procaine Novacaine

28. Common Ophthalmic anesthetics
• Lidocaine
• Proparacaine
• Tetracaine
• Proxymetacaine
[all in hydrochloride form]

29. Lidocaine
• Belongs to amide class
– Trade name Xylocaine
• Most popular local anesthetic agent
• First modern local anesthetic [since 1940]
• Injected through the skin directly to the
targeted body parts to be numbed
• Contraindications in:
– Cardiac arrythmias [heart block]
– Liver, kidney and coronary artery diseases

30. • 90% hepatic metabolism
• Elimination half life is 1.5 to 2 hours
– Prolonged to 3.5 times in pt with liver diseases

31. • Drug interactions: simultaneous use with the
following drugs causes drug interactions. So,
extreme cautions is required:
– Antidepressants [triptyline, imipramine]
– Antipsychotics [phenothiazines, butyrophenones]
– lidocaine has additive effect on CNS depression with
sedatives
– When used in a pt who is using propanolol [beta
blocker], the anesthetic effect of lidocaine is severely
reduced to 47%, 7& co-administered use reduced its
effect to 30%

32. Dosage of Lidocaine
• Retrobulbar block: 2%
– Each dose consists of 4 ml [80mg]
– Anesthesia onsets after 3-5 min
– Duration without epinephrine: 1.5 to 2 min
• Peribulbar: 1%
– Each dose 10-15 ml [100-150mg]
– Anesthesia onsets after 3-5 min
– Duration without epinephrine: 1.5 to 2 min

33. Retrobulbar Block
• Surgery involving cornea, AC, lens regional
anesthetic block
• Local anesthetic is introduced into the muscle
cone. So, it blocks:
– Ciliary nerves
– Ciliary ganglions
– Cranial nerves III, IV and VI
• Does not anesthetize CN VII [7th Nerve]
– Pt is able to close the eye with orbicularis oculi
– But not open with LPS

34. Peribulbar Block
• Local anesthetic introduced into the
orbicularis oculi muscle
• Blocks
– Ciliary nerves
– CN III and VI
– Does not affect optic nerve [CN II]
• Lower complication rate than retrubulbar but
difficult to get complete dense block

35. Tetracaine
• Amino Ester:
• 4-N-butyl benzoic ester
• S/E
– Stinging
– Burning
– Redness

36. • In ophthalmic practice, used in
– Diagnostic- Tonometry, gonioscopy
– therapeutic - paracentesis of AC
– minor surgical procedures-chalazion, corneal
suture or FB removal

37. Dose
• For tonometry and other procedures
– 1-2 drops in the eyes just prior to evaluation
• For minor surgical procedures FB removal or
suture removal
– 1-2 drops every 5-10 min until procedure lasts
• For prolonged anesthesia
– 1-2 drops every 5-10 min upto 3-5 doses

38. Procaine
• Amino ester
• C13 H20N2O2 ; popular trade name: novocain
• 2-(diethylamino)ethyl 4-aminobenzoate
• Produces local or regional anesthesia
• Has the advantage of constricting the blood
vessels-reduces bleeding
• Metabolized in the plasma by the enzyme
pseudocholinesterase through hydrolysis into
PABA

39. • With normal kidney function the drug is
rapidly excreted by tubular excretion
• Dosage
– 0.25%, 0.5% for Local infiltration
– 1%, 2% for peripheral nerve block
• Half life: 7.7 min
• Contraindications
– Known hypersensitivity of procaine or PABA

40. Thank You!