This document provides information on various anesthetic agents used in ophthalmic procedures, including general anesthetics (GA), regional anesthetics (RA), local anesthetics (LA), and topical anesthetics. It describes the types, mechanisms of action, common drugs, dosages, administration routes, indications, and side effects of different anesthetic classes. Key anesthetic agents discussed include nitrous oxide, halothane, ketamine, propofol, lidocaine, bupivacaine, and tetracaine.

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!