Anaesthesia

 

Anaesthesia

Anaesthesia (from Greek an- = without + aisthesis = sensation) is a reversible loss of sensation or consciousness, achieved by the administration of anaesthetic agents, to facilitate surgical or diagnostic procedures without pain or distress.

Types of anaesthesia:

1. General Anaesthesia (GA): 

Reversible loss of consciousness & sensation.

• Inhalational agents: Nitrous oxide, Halothane, Isoflurane, Sevoflurane.
• Intravenous agents: Thiopentone, Propofol, Ketamine, Etomidate.

• By Stage (Guedel’s):

Stage I – Analgesia
Stage II – Excitement
Stage III – Surgical Anaesthesia
Stage IV – Medullary Paralysis (dangerous)

• Eg: Ether, Halothane, Propofol.

2. Local Anaesthesia (LA):

Loss of sensation in a small, specific area without affecting consciousness

• Surface Anaesthesia – Applied topically 
• Infiltration Anaesthesia – Injected into tissue around site.
•   Eg: Lignocaine spray, Bupivacaine, eye drop.

3. Regional Anaesthesia:

Larger area is numbed by blocking nerve conduction.

• Spinal Anaesthesia – Injection into subarachnoid space.
• Epidural Anaesthesia – Injection into epidural space.
• Caudal Anaesthesia – Through sacral canal.
• Nerve Blocks – Peripheral nerves (e.g., brachial plexus block).
• Field Block – Local area blocked (e.g., hernia surgery).
• Eg: Spinal, Epidural, Nerve block.

4. Sedation / Conscious Sedation:

Patient relaxed & pain reduced, but remains awake & responsive.

• General Anesthesia (GA): Loss of consciousness + sensation.
• Sedation / Analgesia: Depressed consciousness but responsive.
• Local / Regional Anaesthesia: Patient fully conscious, only sensation blocked.

Mnemonic

💡“G R L S” = General – Regional – Local – Sedation

                                                                                                              Fig: 01

                                                       -:Thiopental Sodium :- 

Chemical name: Sodium 5-ethyl-5-(1-methylbutyl)-2-thiobarbiturate    

Molecular Formula: C₁₁H₁₇N₂NaO₂S
Molecular Weight: 264.32 g/mol

  Chemical Structure:         O

                                            ║

                       N — C — CH2—C(=O)—N

                              │                    │

                             C2 = S            C5 — (ethyl + sec-butyl groups)

Stability

Stable

Storage Conditions

• Store as a dry powder in airtight, well-closed containers.
• Protect from light and moisture.
• Store below 25 °C (room temperature).
• Solutions should be freshly prepared and used immediately (discard after 24 hours).

Brand Name

• Pentothal
• Trapanal
• Nesdonal

Uses

• Induction of anesthesia (IV anesthetic, rapid onset, short duration).
• Preoperative sedation.
• Its control of convulsions (status epilepticus, drug-induced seizures, electroconvulsive therapy).

                                        -:Ketamine Hydrochloride:-

Chemical Name- 

• IUPAC name: (±)-2-(2-Chlorophenyl)-2-(methylamino)cyclohexanone hydrochloride
• Common name: Ketamine HCl

Chemical Structure

• Belongs to arylcyclohexylamine derivative.
• Structure: contains a cyclohexanone ring substituted with a chlorophenyl group and a methylamino group.

Stability Condition

• Stable under normal temperature and pressure.
• Sensitive to light → prolonged exposure causes degradation.
• More stable in acidic solutions (pH 3–5).

Storage Condition

• Store at 20–25 °C (Room temperature).
• Protect from light and freezing.
• Should be kept in airtight containers.

Brand Names

• Ketalar®
• Ketanest®
• Ketaset®

Uses

1. Used as anaesthetic agent-

• To Induce and maintenance of anaesthesia.
• Preferred in short surgical and diagnostic procedures.

2.  Used as Analgesia to low-dose ketamine for pain management (especially in chronic or cancer pain).

3. Used in emergency & trauma care with shock/low blood pressure.

4. Caused Sedation for minor procedures, dressing changes, etc.

5. Used to psychiatry to low-dose IV infusion in treatment-resistant depression (Esketamine nasal spray also used).

                                                           -: Propofol :-

Chemical Name - 2,6-diisopropylphenol

Molecular Formula: C₁₂H₁₈O

Stability Condition

• Sensitive to light (degrades when exposed).
• Not stable in aqueous solution (soybean oil, glycerol, egg lecithin).
• Can support bacterial growth due to lipid emulsion.

Storage Condition

• Store below 25°C, protected from light.
• Do not refrigerate (emulsion may break).
• Once the vial/ampoule is opened, use within 6 hours (or as per manufacturer).
• Infusion syringes/tubing should not be used for more than 12 hours.

Brand Names

• Diprivan®
• Propoven
• Fresofol
•  Propofol-Lipuro

Uses

• Induction & maintenance of general anaesthesia
• Sedation for mechanically ventilated patients (ICU)
• Conscious sedation during short diagnostic or surgical procedures (e.g., endoscopy, cardioversion)
• Anti-emetic effect (in sub-anaesthetic doses)