General Anaesthesia

General anesthesia (anaesthesia)

State of unconsciousness and loss of protective reflexes resulting from administration of 1 or more general anesthesia agent.

Theories of general anesthesia (put in simple term)


1. Lipid theory - Decrease membrane permeability -> interfere with brain function -> LOC

2. Ion channel theory - Effect brain's ion channel (Na+,K+) ->  interfere with brain function -> LOC

3. Receptor theory - Increase GABA effect -> interfere with brain function -> LOC

Stages of anesthesia


1. Sedation - administration of agent till LOC
2. Excitement - LOC till loss of eyelid reflex
3. Surgical Anesthesia - loss of eyelid reflex till respiratory depression
4. Overdose - respiratory depression - death

Components in GA

1. Loss of consciousness - The use of either intravenous or volatile (gas) GA agent
2. Muscle relaxant - Non depolarizaing / Depolarizing
3. Analgesia - Opioid

General anesthesia agent


- To be continued-


1. IV agent

- Barbiturate: thiopental

- Benzodiazepam: midazolam

- Phenol: Propofol

- Steroid: Ethomidate

- Imine: Ketamine

2. Volatile agent


- Sevoflurane
- Isoflurane
- Desflurane
- Halotane
- Enflurane

Muscle relaxant agent

1. Depolarizing

Suxamethonium

2. Nondepolarizing

Atracurium
Rucororium

Analgesia


Opioid

Reversal agent


Neostigmine
Atropine

Preoperative assessment

Preoperative assessment is done based on

1. History
2. Physical Examination
3. Investigation

1. History


- Presenting complain
- Medical condition: CV/Respiratory/effort tolerance
- Anesthesia history: previous complication/ side effect: difficult airway/nausea/headache
- Family history: malignant hyperthermia/ porphyria/ pseudocholinesterase deficiency 
- Drug history: Anti-hypertensive/ steroids/ OCPs/ anti-convulsion
- Allergy: drug/food/soy
- Social History: smoking/alcohol

2. Physical examination


General: hydration/ temperature
CVS: Pulse/ JVP/ BP/ Heart sound/ Murmur - AS(lean in front) /MS(lean laterally)
Respiatory: Cyanosis/ Auscultation of lungs
Airway: Mallampati score, thyromental distance, neck movement, facial symmetry, tongue size

Mallampati score
Grade 1- full opening
Grade 2- tongue touches tip of uvula
Grade 3- Tongue covering tip of uvula
Grade 4- Tongue covering everything

Thyromental distance (<7cm : suggest difficult airway)

3. Investigation


- FBC: all
- Urinalysis: all
- RF : hx of diarrhea/vomiting/ renal disease
- LFT: liver disease/ alcoholism / nutritional state
- Blood glucose: DM/ vascular disease/ corticosteroid 
- Coagulation profile: coagulation disorder/ chronic liver disease
- ECG: >45 CVS disease
- CXray: Respiratory problem/ Thyroid enlargement


American Society of Anesthesiologists grading (ASA)


Grade
1. Healthy
2. + Disease controlled/ non life threatening
3. + Disease uncontrolled/ non life threatening
4. +  Life threatening
5. Expect to die with or without surgery
6. Dead - for organ donation