General anaesthesia premedication induction, intubation and induction

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These topics covered like a story sequence manner just like a story of anaesthesia very easily very sequence wise

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🩺 The Story of General Anaesthesia

Imagine a patient - let's call him Mr. Rajan - scheduled for an elective abdominal surgery. Follow his journey from the ward to the operating table, and you will understand premedication, induction, intubation, and maintenance as a single, seamless story.

Chapter 1: The Night Before - Setting the Stage

Mr. Rajan is anxious. Surgery is tomorrow. He cannot eat or drink (NPO from midnight). His body is physically ready, but his mind is not.

This is where the story of anaesthesia truly begins - not in the OT, but in the ward.

The anaesthesiologist visits, explains the plan, and orders premedication.

Chapter 2: Premedication - Calming the Storm

Why premedicate? The goals are five-fold, remembered as:

"A SAVE"

Anxiolysis (calm the patient)
Sedation (mild drowsiness)
Amnesia (no memory of the pre-op fear)
Vagolysis (prevent bradycardia from airway manipulation)
Emesis reduction (prevent post-op nausea and vomiting - PONV)

(Miller's Anesthesia, 10e)

The Drugs Given at This Stage

1. Benzodiazepines - The Star of Premedication

The most commonly given class of premedication drugs. They produce anxiolysis, sedation, and anterograde amnesia - meaning Mr. Rajan won't remember anything from this point forward, but his past memories remain intact.

Drug	Route	Dose (Adult)	Special Note
Midazolam	Oral / IV	7.5-15 mg oral	Most popular; works in 10-20 min
Diazepam	Oral	5-10 mg	Longer acting
Lorazepam	Oral	2-4 mg, 2 hrs before	Used in cardiac surgery for prolonged anxiolysis
Temazepam	Oral	10-20 mg	Milder option

Midazolam is the king of premedication - used in adults AND children. In children it can even be given intranasally. At doses up to 1 mg/kg, it has minimal effect on breathing or oxygen saturation. (Miller's Anesthesia, 10e)

2. Opioids (optional) Fentanyl or morphine may be added if the patient is in pain or very anxious before line insertion.

3. Anticholinergics (e.g., Atropine, Glycopyrrolate)

Dry secretions
Prevent bradycardia during laryngoscopy
Vagolysis - the "V" in SAVE

4. Antacids / H2-blockers (e.g., Ranitidine, Pantoprazole)

Raise gastric pH
Reduce aspiration risk if something goes wrong

5. Antiemetics (e.g., Ondansetron, Metoclopramide)

Reduce PONV proactively

Mr. Rajan gets oral midazolam 7.5 mg one hour before surgery. He is now calm, slightly drowsy, and has no memory of being anxious. He is wheeled to the operating theatre.

Chapter 3: Arrival in the OT - The Pre-Induction Setup

Before a single drug is given for induction, the anaesthesiologist prepares the battlefield.

Drugs drawn up and READY at the bedside:

Vasopressors: Phenylephrine, Ephedrine
Inotropes: Ephedrine, Epinephrine
Vasodilators: Nitroglycerin, Nicardipine
Anticholinergic: Atropine
Antiarrhythmics: Lidocaine, Esmolol, Amiodarone
The induction agent (propofol, etomidate, ketamine, or thiopental)
Neuromuscular blocking drug (succinylcholine or rocuronium)

(Miller's Anesthesia, 10e - Induction of Anesthesia)

Monitoring is attached:

ECG (continuous)
Pulse oximeter (SpO2)
Non-invasive BP
Capnograph (EtCO2) ready for after intubation

Pre-oxygenation: Mr. Rajan breathes 100% oxygen via a tight-fitting face mask for 3-5 minutes. This fills his lungs (functional residual capacity) with O2, giving the anaesthesiologist a safe apnoea window of 3-8 minutes after he stops breathing - time to intubate without hypoxia.

Chapter 4: Induction - "Putting Him to Sleep"

This is the most critical phase. Mr. Rajan goes from awake to unconscious in under a minute.

The Standard IV Induction Sequence:

Step 1 - Induction Agent (Loss of Consciousness)

Agent	Dose	Best For	Avoid In
Propofol	1.5-2.5 mg/kg IV	Most elective cases; smooth induction, antiemetic	Egg/soy allergy, hypotension, severe cardiac compromise
Thiopental	3-5 mg/kg IV	Historical gold standard (less used now)	Porphyria
Ketamine	1-2 mg/kg IV	Haemodynamically unstable, trauma, asthma	Raised ICP, hypertension, ischaemic heart disease
Etomidate	0.2-0.3 mg/kg IV	Cardiovascular compromise, cardiac surgery	Prolonged use (suppresses cortisol); PONV risk

Propofol works by enhancing GABA-A receptor-mediated chloride currents, hyperpolarising neurons and switching off consciousness. It causes a dose-dependent fall in blood pressure mainly by reducing systemic vascular resistance. (Miller's Anesthesia, 10e)

Etomidate is the haemodynamic hero - blood pressure barely changes, making it the agent of choice in patients with poor cardiac function or trauma.

Mr. Rajan is healthy, so propofol 200 mg IV is given. Within 30 seconds, his eyes close, his jaw relaxes, and he loses consciousness.

Step 2 - Analgesia (Blunting the Intubation Response)

An opioid is given alongside or just before the induction agent to blunt the sympathetic surge (tachycardia + hypertension) caused by laryngoscopy:

Fentanyl 2-5 mcg/kg IV - most common
Alfentanil 15-25 mcg/kg
Remifentanil 0.5-1 mcg/kg (ultra-short acting, infusion-based)

Alternatively, lidocaine 1.5 mg/kg IV can be given to blunt this response. (Morgan & Mikhail, 7e)

Step 3 - Neuromuscular Blocking Agent (Paralysis for Intubation)

The airway needs to be relaxed and still for safe intubation. Two choices:

A. Succinylcholine (Suxamethonium) - The Fast One

Dose: 1-1.5 mg/kg IV
Onset: 60 seconds
Duration: 10-12 minutes (ultra-short - metabolised by plasma cholinesterase)
Mechanism: Depolarising block (persistent depolarisation at NMJ → fasciculations → paralysis)
Use: RSI, difficult airway scenarios, quick cases

B. Rocuronium - The Modern Alternative

Dose: 0.6 mg/kg (standard) / 1.0-1.2 mg/kg (for RSI)
Onset: 60-90 seconds at high dose
Duration: 30-60 minutes
Non-depolarising (competitive ACh antagonist)
Reversible with Sugammadex - this is its huge advantage over succinylcholine in RSI

(Miller's Anesthesia, 10e)

Chapter 5: The Special Case - Rapid Sequence Induction (RSI)

What if Mr. Rajan had eaten a full meal 2 hours before emergency surgery? Now aspiration of stomach contents into the lungs is a lethal risk.

RSI is the answer. The modified sequence:

Pre-oxygenate (3-5 min, 100% O2)
Cricoid pressure applied (Sellick manoeuvre) - press the cricoid cartilage backward to occlude the oesophagus - 10 N when awake, 30 N after LOC
Induction agent (propofol, etomidate, or ketamine) given rapidly
Succinylcholine 1.5 mg/kg (or rocuronium 1.2 mg/kg) immediately after
NO bag-mask ventilation between induction and intubation (avoids inflating the stomach)
Intubate immediately once paralysis is confirmed (jaw relaxation, no resistance)
Cuff inflated first before any ventilation begins

The goal: zero time between loss of consciousness and a secured, cuffed airway. (Miller's Anesthesia, 10e)

Chapter 6: Intubation - Securing the Airway

The patient is now unconscious, paralysed, and apnoeic. The anaesthesiologist has a 3-8 minute window (thanks to pre-oxygenation).

The Steps of Orotracheal Intubation

Position: Head in "sniffing position" (neck flexed, head extended) - aligns oral, pharyngeal, and laryngeal axes
Laryngoscope inserted: Left hand holds it, blade sweeps tongue to the left, tip placed in the vallecula (base of epiglottis) for curved (Macintosh) blade
Lift the handle upward and forward (NOT rotate/lever) - this lifts the epiglottis and exposes the vocal cords
Visualise the glottis - white cords seen
Insert ETT: Passed through cords, 2-3 cm past the vocal cords in adults (approx 21-23 cm at lips in women, 23-25 cm in men)
Cuff inflated with air (10-20 mL) until no air leak heard
Confirm placement - the critical step:
- Capnography (EtCO2 waveform) - gold standard
- Bilateral chest auscultation (both lungs ventilating equally)
- Absence of sounds over the epigastrium
- Chest rise symmetrical
- SpO2 maintained

ETT Sizes

Patient	Internal Diameter
Adult female	7.0-7.5 mm
Adult male	8.0-8.5 mm
Child (formula)	(Age/4) + 4 mm

Chapter 7: After Intubation - The Transition to Maintenance

Once the ETT is confirmed in place and secured, the story enters a new chapter:

Controlled mechanical ventilation begins
Maintenance anaesthesia is started - either:
- Volatile agent (Sevoflurane, Isoflurane, Desflurane) via the breathing circuit
- Total IV anaesthesia (TIVA) - propofol infusion + remifentanil infusion
Analgesia continued with opioid infusion or supplemental doses
Muscle relaxation top-ups as needed (if surgical access requires deep paralysis)
Monitoring: EtCO2, SpO2, BP, ECG, temperature, urine output

The Big Picture - The Sequence as a Story

WARD (Night before)
      ↓
  NPO instructions + anaesthesia assessment
      ↓
PREMEDICATION (1 hr before)
  → Midazolam (anxiolysis + amnesia)
  → Antacid / antiemetic
      ↓
ARRIVAL IN OT
  → Monitoring applied
  → IV access confirmed
  → Drugs drawn up, checked
      ↓
PRE-OXYGENATION (3-5 min, 100% O2)
      ↓
INDUCTION
  → Opioid (fentanyl) → blunt laryngoscopy response
  → Induction agent (propofol) → loss of consciousness
  → NMBA (succinylcholine / rocuronium) → paralysis
      ↓
INTUBATION (within 60-90 sec of NMBA)
  → Laryngoscope → visualise cords → insert ETT → inflate cuff
  → Confirm with capnography + auscultation
      ↓
MAINTENANCE
  → Volatile agent (sevoflurane) or TIVA
  → Opioid infusion, NMBA top-ups, monitoring
      ↓
SURGERY BEGINS...

Sources: Miller's Anesthesia, 10e | Morgan & Mikhail's Clinical Anesthesiology, 7e | Barash's Clinical Anesthesia, 9e

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