Anesthesiology – Comprehensive Study Notes

1. Core Principles of Anesthesia

Triad of Anesthesia:

1. Analgesia – Loss of pain sensation

2. Amnesia – Loss of memory

3. Anesthesia – Loss of sensation (proprioception, temperature, vibration)

Phases of Anesthesia:

• Induction: Take-off

• Maintenance: Cruising

• Emergence: Landing

Guedel’s Four Stages:

1. Stage 1 – Awake

2. Stage 2 – Excitatory/delirium phase (danger zone; risk of laryngospasm)

3. Stage 3 – Surgical anesthesia (target depth)

4. Stage 4 – Overdose/medullary paralysis

2. Pre-Operative Assessment

Key Elements:

• Baseline vitals, pregnancy status, medications, allergies

• NPO status

• Prior anesthesia complications

Airway Assessment:

• Mallampati Score I–IV (higher = harder intubation)

ASA Physical Status Classification:

1. ASA I – Healthy

2. ASA II – Mild systemic disease

3. ASA III – Severe systemic disease

4. ASA IV – Severe, life-threatening disease

5. ASA V – Moribund

6. ASA VI – Brain-dead organ donor

3. Intraoperative Monitoring & Vitals

Mean Arterial Pressure (MAP):

• Formula: [(Systolic − Diastolic)/3] + Diastolic

• Goal: ≥ 50–55 mmHg (higher for hypertensive patients)

Pulse Oximetry (SpO₂):

• Normal: 95–100%

• Delayed by 30 sec; first on, last off

• Confounders: nail polish, motion, methemoglobinemia (~85%), CO poisoning (false high)

Capnography (EtCO₂):

• Normal: 35–40 mmHg

• Confirms ET tube placement (gold standard = 5 waveforms)

Temperature:

• Hypothermia → arrhythmia, coagulopathy, infection risk

• Best measurement: Pulmonary artery or esophageal probe

BIS Monitoring:

• 100 = awake

• 70–90 = sedated

• 30–60 = surgical anesthesia

• <30 = too deep

4. Pharmacology Overview

A. Inhalation Agents

• Potency ↔ Lipid solubility

• Speed ↔ Inversely related to blood solubility

• MAC (Minimum Alveolar Concentration): 50% immobility threshold

  • 1.2–1.3 MAC = 95% immobile

  • Decreases with age

Common Gases:

Agent	Key Feature	Notes
Sevoflurane	Sweet, fast	Commonest gas
Desflurane	Fastest, pungent	Affected by altitude
N₂O	Adjunct gas	Avoid in closed cavities

Effects: All ↓ MAP, ↑ ICP, ↓ GFR, risk MH (malignant hyperthermia)

B. IV Anesthetics

Drug	Key Effect	Notes
Propofol	↓ BP, resp. depression, no analgesia	Anti-emetic; pain on injection
Etomidate	Stable hemodynamics	Adrenal suppression
Midazolam (Versed)	Amnesia, sedation	No analgesia; reversed with Flumazenil
Ketamine	Analgesia + Amnesia	↑ HR/BP; dissociative; hallucinations

C. Opioids

Drug	Potency (Morphine=1)	Notes
Meperidine	0.1	For shivering
Fentanyl	100	OR boluses
Hydromorphone	10	Post-op pain
Remifentanil	100	Infusions
Sufentanil	1000	Very potent

D. Neuromuscular Blockers (NMBAs)

• Depolarizing: Succinylcholine → short-acting; risks: hyperkalemia, MH

• Non-depolarizing: Rocuronium, Vecuronium → longer, reversible

Reversal:

• Neostigmine + Glycopyrrolate

• Sugammadex (binds Rocuronium/Vecuronium; expensive; affects OCPs)

E. Vasoactive Agents

Purpose	Drug	Receptor	Effect
Hypotension	Phenylephrine	α1	Vasoconstrictor
Hypotension	Ephedrine	Indirect	↑ HR & BP
Vasoconstrictor	Norepinephrine	α1, β1	Potent pressor
Inotrope	Dobutamine	β1	↑ contractility
Inotrope/Vasodilator	Milrinone	PDE3 inhibitor	↑ output, ↓ resistance

5. Fluid Management

Crystalloids:

• NS (0.9%): risk metabolic acidosis

• LR: physiologic; avoid with blood transfusions

Resuscitation Ratio:

• Crystalloids: Blood = 3:1

• Colloids (Albumin): Blood = 1:1

Maintenance Rule:

• 4–2–1 formula or 40 + weight(kg) = mL/hr

6. Post-Op Nausea & Vomiting (PONV)

Risk Factors: Female, non-smoker, history of motion sickness, young age
Prevention: Ondansetron + Dexamethasone
Alternatives: Scopolamine, Promethazine, Metoclopramide
Propofol: antiemetic (good TIVA option)

7. Airway Management (Intubation)

Preparation:

• Machine check, airway tools, suction, IV access

• Pre-oxygenate and confirm ability to ventilate

Position: Sniffing position
Technique:

• Mac blade → vallecula

• Miller blade → under epiglottis

Confirmation:

• 5 EtCO₂ waveforms = gold standard

• Bilateral chest rise, breath sounds

Extubate:

• When awake or deep (not Stage 2)

• Signs: following commands, strong cough/gag, adequate tidal volume

8. Difficult Airway & LMA

LMA: Supraglottic; used in “can’t intubate, can ventilate” cases
Risk Factors: Obesity, short thyromental distance, limited neck ROM, beard
Algorithm: Call for help → Video laryngoscope → LMA → Surgical airway

9. Regional Anesthesia

Type	Space	Features
Spinal	Subarachnoid (CSF)	Single shot, dense block
Epidural	Epidural space	Continuous infusion

Layers:
Skin → Fat → Supraspinous Ligament → Interspinous Ligament → Ligamentum Flavum → Epidural → Dura → Subarachnoid

10. Special Situations

• Cardiac Anesthesia: CABG; A-line, central line, TEE, perfusionist

• One-Lung Anesthesia: Double-lumen ET tube for thoracic surgery

Key Clinical Takeaways

• Know MAP, EtCO₂, SpO₂—they tell the story.

• Propofol: no analgesia, causes hypotension.

• Succinylcholine: rapid, but dangerous in hyperkalemia/MH.

• Dantrolene treats MH.

• Intubate safe; extubate smart.

• Always anticipate complications and communicate clearly with the team.