Isoflurane

• Agent of choice in Cardiac patients.
•  Vasodilation with least cardiovascular depression.
•  Intracranial pressure (moderate increase).
• Not ideal for asthmatics compared to Sevoflurane.

Desflurane

•  Fastest induction & recovery.
•  Minimally metabolized.
• Preferred in shock & renal failure.

Sevoflurane

•  Induction agent in children.
• Maximum bronchodilation (non-asthmatics).
• More cardiodepressant than Isoflurane.

Ether

• Highly explosive  (not used today).
• Classic: Complete anaesthetic agent.
• Causes max emesis.
• Basis of anaesthesia staging (Guedel’s classification).

Intravenous Anesthetic Agents

Intravenous anesthetic agents are crucial in modern anesthesia practice, providing rapid onset of sedation and analgesia. This lecture will cover the most commonly used intravenous anesthetic agents, including their indications, contraindications, and required doses.

1. Benzodiazepines

Overview

Benzodiazepines are primarily used for their anxiolytic (anxiety-reducing) and amnesic properties. They are frequently used in procedural sedation and as adjuncts in general anesthesia.

Common Agents

• Diazepam

  • Dose: 5-10 mg IV (may repeat every 5-15 minutes as needed)
  • Indications: Anxiety, sedation, muscle relaxation, seizure control.
  • Contraindications: Hypersensitivity, severe respiratory depression, acute narrow-angle glaucoma.

• Lorazepam

  • Dose: 1-4 mg IV (may repeat every 6-8 hours as needed)
  • Indications: Anxiety, sedation, preoperative medication.
  • Contraindications: Hypersensitivity, severe respiratory depression, acute narrow-angle glaucoma.

• Midazolam

  • Dose: 1-5 mg IV (may repeat every 2-5 minutes as needed)
  • Indications: Procedural sedation, induction of anesthesia, anxiety reduction.
  • Contraindications: Hypersensitivity, severe respiratory depression, acute narrow-angle glaucoma.

2. Etomidate

Overview

Etomidate is an imidazole derivative used for rapid intravenous induction of anesthesia. It is known for its minimal cardiovascular effects.

Dose

• Dose: 0.2-0.3 mg/kg IV (administered over 30-60 seconds)

Indications

• Induction of anesthesia, particularly in patients with cardiovascular instability.

Contraindications

• Hypersensitivity to etomidate, adrenal insufficiency (due to suppression of adrenal function).

3. Ketamine

Overview

Ketamine is a unique intravenous anesthetic that provides dissociative anesthesia and analgesia. It is known for its ability to increase cerebral blood flow.

Dose

• Dose: 1-2 mg/kg IV (for induction)

Indications

• Induction of anesthesia, analgesia for painful procedures, and in patients with asthma or reactive airway disease.

Contraindications

• Hypersensitivity, severe hypertension, or increased intracranial pressure.

Additional Notes

• Ketamine may offer neuroprotective effects and is often used in pediatric patients due to its safety profile.

4. Barbiturates

Overview

Barbiturates are central nervous system depressants that have been used for induction of anesthesia. They act primarily at the GABA receptor.

Common Agents

• Thiopental

  • Dose: 3-5 mg/kg IV (for induction)

• Methohexital

  • Dose: 1-2 mg/kg IV (for induction)

• Thiamylal

  • Dose: 3-5 mg/kg IV (for induction)

Indications

• Induction of anesthesia, sedation, and as anticonvulsants.

Contraindications

• Hypersensitivity, porphyria, severe respiratory depression.

5. Propofol

Overview

Propofol is an alkylated phenol that provides rapid sedation and is widely used for induction and maintenance of anesthesia.

Dose

• Dose: 1-2.5 mg/kg IV (for induction)

Indications

• Induction and maintenance of anesthesia, sedation for procedures.

Contraindications

• Hypersensitivity to propofol or its components, egg or soy allergy.

Additional Notes

• Propofol is favored for outpatient procedures due to its rapid recovery profile and low incidence of nausea and vomiting.

6. Opioid Analgesics

Overview

Opioids are potent analgesics that act centrally on μ-receptors in the brain and spinal cord. They are often used in conjunction with other anesthetic agents.

Common Agents

• Meperidine

  • Dose: 25-100 mg IV (for analgesia)

• Fentanyl-based compounds

  • Dose: 25-100 mcg IV (for analgesia)

• Morphine

  • Dose: 2-10 mg IV (for analgesia)

• Codeine

  • Dose: 15-60 mg IV (for analgesia)

• Oxymorphone

  • Dose: 1-5 mg IV (for analgesia)

Indications

• Pain management, adjunct to anesthesia.

Contraindications

• Hypersensitivity, respiratory depression, severe asthma, or head injury.

Additional Notes

• Opioids have differing potencies, and equianalgesic doses can result in similar degrees of respiratory depression. Therefore, there is no completely safe opioid analgesic.

Stages of General Anesthesia

 Clinical Notes

• Stage I is often brief due to rapid induction agents.

• Stage II is avoided or minimized with modern anesthetics to reduce risk of complications like laryngospasm.

• Stage III is carefully maintained during surgery.

• Stage IV is considered an overdose and must be prevented.

• Stage III Plane 3 → Surgical anaesthesia
• Most reliable indicator: Regular respiration

•  Contraindicated in: Jaundice, Pheochromocytoma, Obstetric cases.
•  Not contraindicated in: Previous Hepatitis A.
•  Associated complications:
  • Malignant Hyperthermia
  • Hepatotoxicity
  • ↑ Intracranial Tension
  • Predisposes to Arrhythmias
•  Stored: Amber bottles, colorless liquid.
•  Preservative: Thymol
•  Poor analgesic.
• Beta-blocker–like myocardial effects.
• Rapid, smooth induction.
• Dissolves in rubber.

• Hypotension – Common post-op issue.
•  Hypoxic hypoxia – MC intra-op type.
•  Malignant hyperthermia – Not caused by Nitrous oxide.