Pharmacology of Ketamine and Anesthesia Techniques

Ketamine

• Induces dissociative anesthesia, providing amnesia and analgesia while preserving consciousness.
• Administered via IV, IM, oral, or rectal routes.
• Mechanism: NMDA receptor antagonist.
• Notable pharmacokinetics: large volume of distribution and rapid clearance.
• Metabolized in the liver; renal excretion.

Advantages

• No associated vomiting or hypotension.
• Acts as a bronchodilator; beneficial for asthmatics.
• Effective in children through IM or rectal administration.
• Useful for changing burn dressings.
• Minimal impairment of pharyngeal and laryngeal reflexes.

Disadvantages

• No muscle relaxation; may elevate blood pressure.
• Increased cerebral blood flow and oxygen consumption.
• Potential for hallucinations and disorientation.
• Possible involuntary movements.

Contraindications

• Contraindicated during pregnancy due to oxytocic effects.
• Avoid in patients with a history of mental illness, hypertension, glaucoma, or head injury.

Benzodiazepines (Diazepam, Lorazepam, Midazolam)

• Used for induction, maintenance, and supplementation of anesthesia.
• Induce sedation and amnesia within 5 minutes.
• Do not cause respiratory or cardiovascular depression.
• Preferred for endoscopic procedures and cardiac catheterization.

Opioid Analgesics (Morphine & Fentanyl)

• Administered at the beginning of painful procedures.
• Frequently used in cardiac surgeries due to minimal effects on myocardial activity.
• Fentanyl combined with benzodiazepines for diagnostic and minor procedures.

Local Anesthesia

• Provides localized pain relief without loss of consciousness.
• Epidural anesthesia: Medication injected into epidural space; effects occur in 10-15 minutes.
• Spinal anesthesia: Medication injected into CSF; effects last 1-2 hours.

Classifications

• Local anesthetics (LAs) are weak bases, characterized by an amine group and an aromatic ring.
  • Esters (e.g., cocaine, procaine): metabolized by pseudocholinesterase; short duration.
  • Amides (e.g., lidocaine, bupivacaine): metabolized by liver enzymes; longer duration.

Mechanism of Action

• LAs block sodium channels, preventing Na+ influx essential for nerve impulse transmission.

Desirable Properties

• Non-irritating to tissues.
• Should not permanently alter nerve structure.
• Low systemic toxicity.
• Quick onset and sufficient potency.
• Long enough duration for procedure completion.
• Free from allergic reactions.

Adverse Effects

• Potential for apnea, hypotension, respiratory depression, necrosis, and gangrene if injected into arteries.
• Risk of porphyria, shivering, and delirium during recovery.

Contraindications

• Avoid in patients with porphyria, shock, or asthma.

Non-barbiturate Anesthetics

Etomidate

• Wide safety margin; suitable for patients with poor cardiac function (e.g., coronary artery disease).
• Onset: 30-60 seconds; duration: 5-10 minutes.
• Possible injection site pain; may require lidocaine.
• Potential for myoclonic movements; often used with diazepam.

Advantages

• Rapid induction and recovery.
• Does not sensitize myocardium to adrenaline.
• Minimal nausea and vomiting.

Disadvantages

• Involuntary movements may occur during induction.
• Prolonged use may suppress adrenal function and cause electrolyte imbalances.
• Not indicated for status epilepticus.

Propofol

• Similar mechanism of action to thiopental; widely used.
• Onset: 30-40 seconds; duration: 5-10 minutes.
• Extensively metabolized; antiemetic properties.
• Must be discarded 8 hours after opening due to bacterial growth.

Advantages

• Effective for induction and maintenance of anesthesia.
• Safe during pregnancy; crosses the placenta.
• Ideal for outpatient procedures.

Disadvantages

• Can cause hypotension and bradycardia.
• Dose-dependent respiratory depression may occur.

This quiz covers the pharmacological aspects of ketamine, including its mechanism of action, advantages, and uses in dissociative anesthesia. Explore its applications in various settings, such as IV, IM, and oral administration, while understanding how it affects patients without causing nausea or hypotension.