CNS Pharmacology Quiz: Depressants Mechanisms & Effects

Study Notes

Anaesthesia

An altered physiological state characterized by reversible CNS depression, where noxious stimuli are neither perceived nor recalled
The more lipid soluble a drug is, the higher its potency and the lower its MAC (minimum alveolar concentration)

Mechanisms of Anaesthesia

Pre-synaptic mechanism: decrease in presynaptic release of Glutamate and increase in reuptake of Glutamate
Post-synaptic mechanism: inhibition of nicotinic ACH receptor, inhibition of Glutamate receptor, and stimulation of GABA receptor

Levels of Sedation

Conscious sedation: patient responds to command with minimally depressed conscious level and adequate spontaneous ventilation
Deep sedation: patient is not easily aroused, spontaneous ventilation may be inadequate, and airway reflexes may be lost
General anaesthesia: patient loses consciousness and airway reflexes, requires assisted ventilation, and cardiovascular function may be impaired

Types of Anaesthetics

Intravenous anaesthetics
Inhalational anaesthetics
Analgesics
Intraoperative adjuvants for general anaesthesia
Postoperative pain relief

Muscle Relaxants

Depolarizing muscle relaxant: Succinylcholine
Non-depolarizing muscle relaxants: Pancuronium, Atracurium, and Vecuronium
Non-depolarizing muscle relaxant antagonists: Neostigmine and Atropine
Uses: facilitate endotracheal intubation, provide skeletal muscle relaxation during mechanical ventilation, and provide abdominal muscle relaxation to improve operative condition

Antidotes

Flumazenil (Anexate): an antidote for benzodiazepine overdoses (Diazepam and Midazolam)
Naloxone (Narcan): an antidote for narcotic overdose to antagonize CNS depression effects including respiratory depression and analgesic effects
Neostigmine: reverses effects of non-depolarizing muscle relaxants, causes bradycardia and increased secretions, so Atropine should be given

Induction and Maintenance of Anaesthesia

Check anaesthesia machine, related equipment, monitors, and drugs
Measure baseline vital signs to compare intra- and postoperative events with preoperative values
Insert i.v. cannula in a peripheral vein of the upper limb
Pre-oxygenation with face mask for 3 minutes
Methods of induction of general anaesthesia: IV induction for patient with normal upper airway

Pharmacokinetics of IV Drugs

Completely bypass the process of absorption
Distributed according to blood supply and lipid solubility
Rapidly metabolized inside liver, thus has short half-life
Usually excreted as water-soluble product from the kidney

Types of IV Anaesthetics

Uses: mainly used for induction of general anaesthesia for patient with normal upper airway, and maintenance of general anaesthesia by continuous infusion

Factors Affecting Anaesthetic Concentration

Factors affecting inspiratory concentration: decreasing volume and absorption of the anaesthetic machine
Factors affecting alveolar concentration: uptake which depends on solubility of agent, alveolar blood flow, and A-to-a gradient
Factors affecting arterial concentration: mainly V/Q mismatch

Description

Test your knowledge on the altered physiological state induced by drug-induced reversible CNS depression. Explore the mechanisms involving decrease in presynaptic release of Glutamate, increase in reuptake of Glutamate, inhibition of nicotinic ACH receptor, and more.