Pharmacology: CNS Depressants Mechanisms Quiz

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