📖 Anaesthesia

• Benzodiazepines:
  • Produce anterograde amnesia
  • Act on α-subunit of GABA-A receptors
  • Muscle relaxation with Midazolam
  • Flumazenil: Specific antagonist
  • Lorazepam: Difficult reversal

Pharmacodynamics of Nitrous Oxide

Overview

Nitrous oxide (N2O), commonly known as "laughing gas," is an inhalational anesthetic used primarily for its analgesic and anxiolytic properties. Understanding its pharmacodynamics is crucial for safe and effective use in clinical settings.

Pharmacodynamics

1. CNS Depression:

   • Nitrous oxide produces nonspecific central nervous system (CNS) depression.
   • While it is classified as an inhalational general anesthetic, it provides limited analgesia, making surgical anesthesia unlikely unless concentrations that produce anoxia are reached.

2. Potency:

   • Nitrous oxide is the weakest of all inhalation agents, with a minimum alveolar concentration (MAC) of approximately 105%.
   • The MAC is a measure of the potency of an inhalation agent, defined as the concentration required to produce immobility in 50% of patients in response to a surgical stimulus.

3. Effects at Various Concentrations:

   • 30% to 50% Concentration:
     • Produces a relaxed, somnolent patient who may appear dissociated and is easily susceptible to suggestion.
     • Some patients may experience amnesia, but there is typically little alteration in learning or memory.
   • Greater than 60% Concentration:
     • Patients may experience discoordination, ataxia, giddiness, and increased sleepiness.
     • It is recommended that the concentration of nitrous oxide should not routinely exceed 50% to avoid adverse effects.

4. Titration:

   • One of the advantages of nitrous oxide is its ability to be easily titrated.
   • It can be increased for stimulating procedures (e.g., injections) and decreased during less stimulating periods (e.g., restorations).

Physiological Considerations

1. Entrapment in Gas-Filled Spaces:

   • Nitrous oxide can become entrapped in gas-filled spaces such as the middle ear, sinuses, and gastrointestinal tract.
   • This can lead to increased middle ear pressure, which is generally insignificant in patients with normal Eustachian tube function but can induce pain in patients with acute otitis media.

2. Contraindications:

   • Acute Otitis Media: Use should be avoided in patients with this condition due to the risk of increased middle ear pressure and pain.
   • Severe Behavioral Problems and Emotional Illness: Patients who are uncooperative or have a fear of "gas" may not tolerate nitrous oxide well.
   • Claustrophobia: Patients with this condition may feel uncomfortable with the nasal hood placement.
   • Maxillofacial Deformities: Conditions that prevent proper placement of the nasal hood can contraindicate its use.
   • Nasal Obstruction: Conditions such as upper respiratory infections, nasal polyps, or a deviated septum can hinder effective administration.
   • Chronic Obstructive Pulmonary Disease (COPD): Patients with COPD may have difficulty with nitrous oxide due to respiratory issues.
   • Pregnancy: Caution is advised when using nitrous oxide in pregnant patients.
   • High Oxygenation Situations: Situations where high oxygenation is inadvisable, such as during Bleomycin therapy, contraindicate the use of nitrous oxide.

• Ether → Basis of anaesthesia staging
• MAC (Minimal Alveolar Concentration) → Indicator of potency
• Minimum O₂ in mix → 25%
• Agents fluorinated → 🔥 Non-inflammable