Inhalational Methods - Nitrous Oxide - Oxygen

The analgesic potency of nitrous oxide and its lack of toxicity give it special advantages over narcotics and other analgesics. The degree of analgesia increases with the inhaled concentration, and the rapid onset of the effects are useful when pain relief is required urgently. Recovery from its effects is rapid.

If nitrous oxide-oxygen is administered for 10 minutes, an initial plateau concentration is reached and four zones of analgesia are recognised:

• Moderate analgesia - 6-25 percent nitrous oxide: Normal and full contact may be maintained with the patient.
  
• Dissociation analgesia - 26-45 percent nitrous oxide: Marked analgesia is present, increasing with increasing concentration.
  
• Analgesic anaesthesia - 46-65 percent nitrous oxide: Spoken contact can be maintained until the level reached 65 percent, but the patient exhibits amnesia.
  
• Light anaesthesia - 66-80 percent nitrous oxide: This is not recommended, as 33 percent oxygen is necessary to maintain appropriate oxygen tension in the arterial blood during anaesthesia.

Nitrous oxide-oxygen may be administered as a pre-mixed mixture - 50 percent nitrous oxide - 50 percent oxygen - Entonox.