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ain killers can be performed via spinal/epidural route under the supervision of anesthesia personnel with clinically standard monitoring; intramuscular/intravenous route by using morphine, a well-known narcotic and pain relief, extracted from natural opium; and inhalational route by agents relating to the alveolar concentration and affecting on the central nervous system such as Methoxyflurane or Entonox that have been applied in medicine for more than 40 years. Entonox is an equal mixture of nitrous oxide and oxygen. Notably, nitrous oxide, a well-diffusion with second gas effect, produces a rapid increase in alveolar concentration of oxygen. Drug has effect on brain and spinal cord resulting in patient’s pain relief and comfort. Interestingly, patients themselves are able to administer drug following the physicians’ advice by deeply and slowly breathe in 8-10 times. Entonox has peak onset of 3-5 minutes and wean off of 5-8 minutes after discontinuing inhalation. As a result, it is commonly administered in painless labor, intravenous cannulation, dental works or gastrointestinal duodenoscopy. Adverse effects are diffusion hypoxia, numbness and muscle cramp in hands and feet, dizziness, drowsiness, nausea, vomiting, and dryness of mouth. Additionally, since nitrous oxide can diffuse thoroughly into body space and cavity, Entonox should be cautiously managed in some procedure such as bowel obstruction.
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