Inhalational Anesthetic Agents

Nitrous Oxide, N2O ("Lauging Gas")

Nitrous Oxide

Physical Properties

  • colorless
  • odorless
  • nonflammable but, like O2, supports combustion
  • gas in room temp and ambient pressure; liquid under pressure

Organ System Effects

Cardiovascular
  • direct myocardial depressant effect balanced by
  • sympathetic nervous system stimulation
  • so BP and P stable
  • myocardial depression may be unmasked by
    • CAD
    • hypovolemia
  • pulmonary vasoconstriction -> increased PVR
Respiratory
  • tachypnea + decreased VT = stable VE and paCO2
  • BEWARE: inhibits carotid body hypoxic drive
CNS
  • mildly increases CBF, CBV and ICP
  • increases CMRO2
  • analgesia

Biotransformation and Toxicity

  • eliminated by exhalation
  • irreversibly oxidizes cobalt atom of vitamin B12, inhibiting B12-dependent enzymes:
    • methionine synthetase (myelin formation)
    • thymidylate synthetase (DNA synthesis)
  • so prolonged exposure can lead to
    • bone marrow depression (megaloblastic anemia)
    • peripheral neuropathy
    • pernicious anemia
  • controversial:
    • emetogenic? (not especially)
    • teratogenic (maybe not, but not necessary in early pregnancy, so usually avoided)

Contraindications

  • 35 times more soluble in blood than nitrogen, N2
  • so fills and expands any air-containing cavities:
    • air embolism
    • pneumothorax
    • intracranial air
    • lung cysts
    • intraocular air bubbles
    • tympanoplasty
    • endotracheal tube cuff (monitor and reduce pressure periodically)
  • may exacerbate pulmonary hypertension




Send Comments to Greg Gordon MD, gjg@po.cwru.edu
Department of Anesthesiology
The MetroHealth System
2500 MetroHealth Drive
Cleveland, Ohio 44109-1998
Phone: (216) 778-4801
Last updated: