Inhalational Anesthetic Agent1 N2o

1

Inhalational Anesthetic Agents Nitrous Oxide, N2O ("Lauging Gas")

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



o

CAD

o

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



2

Biotransformation and Toxicity  





eliminated by exhalation irreversibly oxidizes cobalt atom of vitamin B12, inhibiting B12-dependent enzymes: o

methionine synthetase (myelin formation)

o

thymidylate synthetase (DNA synthesis)

so prolonged exposure can lead to o

bone marrow depression (megaloblastic anemia)

o

peripheral neuropathy

o

pernicious anemia

controversial: o

emetogenic? (not especially)

o

teratogenic (maybe not, but not necessary in early pregnancy, so usually avoided)

Contraindications  



35 times more soluble in blood than nitrogen, N 2 so fills and expands any air-containing cavities: o

air embolism

o

pneumothorax

o

intracranial air

o

lung cysts

o

intraocular air bubbles

o

tympanoplasty

o

endotracheal tube cuff (monitor and reduce pressure periodically)

may exacerbate pulmonary hypertension

3