General Anesthetics: NITROUS OXIDE

-resonates between 2 structures (one with a single triple bond, the other with two double bonds); is gaseous and marketed in high pressure canisters; nonflammable but supports combustion; Guedel signs work well for nitrous.

-good analgesic, low potency

-relatively insoluble, Oswald coefficient= 0.47

-used in dentistry; 20% concentration results in analgesia, typically dentists used concentrations between 30-50%. Maximum useful dose before pt will enter stage 2 is about 60% (pt gets excited and difficult to control in stage 2). 70% is the maximum allowable concentration, valves are rigged so that you can’t get a greater than 70% concentration of nitrous.

-incomplete anesthetic, can’t reach stage 3 even if you went to 100% nitrous oxide

-induction/emergence is fast and pleasant, benign in many ways—no respiratory irritation, no salivation, no depression of circ. System, not toxic to kidney… BUT nitrous oxidizes vitamin B12 and can cause a deficiency, it inhibits an enzyme called methionine synthetase and can lead to megaloblastic anemia.

-not metabolized, compatible with other drugs

-does not cause neuromuscular blockade, which is something we’d like to occur

-in surgery nitrous is often mixed with something else such as halothane, thus called balanced anesthesia

-reduces MAC from other agents, so they become more potent in the presence of nitrous oxide.

-can also mix nitrous with other kinds of agents such as barbiturates, muscle relaxers, often used as psychosedation in dentistry (to control anxiety)

If you use nitrous oxide in your office, you must have scavenging equipment available. N2O is heavier than air and so will accumulate near the floor and hangs around. The people most at risk are the practitioner and his/her staff because they are exposed more frequently. Dentists who use N20 have higher than average congenital abnormalities in their offspring. Male dentists who used N20 in their offices, have wives who aren’t exposed but their children are still more likely to have birth defects. Female practitioners and staff who are exposed to N2O are more prone to have miscarriages.


The strong analgesic effect of nitrous oxide seems to involve the substantia gelatinosa (spinal cord), causes endorphin release. We know this because we can block this analgesic effect with naloxane, a blocker of the receptors there.


So in summary, nitrous oxide is a nearly ideal due to absence of side effects, but lacks potency and efficacy. It’s a good analgesic, and does not cause muscle relaxation. Its an ideal additive to other agents. It can cause a condition called malignant hyperthermia (MH) a very rare but serious thing to be described at the end of the lecture.

Category: Pharmacology Notes