NITROUS
OXIDE
Nitrous oxide was first synthesized in the late 1700s as a colorless and almost odorless gas, and its anesthetic and
pain-relieving properties were appreciated
almost immediately. For quite a while it remained out of the mainstream of medicine, being used mostly for
recreation and entertain‑
One cannot easily achieve deep surgical anesthesia
with nitrous oxide alone, unless it is applied in an environment where the
atmospheric pressure is raised. Now
it is used medically only to augment other anesthetics and sedatives, or for minor procedures that do
not require the loss of consciousness.
When nitrous oxide is inhaled in sufficient quantity, there is a euphoric feeling that comes along with the
pain relief The term laughing gas
arises from the giddy state that it produces. By comparison to any of the other drugs that people inhale for
recreation, nitrous oxide is safer,
because it has little effect on critical body functions including respiration; brain blood flow; and liver, kidney,
and gastrointestinal tract processes.
The pharmacological mechanisms of nitrous oxide
have not been completely determined.
Certainly it acts like a general anesthetic and under high pressure can
cause loss of consciousness, so, as we suspect with other anesthetics, it may increase GABA inhibition of
nerve cells. Part of its effect may
also be through the brain's built-in opiate system—the same receptors that morphine and heroin activate. One
of the best bits of data that support
this is that the specific opiate antagonist naloxone blocks the pain-relieving properties of this gas in animal
experiments. In fact, nitrous oxide
has been used to treat opiate and alcohol withdrawal symptoms.
The latest research
studies suggest that nitrous oxide may also act on a neuronal receptor for the neurotransmitter
glutamate, the N-methyl-Daspartate (NMDA) receptor. This is the same site at
which ethanol and ketamine act to
produce their dissociative effects—that feeling of being out of your body.
As we described, in
clinical settings nitrous oxide is rather free of toxic effects. However, for recreational users, there are
four dangers: not getting enough oxygen, getting hurt if the gas-delivery
device works improperly, experiencing
a vitamin B12-related problem that might occur with repeated use, and suffering possible brain toxicity
if nitrous oxide is used in
combination with other drugs that are NM DA antagonists.
First, remember that nitrous oxide is an anesthetic
gas that can cause unconsciousness,
or at least make you so disoriented that you lose good judgment. Major problems occur when the user
arranges some sort of
Second, there is the
physical damage to tissues exposed to any gas that is expanding. Anyone who has
ever held her hand in front of an air or gas jet knows that expanding gas is cooling. That's the principle underlying air-conditioning units. Some users try to inhale
the gas right out of the tank with no
regulation of the flow rate, actually injuring their mouths, tracheas, and lungs from the cooling gas. Also,
there is the direct physical
risk of overexpanding
(blowing up) the lungs as the gas flows at a high volume and pressure.
Third, there is an odd
complication of prolonged nitrous oxide use that is similar to a vitamin B12 deficiency. A B12-dependent enzyme is inactivated by nitrous oxide, and that leads to the
destruction of nerve fibers (a neuropathy)
and thus neurological problems. These can include weakness, tingling sensations, or loss of feeling.
There are several case reports in the
medical literature of nitrous oxide causing severe nerve damage.
Some dentists who
regularly administer this gas have been found to experience this type of neuropathy.
Fourth, animal studies
now suggest that NIVIDA-receptor blockers like nitrous oxide can be neurotoxic in certain brain areas. The combination of ketamine and nitrous oxide suggests that using
these drugs together might be
particularly problematic. In animals, they
are synergistic, producing much more
damage together than would be expected from the simple combination of the two drugs. This should serve as a strong cau‑
tion
to recreational users of nitrous oxide not to combine that use with any other NMDA antagonist like ketamine or ethanol.
Tolerance to nitrous oxide can develop, and the
euphoric properties
diminish
with repeated usage. However, in the recreational setting, where it is used only occasionally, tolerance is unlikely.
