NITROUS OXIDE-TIME TO SAY GOODBYE!

Abstract

Nitrous Oxide, our old companion is in use
since long. Its two properties analgesia and
reduction in MAC of inhalational agent make it
a powerful tool in anaesthetic practice.
Importance of nitrous oxide can be judged from
the fact that sizable percentage of anaesthetists
will cancel the elective list if nitrous oxide is
not available!
Widespread and prolonged use of
nitrous oxide has brought into focus certain side
effects. There is almost consensus that chances
of postoperative nausea and vo miting are
increased with intraoperative use of nitrous
oxide.
Nitrous oxide has been blamed for
increased pulmonary artery pressure, pulmonary
hypertension leading to right heart failure in
some cases. Increase in volume and pressure in
closed spaces including intracuff pressure of
cuff endotracheal tubes is long known to
anaesthetist.
Nitrous oxide has been implicated in
few cases of postoperative blindness which
resolved spontaneously. The tag of increased
incidence of spontaneous abort ion and
teratogenic effect remained unresolved issue so
far. Nobody paid much attention to all these side
effect because advantages of nitrous oxide
outweigh its disadvantages.
There is a major safety concern in use of
nitrous oxide.1 There are occasional reports of
administration of hypoxic gas mixture to the
patient leading to hypoxic brain damage and
some occasions leading to death. Reports are
few and far apart but they make big heading in
modern day press.
This was all good when anaesthesia was
important contributor to overall surgical
mortality. Occasional reports of hypoxic
mixture.1-3 administration and death in few cases
were ignored on ground of acceptable mortality.
At that time (1960) anaesthesia was fourth in
causes of direct maternal death in confidential
enquiry into maternal and child health.4 Now
anaesthesia is among uncommon causes in
recent reports. General mortality in anaesthesia
in ASA 1 and 11 cases is in the tune of
1:250000. This exactly is number of cases which
one can maximally perform in h is/her
anaesthetic carrier (more than 13 cases per day
for carrier span of 50 years without having any
break!). So there is no margin of error as far
young and fit patients are concerned.
Nitrous oxide has been the cause of
death in six cases between 200 4-2006 in
Germany, Austria, and Switzerland. There is
tendency toward underreporting of less sever
cases and in developing countries even death
due to nitrous oxide remain unreported in some
occasions.5 The problem is much more
widespread than that normally reported in the
press.
Two main reasons for use of nitrous
oxide-analgesia and reduction MAC of
inhalational agent-can conveniently be
achieved by alternate means. Wide range of
analgesic drugs are available, concepts of
balanced and multimodal analgesia has broaden
our analgesic options.
Reduction in MAC can be achieved by
above mentioned analgesic options and/or use of
wide range of benzodiazepines. Do we require
reduction in MAC with new inhalational agents
is another question? It was in era of halothane
when reduction in MAC was safety concern.
Halothane is gradually fading away from the
scene and new inhalational agents are much less
arrhythmogenic.
Disaster involving nitrous oxide usually
occurs in scenario of repair of existing gas
system or instalment of new gas system. Filling
of wrong gas, cross connection, disconnection
and failure of oxygen-nitrous proportion device
can happen in routine daily life.1,6
Keeping in view safety achieved by
present day anaesthesia practice, nitrous oxide is
major safety hazard and its use in operating
theatres should be discontinued.7
Possible contenders to replace nitrous
oxide are many, two are most promising,
Medical Standard Air and Entonox. Advantages
and disadvantages of each are beyond the scope
of this article.