Ambulance

Clinical Focus on the use of ENTONOX in Pain Management
Entonox – Making the
most of the basics
in pre-hospital pain
management
By Lucas Hawkes-Frost, Paramedic
and Assistant Director of Operations
London Ambulance Service
Entonox: the dusty weather-worn barrel bag in the side cupboard of more or less every ambulance in
the UK, has been a mainstay of pre-hospital pain management since the 1970s; a loyal friend to the
Ambulance Service, there at the birth of the Paramedic profession and along for the ride ever since.
Nitrous oxide, a remarkable substance,
used in rocket fuel among other things, has
long been identified as having analgesic and
anaesthetic properties with use reported
for the relief of pain during labour since
the 1930s, delivered at a concentration of
50% in air, which delivered a useful analgesic
effect with few side effects.
ENTONOX as we know it today, was
developed in 1961 by Dr Mike Tunstall, then
an Anaesthetics Registrar at the Portsmouth
and Oxford United Hospitals, who wrote
to BOC asking about the feasibility of mixing
oxygen and nitrous oxide together under
pressure in a single gas cylinder. BOC duly
Spring 2016 | Ambulancetoday
provided him with grey 48 cu.ft (F-size)
cylinders to continue his development
of portable anaesthetic machines and
ENTONOX was born.
The story of ENTONOX, however,
was very nearly a very short one; at
Oxford, a physicist to the Nuffield Dept
of Anaesthetics and an anaesthetist
exploring this new mix, Drs Epstein and
Cole, discovered that after cooling, the
gas mixture separated and was not stable,
even when re-warmed. ENTONOX was
regarded as being unsafe and it was felt
that it had no future, until Dr Tunstall took
his new development to Aberdeen in 1962
as a consultant. After much development
and experimentation (with the assistance
of Donald’s ice-cream factory), the safety
of ENTONOX was demonstrated through
MRC trials and introduced for pre-hospital
use by unsupervised midwives in 1965.
Since then, ENTONOX has become an
indispensible tool in the formulary of
clinicians working in and out of hospitals,
being a fast-acting, convenient and safe
analgesic ideally suited to managing pain in
a wide range of clinical contexts including
labour, emergency care, procedural
pain, wound care and of course burns.
ENTONOX is especially useful in managing
pain in children without the need for
vascular access or other invasive procedures.
One study, spanning 40 children’s and
general hospitals analysed for children who
received nitrous oxide as a primary sedative.
In total, 1634 nitrous oxide administrations
were identified in the course of the
study, most of which were performed by
advanced nurse practitioners or physician
assistants. The study concludes that while
the likelihood of vomiting increased when
opioids concomitantly, the prevalence of
serious adverse events was very low in the
course of nitrous oxide administration.
Physiologically, the analgesic effect of
ENTONOX and nitrous oxide are not
understood, however the prevailing
evidence suggests that the action is
associated with interaction between
endogenous opioid substances and
noradrenergic systems. This theory has been
developed through observation of a number
of phenomena whereby animals with a
significant morphine tolerance are given
nitrous oxide, the analgesic effects of nitrous
oxide are equally reduced as with opiates,
suggesting similar actions. Indeed, it has
further been observed that the inhibition
or potentiation of specific endogenous
opioid receptors has a similar inhibition or
potentiation of the effects of nitrous oxide
Biography:
Lucas Hawkes-Frost
Lucas Hawkes-Frost is a
Paramedic and an Assistant
Director of Operations for
London Ambulance Service.
Professionally, Lucas has
a background in clinical
operations, clinical education,
quality and patient safety and in addition to
working within the NHS, works with a number
of regulatory agencies and academic bodies
nationally. Lucas has a long standing clinical
interest in pain assessment and management
and has spoken and published around the
subject for a number of years. As a passionate
advocate for the Paramedic profession, Lucas is
a champion for the development of specialist
clinical practice and better collaboration
between professionals and agencies providing
urgent and emergency care.
47 3