Nitrous Oxide, From Discovery to Now - IneedCE.com

Educational Objectives
Upon completion of this course, the clinician will be able
to do the following:
1. Be knowledgeable about the history of nitrous oxide
2. Be knowledgeable about the chemistry and action of
nitrous oxide
3. Understand the dental treatments where use of nitrous
oxide can be useful, as well as know the relative
contraindications to nitrous oxide use
4. Be knowledgeable about the considerations and
recommendations related to nitrous oxide use
and the protocol to be followed on the day of the
patient’s appointment
Abstract
Nitrous oxide was discovered and first prepared in 1793 by
an English scientist and clergyman named Joseph Priestley.
Since then nitrous oxide has proven to be a safe and popular
agent utilized by many dental practices. In this setting,
its use is usually as a mild sedative and analgesic. It helps
to allay anxiety many patients may have toward dental
treatment, and it offers some degree of analgesia. As such,
its use for phobic patients has been well established and
remains its primary indication. Relative contraindications
to the use of nitrous oxide include patients with psychiatric
disorders, blocked eustachian tubes, bowel obstruction,
colostomy bags, gas in the ocular orbit, and large tubercular
lesions in the lung. When administered appropriately,
nitrous oxide is a safe and valuable asset in decreasing the
pain and anxiety experienced by dental patients.
History
Nitrous oxide was discovered and first prepared in 1793 by
an English scientist and clergyman named Joseph Priestley.
He was also the first to prepare and isolate other important
gases, such as oxygen, carbon monoxide, carbon dioxide,
ammonia, and sulfur dioxide. To prepare nitrous oxide,
Priestley heated ammonium nitrate in the presence of iron
filings, then passed the gas through water to remove toxic
by-products before storing the resultant gas, nitrous oxide.
Following Priestley’s work came the study of Humphrey
Davy of the Pneumatic Institute in Bristol, England.
Davy experimented with the gas’ physiologic properties
such as respiration and uptake. Further, he administered
the gas to society visitors of the institute and later coined
the term “laughing gas” after watching its effects on people
who inhaled it. For the next 40 years or so, nitrous oxide’s
primary use was for recreational enjoyment (nitrous oxide
capers) and public show.
Not until the early 1840s did nitrous oxide find its place
in clinical dentistry and medicine. A medical school dropout
named Gardner Quincy Colton went around the country putting
on exhibitions with nitrous oxide. On December 10, 1844,
he put on a demonstration in Hartford, Connecticut, and in the
audience that day was a local dentist named Horace Wells. Dr.
Wells’ interest was sparked when a druggist’s assistant named
Samuel Cooley volunteered to inhale the gas. Afterwards, while
under the effects of nitrous oxide, he bumped into some nearby
benches where he injured his leg. He went back to his seat next
to Dr. Wells, but was unaware of the injury until the effects
of the gas wore off. This tipped off Dr. Wells to the analgesic
qualities nitrous oxide might possess.
After the demonstration, Dr. Wells approached Colton
and invited him to come to his office the next day. Colton
agreed, and the next day he administered nitrous oxide to
Dr. Wells while another local dentist, Dr. Riggs, extracted
one of Dr. Wells’ molars. This personal demonstration
proved successful, since Dr. Wells experienced no pain during
the procedure. Subsequently, Colton taught him how to
manufacture as well as administer the gas to his patients,
which he continued to do throughout the remainder of his
private practice.
In January 1845, Dr. Wells was given the opportunity
to demonstrate the effects of nitrous oxide at the Harvard
Medical School in Cambridge, Massachusetts. A patient was
anesthetized for a tooth extraction, and during the demonstration
the patient responded verbally to the surgical stimulation.
The audience booed and hissed their dissatisfaction,
and the demonstration was deemed a failure, even though
the patient was amnesic during the extraction. This public
humiliation eventually led to the downfall of Dr. Wells and
his suicide in 1848. Little did he know that 150 years later,
he would be recognized as the “Discoverer of Anesthesia.”
Nitrous oxide fell out of popularity after Wells’ suicide
and would not resurge until about 15 years later, largely due
to the efforts and dental practice of Colton in the New England
area. Colton later went on to open numerous “dental
institutes,” utilizing nitrous oxide throughout the country.
During this time, nitrous oxide was administered to patients
in a hypoxic mixture (100%), without supplemental oxygen
or air, to render the patients unconscious. Fortunately, the
procedures were of such a short duration that few suffered
significant morbidity. In fact, Colton administered in excess
of 120,000 such anesthetics without a fatality. Other
contemporary anesthetic agents of the era were ether and
chloroform; however, nitrous oxide is the only agent still in
clinical use today.
Physical Properties
Nitrous oxide (N 2
O) is a colorless, almost odorless gas with a
molecular weight of 44, a specific gravity of 1.53, and a boiling
point of –89°C. It is produced by heating ammonium
nitrate crystals to approximately 240°C. The resultant gas
is then chemically scrubbed to achieve approximately 99.5%
purity, compressed (50 atmospheres) to a liquid form, and
dispensed in pressurized tanks.
The color of the nitrous oxide tank is blue for universal
identification, compared to oxygen tanks, which are
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