Understanding Anesthesiology - The Global Regional Anesthesia ...

Nitrous oxide (N2O)
Class
Nitrous oxide is an inhaled agent but not a volatile agent. It is used as an adjunct to general
anesthesia. It has a weak effect and therefore cannot be used as the sole agent for general anesthesia
and is most commonly used in combination with a volatile agent. It can be used on
its own for sedation or analgesia as can be seen in the obstetric or dental setting.
Mechanism of Action
Uncertain
Dose
Delivered in concentrations of up to 70% in oxygen. Actual MAC is 104%.
Onset
Immediate due to very low solubility.
Duration
Offset of effect is rapid after discontinuation.
Elimination
Pulmonary
Effects
CNS
N 2O is a potent analgesic. It increases cerebral metabolic rate, cerebral blood flow and intracranial
pressure and is therefore not a good choice for patients with decreased intracranial
compliance.
CVS
N 2O has a mild sympathomimetic effect but causes direct myocardial depression. The net effect
is a modest decrease in blood pressure and heart rate. Increased coronary tone may exacerbate
ischemia in susceptible patients.
Respiratory
N 2O produces mild respiratory depression which is potentiated by opioids, hypnotics and
volatile anesthetics. It has no bronchodilatory effect. It exacerbates pulmonary hypertension.
Misc.
N 2O expands the volume of gas-containing spaces as N 2O diffuses across membranes more
readily than nitrogen can diffuse out. Thus the size of a pneumothorax, emphysematous
bleb or distended bowel loop will increase when N 2O is used. Bone marrow suppression
due to inhibition of methionine synthetase, can occur if N 2O is used for extended periods.
N 2O enhances opioid-induced rigidity. Finally, N 2O is an operating room pollutant; N 2O levels
(in parts per million) in the operating room environment are measured regularly to comply
with workplace safety regulations.
Related Glossary Terms
Analgesia, Flowmeter, Four A’s of anesthesia, Inhaled agents, MAC, Volatile
Index
Find Term
Chapter 3 - General Anesthesia
Chapter 3 - General Anesthesia
Chapter 4 - Recovery
Chapter 5 - Obstetrical Anesthesia
Chapter 6 - Drug Finder
Chapter 6 - Inhaled Agents