Week 2: Non-IV Sedation (Part 2)

Who first discovered nitrous oxide?

Joseph Priestley

1795

Who first used N₂O for dental extraction in 1844?

Horace Wells

Who demonstrated ether anesthesia at Massachusetts General Hospital in 1846?

William T.G. Morton

What was William Stewart Halsted's contribution to local anesthesia?

he developed the use of cocaine to block peripheral nerves

What is the min O₂ concentration delivered during N₂O/O₂ sedation?

Greater than 20% O₂ using a failsafe device

What is the onset, peak effect, and recovery time of N₂O sedation?

Onset 2-3 min

Peak 3-5 min

Recovery 3-5 min with 100% O₂

What is the analgesic equivalent of 20% N₂O?

Approximately 10-15 mg morphine (as stated in lecture)

What are the main advantages of N₂O/O₂ sedation?

Rapid onset/recovery, readily titratable sedation, controllable duration, and analgesic effects

What must pediatric patients be able to do for N₂O sedation?

Breathe through the nose and accept the nasal equipment

Why can N₂O/O₂ be useful in cardiovascular disease?

Increases O₂ delivery and reduces anxiety/myocardial O₂ demand

Is N₂O appropriate for patients with asthma?

Yes, it is non irritating to respiratory mucosa

What are the relative contraindications to N₂O sedation?

COPD, 1st trimester pregnancy, claustrophobia

Why is COPD a relative contraindication to N₂O?

some COPD patients rely on decreased O₂ levels to stimulate breathing due to chronic CO₂ retention

vs healthy ppl respond more to increased CO₂ levels

Why should N₂O be avoided during the first trimester of pregnancy?

some concerns about spontaneous abortion and fetal malformation

What are the chemical properties of N₂O?

Relatively insoluble in blood, low potency, 100× more soluble than O₂, and enters air spaces 35× faster than N₂

Why is N₂O contraindicated or used with caution in closed airspace conditions?

rapid diffusion into enclosed spaces can increase gas volume/pressure

What conditions require caution because N₂O expands air spaces?

Pneumothorax, bowel obstruction, tympanoplasty

Concentration effect:

Higher inspired N₂O concentrations produce faster uptake/absorption

Second gas effect:

Rapid N₂O uptake accelerates absorption of a simultaneously administered inhaled anesthetic (ex: Forane)

Does N₂O undergo biotransformation?

no, N₂O is not metabolized in the body

Diffusion hypoxia:

Rapid diffusion of N₂O from blood into alveoli displaces/dilutes O₂ after discontinuation

What are signs of diffusion hypoxia?

Headache, nausea, lethargy

How is diffusion hypoxia prevented?

Administer 100% O₂ for 3-5 minutes after stopping N₂O

What are the CNS effects of N₂O/O₂ sedation?

Mild CNS depression with decreased sight, hearing, touch, and pain sensation

What are the cardiovascular effects of N₂O?

Slight myocardial depression, no change in HR/CO, cutaneous vasodilation causing flushing/perspiration

How is N₂O/O₂ sedation administered?

Begin with O₂ at minute volume

Start N₂O at 20%

Titrate every 60 seconds

Finish with 100% O₂ for 3-5 minutes

What are common pitfalls of N₂O sedation?

excess

Why is scavenging important during N₂O administration?

prevents chronic occupational exposure

What complications are associated with chronic N₂O exposure?

Neuropathy, possible bone marrow suppression, reproductive concerns

What are the concerns with recreational N₂O abuse?

Reported fatalities and altered sensations/behavior

What does Malamed recommend for dismissal after N₂O sedation?

unescorted dismissal may be considered after complete recovery