This document describes the anatomy and physiology of respiration and the effects of nitrous oxide. It discusses how air moves through the nasal cavity, pharynx, larynx, trachea, bronchi and into the lungs and alveoli where gas exchange occurs. It explains that nitrous oxide rapidly diffuses into the bloodstream due to its low solubility, which can temporarily reduce oxygen saturation levels. The document outlines the levels of sedation and safety precautions for nitrous oxide administration.

1. Chapter 8
Based on
Handbook of Nitrous Oxide & Oxygen Sedation, 3rd edition
Morris S. Clark
Ann L. Brunick
Nitrous Oxide & Oxygen Sedation

2.  Functions to exchange
gases
 CO2 & O2
 Driven by
 Brainstem
 Cerebral Cortex

3.  Nose
 Warms air
 Humidifies air
 Filter macroparticles
 Must be clear for Nitrous
to be administered

4.  Pharynx
 Muscular tube 12 – 14
cm long
 Nasopharynx
 Adenoids, tonsils,
eustachian tube opening
 Soft Palate separates
Nasopharynx from
Oropharynx

5.  Oropharynx
 Opens into mouth
 Link between
nasopharynx and
laryngopharynx
 Entrance to esophagus

6.  Larynx
 Vocal cords
 Narrowest point of airway
 Muscles will adduct to prevent
aspiration of foreign object
 defensive cough reflex when
irritated
 Trachea
 Cartilaginous rings horseshoe
shaped
 Bifurcates to right and left
bronchi
 Carina – at bifurcation -
second defense and will
initiate a cough reflex when
stimulated

7.  Bronchi
 Right deviates slightly from
trachea and aspirations are
usually in the right side due to
minimal deviation
 Divides into three branches
 Left Bronchi bifurcates into
two branches
 Bronchioles
 Continuation of bronchi
 Identified by lack of cartilage
 First 16 generations of 23 are
conduction only
 17 to 23 will exchange gases –
beginning respiratory zone

8.  Active inspiration
 Diaphragm, external
intercostal muscles,
scalenes, and
sternocleidomastoids
 Produces change in air
pressure inflating or
deflating lungs
 Plerural cavity – fluid
filled space that causes
lungs to expand with
chest movements

17.  Tidal Flow
 Automatic ebb-and-flow of inspiration and expiration
 Tidal Volume
 Volume or gas inspired and expired
 Respiration rate = # gas exchanges / minute
 Tidal volume = amount of gas exchange per inspiraton
 Minute Ventilation
 Respiration Rate x Tidal Volume
 Amount of gas per minute

19.  Amount of air per minute entering alveolar units
 Less than minute volume
 Not all air enters alveoli
 Conduction or dead space
 Subtract dead space from tidal volume and multiply by
respiration rate
 (Tidal Volume – Dead Space) x Respiration Rate

20.  Dependent on partial
pressure of gas in
 Lung / alveoli
 Blood
 Amount of gas dissolving
in blood depends on its
 solubility
 partial pressure
 Moves from high to low
pressure / concentration
 Rate of dissolving depends
on pressure gradient

22.  Amount of gas absorbed by blood is its solubility
 Low solublity = high diffusion rate (RAPID)
 Little gas is absorbed by blood elements
 Rapid onset due to rapid diffusion and low solubility
 Rapid rate is the same when pressure gradient is
reversed
 Rapid Recovery

23.  Rapid Diffusion due to low solubility
 N2O exits rapidly
 More rapid than Oxygen replacing it
 Alveolar O2 is diluted / displaced
 Reducing PO2 saturation
 Pulse oximetry – oxygen saturation = oxyhemoglobin
 Amount of oxygen carried in blood
 100% Oxygen 3-5 minutes after nitrous prevents this

26.  Nitrous level greater than 50%
 Practitioner is responsible for intended level and next
level of sedation
 Intended level is minimal < 50%
 Next level is Moderate
 Some patients are hyper-responders
 Some patients take medications and effect is additive
 Pre procedural fasting may be needed if moderate
sedation is used to prevent aspiration

28. Minimal Sedation
Responsible For Moderate

30. Responsible for Deep Sedation
Protective Reflexes & Spontaneous Breathing Lost
Advanced Airway Rescue Needed

32.  Deeper sedation
 tongue may occlude airway
 Foreign body aspiration is a risk (silent regurgitation)
 During minimal and moderate sedation
 Laryngeal and pharyngeal reflexes should remain intact
 Cough and gag reflexes protect the airway
 Titration is Paramount for safety
 Hyper-responders may drift down to next level
 Unknown medications …….

33.  Head tilt - chin lift
 Positive pressure ventilation
 Full face mask and ambu bag
 Aspiration of vomitus is unlikely
 If protective reflexes are intact
 If vomiting occurs
 suction pharynx
 Oxygen 100%
 DC dental care

34.  Used for moderate sedation
 Intentionally or unintentionally
 Light meal with no fried or fatty foods
 Within 6 hours
 No liquids 2 hours prior