Nitrous Oxide & Oxygen Sedation - Anatomy & Physiology

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