Oxygen Therapy & Humidification (Wk1) Flashcards
what is O2 therapy used for?
- hypoxaemia ( low concentration of oxygen in the blood)
- some cardiac conditions
what is O2 therapy titrated to meet?
target SpO2/ PaO2 which depends on the patient’s:
- age
- clinical condition
- risk factors for receiving supplemental O2
Target SaO2 for acutely ill patients
94-98%
Target SaO2 for those at risk of hypercapnic respiratory failure
88-92%
medical management to improve PaO2
- increase FiO2 via oxygen therapy
- increase SA (FRC) for gas exchangeh
how does increasing the FiO2 via O2 therapy increase PaO2
increases PAO2 (in alveoli), and therefore by diffusion, increases PaO2 in arteries (arteries surround the capillaries; oxygen diffuses across the alv cap membrane into artieries)
physio strategies to increase PaO2 in hypoxaemic patients
increase SA (FRC) for gas exchange (e.g. via positioning, DB with IH)
how much O2 is in room air?
21%
how much CO2 is in room air?
0.03%
how much N2 is in room air?
79%
PO2 journey through body
air –> upper airways –> alveoli –> interstitium –> blood –> tissues/cells
is the PO2 in the air the same as the Po2 in the blood?
no
factors that contribute to the difference in the partial pressure of the O2 in air vs in blood
- humidification of inspired gas
- gas mixing in airways
- gas exchange across the alveoli-capillary unit
PO2 in air
21% x 760 mmHg = 159 mmHg
what reduces the PO2 in the upper airway?
air is warmed and humidified, introducing significant water vapor, reducing the PO2
PO2 in the upper airway
21% x (760-47) = 149 mmHg
why is the PO2 in the alveoli < than the PO2 in the upper airway?
gas mixing occurs (alveolar & dead space) so that the PO2 in the alveoli is less than in the upper AW
what is the PaO2 in the blood vs to PAO2 in alveoli?
lower
what is the difference between PaO2 and PAO2 known as?
A-a gradient (alveolus-arterial blood supply)
what is a normal A-a gradient for a young adult smoker on room air?
5-10 mmHg
does the A-a gradient increase or decrease with age?
increase (range 5-25mmHg)
normal PaO2
80-100 mmHg
OXYGEN TRANSPORT SYSTEM
what is external air affected by?
- FiO2
- Barometric pressure
- amount of fresh gas inspired
OXYGEN TRANSPORT SYSTEM
what are alveoli affected by?
decreased surface area for gas exchange
OXYGEN TRANSPORT SYSTEM
what are the interstitium affected by?
decreased diffusion
OXYGEN TRANSPORT SYSTEM
what is PaO2 in blood affected by?
- decreased lung perfusion
- decreased cardiac output
OXYGEN TRANSPORT SYSTEM
what is O2 in the tissues/ cells affected by?
decreased oxygen extraction & utilisation
options for oxygen therapy delivery?
- piped system (through the wall) (cold & dry)
- O2 cylinder (cold & dry)
- O2 concentrator (at room temp & humidity)
what 2 factors determine how much O2 the patient receives on O2 therapy?
- FLOW from the O2 therapy device
- the patient’s demand for FLOW
what is the definition of the the FLOW from the O2 therapy device?
the flow rate of the O2 that’s being delivered to the patient (e.g. in L/min)
are O2 delivery systems/ devices classified as high/ low flow?
either
what is the patient’s demand for FLOW?
ptnt’s own camera inspiratory flow rate (PIFR)
can patient’s have a normal / higher than normal IFR?
both
