This document provides an overview of oxygen therapy, including relevant terminology, oxygen transport and monitoring, causes of hypoxemia and hypoxia, administration of oxygen therapy, and clinical situations where oxygen is commonly used. Key points covered include the partial pressure of oxygen in the lungs and blood, how supplemental oxygen increases this pressure gradient and oxygen saturation, and the five major categories where oxygen therapy is generally applied: medical emergencies, pulmonary disease, the perioperative period, the ICU, and home oxygen therapy.

1. R E S 4 8 1 0
Introduction to Oxygen Therapy

2. Relevant Terminology
 Hypoxia: Inadequate oxygen at the tissue level
 “Hypo” = less than normal or normally
 “Oxia” = relating to Oxygen
 Hypoxemia: Decreased oxygen tension (partial
pressure) in the blood;
 “Hypo” = less than normal or normally
 “Emia” = in the blood
 Normal PaO2: 80 - 100 mmHg
 The partial pressure of Oxygen, arterial
 This is a large contributing factor to subsequent tissue
hypoxia (but not the only one).

3. Oxygen Transport:
Once oxygen enters the blood it is carried in 2 forms:
 Dissolved in plasma – ___%
 Very small amount of transport capability to body tissues
 Combined with hemoglobin – ____%
 Hb is the major protein in red blood cells

4. Oxygen Transport:
 Both the amount of oxygen dissolved in the plasma and
the percent of hemoglobin saturated with oxygen are
directly proportional to the partial pressure of
oxygen in arterial blood
Therefore: ↑ PaO2 = ↑ SaO2 and ↑ O2 plasma

5. Partial Pressure of O2 as it travels to the Lungs
Important: The partial pressure of a gas in ambient
air is a function of its atmospheric fraction:
 Normal barometric pressure at sea level: 760mmHg
 Fraction of oxygen (FiO2) = 0.21
 Partial pressure of oxygen (PIO2) in dry air is:
 PIO2 = FiO2 x PB
 PiO2 = 0.21 x 760 = 159 mmHg
 Partial pressure of nitrogen (PN2) in RA is:
 PN2 = (0.79 x 760) or (760 – 159 mmHg)  600 mmHg

6. What happens in terms of PIO2 as oxygen enters the
respiratory tract?
PIO2 is less in the bronchi, where inspired gas is fully
saturated with water vapour at body temperature
PIO2 (partial pressure of inspired O2) =
PIO2 = (PB – (PH2O @ 37C)) x FiO2
PIO2 = (760 – 47 mmHg) x 0.21
= 713 mmHg x 0.21
= 149 mmHg

7. How do things work at the level of the alveolus?
PAO2 (partial pressure of oxygen in alveolus) =
PiO2 – (PaCO2/R)
Where
 PaCO2 = partial pressure of carbon dioxide in arterial blood
(normally around 40 mmHg)
And
 R = respiratory exchange quotient - the ratio between the
normal rates at which CO2 diffuses out of the blood and into
the alveolus at the AC membrane and O2 diffuses out of
alveolus into the blood at the AC membrane
 R is normally equal to 0.8

8. Therefore; The ALVEOLAR AIR EQUATION
PAO2=[(PB – PH2O) x FiO2] – (PaCO2/0.8)
PAO2 = 149.73 or 150 mmHg – (40 mmHg/0.8)
 100 mmHg
Airway Alveoli

9. What are we doing when we give supplemental O2?
By increasing the fraction of inspired oxygen (FiO2) to 0.40:
PO2 @ 0.40 at atmospheric pressure
= 0.40 x 760 = 340 mmHg
PIO2 = (760 – 47) x 0.40 = 285 mmHg
PAO2 = 285 mmHg – (40/0.8) = 235 mmHg

10. By giving an increased FiO2 we:
 ↑ the PAO2, which ↑ the PRESSURE GRADIENT
between the O2 present in the alveolar spaces and that
present in the pulmonary capillary blood
 This ↑’d pressure gradient between the alveoli and the
pulmonary capillaries, ↑’s the rate of O2 diffusion across
the membrane, increasing the partial pressure of O2
in the arterial blood

11. How do we monitor oxygen levels in the blood?
1. Non-invasively:
 Pulse Oximetry
 a finger clip that sends different wavelengths of light to
measure a pt’s oxygen saturation.
 SpO2 – O2 saturation by pulse oximetry
 Expressed as a percentage; measures number of Hb
molecules saturated with O2 relative to the number of Hb
molecules available
 Normal SpO2 = 95 – 98%,
 SpO2  92% clinically acceptable under most
circumstances

12. How do we monitor oxygen levels in the blood?
2. Invasively:
 Direct measurement of PaO2 and SaO2 (oxygen saturation
as measured in arterial blood) by arterial blood gas
sampling

13. How do we monitor oxygen levels in the blood?
3. Clinical Assessment:
 Look at your patient!
 What are some signs of poor oxygenation?
 Tachycardia ( HR)/possible ECG changes (dysrhythmias or
signs of myocardial ischemia)
 Dyspnea (pt. c/o SOB)/tachypnea (RR)/accessory muscle
use ( WOB)
 Cyanosis (blue discoloration of mucous membranes 2 poorly
saturated hemoglobin)
 Decreased LOC/decreased mental capacity , headache,
confusion

14. Hypoxemia and Hypoxia
What are some possible reasons for a patient's PaO2
to be decreased (or for hypoxemia to occur)?
 Inadequate fraction of oxygen in inspired gas
 Decreased partial pressure of oxygen
 Lung disease/trauma/infection

15. What are possible reasons for a patient to become
hypoxic?
REMEMBER mnemonic acronym HASH
 Hypoxemia – Less oxygen in blood
 Anemia - less functional hemoglobin to deliver oxygen to
tissues
 Stagnant - the blood is well oxygenated, but the
circulation is slow, and the oxygen isn’t getting to the
tissues - eg. cardiogenic shock
 Histotoxic: the cells receive plenty of oxygen, but are
unable to utilize it, eg. in cyanide poisoning

16. What kind of metabolism will occur at the tissue
level if hypoxia occurs?
tissue hypoxia

anaerobic metabolism

ATP production decreases

Waste products (lactic acid)

Cellular function?

17. Once the need for oxygen therapy has been
established we need to determine:
1. The best route of administration
2. The amount of oxygen required

18. 1. Route of Administration
 Nasal Prongs
 Mask – several types
 Face tent/Trach Hood/T-piece
 Oxyhood/Mist Tent (pediatric applications)
 Non-invasive ventilation
 Ventilator Circuit
 Over your time here in the program, you will
learn about all of these applications, and be
required to set them up for patient treatment.

19. 2. Amount of Oxygen Required
 Written order, medical directive or titration protocol
 Examples:
 Adjust FIO2 to maintain PaO2 > 80 mmHg
 Admit patient to surgical floor on O2 @ 3L/min NP
 Titrate O2 to Keep SpO2  92%; Titrate O2 to Keep SpO2 88
– 92%

20. Clinical situations in which oxygen is used
generally fall into five major categories:
1. Medical and Surgical Emergencies
 virtually all pts with medical or surgical emergencies are
given O2, usually by face mask, either when transported by
ambulance or on arrival to the ED
 ex. pts with suspected AMI or ischemia, severe asthma,
CHF, and major trauma

21. Clinical situations in which oxygen is used
generally fall into five major categories:
2. Pulmonary Disease
 patients hospitalized with acute or chronic lung disease
may receive O2;
 ex. pneumonia, asthma, bronchitis, emphysema, lung CA
3. The Peri-operative and Post-operative Period
 supplemental O2 is almost always given during and after
surgery, even to otherwise healthy pts
 rationale: anesthetic agents, muscle relaxants, positive
pressure ventilation and prolonged periods of time in the
same position may cause a certain amount of atelectasis
(alveolar collapse)

22. Clinical situations in which oxygen is used
generally fall into five major categories:
4. Intensive Care Unit
 many ICU patients are mechanically ventilated and require
increased FiO2
5. Home Oxygen Therapy
 many chronic pulmonary patients benefit from low-flow
O2 therapy at home, usually given via nasal prongs at flow
rates of 1-5 L/min (may be higher in some cases)