Oxygen Therapy: Theory

Front 1

RT Authorized Act

Back 1

RHPA – 5th authorized act:
“Administering a prescribed substance by
inhalation”

- CRTO Clinical Best Practice Guideline (CBPG)

for administering oxygen

- Oxygen is considered a drug – Food & Drug

Act Drug Identification Number, DIN

Front 2

Oxygen Facts

Back 2

- Makes up 50% of Earth’s crust by weight

- Able to combine with all other elements,
except inert gases, to form oxides

- Ozone (O) is also a pure form of oxygen

Front 3

Oxygen Facts

Back 3

- > 23% considered an oxygen enriched environment = fire hazard

- 21% is normal

Front 4

Clinical Indications for Oxygen Therapy

Back 4

1. Low blood oxygen levels: hypoxemia

2. Severe trauma – ie. +++ blood loss

3. Minimize cardiac workload

4. Short-term prophylactic use

Front 5

Clinical Indications for Oxygen Therapy

Hypoxemia

Back 5

Documented acute or chronic low blood
oxygen levels - hypoxemia:
– PaO2: <60 mm of Hg
– SaO2: <90%
– Correct and alleviate symptoms of shortness of breath (SOB)
– Pneumonia, COPD, bronchiectasis, CF,
pulmonary fibrosis

Front 6

Clinical Indications for Oxygen Therapy

Hypoxemia

Back 6

“An abnormal deficiency of oxygen in the
arterial blood”

“Refers to low oxygen tension of oxygen in the blood.”

Front 7

Clinical Indications for Oxygen Therapy

Hypoxemia

Back 7

Adult PaO (mmHg)

Hyperoxemia >100

Normoxemia 80-100
Mild hypoxemia 60-79
Moderate hypoxemia 45-59
Severe hypoxemia <45

Front 8

Clinical Indications for Oxygen Therapy

Hypoxemia

Back 8

Total oxygen content of blood

– Combination of dissolved & bound to Hb

– CaO2 = (0.003 x PaO2) + (Hb x 1.34 x SaO2)

– Normal is 16-20 mL/dL

Normal arteriovenous difference (~5 mL/dL)

Front 9

Clinical Indications for Oxygen Therapy

Trauma

Back 9

Blood loss
- Not enough blood/hemoglobin to carry O

Head injury
- keep PaO2 levels high -> induce cerebral vasoconstriction -> reduce cerebral blood flow -> reduce ICP -> protect injured brain

Front 10

Clinical Indications for Oxygen Therapy

Cardiac Workload

Back 10

Congestive heart failure (CHF)
- heart unable to pump properly so “back-up” of blood and fluids into pulmonary system – less able to exchange O2/CO2

Myocardial infarct
- high FiO2 for 24-48h to decrease spread of infarct

Front 11

Clinical Indications for Oxygen Therapy

Short-Term Use

Back 11

Post-anesthesia / surgical recovery
- Until patient fully awake, adequate respiratory rate, able to deep breathe, cough, etc.

Front 12

Contradictions to Therapy

Back 12

None!
- But…
- Must ensure indications FOR therapy are

present

Front 13

Complications of O2 Therapy

Back 13

1. Oxygen Toxicity

2. Depression of Ventilation

3. Absorption Atelectasis

4. Retinopathy of Prematurity

Front 14

Complications of O2 Therapy

Oxygen Toxicity

Back 14

Over-production of oxygen free radicals –
cannot be controlled by antioxidants
- Damage or kill cells
- Affect lungs and CNS primarily
– destroys alveolar-capillary membrane
– leads to further low blood oxygen
• Determining factors: PaO2 & exposure time

Front 15

Complications of O2 Therapy

Oxygen Toxicity

Back 15

# Hours Physiological Response
0-12 -Normal pulmonary function
-Tracheobronchitis
-Substernal chest pain

12-24 -Decreasing vital capacity

Front 16

Complications of O2 Therapy

Oxygen Toxicity

Back 16

# Hours Physiological Response

24-30 -Decreasing lung compliance
-Increasing P(A-a)O
-Decreasing exercise PO2

30-72 -Decreasing diffusing capacity

Front 17

Complications of O2 Therapy

Depression of Ventilation

Back 17

- Small percentage of patients with chronic lung diseases (COPD)

- Lung tissue damaged so have chronically high PaCO levels

- To compensate, the drive to breathe depends
on the PaO2

Front 18

Complications of O2 Therapy

Absorption Atelectasis

Back 18

At FiO2’s > 50%, alveolar N2 levels drop
- venous blood levels of N2 also fall

- all gases from alveoli diffuse into venous system

due to high pressure gradients

- areas of lung collapse – atelectasis

- further hypoxemia due to shunting

Front 19

Complications of O2 Therapy

Retinopathy of Prematurity (ROP)

Back 19

Premature or low birth-weight infants
High PaO2 levels cause retinal vasoconstriction resulting in:
- ++ vessel necrosis
- increased formation of new vessels
- haemorrhaging, which causes:

- scarring behind retina
- retinal detachment and blindness

Front 20

Physiological Assessment for Treatment

Back 20

1. Laboratory measurements:
– ie. PaO2, SaO2, hemoglobin, hematocrit,

oxyhemoglobin dissociation curve

2. Clinical problem or condition

3. Clinical assessment and/or patient symptoms

*UNLESS pt presents S&S indicate need it sooner

Front 21

Terminology

Back 21

FiO2: fraction of inspired O2; 0.21-10.

PaO2: partial pressure O2 in arterial blood; >60
mm Hg

SaO2: saturation of hemoglobin with O2; > 90% (60 mm Hg)