Oxygen therapy

1. DR TR SHRESTHA, KMCTH

2. Contents
▪ Introduction
▪ Indications
▪ Classification
▪ Low flow system
▪ High flow system

3. Introduction
▪ Joseph Priestley, who discovered oxygen in 1774,
suggested that it might be “peculiarly salutary to
the lungs in certain morbid cases”
▪ Administration of oxygen at concentrations
greater than that in room air to treat or prevent
hypoxemia

4. O2 therapy: recommendations
▪ Cardiac and respiratory arrest
▪ Hypoxemia (PaO2 < 60 mm Hg, SaO2 < 90%)
▪ Hypotension (systolic BP < 100 mm Hg)
▪ Low cardiac output and metabolic acidosis
▪ Respiratory distress (respiratory rate > 24/min)

5. Indications for postoperative patients
Patient factors
▪ Cardiorespiratory disease, elderly, shivering,
obesity
Surgical factors
▪ Thoracic surgery, upper abdominal surgery
Physiological factors
▪ Hypovolemia, hypotension, anemia

6. Classification
Performance of the device
▪ Fixed (venturi mask)
▪ Variable performance (nasal prong, face mask)
Flows delivered by the device
▪ Low flow (nasal prongs, face mask)
▪ High flow (venturi mask)

7. Patient dependency
▪ Dependent (face mask, nasal prongs, CPAP device)
▪ Patient-independent (Ventilators)
Degree of dependency
▪ Low dependency (face mask, nasal prongs)
▪ Medium dependency (CPAP mask and equipment)
▪ High dependency (noninvasive or invasive positive
pressure ventilation)

8. Low flow O2 delivery system
Nasal cannula
▪ Low flow variable performance device with no capacity
▪ Patient’s nasopharynx: anatomic reservoir
▪ During inspiration, oxygen diluted with room air
▪ FiO2 depends on flow rate of oxygen, patient’s minute ventilation and
inspiratory flow and volume of the nasopharynx
Flow
▪ 1 L/m: 24% 2 L/m: 28% 3 L/m: 32%
▪ 4 L/m: 36% 5 L/m: 40%

9. Advantages Disadvantages
▪ Comfortable for patient
▪ Ideal for claustrophobic patients
▪ Ideal for oxygen dependent
patients requiring small amounts
of oxygen esp at home
▪ Humidification not required up to
4 L/m
▪ Unpredictable FiO2
▪ Maximum estimated FiO2 0.4
▪ Not appropriate in respiratory
distress
▪ High flow: drying and irritating
effect on nasal mucosa
▪ Use may be limited by presence of
excessive mucus, mucosal edema,
or a deviated septum

10. Face mask
▪ Low flow variable performance device with small capacity
▪ Pediatric face masks (70–100 mL), adult (100–250 mL)
▪ Higher FiO2 →delivered if mask volume increased
▪ O2 that gets collected in the apparatus dead space at the
end of expiration is inhaled at the beginning of the next
breath
▪ Exhaled gases vented out through holes on each side of the
mask, which also serve as room-air entrainment ports.

11. Flow
▪ 5-6 L/m: 40% 6-7 L/m: 50% 7-8 L/m: 60%
Advantages
▪ Quick and easy to setup and apply
Disadvantages
▪ Unpredictable FiO2
▪ Not more than 0.5 FiO2 can be delivered
▪ CO2 rebreathing with flow rates <2 L/m

12. Reservoir Face mask
▪ High capacity, low-flow, variable performance
device
▪ Higher FiO2 due to reservoir bag attached
▪ O2 flows directly into reservoir bag
▪ Flow rate of O2 adjusted so that bag remains
completely/ partially distended

13. Partial rebreathing mask
▪ Simple mask with a reservoir bag
▪ Oxygen flow should be supplied to
maintain reservoir bag at least 1/3 to 1/2
full on inspiration
▪ Reservoir receives fresh gas plus exhaled
gas approximately equal to the volume of
the patient’s anatomic dead space
▪ Exhaled gases combine with fresh O2
▪ At a flow of 6–10 L/min →40–70% oxygen

14. Non-rebreathing masks
▪ Do not permit mixing of exhaled gases with fresh
gas
▪ One-way valve over reservoir bag→ prevents entry
of expired gas
▪ One-way valve over one of the side ports limits
entrainment of room air during inspiration
▪ Higher FiO2 than simple, partial-rebreathing masks
▪ FiO275–90% at flow rates of 12–15 L/m

15. Venturi mask
▪ Venturi effect based on Bernoulli principle
▪ As the velocity of a fluid ↑, pressure exerted ↓
▪ When a fluid flows through a constriction the fluid
velocity must increase to satisfy the equation of
continuity
▪ Describes how a second fluid can be entrained into the
stream of the first

16. Air-entrainment mask

17. ▪ High-flow, fixed performance device
▪ O2 supplied to mask through narrow bore oxygen tubing
▪ A negative pressure created→room air entrained through
the apertures in the Venturi barrel
▪ Resultant air-oxygen mixture containing the prescribed O2
concentration flows into face piece for patient breathing
▪ Excess gas flushes out the expired CO2 through the holes on
the sides of the mask →No rebreathing

18. FiO2 provided
by the Venturi
valve
O2 flow to
the valve
(L/min)
Amount of
air entrained
(L/min)
Total flow to
patient
(L/min)
0.24 2 51 53
0.28 4 41 45
0.31 6 41 47
0.35 8 37 45
0.40 10 32 42
0.60 15 15 30

19. Medium dependency system: CPAP
▪ Used when respiratory assistance with O2 supplementation
needed
▪ Can only be used in spontaneously breathing patients
▪ CPAP mask: Face mask with head strap, O2-CPAP valve,
flow generator and wide bore tubings
▪ O2-CPAP valves provide CPAP from 2.5–20 cm of H2O
▪ Flow generator can be plugged into wall outlet for O2
▪ Wide bore tubing connects the flow generator to the mask
▪ 2 one way valves: inlet valve and outlet valve

20. Enclosure systems
▪ Oxygen hood: Transparent enclosure, surrounds head of neonate/
small infant
▪ Well-tolerated, and allow easy access to chest, trunk, and extremities
▪ Continuous flow of humidified O2 is supplied to the hood
▪ Deliver 80–90% oxygen at a flow rate of 10–15 L/m
▪ Limitation
▪ Size: Children <1 year of age
▪ Decrease in O2 concentration when enclosure is opened
▪ Risk for cutaneous fungal infection (humidified O2)
▪ Use of an improperly sized hood→skin irritation
▪ Hypoxia or hypercapnia from inadequate or loss of gas flow

21. High-flow nasal cannula
▪ High-flow nasal O2 using heated and
humidified gas
▪ Heated to body temperature and
supersaturated with water (to a relative
humidity of 99%)
▪ O2 flow rates up to 40–60 L/min
▪ Wide nasal prongs without discomfort and
mucosal injury
▪ Improved oxygenation and gas exchange
▪ Avoiding intubation and mechanical
ventilation

22. Toxic nature of Oxygen
Hydrogen
peroxide
Super-
oxide
Hydroxyl
Radical
Hypochlorous
Acid
Singlet
Oxygen
O2 Metabolism

23. Safe FiO2
Pulmonary oxygen toxicity
▪ Inflammatory lung injury in patients who have inhaled
gas with an FiO2 >60% for longer than 48 hours
▪ If antioxidant stores in lungs depleted, O2 toxicity
expected at FiO2 <60%
▪ FiO2 above 21% can represent toxic exposure to
oxygen in critically ill patients
▪ Best practice: FiO2 to the lowest tolerable level