OXYGEN THERAPY

(Non-invasive O2 therapy in patient >8yrs)

Learning aims

• Indications and precautions for O2 therapy

• Targets of therapy

• Standard notation

• O2 delivery devices

• Taps, tanks and tubing

Notation

FiO2 = fraction of inspired oxygen (0 - 1.0)

PAO2 = alveolar partial pressure of O2

PaO2 = arterial partial pressure of O2

Goal of O2 therapy

To give the patient as much oxygen as is required to return the PaO2 to what is normal for the particular patient.

• Mitochondria are at the end of the oxygen cascade

• Must restore normal tissue oxygenation and substrate delivery

• There is nothing to be gained by giving too much oxygen, and a huge amount to be lost by not giving enough.

How to increase PO2 in acute settings

How does PO2 relate to saturations

4-5-6 , 7-8-9 rule:

If sats 90%, the PO2 is probably around 60

If sats 80%, the PO2 is probably around 50

If sats 70%, the PO2 is probably around 40

Saturation notations

SaO2 = arterial sats (ABG)

SpO2 = peripheral capillary bed sats (pulseOx)

ScvO2 = central venous sats (sup. vena cava)

SvO2 = mixed venous sats (prox. pulm artery)

Normal SpO2

• Adults <70y, at rest, at sea level, and awake 96% - 98%.

• Adults >70y, at rest, at sea level, and awake >94%.

• Normal patients of all ages may have transient dips as low as 84% during sleep.

Target O2 Sats

• 94-98% for most acutely unwell patients

• 88-92% for those at risk of hypercapnic respiratory failure (rely on hypoxic drive):

• Chronic hypoxic lung disease

– COPD

– Severe chronic asthma

– Bronchiectasis / Cystic fibrosis

• Chest wall disease

– Kyphoscoliosis

– Thoracoplasty

• Neuromuscular disease

• Obesity-hypoventilation

Target O2 Sats (2)

• In acute coronary syndrome and stroke, only give O2 if sats <95%.

• Certain specific conditions (e.g. CO poisoning) may require sats >98%

Hazards of O2 therapy

• Decreased drive to breathe in CO2 retainers*

• In adults, FiO2 > 0.6 for 48hrs can cause oxygen toxicity: CNS, pulmonary and eye damage.

• In neonates, retinopathy of prematurity

• O2 is relatively contraindicated in:• Paraquat poisoning• Bleomycin-induced pulmonary fibrosis

Other complications

• Absorption atelectasis

• Drying of mucosa

• Fire hazard

• Skin irritation

• O2 mask = aspiration risk

• Lower FiO2 than intended due to

• Higher minute volumes

• Inappropriate delivery device

O2 flowmeter

How does it attach?

How do you adjust the flow?

What is the maximum flow rate?

Non-invasive O2 Delivery

Device Performance Maximum FiO2

Nasal prongs Variable 0.4

Hudson mask Variable 0.6

Venturi mask Fixed 0.6

Non-rebreathermask

Variable 1.0

Bag-valve mask Variable 1.0

High Flow mask/nasal prongs

Fixed 1.0

CPAP/BiPAP Fixed 1.0

Nasal Prongs

• Use the dead space of the nasopharynx as a reservoir for oxygen.

• When the patient inspires, entrained air mixes with the reservoir air and the inspired gas is enriched.

• A variable delivery system: the FIO2 depends on the magnitude of flow of oxygen, the patient’s minute ventilation and peak flow.

• The main advantage is comfort: patient can speak, eat, wear glasses, and vomit more easily.

Nasal Prongs (2)• Flow rate 1-6 L/min

• Generally, each additional 1 L/min of O2 flow equals an increase in the FIO2 by 0.04.

1 L = 0.24

2 L = 0.28 etc….

At 6 L (0.44), it is not possible to raise the FIO2 further, due to turbulence.

Also most local guidelines advise max 4 L/min as more than this may cause painful mucosal dryness or epistaxis.

Nasal Prongs (3)

• Very easy for disoriented patients to dislodge

• Not a great difference for mouth-breathers, but not very effective for nose-exhalers.

• Typical notation: “2L O2 via NP”

• N.B. nasal prongs with reservoir attachment: • pts using home O2 may present with these• reduce gas bottle consumption rate by half

Face mask (Hudson)

• Variable performance device

• Expired gas and excess gas from the oxygen source is vented through lateral perforations in the mask and during inspiration air can enter through these perforations.

• Flow rate needs to be minimum 6 L/min to flush CO2 from mask.

• Mask size important

• Reconsider device choice after 2hrs

Face Mask (2)

The FiO2 will depend on:• The source flow rate of 100 % oxygen.

• The patient’s ventilation.

Flow rate (L/min) FiO2 in resting adult FiO2 in dyspnoeic adult

6* 0.50

8 0.55

10 0.60

12 0.65

15 0.70 0.60 max

30 (Y connector) 0.90

Two important concepts when using variable performance masks

1) The effect of the inspiratory flow rate:

2) The effect of the minute volume:• If patient’s MV > 15 L/min (wall supply), air is entrained

and FiO2 will drop.

Resting adult Dyspnoeic adult

Tidal volume 500 mL 600mL

Respiratory rate 15 /min 30 /min

Minute volume 7.5 L/min 18 L/min

Inspiratory flow rate 30 L/min 72L/min

Y connector

Face mask + nebuliser

• Needs 5 L/min to drive the neb

• Driver gas will be O2 for most patients

• If type 2 resp failure patient, can put nasal prongs on at 2L underneath nebuliser mask driven by medical air.

Venturi mask

• Fixed delivery device

• FiO2 range 0.24-0.6

• O2 flow rate specific to each valve

• Humidification issues at higher flows

Non-rebreather

• Reservoir holds up to 2L

• Refills continuously

• 6 L/min…………FiO2 0.7

• 10 L/min………..FiO2 > 0.9

Bag-Valve-Mask with reservoir

• One way expiratory valve important if patient is spontaneously breathing• Valve present, FiO2 >0.9• Valve absent, FiO2 0.6

• With reservoir bag attached:• 3 L/min……..FiO2 0.56• 5 L/min……..FiO2 0.8• 10 L/min……FiO2 1.0 (but use 15 L/min)

• Technique important

Know your equipment

• Humidification system

• Nebuliser

• Regulators

• Tubing

• Portable tanks

Wall ports in the ED

What gas is this?