Oxygen Therapy

Question 1

Sources

Answer 1

Cylinders: widely available, various sizes, limited length of supply, suitable for short duration, expensive, 100% O2
Wall Supply: in hospital only, central supply, supply 100% O2
Oxygen Concentrators: mains operated machines, molecular sieve, removes N2, 90% conc, regional suppliers with franchise for installation and support
Liquid oxygen: more highly compressed, larger gaseous volume per cylinder, allow higher flow rates

Question 2

Patient Interfaces

Answer 2

Nasal Cannulae: usually well tolerated, accepts flow rates 1-4 L/min, delivers 24-40% O2 - percentage delivered depends on many factors; uses mild hypoxaemia, not critically ill
Uncontrolled masks: simple face/Hudson mask: 30-60% O2, flow rate 5-10L - mix O2, room air and exhaled air in mask, used less often. non re-breathe mask: 85-90% O2 within 15L/min flow rate - bag one way valve stops - mix room air and expired air; use - acutely unwell patients - step down ASAP
Controlled mask: venture mask - controlled O2, valve allows delivery of fixed conc of O2

Question 3

Clinical Indications for O2

Answer 3

Treatment for hypoxaemia, not breathlessness
Chronically hypoxaemic COPD patients with acute exacerbation/are stable
Palliative use in advanced malignancy
Sats: <90% & breathless, though often multifactorial

Question 4

Target Oxygen Sats

Answer 4

Normal young adult average: 96-98% (over 70: 94-98%)
Those at risk of hypercapnia resp failure (High PaCO2) = 88-92%)
Portable Oxygen: may improve breathlessness in some; may extend duration of LTOT; but most breathlessness not due to low PO2

Question 5

Acute breathlessness with hypoxaemia

Answer 5

Risk acute hypoxaemia -> acute cardiac dysrhythmia & organ failure
Treatment: max O2 treatment, high flow uncontrolled mask - alter flow and delivery device when stable; target SpO2: 94-98%
Secure and maintain airway latency, enhance circulation, avoid/reverse resp depressants
Establish reason for hypoxaemia and treat

Question 6

Who is at risk of hypercapnia with high dose O2

Answer 6

chronic hypoxic lung disease (COPD/bronchiectasis/CF)
Chest wall disease (kyphoscoliosis thoracoplasty)
Neuromuscular disease
Obesity related hypoventilation

Question 7

Chronically hypoxaemic patients with COPD who have acute exacerbation

Answer 7

Rely on hypoxaemic drive - if you overcorrect, you may switch off their resp drive
Leading to further CO2 retention worsening acidosis, narcosis, and death
Hypoxaemia may still be a risk to them
Aims of treatment: modest oxygenation, preventing CO2 retention and acidosis, deliver O2 by fixed % Venturi mask, target sats 88-92%

Question 8

How to assess response to treatment

Answer 8

arterial blood gases - pO2, pCO2, pH-adjust dose of O2 accordingly
If not improving may need non invasive ventilation
Dont use cannula - potentially dangerous as actual inspired O2 % varies according to patient resp characteristics; uncontrolled therapy

Question 9

Prescribing Oxygen

Answer 9

Target O2 sat, device delivery and dose (flow rate/% inspired)
Should be prescribed on drug chart
Oxygen is a drug

Question 10

Chronically hypoxaemic patients (with COPD) - Long term Oxygen treatment

Answer 10

Special assessment in patients stable state - no sooner than 4 weeks after exacerbations
Indications: COPD patients with pO2 < 7.3 kPa or pO2 7.3 < kPa and: secondary polycythaemia, nocturnal hypoxaemia, PE, evidence of RV failure, evidence of pulmonary hypertension
Provided from an O2 concentrator, regional concentrator supply service - O2 treatment for >15 hours/day
Benefits: improved long term survival, sleep quality, renal blood flow, reduction of polycythaemia and cardiac arrhythmias
prevention of deterioration of pulmonary hypertension