P9. Oxygen therapy

Long-term oxygen therapy (>15 h/day) prolongs life in hypoxaemic patients
(Pao2 < 55 mmHg, or 7.3 kPa) (Medical Research Council Working Party, 1981),(Nocturnal Oxygen Therapy Trial Group, 1980),(Weitzenblum et al., 1985, Gorecka et al., 1997, Zielinski et al., 1998),(American Thoracic Society, 1995),(Siafakas et al., 1995, Tarpy and Celli, 1995) [evidence level I]

Long term oxygen therapy reduces mortality in COPD. (Medical Research Council Working Party, 1981),(Nocturnal Oxygen Therapy Trial Group, 1980), Gorecka et al., 1997, Zielinski et al., 1998),(American Thoracic Society, 1995),(Siafakas et al., 1995, Tarpy and Celli, 1995)It may also have a beneficial impact on haemodynamics, haematological status, exercise capac­ity, lung mechanics and mental state.(Weitzenblum et al., 1985), (Zielinski et al., 1998),(Tarpy and Celli, 1995) Although effective, it is a potentially expensive therapy that should only be prescribed for those in whom there is evidence of benefit (see below). Information on prescribing oxygen therapy is given in Appendix 3.

Long-term continuous oxygen therapy: (at least 15 hours a day) is appropriate for patients who have Pao₂ consistently < 55 mmHg (7.3 kPa; Spo₂ 88%) (Medical Research Council Working Party, 1981),(Nocturnal Oxygen Therapy Trial Group, 1980) when breathing air, at rest and awake [evidence level I]. If oxygen is prescribed when the patient’s condition is unstable (eg, during an exacerbation), then the requirement for it should be reviewed four to eight weeks after initiation. At assess­ment for ongoing therapy, the patient’s condition must be stable, all potentially reversible factors must have been treated and the patient must have stopped smoking at least one month previously.

Polycythaemia (haemoglobin level > 170 g/L), clinical or electrocardiographic evidence of pulmonary hypertension, as well as episodes of right heart failure, are consistent with the systemic effects of chronic hypoxaemia, and continuous oxygen should be supplied if the stable Pao₂ is 55– 59 mmHg (7.3–7.9 kPa; Spo₂ < 90%).(Siafakas et al., 1995),(American Thoracic Society, 1995) Continuous oxygen therapy is of most benefit for patients with increased arterial Paco₂ (> 45 mmHg, or 6 kPa).(Nocturnal Oxygen Therapy Trial Group, 1980)

Government funding is available on the basis that the prescribing doctor is an approved prescriber (usually a respiratory physician). Oxygen is usually supplied to patients meeting specific criteria and means testing by state or regional health departments in Australia and New Zea­land. (Serginson et al., 2009)

Intermittent oxygen therapy: Available evidence does not allow any firm conclusions to be made about the effectiveness of long-term intermittent ambulatory domiciliary oxygen therapy in patients with COPD. (Ram and Wedzicha, 2002) However, use of inter­mittent oxygen therapy may be considered for:

• People who experience oxygen desaturation on exertion. (Ram and Wedzicha, 2002) A Cochrane review of 31 studies found that ambulatory oxygen was efficacious in single assessment studies when comparing an exercise test performed breathing oxygen or air in patients with moderate to severe COPD. Benefits were shown in endurance exercise capacity, dyspnoea at isotime and oxygen saturation. (Bradley and O'Neill, 2005) However, the minimum clinically important difference in these variables with oxygen therapy is unknown, Because of the heterogeneity of the studies, subgroup analyses were not possible to determine which patients were more likely to benefit. Benefit cannot be predicted by a resting test. Acute benefit may be established by comparing exercise endurance on a walking test (e.g. six minute walk test, incremental or endurance shuttle walk test or treadmill test) when breathing oxygen and when breathing room air. The oxygen system used in the assessment should be the same as the system the patient would use if oxygen were prescribed (e.g. trolley or shoulder bag to transport the cylinder). A stationary bicycle should not generally be used for the test as oxygen desaturation is significantly greater in COPD patients when walking as compared to cycling. (Turner et al., 2004),(Cockcroft et al., 1985),(Poulain et al., 2003) Although oxygen may be used during exercise training with a similar aim, a systematic review of the small number of suitable studies reported to date does not allow a conclusion to be drawn about the use of oxygen in this circumstance. (Nonoyama et al., 2007) As the relationship between single assessments and long-term benefits is unclear, the acute assessment should form only part of the determination and benefit of ongoing ambulatory oxygen therapy. Long-term review and determination of oxygen usage are also important (Bradley et al., 2007).
• Patients living in isolated areas or prone to sudden life- threatening episodes while they are awaiting medical atten­tion or evacuation by ambulance;
• Patients travelling by air. Flying is generally safe for patients with chronic respiratory failure who are on long- term oxygen therapy, but the flow rate should be increased by 1-2 L/minute during the flight (see also below).

It is to be noted that short-burst oxygen i.e. oxygen inhaled immediately prior and/or following exertion with the aim of relieving breathlessness or improving exercise tolerance is not effective (O'Neill et al., 2006) [evidence level I].

Nocturnal oxygen therapy: Patients with hypoxaemia during sleep may require nocturnal oxygen therapy. Noctur­nal hypoxaemia should be considered in patients whose arterial gas tensions are satisfactory when awake, but who have daytime somnolence, polycythaemia or right heart failure. Oxygen is indicated for patients whose nocturnal arterial oxygen saturation repeatedly falls below 88%. Sleep apnoea should be excluded.