It is important that patients are assessed when they are clinically stable. The gradual improvement in PaO2 after an acute exacerbation is well recognized . Nonetheless, in the UK significant numbers of prescriptions are still inappropriately initiated when the patient is unstable, often at the time of hospital discharge. Of 176 patients on LTOT in London, 25% did not meet the criteria for hypoxaemia . Out of more than 500 Scottish patients on LTOT, 61% were assessed when unstable and 33% were assessed as in-patients following an exacerbation . The pressure to start patients with COPD on LTOT at the time of hospital discharge, when they are not yet stable, needs to be countered by raising awareness of the natural history of COPD and the rationale for LTOT.
Both the original and 1999 UK guidelines recommend arterial blood gas tensions should be measured on two occasions not less than three weeks apart when the patient is stable. This guideline has not been followed for 15 years and needs examining critically. In one study only 6% of patients had arterial blood gases repeated . A bigger problem is that 15-25% of patients are prescribed LTOT without arterial blood gases at all, let alone while stable [16,17]. The appropriate focus should be on ensuring all patients are formally assessed for LTOT, and that this is done with one set of arterial blood gas tensions measured when the patient meets the clinical definition of stability. Clinical stability is defined as the absence of an exacerbation of COPD and of peripheral oedema for the previous 4 weeks . It is unrealistic and unnecessary to insist on two sets of arterial blood gases, provided the patient is assessed when clinically stable.
Guidelines also recommend that arterial blood gas tensions are repeated after breathing oxygen for 30min to confirm that the PaO2 increases above 8 kPa (60 mmHg). This is also poorly done in practice. It was only measured in 59% of patients in one study , and in another study follow-up oximetry on oxygen showed undercorrection in 17% of patients . As the aim of LTOT is to improve survival, it is rational that there should be formal arrangements for follow-up of these patients to ensure adequate correction of hypoxaemia, optimize compliance, detect deterioration, and identify continuing requirement for LTOT. The majority of patients, 92-97%, are already under follow-up [16,17], although more than 40% do not have arterial blood gases repeated . There are no randomized studies to indicate whether active follow-up improves prognosis or reduces inappropriate use of LTOT. Currently, follow-up is patchy, with no systematic arrangements in the UK, although this is improving as respiratory nurse specialists take on this role in many centres.
A further problem has been poor communication about patients on LTOT between clinicians in the community and hospital . The use of a register for patients on LTOT with standardized forms providing a two-way flow of information is one suggested way for improving this situation .
The benefits of LTOT are evidenced-based. Therefore it should be possible for the prescription of LTOT to be rational and objective. We need to make sure that patients with COPD are not missing out on the only treatment (apart from stopping smoking) that reduces mortality.
All patients with severe COPD should be screened with oximetry. Those with a resting SaO2 of 92% or below need to have arterial blood gases performed on one occasion when stable. If the PaO2 is below 7.3 kPa (55mmHg), LTOT should be prescribed for as much time as possible in 24 h, but at least 15 h. Patients with a PaO2 between 7.3 and 8 kPa (55 mmHg and 60mmHg), and with secondary polycythaemia or peripheral oedema, should also be prescribed LTOT. The evidence for treating patients with moderate hypoxaemia and pulmonary hypertension, or nocturnal hypoxaemia detected by overnight screening oximetry, is not compelling, although such treatment is recommended in the latest UK guidelines . Patients on LTOT should have annual follow-up as a minimum and correction of hypoxaemia should be confirmed.
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