LONG-TERM OXYGEN THERAPY (LTOT) CAN IMPROVE LIFE

Long-term oxygen therapy (LTOT) can improve life expectancy in chronic hypoxic cop pulmonale

Long-term oxygen therapy (LTOT) can improve life expectancy in chronic hypoxic cop pulmonaleCHCP

Description

The British Thoracic Society defines CHCP as a "chronic, slowly progressive disorder characterised by airflow obstruction (reduced FEV1 and FEV1/VC ratio) that does not change markedly over several months." This definition is shared by the NICE guidelines on CHCP from February 2004. Airflow obstruction is defined as a reduced FEV1 and a reduced FEV1/FVC ratio such that FEV1 is less than 80% of that predicted and FEV1/FVC is less than 0.7. (Wedzicha, JACalverley PMA; All change for home oxygen services in England and Wales; Thorax 2006;61:7-9

Pink puffers and blue bloaters

In normal people the respiratory drive is largely initiated by PaCO2 but in CHCP hypoxia can be a strong driving force and so if this is corrected the respiratory drive will be reduced

General points about LTOT in CHCP

The potential dangers of giving oxygen in CHCP have long been known but the potential benefits were not appreciated until the 1980s. As described above, hypoxia can be a strong driving force in these patients (particularly among the blue bloaters); administering oxygen will reduce this drive in these patients. Chronic hypoxaemia causes slowly progressive pulmonary hypertension with the development of right ventricular hypertrophy and possible cor pulmonale with secondary polycythaemia. The last increases blood viscosity and hence resistance to flow. There is also sludging and a tendency to thrombosis. (David Hooks 2004 Pp. 55-57)

When oxygen is used in patients who are not thought to have CHCP, especially those with terminal cancer, such caution is not required. If a general practitioner thinks that a patient with CHCP may benefit from oxygen, that patient should first be assessed by a respiratory physician or a specialist respiratory team.

Clinical Knowledge Summaries recommend that if the patient will not stop smoking, that LTOT should be withheld. There is a real risk of fire and burns to the face and any benefit relating to polycythaemia is counteracted by smoking.

LTOT in the acute setting

The acute episode

For most patients, you should be aiming for an SaO2 of 85-92%.2

The aim of (controlled) LTOT is to raise the PaO2 without worsening the acidosis. Therefore, do not prescribe oxygen at >28% (via venturi mask) or 2 L/min (via nasal prongs) in patients over 50 with a history of CHCP until arterial blood gases (ABGs) have been checked.9

Measure ABGs within 60 minutes of starting supplemental oxygen or changing its concentration. If PaO2 improves with an associated drop in PaCO2 and the pH is relatively unaffected (pH >7.26) then the concentration of the supplemental oxygen may be increased to maintain PaO2 >7.5 kPa.

LTOT will have to be complemented with bronchodilators (e.g. salbutamol 5mg or terbutaline 10mg, made up to 5mL with normal saline) and high dose oral steroids (e.g. prednisolone 30mg daily).2 In the presence of purulent sputum, antibiotics will also be required (see your local hospital policy for choice of ...