- Graeme P Currie, specialist registrar,
- J Graham Douglas, consultant
- Respiratory Unit, Aberdeen Royal Infirmary, Aberdeen.
Administering oxygen for chronic obstructive pulmonary disease (COPD) is not without risk and it should be properly prescribed—in terms of flow rate and mode of delivery—like any other drug. Giving high concentrations of oxygen to hypoxaemic patients with hypercapnia can result in individuals losing their hypoxic drive to breathe, with development of CO2 retention, respiratory acidosis, and even death.
However, in acute and chronic ventilatory failure, oxygen supplementation is essential to maintain adequate delivery of oxyhaemoglobin to organs such as the heart, kidneys, and brain. Many patients who are chronically hypoxic are able to cope satisfactorily with an oxygen saturation of arterial blood of around 90%. However, at saturations below this, the oxygen dissociation curve rapidly steepens, and a sharp fall in oxygenated haemoglobin occurs with reduction in oxygen supply to vital organs.
Oxygen during an exacerbation of COPD
During an exacerbation of COPD, give 24% or 28% oxygen via a Venturi facemask to patients with hypercapnia in order to maintain an oxygen saturation > 90%. In patients without hypercapnia, titrate the oxygen concentration upwards to keep the saturation > 90%. Check arterial blood gases at 30-60 minutes later to check for any rise in CO2. Nasal cannulas deliver less reliable fractions of inspired oxygen than a facemask but allow patients to communicate, eat, and drink more easily.
Long term oxygen therapy
Two large trials have shown that using oxygen for at least 15 hours a day improves survival of hypoxaemic patients with COPD. Consider long term oxygen therapy in non-smoking patients …