Harms of overoxygenation in patients with exacerbation of chronic obstructive pulmonary disease

Dear Editor;
Dr Rocker addresses a very important consideratin in the treatmentof exacerbations of COPD. Namely, the risk of overoxygenation. However, he implies a common mis-understanding of what drives the respiratory center. It is PaCO2 (therefore, hydrogen ion concentration) and not PaO2. Until the respiratory center becomes relatively desensitized to rising PaCO2 levels in severe COPD, repiration is not depressed by rising PaO2 levels. This is well demonstrated in hyperbaric oxygen therapy for various disorders when PaO2 levels may reach 2000mmHg or higher without causing CO2 retention.

In those COPD patients who may have CO2-retention, first--responders must be aware of the risks of O2 administration and assess PaCO2 at the earliest opportunity and continue to follow it with repeated blood-gas analysis or end-tidal CO2 monitoring. It should then be possible to avoid ICU admission caused by excessive O2, although the event precipitating the medical intervention may still require ICU admission.

I accept the importance of Dr. Rocker's caution but believe it is also important to avoid the pitfall of thinking that respiratin is driven by PaO2 levels.

Thank you
Ross E. Harrison