When treating a patient with emphysema in the acute care setting who appears to be hypoxic, short of breath, and requires increased effort to breathe, be very careful before using oxygen therapy. In a normally functioning patient, the respiratory drive is largely directed by PaCO2 levels in the brain since H+ readily crossed the blood brain barrier.

In this patient, PaCO2 becomes chronically elevated, and thus the body shifts its respiratory controllers to become more responsive to PaO2 levels. After this paradoxical shift, treating a chronic emphysema patient with oxygen increased the blood oxygen levels too rapidly. This may result in knocking out his hypoxic drive, causing further depression of the respiratory drive.

This counter-effect may also require close monitoring and/or intubation. Thus, the rule of thumb is not to be alarmed by low SpO2 levels, and to use arterial blood gas values to guide treatment. A venture mask, which can provide high flows with titratable FiO2, offers great advantages over nasal cannulas. — RAKESH PATEL, MD, RRT, Houston. (200-3)

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