The two most effective cluster abortive agents are injectable sumatriptan and inhaled oxygen. Because most cluster headache sufferers are cigarette smokers and at high risk of coronary artery disease, many develop contraindications to triptans. Oxygen, the safest of all cluster therapies, is not effective for every patient. In Kudrow's landmark study, 75% of patients responded to 100% oxygen at 7 L/min, although only 57% of older chronic cluster headache patients had relief. A recent study documented a gender difference in response to oxygen because only 59% of female cluster patients responded to oxygen, whereas 87% of men did. In most textbooks and articles on cluster headache treatment, patients are instructed to use 100% oxygen via a nonrebreather face mask at 7 to 10 L/min. The rationale behind this prescribed oxygen-flow rate is unknown but has become doctrine since the Kudrow study. Prescribing higher flow rates of oxygen up to 12 L/min has recently been suggested, but there is no documentation that this may improve efficacy. Higher oxygen-flow rates (up to 15 L/min) are not known to benefit cluster headache patients refractory to standard oxygen therapy. Three cluster headache patients who demonstrated no response to standard oxygen therapy were exposed to higher flow rates of oxygen (14 to 15 L/min) to assess response.

Comments: Once again, Dr. Todd Rozen's observations will change my clinical practice!—Stewart J. Tepper, MD

I have questions: Were these empirical observations or do Drs. Kudrow and Rozen know how rate of flow affects oxygen delivery? Is oxygen uptake higher with higher flows? After all, 100% oxygen is 100% oxygen unless under hyperbaric pressure! Perhaps higher flow rates dry the nasopharyx to a greater extent. If patients perceive a higher flow rate, might this be an enhanced placebo effect? It seems like an interesting study to be conducted, and it would be useful to test if using nasal cannulae is just as good. Pulse oximetry and arterialized capillary blood gases could be used to monitor oxygen saturation and CO2 retention/carboxyhaemoglobin levels in smokers.—David S. Millson, MD