LAS VEGAS – The flow rate of oxygen routinely prescribed to abort cluster migraine is too low to be effective in many patients, Todd D. Rozen, M.D., said at a symposium sponsored by the American Headache Society.
Since the effectiveness of inhaled 100% oxygen for cluster headache was demonstrated in 1981, clinicians have typically prescribed flow rates of 7–10 L/min, said Dr. Rozen of the Michigan Head-Pain and Neurological Institute in Ann Arbor.
About 30% of patients fail to respond to flow rates in this range. In a recently published case series, Dr. Rozen described three patients whose headaches were apparently refractory to oxygen but who all responded well when the flow rate was pushed to 15 L/min–about the maximum flow rate delivered by most medical-grade oxygen regulators (Neurology 2004;63:593).
“I'm now telling my patients that you're not resistant to oxygen until you try 15 L/min,” Dr. Rozen said.
There are a number of caveats regarding oxygen therapy for cluster headache. The gas must be delivered through a nonrebreather face mask, and patients must be cautioned strongly about the highly flammable nature of pure oxygen. In addition, the higher flow rates may be dangerous in patients with chronic obstructive pulmonary disease.
Oxygen is thought to exert its effect on cluster headaches through cerebral arterio- and vasoconstriction. Many people whose headaches appear refractory to oxygen therapy are smokers; according to the pulmonary literature, smokers exhibit less vasoconstriction in response to 100% oxygen than do nonsmokers.
Dr. Rozen hypothesized that in some individuals, a higher oxygen flow rate is needed to obtain a clinically meaningful degree of vasoconstriction.
Cluster headache is the most severe head-pain syndrome known, and rapid abortive therapy, either at home or in the emergency department, is critical. The goal of abortive treatment is to stop the pain within 10–15 minutes.
Oxygen therapy is a good choice for patients whose cardiovascular risk factors render them unsuitable candidates for injected sumatriptan.
“I don't know how many times I've seen cluster patients who have never tried oxygen,” Dr. Rozen said. “You have to remember that they are smokers; they have cardiovascular risk factors over time. At some time, they're not going to be able to take sumatriptan injection any more, so you want to try oxygen.”
In the United States, patients must have a physician's prescription to get oxygen for home use.