Level of exhaled nitric oxide during human anaphylaxis

Background: Nitric oxide (NO) seems to play an important pathophysiologic role in modulating the systemic changes associated with anaphylaxis. Even if some effects of NO may be protective, animal models of anaphylaxis have shown that the summation effects of NO are deleterious, resulting in hypotension and loss of intravascular volume. There are no studies of NO production during anaphylaxis in humans. Objective: To measure the level of exhaled NO during anaphylaxis induced by bee venom cluster immunotherapy in a 34-year-old beekeeper. Methods: Exhaled NO was measured using a chemiluminescence analyzer at different flow rates, and alveolar NO concentration and airway NO production were calculated. Results: We measured a high level of exhaled NO (78 ppb at 50 mL/s, with increased alveolar concentration and airway production) during anaphylaxis induced by bee venom immunotherapy in this patient. Normal values of exhaled NO were measured in the same patient 1 week later before and after a modified regimen of desensitization. Conclusions: Nitric oxide production was increased in the respiratory tract during anaphylaxis. Having excluded all the common causes of increased exhaled NO levels, these results support the hypothesis that NO plays an important role in anaphylaxis.