Sex differences contribute to anesthesia resistance in women

Editor's Note: 

Due to sex hormones, “the female brain is more resistant to the hypnotic effects of volatile anesthetics,” concludes a study published January 8 in the Proceedings of the National Academy of Sciences.

General anesthetics work in part by modulating the activity of hypothalamic circuits, which regulate sleep and wakefulness to produce a hypnotic effect. Although brain regions affected by anesthetics vary in men and women, the researchers focused specifically on understanding of the effects of sex hormones on anesthetic sensitivity. Examining the impact of anesthesia in mice and human volunteers revealed that both women and female mice were more resistant to hypnotic effects, required more time to become anesthetized, and emerged faster from anesthesia than males.

Further, the authors found that testosterone led to higher sensitivity to anesthesia in men, with castrated male mice exhibiting increased resistance and injections of testosterone resulting in increased sensitivity. Also, in whole brain activity mapping of mice under anesthesia, they revealed higher levels of activity in male mice in hypothalamic regions known to promote natural sleep. 

The researchers theorize that this resistance to anesthetics may explain the higher incidence of awareness under anesthesia in females.