The study compared the effects of different doses of alfentanil on the body's stress reactions during the insertion of a breathing tube during ambulatory hysteroscopic surgery.[1] Patients were randomly divided into four groups receiving different doses of alfentanil (20, 30, and 40 μg/kg) or fentanyl (4 μg/kg) during induction of anesthesia.[1] The primary measure was the level of the hormone norepinephrine in the blood 1 minute after the tube was inserted, while other indicators such as blood pressure, heart rate and postoperative pain were also monitored.[1] The results showed that doses of 30 and 40 μg/kg alfentanil significantly reduced the stress response and hemodynamic changes compared to the lower dose and fentanyl.[1] The 30 μg/kg alfentanil group had a lower incidence of increased blood pressure and increased heart rate compared to the 20 μg/kg group.[1] However, the 40 μg/kg alfentanil group showed a significantly higher incidence of low blood pressure and slowed pulse.[1] In conclusion, the authors recommend a dose of 30 μg/kg alfentanil as more suitable for ambulatory hysteroscopic surgery because it provides optimal protection against stress reactions without the adverse hemodynamic effects of a high dose.[1]