Menstrual cycle affects body's response to tracheal intubation: Research

Aug 3 2010

In women undergoing surgery, the heart rate and blood pressure response to ventilation tube placement varies at different times of the menstrual cycle, according to a study in the August issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

Tracheal intubation - passing a breathing tube into the trachea ("windpipe") - is among the most unpleasant and stressful experiences for a patient undergoing anesthesia and surgery. Anesthesiologists typically wait until the patient is unconscious before passing the breathing tube into the trachea, so that the patient is oblivious. Still, the body notices. Tracheal intubation is often accompanied by a rise in blood pressure and heart rate, the body's hemodynamic response to the very unpleasant stimulation from the breathing tube.

The hemodynamic response to tracheal intubation appears greater during the luteal phase of the menstrual cycle, when hormone levels are higher. This suggests that, when possible, it might be best to schedule surgery for soon after a woman's menstrual period—in the follicular phase, when hormone levels are lower.

Hormone Levels Affect Response to Intubation
Led by Dr. Volkan Hancı of Zonguldak Karaelmas University, Turkey, the researchers designed a study to determine the effect of the menstrual cycle on the hemodynamic response to tracheal intubation in 62 healthy women. Half of the women were in the follicular phase of the menstrual cycle, one to twelve days after the start of their last menstrual period. The other half were in the follicular phase, 20 to 24 days after their last period.

Monitoring data on the heart rate and blood pressure were used to calculate the rate pressure product, an indicator of the heart's demand for oxygen. Responses to tracheal intubation were compared between the two menstrual cycle groups.

As expected, both groups showed a significant increase in heart rate and blood pressure after tracheal intubation. In the first minute after intubation, rate pressure product was significantly higher for women in the luteal phase (higher hormone levels) than in the follicular phase (lower hormone levels). Overall, the hemodynamic response to tracheal intubation was about 30 percent greater for women in the luteal phase.

A wide range of hormonal, physical, and psychological fluctuations occur during the menstrual cycle. Previous studies have shown significant differences in the need for anesthetics and analgesics (pain-relieving drugs) for women in different stages of the cycle.

The new results show that the menstrual cycle also has a significant impact on the body's response to the "noxious stimulation" of tracheal tube placement. The reason for this difference is unknown, although it may reflect increased sympathetic nervous system responsiveness. Future studies evaluating the hemodynamic response to events during surgery should consider the effects of the menstrual cycle, the researchers note.

"The hormones that govern the menstrual cycle, estradiol and progesterone, have significant analgesic properties," comments Dr. Steven L. Shafer of Columbia University, Editor-in-Chief of Anesthesia & Analgesia. "It is not surprising that fluctuations in these hormones might be associated with different responses to tracheal intubation, depending on the phase of the menstrual cycle."

"This suggests that the best time for surgery is right after menses, in the follicular phase," Dr. Shafer adds.

SOURCE Anesthesia & Analgesia