In the perioperative period, it may be inappropriate to monitor vital signs during endotracheal intubation using the same interval as during a hemodynamically stable period. The aim of the present study was to determine whether it is appropriate to use the same intervals used during the endotracheal intubation and stable periods to monitor vital signs of patients under general anesthesia.

The mean arterial pressure (MAP) and heart rate (HR) were continuously measured during endotracheal intubation (15 min after intubation) and hemodynamically stable (15 min before skin incision) periods in 24 general anesthesia patients.

Data was considered "unrecognized" when continuously measured values were 30% more or less than the monitored value measured at 5- or 2.5-min intervals. The incidence of unrecognized data during endotracheal intubation was compared to that during the hemodynamically stable period.

There were significantly more unrecognized MAP data measured at 5-min intervals during endotracheal intubation than during the hemodynamically stable period (p value <0.05). However, there was no difference in the incidence of unrecognized MAP data at 2.5 min intervals or HR data at 5 or 2.5 min intervals between during the endotracheal intubation and hemodynamically stable periods.

In the present study, at 5-min intervals, there was a higher incidence of unrecognized MAP data when monitoring vital signs during the endotracheal intubation period than when monitoring during the hemodynamically stable period.

Sympathetic stimulus caused by tracheal intubation can be different based on various factors related to anesthesia and tracheal intubation. To reduce the diversity of patients' hemodynamic responses to sympathetic stimulation, we used the same anesthetic method, including the anesthetic drug, tracheal intubation technique, and protocol for controlling vital signs.

During perioperative periods showing a more severe change in vital signs than in the present study, the time interval for monitoring vital signs should be shorter than 2.5 min. However, monitoring arterial pressure using non-invasive blood pressure at 1-min intervals or using an intra-arterial catheter might cause complications such as an injury to the nerve or an ischemia of the extremes.

The present study had several limitations. First, patients in this study were healthy and young. Applying our results to elderly patients or individuals with cardiovascular disease should be done with caution.

Second, MAP and HR during anesthesia are influenced by the anesthetic method, including anesthetic drugs, intubation technique, and the protocol for managing MAP and HR. If a different anesthetic method had been used, vital signs and the incidence of unrecognized data may have been different from those of the present study.Third, the MAP was monitored and managed based on data obtained from continuous monitoring with an intra-arterial catheter.

 If the MAP were measured using a non-invasive blood pressure monitor with 2.5- or 5-min intervals, the change in vital signs could have been greater than that observed in the present study. This may have resulted in a higher incidence of unrecognized data than found in the present study.