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Release: April 8, 1999

UI researcher determines vital sign norms for cesarean section procedure

IOWA CITY, Iowa -- A University of Iowa researcher, with data and assistance from Duke University, has found that it is quite normal for blood pressures in women to drop or increase dramatically during cesarean sections.

Using records of 1,300 women who had cesarean sections, Franklin Dexter, M.D., Ph.D., UI associate professor of anesthesia, and Duke researchers sought to establish how vital signs changed during such deliveries. The investigators are among the first to look at how anesthetics affect vital signs during a surgical procedure. Because anesthetics are safe, nobody had felt the need to establish surgery vital sign benchmarks.

"People talk about normal blood pressure being 120/80 millimeters mercury, which results in an average blood pressure of 100 millimeters mercury," said Dexter, the principal investigator for the analysis. "But, in women with high blood pressures who have regional anesthesia and are awake when their babies are born, the decrease in the average blood pressure with the start of anesthesia can be as much as 70 millimeters mercury."

In healthy women who have general anesthesia and are asleep when their babies are born, the average blood pressure with the start of anesthesia can increase to as much as 160 millimeters mercury, Dexter added.

"What's dramatic is very large changes in blood pressure occur in the operating room yet women and their babies do well," he said.

Duke researchers contacted Dexter to perform the record analysis because the institution wanted to see if there was a way to improve patient outcomes. Duke researchers also understood that establishing acceptable levels for surgery could have important implications in malpractice cases. Duke University is unique because it has used an automated information system for collecting vital sign information during all of its anesthetics, including cesarean sections, for many years.

Although malpractice involving cesarean sections is not a huge problem, vital sign reference limits may play a role in such cases when an expert, using recorded vital signs as evidence, claims that an anesthesiologist's care was substandard. Until now, experts have relied on their own clinical judgment to estimate reference limits. Dexter's analysis of the data from Duke provides a benchmark to either confirm or refute these claims.

"The importance in terms of malpractice cases is that when you see very large, seemingly abnormal changes in vital signs in the operating room, it does not necessarily indicate that care has somehow been substandard," Dexter said.

Dexter examined records from 1,300 women who underwent cesarean section at Duke with general or spinal anesthesia between April 21, 1992 and July 9, 1997. Dexter and his associates evaluated normal values for the minimum and maximum heart rate, oxyhemoglobin saturation, minimum and maximum mean arterial pressure, and increases and decreases in mean arterial pressure.

Dexter's work appears in a recent issue of the Journal of Clinical Monitoring and Computing.