Background: We have previously reported that measurement of non-invasive blood pressure during caesarean section under spinal anaesthesia fails in over 50% of cases. We felt that errors would be less likely if blood pressure could be measured at the ankle as it is immobile during caesarean section. The purpose of our study was to determine whether blood pressure measurement at the ankle was equivalent to the arm.
Method: Following ethical approval, informed consent was obtained from 30 women scheduled for elective caesarean section. Two non-invasive blood pressure cuffs, one on the upper arm and one on the ankle, were used to measure blood pressures at three timed intervals: before spinal insertion, before surgery and after delivery of the neonate.
Results: Using the method of Bland and Altman we found that there was only marginal agreement between the two methods. On eight out of 15 occasions where there was a greater than 20% fall in arm systolic blood pressure, this was not detected at the ankle.
Conclusion: We cannot recommend the use of the ankle to measure blood pressure during caesarean section.