Ability of radial arterial palpation and observation of the pulse oximetry trace to estimate non-invasive systolic pressure in healthy volunteers and in women undergoing spinal anaesthesia for elective caesarean section. 
We assessed the ability of palpating the radial arterial pulse and observing the oximeter trace to estimate the automated non-invasive systolic pressure reading in 20 healthy female volunteers and 20 parturients undergoing spinal anaesthesia for elective caesarean section.  Using real-time values of cuff pressure during inflation/deflation, the pressure was recorded when the manually palpated radial arterial pulse or pulse oximeter waveform disappeared and reappeared.  The actual measured systolic pressure was noted and the results compared using Bland-Altman analysis.  In the volunteers, the bias/precision for radial arterial palpation was -12.9/22.1 mmHg (inflation) and -9.7/16.7 mmHg (deflation), and for oximetry 29.5/18.8 mmHg (inflation) and -20.7/21.7 mmHg (deflation).  In the parturients, the bias/precision was -19.0/47.6 mmHg (inflation) and -15.5/51.0 mmHg (deflation) for arterial palpation, and 22.6/16.1 mmHg (inflation) and -14.2/19.9 mmHg (deflation) for oximetry.  Our results suggest that neither method is accurate at estimating the non-invasive systolic pressure, with all except oximetry (inflation) underestimating it by approximately 10-20 mmHg and with poor precision.