This study was undertaken to determine the effect of patient position on the incidence of vasovagal responses to venous cannulation in ambulatory surgery patients.
Three hundred surgical outpatients, aged 18 to 40 years, were randomly assigned by week to the sitting or recumbent position. Blood pressure and heart rate were recorded during and for 6 minutes following venous cannulation. An observer recorded signs and symptoms suggestive of a vasovagal response.
A vasovagal reaction occurred in 12.6% of sitting patients and 2.1% of recumbent patients. Two sitting patients, 1.3%, experienced frank syncope. Symptomatic patients were more likely (39.1%) than asymptomatic patients (8.3%) to have a history of fainting. In symptomatic patients who were sitting, mean arterial pressure fell from 90.4 mm Hg (SD, 10.6) at baseline to 64.4 mm Hg (SD, 14.3) during cannulation. Similarly, heart rate fell from 76.6 beats per minute (SD, 15.6) at baseline to 59.0 beats per minute (SD, 11.7) after cannulation.
The vasovagal response during venous cannulation occurs more frequently in the sitting patient who has a history of fainting and is associated with a significant decline in blood pressure and heart rate.(Arch Intern Med. 1993;153:1698-1704)