Epidural anesthesia affects pulse oximeter readings and response time.

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo2) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo2 and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo2 was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo2 at both the finger and toe was decreased by the anesthesia. ΔSpo2 (Spo2 at the finger minus Spo2 at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo2 and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.