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.