Monitoring intraoperative effectiveness of caudal analgesia through skin temperature variation

A reliable noninvasive intraoperative marker of caudal analgesia effectiveness remains elusive. Caudal analgesia causes sympathetic inhibition resulting in vasodilatation, increased blood flow, and a resultant increase in temperature in the affected dermatomes. The authors hypothesize that this change in temperature between the affected and unaffected dermatomes is measurable and may represent a noninvasive method of monitoring effectiveness of caudal analgesia.

Children undergoing lower abdominal surgery participated in the caudal or noncaudal (control) analgesia arm of the study. After induction of general anesthesia, 0.25% bupivicaine (1 mL/kg) was infiltrated for a field block in control patients or a caudal block in the experimental group. Temperature was measured at the C4 and L2 dermatomes starting after induction and 5 minutes before the caudal or field block and every 5 minutes after. T(o) is defined as the difference between the C4 and L2. Delta T (DeltaT) is the temperature variation between T(o). A change in the DeltaT is defined by an increase in the L2 temperature.

Forty-six families enrolled (36 experimental, 10 control). The DeltaT for controls was 0.2+/-0.09 degrees C (SEM). Each child in the experimental group had 2 temperature measurements before the caudal with an average DeltaT of 0.3+/-0.07 degrees C (SEM), thus, were internal controls. A marked increase in DeltaT at 5 minutes 0.5+/-0.06 degrees C (SEM) and at 10 minutes 0.6+/-0.07 degrees C (SEM; P <.05) was noted in the experimental group.

A significant transient change in temperature is observed after caudal analgesia and maybe a noninvasive marker of effectiveness. Further study may clarify its clinical utility.