Assessment of skin temperature change in determining success of transversus abdominis plane block

Background: To observe the skin temperature changes on the blocked area and its response to pinprick testing in ultrasound-guided transversus abdominis plane block (TAP block), and to explore the accurate predictor of the temperature measurement for TAP block success. Methods: A total of 30 patients underwent lower abdominal surgery were enrolled. Bilateral ultrasound-guided TAP blocks were performed before the surgery, after obtaining the view of transversus abdominis plane and the needle tip, 30 mL of 0.25% ropivacaine was injected for each side. Two measuring points in each unilateral TAP blocked area were randomly selected, where the results of pinprick testing and skin temperature at the time of 10 minutes before and after local anesthetics injection were collected. Based on defined standard (pinprick testing results), the sensitivity and specificity, the area under the receiver operating characteristic curve (AUC) and the diagnostic cut-off value of skin temperature change responding to TAP block success were assessed by analyzing the receiver operating characteristic curve (ROC curve). The correlation between the skin temperature changes and the pinprick testing results was assessed by Pearson correlation analysis. Results: The AUC value of skin temperature change upon the blocked area to TAP block success was 0.909 (95% CI 0.832-0.985). Importantly, the ROC analysis displayed that the diagnostic cut-off value was 0.55°C, with a sensitivity of 86.3% and specificity of 88.9%. The value of Pearson’s correlation coefficient (r) was 0.588 (95% CI 0.403-0.723). Conclusions: Our study suggests that the skin temperature change is a strong predictor for a successful TAP block. We can conclude that a TAP block is probable success if value of skin temperature change is more than or equal to 0.55°C, and TAP block failure if less than 0.55°C with a sensitivity of 86.3% and specificity of 88.9%. Skin temperature measurement is a valuable predictor in determining TAP block effect when sensory testing is impossible.