Infrared thermographic assessment of cutaneous temperature changes during labour epidural analgesia initiation: an observational pilot study

Abstract

Background

Inadequate labour epidural analgesia within 30 to 45 minutes of insertion is typically considered primary epidural failure and deemed unsuccessful. Early prediction of analgesic success would have clinical benefit, enabling corrective interventions. Sympathectomy accompanying a successful epidural block can cause foot temperature changes. We sought to evaluate the relationship between foot temperature changes and successful epidural, defined as adequate analgesia in 45 minutes of epidural administration. For the purpose of this study, we defined primary epidural failure as inadequate analgesia within 45 minutes of administration.

Methods

Following ethical committee approval, this observational study was conducted in a tertiary level obstetric centre between January 2021 and March 2024. Patients attending for induction of labour were included: those with labour epidural analgesia comprised the epidural study group, and those without served as a control group. A FlirT540 infrared thermography camera was used to take bilateral foot images every 5 minutes for 30 minutes. Images were taken following epidural administration in the epidural group, and at any convenient time once in established labour in the control group. We studied temperature changes over time in the both groups, and compared the temperature changes in patients with successful and failed epidurals.

Results

Thirty-eight patients were included in the epidural group and 11 in the control group. Twenty-nine patients (76.3%) had successful analgesia and nine patients (23.7%) had primary epidural failure. Patients with successful analgesia had a statistically significant rise in temperature after 10 minutes. The maximum rate of increase was between 5 and 15 minutes and was 0.5 (0.1)°C per minute on both sides. Primary epidural failure was associated with minimal temperature changes, while all patients who had a 2°C rise in hallux temperature at 10 minutes had successful analgesia.

Conclusions

Sympathetic blockade associated with a successful analgesic epidural block produces cutaneous temperature elevation at the plantar surface of the hallux. These can be detected within 10 minutes of epidural administration and have a potential role in guiding timely troubleshooting of an unsuccessful epidural.