The association between pain intensity during epidural labour analgesia and intrapartum hyperthermia: a multicentre prospective observational study.

BACKGROUND

Some women receiving epidural labour analgesia become hyperthermic. Assuming a causal mechanism, denser and more extensive sympathetic blocks might promote hyperthermia by inhibiting sweating. We therefore tested the hypothesis that hyperthermia is most common when epidural blocks are particularly effective, as indicated by excellent analgesia.

METHODS

In this multicentre prospective observational study, we enrolled nulliparous women with term cephalic singleton pregnancies who planned vaginal delivery with epidural analgesia. Pain intensity was assessed using an 11-point numerical rating scale (0-10) during uterine contractions before analgesia, at 10, 30, and 60 min after initiating analgesia, and then hourly until the end of the third stage, and calculated as time-weighted average, average, area under the curve, and peak scores. Our primary endpoint was intrapartum hyperthermia (≥38°C).

RESULTS

Intrapartum hyperthermia occurred in 13% (124/952) of participants (median age 29 yr). After adjustment for confounding factors, lower pain intensity was associated with higher odds of intrapartum hyperthermia across all four measures: time-weighted average (odds ratio 1.64; 95% CI 1.40-1.91; P<0.001), average (1.56; 1.35-1.81; P<0.001), area under the curve (1.05; 1.03-1.07; P<0.001), and peak scores (1.19; 1.09-1.30; P<0.001). The identified inflection points were a time-weighted average score ≤3 points (odds ratio 8.67; 95% CI 4.19-17.9; P<0.001), average score ≤3 points (6.63; 3.56-12.3; P<0.001), area under the curve ≤30 point⋅h (13.0; 3.75-45.0; P<0.001), and peak score ≤4 points (2.53; 1.65-3.89; P<0.001), all of which were associated with increased intrapartum hyperthermia.

CONCLUSIONS

Among nulliparous women receiving epidural analgesia for labour, lower pain scores were associated with higher odds of hyperthermia. Extensive sympathetic blockade may promote maternal hyperthermia.

CLINICAL TRIAL REGISTRATION: NCT04940091.