Background and Aims The circadian rhythm plays a significant role in affecting the pharmacological properties of many anesthetic agents. The aim of this study was to investigate the effect the circadian rhythm may have on the duration of spinal anesthesia for parturient patients undergoing fetal delivery by caesarian section.

Methods In the present study, which was approved by our hospital scientific/ethics committee, ref. number: 35/4th/7298/18–5-2017, ninety parturient patients, ASA I-II, presented for caesarean section, urgent and/or elective, under spinal anaesthesia, were assigned to three equal groups, A (morning/afternoon group), B (evening group), C (night group), which were monitored for 8 hours, according to the time-point of the intrathecal drug administration. The same levobupivacaine and fentanyl dose was given to all patients. Pinprick or cold test, the four-point modified Bromage scale (0–3), and the numerical scale (NRS 0–10) were used respectively for the assessment of sensory and motor blockade, and post-anesthetic pain. The duration of sensory and motor blockade, the time of study drug administration to first postoperative analgesic request and pain score at first analgesic request were recorded.

Results We observed prolonged duration of motor blockade, sensory blockade and time of study drug administration to first postoperative analgesic request in group A compared to groups B(p<0.001) and C(p<0.001).Higher pain scores at first postoperative analgesic request were observed in group C compared to groups A(p<0.001) and B(p<0.001).

Conclusions We assume that time-point of intrathecal drug administration contributes to anaesthesia’s duration and that the intensity of postoperative pain at first analgesic request is partially related to circadian conditions.