Fig. 2

Kaplan–Meier curves for time to achieving adequate analgesia after loading dose. The difference between groups was significant, P = 0.003. According to the univariate Cox regression analysis, parturients in the IND group had a significantly faster onset of achieving VAS pain score ≤ 3 than that in the CON group (hazard ratio (HR) = 2.069; 95% CI, 2.187–3.606; P = 0.010). The VAS scores were recorded at every time of active uterine contractions and the onset time was recorded as the time from beginning of epidural block to achieving adequate analgesia. “Adequate analgesia” was defined as VAS score ≤ 3 during active uterine contractions. CON, the conventional PIEB group; IND, the PIEB with intranasal dexmedetomidine group; PIEB, programmed intermittent epidural bolus