Assessment of pupillary diameter variation rate in determining noxious stimulation during general anesthesia

Objective To observe the reactivity of pupillary diameter (PD) variation responding to the variation of heart rate (HR) or systole blood pressure (SBP) after operative incision, and evaluate pupillary diameter for noxious stimulation. Methods One hundred and fifty patients underwent surgery were selected, after endotracheal intubation under intravenous induction, 1 μg/kg fentanyl was administered before operation. The HR, SBP, PD were measured and recorded subsequently before surgical incision (T0), after surgical incision (T1), each 5 s in 1 min after incision[5 s (T2), 10 s (T3), 15 s (T4), 20 s (T5), 25 s (T6), 30 s (T7), 35 s (T8), 40 s (T9), 45 s (T10), 50 s (T11), 55 s (T12), 60 s (T13)]. The variation rate of HR or SBP responding to the value at T0 and the maximum variation rate of PD responding to the value in T0 were calculated, marked with name of △HR, △SBP and △PD. With the 15% variation rate of HR or SBP as a criteria for noxious stimulation/anti-noxious stimulation, the reactivity of △PD responding to △HR or △SBP were assessed respectively by analysis the receiver operating characteristic curve (ROC) for the result of sensitivity and specificity and the area under the receiver operating characteristic curve (AUC), and Pearson rank correlation were analyzed. The time of HR, SBP and PD responding to noxious stimulation were compared. Results The AUC value of △PD responding to △HR and △SBP were 0.936 (95%CI 0.894-0.997) and 0.921 (95%CI 0.884-0.971) respectively. Importantly, their ROC analysis displayed that the diagnostic cutoff value of △PD responding to △HR was 44.5% with a sensitivity of 89.7% and a specificity of 92.5%, and △PD responding to △SBP was 46.5% with a sensitivity of 88.6% and a specificity of 89.1%. The value of Pearson′s correlation coefficient between △PD and △HR was r△PD-△HR=0.721(95%CI 0.617-0.786), between △PD and △SBP was r△PD-△SBP=0.679 (95%CI 0.605-0.758). The time of HR, SBP and PD responding to noxious stimulation were (5.5±2.7), (28.3±9.9) s and (32.7±7.2) s respectively. Conclusions This study demonstrated that high accuracy in PD variation rate responding to noxious stimulation/anti-noxious stimulation during operation with shorter responding time. PD is a valuable parameter for determining noxious stimulation. Key words: Pupillary diameter; Noxious stimulation; Pain; Heart rate; Systolic blood pressure