Background and aims Pupillary Pain Index (PPI) has showed its effectiveness to assess intraoperative analgesia. With a scale from 1 to 10, the index reflects nociception via pupillary reaction to a defined electrical stimulus delivered by the device. We aimed that PPI can evaluate effectiveness of adductor canal block (ACB) or fascia iliaca block (FIB) in orthopedic patients undergoing total hip (THR) or knee replacement (TKR) and predict postoperative pain levels as measured by numeric rating scale (NRS).
Methods Prospective observational study with measurement of PPI with videopupillometry in patients undergoing THR or TKR. Electrodes were applied at the skin area of block activity. PPI was measured before performing of neuraxial block after intubation (PPI1) and at the end of surgery at the time of skin closure (PPI2). NRS was used to evaluate pain at 24 (NRS24) and 48 hours (NRS48) at rest and with activity.
Results 37 patients enrolled to the study; 19 patients underwent THR and 18 TKR. Median (quartiles) PPI scores significantly decreased at time of skin closure from 2 (2,6) to 1 (1,2) (p<0.001) (figure 1). There were positive correlations (Spearman) between PPI2 and NRS24 at rest (r=0.375; p=0.034) and NRS48 with activity (r=0.458; p=0.008). Patients with PPI2 more than 1 had higher NRS scores after 24 hours at rest (p=0.03) and NRS scores after 48 hours with activity (p=0.006) (figure 2).
Conclusions PPI index can be used as predictor of postoperative pain in orthopedic patients with ACB and FIB. Videopupillometry is a promising tool for evaluation of effectiveness of peripheral nerve blocks.
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