The effect of atropine on the accuracy of pupillometry as a method of diagnosing the analgesic component of general anaesthesia

Introduction. Modern approaches to the assessment of nociception include methods of monitoring the vegetative response of the body to a damaging stimulus. Pupillometry – the technique is based on the registration of changes in the diameter of the pupil that occur in response to pain stimulation and reflect the activity of the sympathetic nervous system. The advantage of this technology is the high reaction rate and accurate registration of the pupillary reflex. However, diagnostic difficulties arise in patients receiving cholinolytics such as atropine, as it causes mydriasis.

The objective was to determine the effectiveness of pupillometry for assessing analgesia after atropine administration during the intraoperative period.

Materials and methods. A blinded, placebo-controlled, prospective, single-center, randomized (envelope method) study was conducted to analyze the effect of atropine on pupillometric assessment of analgesia. Pupil diameter was measured in 100 patients under combined anesthesia, divided into two groups based on atropine administration: Group 1 – patients who received 0.5 mg of atropine during anesthesia induction; Group 2 (control) – patients who received 0.9% NaCl during induction. Both groups underwent the same induction protocol: propofol 1.5–2 mg/kg, cisatracurium besylate 0.15 mg/kg, and fentanyl (F) 200–300 mcg. Anesthesia was maintained with sevoflurane (0.7–1.5 MAC). No fentanyl was administered before skin incision. Hemodynamic parameters (mean arterial pressure [MAP], heart rate [HR]) and changes in pupil diameter were assessed at the following stages: 1 – after induction (baseline); 2 – skin incision. Pupil diameter was measured using the AlgíScan videopupillometer for analgesia monitoring, with an accuracy of 0.1 mm.

Results. After skin incision, an increase in pupil diameter from baseline (post-induction pupil diameter) was observed in both groups, suggesting sympathetic stimulation in response to nociceptive stimulation and insufficient analgesic depth. The pupillometry findings were supported by increases in MAP and HR in response to skin incision.

Conclusion. The conducted study shows that the pupil’s reaction to the pain stimulus persists. This makes pupillometry a valuable tool in the anaesthetic practice of assessing the analgesic component of anaesthesia.

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