Analgesic Depth Evaluation During General Anesthesia With Dexmedetomidine-remifentanil Infusion. A Pilot Study

In recent years, different strategies have been proposed to reduce opioid use during the perioperative period, i.e., the so-called OFA (opioid free anesthesia) or OSA (opioid sparing anesthesia), in order to reduce some opioid-related side effects with equivalent intraoperative analgesia compared to opioid-based anesthesia.

Dexmedetomidine is a highly selective α2-agonist, with sedative and pain-relieving effects. The use of perioperative dexmedetomidine seems to reduce intraoperative opioid and hypnotic consumption, postoperative pain intensity and postoperative opioid use.

A dexmedetomidine-based protocol for anesthesia in obese patients was introduced in our department towards the end of 2018. All patients undergoing bariatric surgery have been treated with a premedication of dexmedetomidine and a steady infusion of dexmedetomidine as an opioid-savings adjuvant during general anesthesia. In this context, the amount of fentanyl (induction of anesthesia) and remifentanil (maintenance of anesthesia) has been reduced empirically and clinically.

Traditionally, during general anesthesia, the level of nociception is indirectly assessed by observing heart rate, blood pressure and surgical steps. In recent years, new indicators have been proposed to obtain an objective and standardized nociception assessment. Pupillary dilation reflex (PDR) can be related to both painful stimulation and analgesic depth, but not to neuromuscular blockade or hypnotic drug administration. Recently, another rating scale for nociception has been proposed: the PPI (pupillary pain index). This index is based on tetanic stimulation of increasing intensity delivered by two skin electrodes placed on the forearm, evaluating the PDR at each stimulus. A PPI from 1 to 3, from 4 to 6, or from 7 to 9 describes a numbed PDR and deep analgesia, a medium PDR and suboptimal analgesia and a highly reactive PDR and uncontrolled pain, respectively.

The investigators proposal is to study the feasibility of an evaluation of the nociception during an Opioid Sparing Anesthesia (OSA), with continuous infusion of dexmedetomidine and remifentanil, vs "traditional" anesthesia without adjuvant, using the PPI as an indicator of nociception.

Inclusion criteria

• Patients underwent open surgery involving at least one surgical incision of more than 5 cm
• use of remifentanil as an intravenous analgesic.

Exclusion criteria

• implanted pacemaker or ICD
• ophthalmological comorbidities
• chronic opioid use
• peripheral neuropathy
• continuous infusion of adjuvant drugs other than dexmedetomidine
• epidural analgesia or loco-regional block