Evaluating the Predictive Value of the Nociception Level Index NOL

Evaluating the Predictive Value of the Nociception Level Index NOL: a Pilot Study

Opioids remain the cornerstone for perioperative analgesia, albeit frequently associated with side effects. Most of these side-effects are dose-dependent.

Thus intra-operative monitors are necessary to measure the balance between Nociception and Anti-Nociception (NAN balance) by an adequate opioid administration.

Recently the NOL monitor was released.The NoL index ranges from 0 to 100 and is based on a nonlinear combination of nociception-related physiologic variables, specifically heart rate (HR), heart rate variability at the 0.15- to 0.4-Hz band power, photoplethysmograph wave amplitude (PPGA), skin conductance level, number of skin conductance fluctuations, and their time derivatives. The NoL index estimates the nociceptive/antinociceptive state from these component measures using random forest regression.

In our department, a combination of TCI propofol (Schnider model) and remifentanil (Minto model) is used to for most of the anaesthetic procedures, including cardiac anaesthesia. Remifentanil is titrated to prevent an increase in blood pressure and hearth rhythm at noxious stimuli, such as surgical incision, and adapted following hemodynamic trend during surgery.

The hypothesis of this study is to develop a calibration test using the NOL index variation to define the individual most appropriate NAN balance using remifentanil TCI before the start of surgery and before a very strong noxious surgical stimulus such as surgical incision in non-cardiac and cardiac surgery.

Before the start of surgery, the investigators want to titrate in each patient the remifentanil Ce required to abolish the NOL index response to a calibrated noxious tetanic stimulus (Tetanus 60 mamp, 100 Hz, 30 seconds). Thus this individual remifentanil Ce will be the remifentanil level programmed before surgical incision. NOL and hemodynamic responses will be recorded during the entire duration of surgery.

Study protocol amendment: validation of the calibration study: Data from the calibration phase will be used to derive a formula to predict individualised anti-nociception for incision.

Inclusion Criteria:

• Patients undergoing non-cardiac surgery
• Patients undergoing cardiac surgery (coronary artery bypass graft)
• Knowledge of French, English or Dutch is required.

Exclusion Criteria:

• Pregnancy
• Allergy or contraindications to one of the study drugs
• BMI >30
• History of drug and alcohol abuse,
• preoperative analgesic drug use
• Heart rhythm disturbances (Atrial fibrillation, atrial flutter).
• the use of Alpha-2 adrenergic agonists