Can the effect of Remifentanil (generic name: remifentanil) be monitored using a BIS (Bispectral Index) monitor?

BIS Monitoring of Remifentanil Effects

BIS monitoring has limited utility for directly monitoring remifentanil's analgesic effects, but it can detect the sedative component when remifentanil is combined with hypnotics like propofol, and it effectively tracks changes in consciousness level during painful stimulation. 1, 2

Understanding BIS and Opioid Monitoring

Opioids, including remifentanil, have minimal and variable effects on BIS values because BIS primarily measures hypnotic depth rather than analgesia. 3, 1 This fundamental limitation means:

• Remifentanil alone does not significantly alter BIS readings in the absence of painful stimuli 2
• BIS values remain relatively unchanged when remifentanil is added to propofol anesthesia before noxious stimulation occurs 2
• The monitor cannot distinguish between adequate analgesia and inadequate analgesia when patients are deeply sedated 1

When BIS Can Detect Remifentanil Effects

BIS becomes useful for monitoring remifentanil only during noxious stimulation, such as laryngoscopy and intubation. 2 In this context:

• Remifentanil dose-dependently attenuates BIS increases during painful procedures, with effect-site concentrations correlating negatively with BIS changes (P < 0.0001) 2
• At remifentanil concentrations of 8-16 ng/mL, BIS increases after intubation are significantly blunted compared to lower doses 2
• BIS changes during painful stimuli are as sensitive as hemodynamic responses (blood pressure and heart rate) for detecting inadequate analgesia 2

Clinical Applications in Combined Anesthesia

When remifentanil is combined with propofol, BIS monitoring shows more practical utility:

• Significant correlation exists between BIS and both propofol (r=0.547, P<0.001) and remifentanil (r=0.533, P<0.001) predicted effect-site concentrations during craniotomy procedures 4
• Multiple regression analysis demonstrates that BIS reflects the combined effects of both drugs (r=0.7341, P<0.001) 4
• During propofol-remifentanil anesthesia, BIS monitoring allows modest reduction in volatile anesthetic consumption when desflurane is added 5

Important Limitations and Caveats

BIS monitoring should not be used as the primary method to assess remifentanil's analgesic adequacy for several critical reasons:

• BIS cannot predict hemodynamic or motor responses to stimulation, which are key indicators of inadequate analgesia 1
• The monitor shows paradoxical increases with certain anesthetics (ketamine, sevoflurane) despite adequate depth 3, 1
• BIS cannot distinguish between deep sedation and general anesthesia, limiting its utility for titrating total anesthetic depth 3, 1
• Wide individual variation exists, particularly in awake baseline values 6

Practical Monitoring Strategy

For remifentanil-based anesthesia:

• Use BIS primarily to monitor the hypnotic component (propofol, volatile agents), targeting values of 40-60 for general anesthesia 7
• Rely on hemodynamic responses (heart rate, blood pressure) as the primary indicators of remifentanil adequacy 2
• Consider BIS changes during noxious stimulation as an adjunctive measure, recognizing that increases suggest inadequate analgesia 2
• In paralyzed patients receiving neuromuscular blockade, BIS may serve as a useful adjunct when clinical assessment is impossible 3, 1

Special Considerations

In ICU settings, objective monitors like BIS are inadequate substitutes for subjective sedation scoring systems in non-paralyzed patients and should not be used as the primary monitoring method. 3 However, they may be suggested as adjuncts in paralyzed ICU patients where subjective assessment is unobtainable. 3

When using remifentanil at high doses (4 mg/kg), expect prolonged apnea (12.8 minutes) and significant hemodynamic effects, with return to consciousness taking approximately 529 seconds after propofol 2 mg/kg based on BIS monitoring. 3