BIS and Entropy Nociception Monitoring

Background: Reports have been appearing in literature over the past years of various nociception-antinociception monitors, introduced and promoted from major manufactures. Recently a new term Practice misalignment" has been recently coined indicating research study groups that are distant from daily anesthesia practice, with some scientific relevance but very little clinical relevance simulating "purely hypothetical" conditions that are not related to "everyday" anesthesia practice. These proposed new nociception-antinociception parameters are assumed to be "immune" from confounding factors commonly encountered such as neuromuscular block, remifentanil, or cardiovascular haemodynamically active drugs.

Methods: Investigators sought to quantify the basic components of these new nociception-antinociception parameters in response to various noxious stimuli, and then test them against the most confounding factors namely neuromuscular blocking agents (NMBAs) for sEMG, remifentanil analgesia and haemodynamic changes, while at the same time analysing the EEG and blood levels. Investigators examined two nociception -antinociception parameters basic components sBIS/sEMG and Response Entropy-State Entropy difference from the two main manufacturers GE and Medtronic.

Fifty patients, aged 18-65 years, undergoing general surgery on the lower limb were randomly allocated to the BIS 25 or BIS 50 groups. Exclusion criteria included alcohol or drug abuse, chronic treatment with antihypertensive or cardiovascular medications including β-blockers, and medications acting on the central nervous system such as benzodiazepines, antiepileptic and neuroleptic medications, After capnographic verification of proper lungs ventilation with 40% oxygen in air, either BIS 50 levels or BIS 25 were subsequently maintained via propofol TCI 0.2 microg mL-1 TCI adjustments. Stable BIS values that showed no further decline and remained within BIS ±5 of either BIS 50 levels or BIS 25 of the previous BIS value were considered an indicator of pseudo-steady state plasma effect-site equilibration. Two silver/silver chloride surface stimulating electrodes were placed 4 cm apart on the ulnar nerve at the wrist and connected to Innervator NS272 (Fisher & Paykel, Auckland, New Zealand) peripheral nerve stimulator. The ulnar nerve was stimulated in an ascending sequence of single twitch electric stimulations starting from 10 mA, up till 80 mA for a period of 10 s with a 3 min period between stimulations. BIS and Entropy data were recorded. After which patients were re-stimulated under remifentanil and again re-stimulated under NMBAs.

Inclusion criteria

• age 18-65 years

Exclusion criteria

• Alcohol or drug abuse,
• chronic treatment with antihypertensive or cardiovascular medications
• medications acting on the central nervous system such as benzodiazepines, antiepileptic neuroleptics