What is the target Bispectral Index (BIS) for a paralyzed patient?

BIS Monitoring in Paralyzed Patients

BIS monitoring is unreliable as a primary sedation assessment tool in paralyzed patients, but should be used as an adjunct to clinical judgment with a target range of 40-60 for general anesthesia depth, recognizing that neuromuscular blocking agents themselves artificially lower BIS values independent of actual sedation level. 1

Critical Limitation: NMBAs Confound BIS Readings

• Neuromuscular blocking agents (NMBAs) directly reduce BIS scores even in awake, unsedated volunteers, making BIS values unreliable indicators of true sedation depth 1
• Studies demonstrate that awake volunteers who received NMBAs without sedatives showed significant BIS reductions, and the monitor failed to detect awareness in completely paralyzed subjects 1
• Electromyographic (EMG) interference and variability in patient response further reduce the utility of processed EEG signals as reliable sedation monitors in critically ill patients 1

Guideline-Based Approach to Sedation in Paralyzed Patients

Primary Recommendation: Deep Sedation is Mandatory

• All paralyzed patients must receive adequate analgesia and sedation targeting deep sedation levels before and throughout neuromuscular blockade 1
• NMBAs have zero analgesic or sedating properties, making inadequate sedation during paralysis a high-risk scenario for awareness and recall 1
• Recall of events during paralysis is not uncommon, warranting aggressive sedation strategies 1

BIS Target Values (When Used as Adjunct)

• Target BIS 40-60 for general anesthesia depth when using BIS as an adjunctive monitor in paralyzed patients 2
• BIS values below 40 represent deep hypnosis and should generally be avoided except when maximum reduction in neuronal metabolism is specifically required 3
• The Society of Critical Care Medicine suggests using objective measures like BIS as adjuncts (not primary monitors) when subjective sedation assessments are impossible due to paralysis 1

Practical Monitoring Strategy

Clinical Assessment Remains Primary

• Do not rely on BIS alone—incorporate vital signs (heart rate, blood pressure), diaphoresis, and lacrimation, though these signs lack specificity 1
• Implement scheduled interruptions of NMBA infusions or use bolus dosing to permit periodic assessment of actual sedation adequacy and ongoing paralysis necessity 1
• Provide frequent verbal reassurance to paralyzed patients given the risk of awareness 1

Sedation Scale Correlation

• When BIS is used in paralyzed ICU patients, a BIS <60 has 100% sensitivity for predicting deep sedation (RASS -4 to -5) but only 35.7% positive predictive value, meaning many patients with BIS <60 may not actually be deeply sedated 4
• Approximately 1 in 10 critically ill patients receiving therapeutic paralysis may be inadequately sedated despite standard monitoring 4
• BIS monitoring showed no significant correlation with Richmond Agitation Sedation Score (RASS) upon emergence from paralysis (r = 0.27, p = 0.14) 4

Common Pitfalls to Avoid

• Never discontinue analgesics or sedatives while NMBAs are running—this is a critical safety error 1
• Do not assume BIS values in paralyzed patients reflect the same sedation depth as in non-paralyzed patients 1
• Avoid using BIS as the sole determinant of sedation adequacy in paralyzed patients, as studies show extensive overlap and poor discrimination between sedation levels 1
• Remember that deeply sedated patients may not show significant BIS changes after NMBA administration, while lightly sedated patients show marked reductions 1

Alternative Monitoring Considerations

• Train-of-four (TOF) monitoring via peripheral nerve stimulation should be incorporated into overall assessment but not used alone for monitoring neuromuscular blockade depth 1
• Consider continuous EEG monitoring (not just processed BIS) for detecting nonconvulsive seizures in patients with known seizures or unexplained depressed consciousness 1, 5