What is the target Bispectral Index (BIS) range prior to administering a neuromuscular‑blocking (paralytic) agent?

BIS Goal Prior to Starting Paralytic

Ensure deep sedation with a target BIS of 40–60 before administering any neuromuscular blocking agent, recognizing that BIS monitoring becomes unreliable once paralysis is established.

Critical Principle: Deep Sedation Must Precede Paralysis

• Administer analgesic and sedative drugs prior to and during neuromuscular blockade, with the goal of achieving deep sedation. This is a fundamental requirement because neuromuscular blocking agents have no analgesic or sedating properties. 1

• Target a BIS of 40–60 to confirm adequate depth of sedation before initiating paralysis. 2, 3

• Never rely on BIS values alone after paralysis begins, as neuromuscular blocking agents artificially reduce BIS scores even in awake, unsedated patients. 3, 4

Why BIS Becomes Unreliable After Paralysis

• In awake volunteers who received neuromuscular blockade without sedation, BIS values dropped to as low as 44–47, falsely suggesting deep sedation or anesthesia. 4

• The BIS monitor requires muscle activity in addition to an awake EEG to generate accurate values indicating consciousness. 4

• Studies demonstrate that paralyzed patients show a significant reduction in BIS scores following administration of neuromuscular blocking agents, independent of sedation level. 1

• This means a low BIS value during paralysis does not guarantee adequate sedation—the patient could be awake and aware despite a BIS of 40–60. 3, 4

Pre-Paralysis Protocol

Step 1: Establish Deep Sedation First

• Titrate sedatives (propofol, benzodiazepines) and analgesics (opioids) to achieve clinical signs of deep sedation before considering paralysis. 1

• Confirm adequate sedation using the Richmond Agitation-Sedation Scale (RASS), targeting RASS –4 or –5 (no response to verbal stimuli, minimal or no response to physical stimuli). 3

• Simultaneously monitor BIS values of 40–60 as an adjunct to clinical assessment. 2, 3

Step 2: Verify BIS Target Range

• Ensure BIS is consistently 40–60 for several minutes before administering the neuromuscular blocking agent. 2, 5, 6

• Avoid BIS values below 40, as this indicates excessive anesthetic depth and increases risk of hemodynamic instability. 2, 3

• In elderly patients (>60 years), target BIS ≈50 (range 40–60) to reduce postoperative delirium risk. 2

Step 3: Maintain Sedation During Paralysis

• Do not discontinue or reduce analgesic and sedative medications while the patient is receiving neuromuscular blockade. 1

• Continue targeting the same sedative and analgesic doses that achieved the pre-paralysis BIS of 40–60. 3

Monitoring Strategy After Paralysis Begins

• Use multimodal assessment rather than BIS alone: monitor heart rate, blood pressure, diaphoresis, and lacrimation as indirect indicators of inadequate sedation, though these lack specificity. 1, 3

• Consider scheduled interruption of neuromuscular blockade (daily sedation holidays) to permit reassessment of sedation adequacy and the ongoing need for paralysis. 1

• BIS may serve as a rough adjunct during paralysis (targeting 40–60), but clinical judgment and hemodynamic parameters must guide sedation titration. 3

Common Pitfalls to Avoid

• Never administer a paralytic without first confirming deep sedation. Recall of events during paralysis is not uncommon and can cause severe psychological trauma. 1

• Do not assume a low BIS value during paralysis means the patient is adequately sedated. The neuromuscular blocker itself lowers BIS independent of consciousness level. 3, 4

• Do not use BIS as the primary monitoring method in paralyzed patients—it is only an adjunct when clinical scales cannot be applied. 3

• Certain anesthetics (ketamine, sevoflurane) may paradoxically increase BIS values despite adequate anesthesia depth, further limiting BIS reliability. 2, 3

Special Populations

Elderly Patients (>60 years)

• Target BIS ≈50 (range 40–60) rather than deeper values to reduce postoperative delirium. 2

• Avoid burst-suppression EEG patterns, which are associated with increased delirium risk. 2

Cardiac Surgery with Cardiopulmonary Bypass

• Recognize that hypothermia reduces BIS by approximately 1.2 units per 1°C reduction in temperature. 1, 2

• During rewarming, anesthetic requirements increase and BIS may rise despite adequate sedation. 1

High-Risk Awareness Situations

• In emergency surgery or patients with limited cardiac reserve, BIS-guided anesthesia (targeting 40–60) before paralysis may reduce awareness risk. 2, 7