Assessment of Deep Sedation in Adult ICU Patients

Validated Clinical Scales (Primary Method)

• The Richmond Agitation‑Sedation Scale (RASS) and the Sedation‑Agitation Scale (SAS) are the most valid and reliable tools for measuring sedation depth in adult intensive‑care patients. High psychometric evidence supports their use. 1
• RASS is the preferred scale, demonstrating high inter‑rater reliability and the ability to discriminate between different sedation levels. 1
• Deep sedation corresponds to RASS ‑4 or ‑5:
  
  • RASS ‑4 – no response to verbal stimuli but movement or eye opening to a physical stimulus. 1
  • RASS ‑5 – no response to either verbal or physical stimuli. 1
• RASS scores show a moderate‑to‑high correlation with electroencephalogram (EEG) and Bispectral Index (BIS) values. 1
• SAS is an equally valid alternative to RASS, with high inter‑rater reliability among ICU clinicians and the capacity to discriminate sedation levels across diverse clinical situations. 1

Objective Monitoring (Adjunct Method)

• A Bispectral Index (BIS) of 40–60 indicates general anesthesia or deep sedation. 2
• A BIS of 60–69 corresponds to deep sedation (but not full anesthesia). 2
• BIS should not be used as the primary monitoring method in non‑comatose patients who are not receiving neuromuscular blockade, because it cannot replace subjective clinical scales. 1
• BIS may be employed only as an adjunct when clinical scales cannot be applied (e.g., patients under neuromuscular blockade). 1

Practical Evaluation Algorithm

Patients without neuromuscular blockade

• First assess sedation with RASS or SAS. 1
• A score of RASS ‑4 or ‑5 defines deep sedation. 1
• BIS is not required nor recommended as a primary tool in this setting. 1

Patients with neuromuscular blockade

• Clinical scales are infeasible; therefore, use BIS as an adjunct, targeting a value of 40–60. 1

Complementary Physiologic Monitoring

Capnography

• Capnography can detect early hypoventilation before oxygen desaturation occurs. 3
• End‑tidal CO₂ > 50 mmHg, an absent waveform, or an absolute change > 10 mmHg from baseline may signal respiratory depression. 3
• No correlation exists between ETCO₂ values and sedation depth measured by clinical scales. 3

Pulse Oximetry

• Pulse oximetry should be applied to patients at higher risk of hypoxemia (e.g., high drug doses, multiple sedatives, significant comorbidities). 3
• It does not replace clinical assessment but serves as a reliable adjunct. 4

Common Pitfalls to Avoid

• Do not rely solely on BIS in non‑paralyzed patients; clinical scales provide superior assessment of sedation depth. 1
• Do not assume that a low BIS value in paralyzed patients reflects adequate sedation, because neuromuscular blockers can artificially lower BIS readings. (This caution is supported by the recommendation to use BIS only as an adjunct.) 1

Target BIS Range for Paralyzed and Sedated Patients

Critical Understanding: NMBAs Confound BIS Readings

• The American College of Cardiology is not mentioned, however, the article suggests that for paralyzed and sedated patients, a BIS range of 40-60 should be targeted, recognizing that neuromuscular blocking agents artificially lower BIS values and make this monitoring unreliable as a sole indicator of adequate sedation depth 5
• Neuromuscular blocking agents directly reduce BIS scores even in awake, unsedated patients, making BIS values unreliable indicators of true sedation depth 5
• All paralyzed patients must receive adequate analgesia and sedation targeting deep sedation levels before and throughout neuromuscular blockade, regardless of BIS values 5

Recommended BIS Targets During Paralysis

• The European Society of Cardiology is not mentioned, however the article suggests maintaining BIS values between 40-60 during general anesthesia and therapeutic paralysis 6
• BIS values below 40 denote deep hypnosis and should be avoided as they increase risk of hemodynamic instability 6
• For cardiac arrest patients undergoing targeted temperature management with paralysis, deep sedation is required during the induction phase, with moderate sedation during maintenance, as suggested by the European Heart Journal 7

Multimodal Monitoring Strategy

• 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 5
• Vital signs monitoring, such as heart rate and blood pressure, should be used in conjunction with BIS, though these lack specificity 5
• Physical signs, such as diaphoresis and lacrimation, should also be used, though also non-specific 5

Special Considerations for Specific Populations

• For cardiac arrest patients undergoing targeted temperature management, deep sedation is required during induction phase, moderate sedation during maintenance phase, and light sedation during rewarming, as suggested by the European Heart Journal 7
• Neuroprognostication should be delayed ≥72 hours after rewarming and discontinuation of sedation, as suggested by the European Heart Journal 7
• For non-paralyzed patients undergoing procedural sedation, optimal BIS range is 70-85, balancing adequate sedation with lower respiratory depression rates, as suggested by the American College of Emergency Physicians 8

Common Pitfalls to Avoid

• Certain anesthetics, such as ketamine and sevoflurane, may paradoxically increase BIS values despite adequate anesthesia depth 6, 9
• Temperature changes affect BIS values—hypothermia reduces anesthetic requirements by approximately 1.2 BIS units per 1°C reduction 6

Pre‑Paralysis Deep Sedation and BIS Monitoring

Requirement for Analgesia and Sedation Before Neuromuscular Blockade

• Analgesic and sedative agents (e.g., opioids, propofol, benzodiazepines) must be administered before and during neuromuscular blocking agents to achieve deep sedation, because paralytics have no analgesic or sedating properties. [10] [11]

Effect of Neuromuscular Blockade on BIS Values

• In patients who receive a neuromuscular blocking agent, BIS scores decrease significantly independent of the actual depth of sedation, demonstrating that paralysis itself lowers BIS values and can produce falsely low readings. [12] [10] 11

Pre‑Paralysis Sedation Protocol

• Sedative and analgesic titration (propofol, benzodiazepines, opioids) should be performed until clinical signs of deep sedation are evident before any paralytic is given. [10] [11]
• Continuous analgesic and sedative infusions must be maintained throughout the period of neuromuscular blockade; doses should not be reduced or stopped once paralysis begins. [12] [10] 11

Monitoring Strategy After Paralysis Initiation

• A multimodal assessment (heart rate, blood pressure, diaphoresis, lacrimation) should be used in place of relying solely on BIS, as these physiologic signs can indicate inadequate sedation despite low BIS values. [12] [10] 11
• Daily sedation holidays (scheduled interruption of the neuromuscular blocker) are recommended to allow reassessment of sedation adequacy and to determine whether continued paralysis is necessary. [10] [11]

Patient Safety Considerations

• Administration of a paralytic must not occur until deep sedation has been confirmed; failure to do so can lead to intra‑operative awareness and severe psychological trauma. [10] [11]

Special Population: Effects of Temperature on BIS (Cardiac Surgery)

• Hypothermia reduces BIS by approximately 1.2 units for each 1 °C decrease in core temperature. 13
• During rewarming, anesthetic requirements increase and BIS may rise even when sedation depth remains adequate. 13