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Levels of Sedation and Sedation Scales

Notes for MD Anaesthesiology Examination

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1. Introduction and Concept of the Sedation Continuum

Key principle: The transition from one level to the next is often unpredictable and varies between patients. There is no sharp boundary - a patient intended to be at moderate sedation can inadvertently drift into deep sedation or general anesthesia.

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2. ASA Continuum of Depth of Sedation (2019)

ASA Table: Continuum of Depth of Sedation

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3. Detailed Description of Each Level

3.1 Minimal Sedation (Anxiolysis)

• Patient responds normally to verbal stimulation
• Cognitive function and coordination may be impaired
• Ventilatory and cardiovascular functions are completely unaffected
• Airway reflexes are fully intact
• Example agents: low-dose oral/IV benzodiazepines, low-dose nitrous oxide

3.2 Moderate Sedation/Analgesia ("Conscious Sedation")

• Patient responds purposefully to verbal commands alone or with light tactile stimulation
• Patient maintains a patent airway independently
• Spontaneous ventilation is adequate - no airway support required
• Cardiovascular function is usually maintained
• Patient can be aroused, can follow commands, and often retains partial memory
• Previously termed "conscious sedation" - this term is now discouraged as it implies a discrete state rather than a continuum
• Clinically used for: colonoscopy, minor procedures, endoscopy, cardioversion, fracture reduction

3.3 Deep Sedation/Analgesia

• Patient cannot be easily aroused but responds purposefully to repeated or painful stimulation
• May be accompanied by partial or complete loss of protective airway reflexes
• Airway assistance may be required
• Spontaneous ventilation may be inadequate
• Cardiovascular function is usually maintained
• Critical clinical point: A practitioner intending moderate sedation must be prepared to rescue a patient who enters deep sedation

3.4 General Anesthesia

• Patient is unarousable even with painful stimuli
• Ability to independently maintain ventilatory function is impaired - requires assisted or controlled ventilation
• Airway intervention is often required (ETT, LMA)
• Cardiovascular function may be impaired
• Loss of all protective airway reflexes

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4. Special Category: Dissociative Sedation

• Maintains airway reflexes and spontaneous respiration better than other agents at equivalent depth
• Produces bronchodilation - useful in asthmatic patients
• Increases heart rate, blood pressure, and cardiac output
• Risk of emergence reactions (hallucinations, dysphoria) - mitigated by co-administration of a benzodiazepine

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5. Sedation Scales

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5.1 Ramsay Sedation Scale (RSS) - 1974

• Target in ICU: Scores 2-3 for awake/cooperative patients; 4-5 for sedated ventilated patients
• Limitation: Does not distinguish agitation subtypes; no level for alertness beyond "cooperative"

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5.2 Modified Ramsay Sedation Scale (2003)

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5.3 Richmond Agitation-Sedation Scale (RASS) - 2002

1. Observation (first 30 seconds)
2. Response to auditory stimuli (call patient's name)
3. Response to physical stimuli (shoulder shake or sternal rub)

• Goal RASS 0 to -2 for most ICU patients (alert/calm to light sedation)
• RASS -4 to -5 reserved for specific indications: status epilepticus (SE), ARDS, refractory intracranial hypertension
• RASS more negative than -2 is associated with: longer ICU stays, longer time to extubation
• RASS more positive than +1 is associated with: self-harm, self-extubation

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5.4 Riker Sedation-Agitation Scale (SAS)

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5.5 Observer's Assessment of Alertness/Sedation Scale (OAA/S)

• Responsiveness
• Speech
• Facial expression
• Eyes

• Demonstrated excellent inter-rater reliability
• The responsiveness component most often correlates with the composite score
• Widely used in procedural sedation studies
• Modified versions have been published to better align with the ASA Continuum of Depth of Sedation

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5.6 Correlation of Scales with ASA Sedation Levels

Exam note: The RASS positive scores (+1 to +4) reflect agitation, not anxiolysis/minimal sedation - they do NOT map directly to the ASA minimal sedation category.

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6. Processed EEG - Bispectral Index (BIS)

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7. Monitoring Standards for Sedation

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8. Important Clinical Pearls for the Exam

1. The continuum is non-linear and non-predictable: Any patient receiving sedation may inadvertently progress to the next deeper level; practitioners must be capable of rescue at least one level deeper than intended.
2. Reflex withdrawal is NOT purposeful response: A patient withdrawing a limb from a painful stimulus is NOT in moderate sedation - this is a spinal reflex.
3. MAC (Monitored Anesthesia Care): MAC is a billing/service term, not a level of sedation. It refers to the anesthesia service itself and may include any level of sedation including general anesthesia if needed.
4. "Conscious sedation" terminology: This term is now discouraged. The preferred term is "moderate sedation/analgesia" as it better reflects the continuum concept.
5. RASS is the most recommended scale for ICU sedation monitoring per SCCM guidelines. It has high inter-rater reliability across all healthcare providers.
6. Ramsay Scale (original) has only 6 levels (3 awake + 3 asleep); the modified version has 8 levels.
7. OAA/S: 4 domains (responsiveness, speech, facial expression, eyes); score 0-5; responsiveness item most important.
8. Risk equivalence: ASA closed claims data shows that risk of death or permanent brain damage during procedural sedation is similar to that of general anesthesia - most commonly due to respiratory depression from opioids and sedative-hypnotics.
9. Ketamine (dissociative sedation): Unlike non-dissociative agents, it preserves airway reflexes and spontaneous ventilation while providing profound analgesia. Cardiovascular effects are stimulatory (elevated heart rate and BP).
10. RASS target in ICU: Generally -2 to +1; avoid deep sedation (RASS < -2) unless specifically indicated.

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Summary Table: Key Features of Sedation Scales

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• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9th Ed., Chapter 30 (MAC and Sedation)
• Miller's Anesthesia, 10th Ed., Chapter 68 (Day Case Surgery)
• Rosen's Emergency Medicine, 10th Ed., Chapter 7 (Procedural Sedation)
• Cummings Otolaryngology Head & Neck Surgery, Chapter 104/184 (Anesthesia)
• Fischer's Mastery of Surgery, 8th Ed., Chapter 10 (ICU Sedation and Analgesia)
• Fishman's Pulmonary Diseases and Disorders, 6th Ed., Chapter 151 (Critical Care Sedation)