Sedation/Anesthesia During Mechanical Ventilation

Patients receiving mechanical ventilation often require sedation and/or anesthesia to ensure comfort, facilitate ventilation, and prevent complications. This lesson will cover the indications, commonly used drugs, dosages, and weaning strategies for sedation and anesthesia in mechanically ventilated patients.

I. Indications for Sedation/Anesthesia

Sedation and anesthesia are used in mechanically ventilated patients for several reasons:

• Patient comfort and anxiolysis: Mechanical ventilation can be uncomfortable and frightening for patients. Sedation helps to reduce anxiety and promote relaxation.
• Facilitation of mechanical ventilation: Sedation can reduce patient-ventilator asynchrony, allowing for more effective delivery of mechanical breaths.
• Prevention of self-extubation: Sedation can help to prevent patients from removing the endotracheal tube prematurely.
• Reduction of oxygen consumption: By reducing patient agitation and muscle activity, sedation can decrease oxygen demand.
• Control of intracranial pressure: In patients with head injuries, sedation can help to reduce intracranial pressure.
• Management of agitation: Sedation can be used to manage agitation and delirium, which can be common in critically ill patients.
• Procedural sedation: Sedation is often required for procedures performed on mechanically ventilated patients.

II. Commonly Used Drugs

Several classes of drugs are used for sedation and anesthesia in mechanically ventilated patients. The choice of drug depends on the patient’s condition, the desired level of sedation, and the duration of mechanical ventilation.

• Benzodiazepines:
  • Examples: Midazolam, lorazepam, diazepam
  • Mechanism of action: Enhance the effect of GABA, an inhibitory neurotransmitter.
  • Effects: Anxiolysis, sedation, amnesia, muscle relaxation.
  • Dosage:
    • Midazolam: 0.02-0.1 mg/kg IV bolus, followed by 0.02-0.1 mg/kg/hr infusion.
    • Lorazepam: 0.02-0.06 mg/kg IV bolus, followed by 0.01-0.1 mg/kg/hr infusion.
  • Special considerations:
    • Risk of respiratory depression, especially when combined with opioids.
    • Prolonged use can lead to tolerance and dependence.
    • Midazolam has a short half-life, while lorazepam has a longer half-life.
• Propofol:
  • Mechanism of action: GABA receptor agonist.
  • Effects: Rapid sedation and amnesia.
  • Dosage: 0.3-3 mg/kg IV bolus, followed by 0.5-5 mg/kg/hr infusion.
  • Special considerations:
    • Rapid onset and short half-life.
    • Can cause hypotension, especially in hypovolemic patients.
    • Risk of propofol infusion syndrome (PRIS) with prolonged, high-dose infusions.
• Dexmedetomidine:
  • Mechanism of action: Alpha-2 adrenergic agonist.
  • Effects: Sedation, anxiolysis, analgesia.
  • Dosage: 0.2-1 mcg/kg IV loading dose over 10 minutes, followed by 0.2-0.7 mcg/kg/hr infusion.
  • Special considerations:
    • Provides “awake” sedation with minimal respiratory depression.
    • Can cause bradycardia and hypotension.
• Opioids:
  • Examples: Morphine, fentanyl, hydromorphone
  • Mechanism of action: Bind to opioid receptors in the central nervous system.
  • Effects: Analgesia, sedation.
  • Dosage: Varies depending on the specific opioid.
  • Special considerations:
    • Risk of respiratory depression, especially when combined with sedatives.
    • Can cause hypotension and bradycardia.
    • Fentanyl has a rapid onset and short duration of action.
• Ketamine:
  • Mechanism of action: NMDA receptor antagonist.
  • Effects: Dissociative anesthesia, analgesia, amnesia.
  • Dosage: 0.5-1 mg/kg IV bolus, followed by 0.2-0.5 mg/kg/hr infusion.
  • Special considerations:
    • Can cause hallucinations and vivid dreams.
    • May increase heart rate and blood pressure.
    • Useful for patients with bronchospasm.

III. Assessment of Sedation Level

It is crucial to regularly assess the level of sedation in mechanically ventilated patients to ensure that they are receiving the appropriate amount of medication. Several sedation scales are used for this purpose:

• Richmond Agitation-Sedation Scale (RASS): A commonly used scale that ranges from +4 (combative) to -5 (unarousable). The goal is typically a RASS score of 0 to -2 for mechanically ventilated patients.
• Sedation-Agitation Scale (SAS): Similar to the RASS, ranging from 1 (dangerously agitated) to 7 (unarousable).
• Ramsay Sedation Scale: A simpler scale that ranges from 1 (anxious, agitated, or restless) to 6 (no response to painful stimulus).

IV. Weaning of Sedation and Anesthesia

As the patient’s condition improves and the need for mechanical ventilation decreases, sedation and anesthesia should be gradually reduced. Sedation weaning is an important step to facilitate liberation from the ventilator and reduce the risk of complications.

• Daily sedation interruption (DSI):
  • Involves temporarily stopping the continuous infusion of sedative medications until the patient is awake and able to follow commands or becomes agitated.
  • Has been shown to reduce the duration of mechanical ventilation and ICU stay.
  • Contraindications: Increased intracranial pressure, status epilepticus, ongoing agitation, hemodynamic instability.
• Gradual reduction of infusion rates:
  • If DSI is not appropriate, sedative infusions can be gradually reduced while closely monitoring the patient’s response.
• Transition to shorter-acting agents:
  • Switching from longer-acting benzodiazepines (e.g., lorazepam) to shorter-acting agents (e.g., propofol, dexmedetomidine) can facilitate more rapid awakening.
• Use of sedation scales:
  • Regular assessment using sedation scales (e.g., RASS, SAS) can help guide the titration of sedative medications.
• Multidisciplinary approach:
  • Sedation weaning should be coordinated with other aspects of patient care, including ventilator weaning, pain management, and delirium prevention.