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An introduction to sedation of patients  in ICU

Sarah Ramsay


  • Relieve anxiety

  • Ensure appropriate level of analgesia if necessary

  • Provide sleep or deeper level of unconsciousness 

  • Enhance tolerance of ETT and mechanical ventilation 

  • Allow therapeutic and monitoring procedures

Level of sedation

Usually needs to be deeper in early stages of ventilation

  • some ventilator modes are “unphysiological” and poorly tolerated
  • patient “interference” with ventilation can lessen the benefit of a particular mode
  • paralysis may be required to permit such modes which in turns requires deeper sedation to avoid awareness
  • more procedures are often required at this time
  • may also be necessary due to disease in other organ systems – eg to help control of raised intracranial pressure or seizure activity

Can be reduced as patient’s condition improves

Improvements in ventilator technology (in addition to good nursing care and comfortable environment) mean lighter levels of sedation can be used, .

Too high a level of sedation will result in side effects of sedative agents, delayed weaning and possibly contribute to development of withdrawal phenomena. Too low a level of sedation will lead to patient distress with respiratory, haemodynamic and psychological consequences. Self extubation, removal of lines and other critical incidents are more likely during this time.

Variety of scoring systems available to assess sedation eg Ramsay score, GCS

Amount of drug required will depend on patient’s physiological and psychological state.

Failure to wake up after cessation of sedation

Potential causes:

  • Renal and hepatic dysfunction can contribute to accumulation of sedative agents

  • Septic encephalopathy

  • Unrecognised intracranial event (coagulopathy related bleeding, ischaemic or embolic events)

Agitation after cessation of sedation

May be due to:

  • Withdrawal phenomena

  • Unrecognised cause of distress – eg constipation

  • New sepsis

Drugs and dosages

  • Drugs can either be given by intermittent bolus or continuous infusion.

  • Intubated patients who are improving and are able to tolerate the endotracheal tube well

    • intermittent sedation is preferable to allow uncomfortable procedures and assist in sleep

  • More agitated patients and those still in the more severe stages of their disease

    • continuous infusion with regular assessment of conscious level is the better option. 

  • Sedation of the un-intubated patient with hypoxia and agitation is difficult due to the risk of respiratory depression. An agent such as haloperidol given in small IV increments (1-2mg at a time) will often calm agitation with minimal respiratory depression, small bolus if IV midazolam (1mg) can also be used with close attention to respiratory status.


  • dose: bolus 10-50 mg (1-5 ml). Infusion 1-3 mg/kg/hour

  • preparation: 10mg/ml

  • advantages

    • anxiolysis and hypnosis

    • reduced respiratory drive

    • very short acting and easily titratable

    • limited accumulation on prolonged infusion

    • not reliant on renal or hepatic excretion

    • no tolerance

    • no withdrawal effects

  • disadvantages

    • haemodynamic instability due to vasodilatation

    • high lipid load in prolonged infusion

    • can equate to considerable daily volume

    • expensive

    • associated with anaphylaxis/ anaphylactoid reactions

    • no analgesic effect

Morphine and midazolam

  • dose: For preparations containing 1 mg/ml of morphine and 1 mg/ml of midazolam: bolus 1-3 ml IV, usual infusion range 0.5-10 ml/h

  • advantages

    • anxiolysis, hypnosis, analgesia and ?amnesia

    • reduced respiratory drive

    • better haemodynamic stability

    • cheap

  • disadvantages

    • reliant on hepatic and renal excretion

    • accumulation on prolonged infusion

    • associated with anaphylactoid reactions

    • tolerance

    • withdrawal phenomena

    • delayed gastric emptying and constipation


  • intravenous anaesthetic induction agent

  • used for intubation as a bolus

  • dose 0.1-0.2 mg/kg of premixed solution

  • reduced dose if haemodynamic instability

  • advantage

    • more haemodynamically stable than propofol or thiopentone

    • rapid onset

  • disadvantages

    • painful on injection

    • anaphylactoid reactions

Muscle relaxant agents


  • dose: 1mg/kg (concentration 50 mg/ml)

  • used at intubation to provide rapid and good visualisation of the larynx

  • a depolarising agent that causes muscle fascicualtion

  • “dirty” drug with numerous side effects including bradycardia, release of potassium, anaphylaxis, suxamethonium apnoea, malignant hyperthermia

  • avoid in:

    • states where potassium is high or may climb rapidly – eg renal failure, burns or extensive muscle injury.

    • alternative is high dose non-depolarising agent (eg rocuronium 2-3mg/kg) which will take slightly longer to act than suxamethonium but should still give good intubating conditions. The prolonged action of such a high dose can lead to problems if intubation is impossible (prolonged bag and mask ventilation with cricoid pressure required till drug wears off), or worse still if intubation and ventilation are impossible, in which case emergency airway procedures such as cricothyroidotomy or tracheostomy will be required


  • non-depolarising muscle relaxant. Use of these drugs has declined as sedation techniques and ventilator technology has improved.

  • Uses

    • intubation (elective [dose 1mg/kg] or emergency [as described above]). Usual concentration 10 mg/ml

    • intermittent bolus doses [dose 0.5-1mg/kg] or continuous infusion [dose 0.5-1mg/kg/hr] to improve patient-ventilator synchrony. Intermittent doses are preferable and often required immediately after intubation while ventilation is being established and to assist restoration of ventilation after sudden changes in clinical condition – eg choking or biting on ETT. Continuous infusions are often necessary for the more unphysiological modes of ventilation and in control of raised ICP or seizures.
      REMEMBER: muscle relaxants have NO analgesic or sedative properties, when used adequate doses of sedative drugs MUST be used to avoid awareness (awake but paralyzed)

  • Disadvantages

    • accumulation

    • prolonged infusion causes muscle atrophy, contributes to critical illness neuropathy and delays weaning

    • risk of awareness


© Sarah Ramsay April 2003

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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