Factors impacting opioid selection in critically ill patients with moderate to severe nonneuropathic pain

Condition	Suitable opioid	Comments
Mechanically ventilated	Intravenous fentanyl, hydromorphone, or morphine (mostly as a continuous infusion)	These agents are effective, fast-acting, and titratable. Fentanyl may be preferred in unstable patients. Morphine is the least commonly used.
Spontaneously breathing	Intravenous fentanyl, morphine, or hydromorphone (mostly bolus dosing)
Renal and/or hepatic insufficiency	Intravenous fentanyl, hydromorphone, remifentanil	Morphine should be avoided due to its renal clearance. Remifentanil use is limited in the United States due to concerns of tachyphylaxis, cost, and possible hyperalgesia after discontinuation.
Hemodynamic instability	Intravenous fentanyl	Morphine and hydromorphone may be avoided due to a longer duration of action. Morphine also causes histamine release, which can exacerbate hypotension.
Bronchospasm	Intravenous fentanyl or hydromorphone	Histamine release by morphine can worsen bronchospasm.
Frequent neurologic assessments required	Intravenous remifentanil or fentanyl	Short duration of action permits more accurate assessment.
Fluid restriction required	Intravenous hydromorphone	Hydromorphone is available in a concentrated preparation (10 mg/mL).
Pain of extended duration (eg, burns)	Methadone	Methadone has a long duration of action and can be administered orally or intravenously as an intermittent bolus.

For patients who only need bolus dosing, hydromorphone is often preferred due to its longer duration of action when compared to fentanyl or morphine.

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