Sedation is necessary for most ICU patients. While the appropriate use of sedative drugs can provide comfort, most have cardiovascular and respiratory side-effects. Objective assessment of the depth of sedation is necessary to ensure that comfort does not give way to excessively and dangerously deep levels of sedation. All sedatives are potentially cumulative so doses must be kept to a minimum.

Benzodiazepines have the advantage of being amnesic. Diazepam is mainly administered as an emulsion in intralipid as organic solvents are extremely irritant to veins. Midazolam is shorter acting than diazepam although 10% of patients are slow metabolisers. All benzodiazepines accumulate in renal failure; care must be taken to avoid excessive dosage by regular reassessment of need. Some patients suffer unpredictable severe respiratory depression with hypotension.

Propofol used in subanaesthetic doses is short-acting though effects are cumulative when infusions are prolonged or with coexisting hepatic or renal failure. It is given as an emulsion in 10% intralipid so large volumes may contribute significantly to calorie intake.

As chlorpromazine and haloperidol antagonise catecholamines, they may cause vasodilatation and hypotension. Dystonic reactions and arrhythmias are also occasionally seen.

a2 antagonists also provide analgesia and are synergistic with opiates. Dexmedetomidine causes minimal respiratory depression and the patient is easily rousable. Bradycardia and hypotension may occur, especially with the loading dose.

Isoflurane is largely exhaled unchanged and is therefore short acting. Cumulative effects have been recorded with prolonged use, carrying the theoretical risk of fluoride toxicity. Exhaled isoflurane should be scavenged.


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