Compare the use of propofol and dexmedetomidine when used for sedation in the mechanically ventilated patient  with specific reference to
A) pharmacodynamics
B) indications
C) complications
for each of the drugs. (You may tabulate your answer).

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College Answer

Propofol 
Pharamcodynamics
•    GABA receptor action, though different from benzodiazepine receptor
•    Hydrophobic with high lipid solubility that allows it to cross blood brain barrier rapidly. Lipid solubility allows rapid redistribution to tissues so duration of action is only a few minutes.

B)         Indications
•    Sedation in ICU for ventilation
•    Sedation for procedures such as ETT, endoscopy, TOE etc
•    Sedation for transport
•    Effective anticonvulsant.

C)  Complications

•    Cardiovascular: hypotension from preload reduction due to dilation of venous capacitance vessels & mild myocardial depression.
•    Hyperlipidaemia possible: monitor triglyceride levels. Adjust TPN accordingly
•    Propofol infusion syndrome: dysrhythmias, heart failure, metabolic acidosis, hyperkalaemia, rhabdomyolysis. Beware of high doses ( > 80 microg/kg/min) and/or higher concentrations ( 2% vs 1% ).

Dexmedetomidine

A)
Selective alpha-2 agonist with both sedative and analgesic properties.

B) Indications
Patients are sedated when undisturbed but they arouse easily with minimal stimulation, allowing frequent neurologic examinations. Useful in the agitated, ventilated patient.

•    Analgesic sparing in post operative patients.
•    Results in less delirium compared to benzodiazepines.

C) Complications
•    Cardiovascular: bradycardia & hypotension. ( Vasoconstriction & hypertension have been reported with higher doses )
•    Not well studied for long term administration to critically ill, mechanically ventilated patients.Licensed for use in Australia for 24 hours only, though utilised in trials for up to 120 hours.

Discussion

Agian, the college has effectively and concisely summarised everything in their answer.
But, they didn't tabulate it, even though they invited the candidates to do so.

I have tabulated it for them.  

Feature

Propofol

Dexmedetomidine

Pharmacodynamics

GABA agonist; 
General anaesthetic

Centrally acting alpha-2 receptor agonist;
Sedative

Indications

Sedation (rapid onset)
Anaesthesia
Rapid induction of anaesthesia (eg. for intubation)
Decrease of cerebral metabolic demand

Sedation (slower in onset)
Analgesia: synergy with opiates
Management of agitation in both intubated and non-intubated patients

Less delirium than with benzodiazepines

Complications

Loss of airway reflexes
Hypotension
Hyperlipidemia
Propofol infusion syndrome

Bradycardia
Hypotension

More adverse effects than with benzodiazepines

 

References