Propofol is an intravenous anesthetic used for procedural sedation, during monitored anesthesia care, or as an induction agent for general anesthesia. It may be administered as a bolus or an infusion, or some combination of the two. Propofol is prepared in a lipid emulsion which gives it the characteristic milky white appearance. Strict aseptic technique must be used when drawing up propofol as the emulsion can support microbial growth. It has both approved and off-label uses. This activity outlines the indications, mechanism of action, methods of administration, important adverse effects, contraindications, monitoring, and toxicity of propofol, so providers can direct patient anesthesia where it is indicated, as part of the interprofessional team.
Currently, propofol has superseded thiopentone as an intravenous anaesthetic, both for induction as well as maintenance. It is an oily liquid employed as a 1% emulsion. Sensitive patients may develop allergic reaction to the emulsifier. Unconsciousness after propofol injection occurs in 15-45 sec and lasts 5-10 min. Propofol distributes rapidly (distribution t½ 2-4 min). Elimination t½ (100 min) is much shorter than that of thiopentone due to rapid metabolism.
Hepatic clearance is approximately 60%, with extrahepatic clearance making up the remaining 40%, most of which is via the kidneys. Propofol is bi-phasic, with its initial half-life being relatively quick, around 40 minutes, and its terminal half-life usually being 4 to 7 hours. Half-time may be up to 1 to 3 days after a 10-day infusion. The clinical effect of propofol is much shorter in duration. After a single bolus or short-term infusion, the termination of action is primarily by redistribution, owing to the lipophilicity of the drug. Metabolism and excretion play minor roles in the termination of effects following a single bolus. Prolonged infusions may lead to slower emergence from anesthesia once the tissues and blood have reached a steady state concentration.
Propofol is believed to cause CNS depression by enhancing GABA receptor mediated neuronal inhibition. Intermittent injection or continuous infusion of propofol is also used for total intravenous anaesthesia when supplemented by fentanyl. It lacks airway irritancy and is not likely to induce bronchospasm, therefore preferred in asthmatics. It is particularly suited for outpatient surgery, because residual impairment is less marked and shorter-lasting. Incidence of postoperative nausea and vomiting is low; patient acceptability is very good. Excitatory effects and involuntary movements are noted in few patients. Induction apnoea lasting ~1 min is common. Fall in blood pressure is more profound than that with thiopentone. This is due primarily to vasodilatation with less marked cardiac depression. However, hypotension is short lasting. Baroreflex is suppressed; heart rate remains unchanged or may decrease. Maintenance anaesthesia with propofol produces dose dependent respiratory depression which is more marked than with thiopentone. Effect on cerebral blood flow and oxygen, consumption is similar to that of thiopentone. Pain during injection is frequent; but can be minimized by combining with lidocaine.
Propofol is contraindicated in any patient that has any known hypersensitivity reaction to the drug. Caution is necessary for any patient with abnormally low blood pressure. Some package inserts state that propofol should not be given to those with reported allergies to eggs, egg products, soy, or soy products. An allergic reaction occurs secondary to exposure to specific proteins from both egg and soy sources and not the fats (lecithin and oil, respectively) that make up the emulsion. The oils used to manufacture propofol are unlikely to contain quantities of proteins significant enough to produce an allergic cross-reaction.