Background
Propofol is a phenolic derivative with sedative and hypnotic properties. It is highly lipophilic allowing it to easily cross the blood brain barrier resulting in rapid onset of action. Emergence is also very quick due to fast redistribution to the peripheral tissues and fast metabolic clearance of propofol1.
Propofol has been used by anaesthetists in sedation since the 1980s2. It is the most commonly used agent for procedural sedation in the emergency department and is normally administered as a bolus dose3. For procedures, such as reducing fractures, the goal is to achieve a ‘moderate’ level of sedation and analgesia. This is defined as:
“Procedural sedation and analgesia should provide pain relief and produce a state of reduced consciousness where the patient is still able to respond to a verbal or physical stimulus and to continuously maintain a patent airway and adequate ventilation”4.
Propofol can have adverse effects, notably hypotension and loss of airway patency5,6. There is also a risk of progressing to deep sedation or even general anaesthesia4.
Target controlled infusion (TCI) allows the operator to target a specific clinical effect of propofol3. Patients’ height and weight are inputted into an infusion pump which uses an equation to target a specific plasma concentration of the infused substance3. In theory, this uses the minimal quantity of drug required to achieve the clinical effect and reduces the risk of overdosing and/or adverse events and there is a body of evidence available to support this theory.
A randomised controlled trial published in 1993 compared midazolam against computer controlled propofol sedation in outpatient bronchoscopy in 42 patients. Memory and motor reaction did not differ between the groups7.
A partially blinded randomised controlled trial published in 2004 compared patient-maintained propofol sedation versus operator-controlled midazolam sedation in patients requiring molar extraction. These used TCI of propofol initially before the patient was given control of bolus administration in the patient-controlled arm. Propofol was shown to be well tolerated and safe with superior anxiolysis, quicker recovery, less amnesia and less depression of simple psychomotor function than operator-controlled midazolam8.
Audit data published in 2010 regarding sedation for oocyte retrieval using TCI of propofol and incremental alfentanil by non-anaesthetists showed that safety was acceptable with a low respiratory adverse incident rate of 0.5 per 1000 cases. Patient satisfaction with the sedation was high2.
There is further randomised control trial evidence published in 2013 and carried out in Taiwan by Chan et al. This work compared TCI of propofol (using the Marsh model) vs bolus administration of sedatives for deep sedation in GI Endoscopy in 220 patients. The authors found there to be a reduction in cardiovascular and respiratory side effects in the TCI arm9.
As a note, cast your mind back to your anaesthetic blocks – TCI relies upon certain pharmacokinetic mathematical models. We didn’t go into emergency medicine to ponder these in too much detail, but just know there’s a couple of widely used models (Marsh and Schnider). Marsh adjusts for weight, whilst Schnider does not adjust (not age or height). If you do want to ponder this in more detail, consider this article10.
More recently, a systematic review published in the European Journal of Emergency medicine in 2020 by Burton et al. looked at the effect of TCI propofol in reducing the incidence of adverse events for procedural sedation in the ED. They recommended a standardised tool should be used in reporting adverse events. They looked at 7 studies and three of these showed a reduction in cardiovascular and respiratory adverse events11. They were unable to determine if TCI propofol showed reduced incidences of adverse events compared to other methods of propofol administration.
While this evidence appears to support that propofol TCI can successfully be utilised for sedation, further evidence is required to determine the suitability of this method for Emergency Department sedation and its acceptability for both patients and clinicians.