[Pharmacokinetics of propofol injected after deliberate preoperative hemodilution]

Effect of acute hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC50 of propofol at two clinical endpoints in patients

Preoperative acute hypervolemic hemodilution (AHHD) is a technique used in anesthesia to reduce the number of blood cells lost during intraoperative bleeding. The aim of the present study was to evaluate the effect of the hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC₅₀ of propofol at two clinical endpoints. A total of 20 patients undergoing AHHD following epidural anesthesia were studied, and 20 patients who did not receive hemodilution were used as a control group. All patients were American Society of Anesthesiologists grade I, aged 20-40 years and undergoing hip arthroplasty surgery. In the AHHD group, 10 ml/kg lactated Ringer's solution was infused over 20 min at the same time as the epidural test dose. The infusion was followed by the infusion of 6% hydroxyethyl starch 130/0.4 over 30 min. Patients in the control group received 10 ml/kg Ringer's solution over 50 min. Propofol was then delivered by a Diprifusor target-controlled infusion. The predicted blood and effect-site propofol concentrations were recorded at loss of consciousness (LOC) and return of consciousness (ROC). Probit analysis was used to estimate the values for predicted blood and effect-site concentrations at the two clinical endpoints. The results showed that the potency of propofol was decreased during AHHD. Compared with the controls, the predicted blood and effect-site concentrations of propofol at LOC were higher in patients of the hemodilution group, resulting in higher EC₅₀ values (P=0.001 and 0.025, respectively). At ROC, the effect-site EC₅₀ was 2.9 µg/ml [95% confidence interval (CI), 2.8-3.0] in hemodilution patients and 2.5 µg/ml (95% CI, 2.2-2.6) in control patients (P=0.001). With AHHD, the LOC time was significantly longer and the propofol dose was higher, while ROC times were comparable. In conclusion, AHHD increases the requirement for propofol at LOC and prolongs LOC time. Patients with AHHD recovered consciousness at higher effect-site concentrations of propofol. Thus, the induction dose of propofol should be increased during AHHD.

[Use of Diprivan for prehospital emergencies]

The use of propofol at the scene of an accident or during transport to the hospital: 1. Should be restricted to fully qualified anaesthetists of an Emergency Mobile Hospital Unit. 2. Is probably rather limited, as: the indications for anaesthesia in this context are relatively rare; they are dominated by trauma cases (which represent 20 to 30 per cent of the activity of an Emergency Mobile Hospital Unit) and other accident-related conditions; furthermore, in most emergency situations, sedation and/or analgesia of varying depth are more often required; the indications for propofol would be rare because of: its haemodynamic effects, especially as hypovolaemia is extremely frequent, as neurological damage is often existing, and the medical history of the patient is frequently unknown; the possible choice of other agents, such as midazolam, which is widely used as well as etomidate or ketamine; 3. Should follow the same guidelines as those in use for its intra-hospital administration: propofol is undoubtedly a valuable agent as it allows a rapid induction, depresses the pharyngo-laryngeal reflexes, and has the advantage of producing a rapid, good quality recovery which provides an important element of safety; however, for as long as prospective comparative studies have not specifically been carried out in the area of pre-hospital anaesthesia, the greatest circumspection is required. Any contraindication and precaution recommended from hospital use should be strictly adhered to and amplified because of the difficult circumstances and the other available alternatives kept in mind.

Propofol in patients with cardiac disease

Propofol is an intravenous anaesthetic which is chemically unrelated to other iv anaesthetics. Most anaesthetists are now becoming familiar with propofol's pharmacokinetic and pharmacodynamic properties. It has proved to be a reliable drug that can be used safely for induction and maintenance of anaesthesia for most surgical procedures and unlike other anaesthetic agents, it can especially be extended into the postoperative setting or intensive care unit for sedation. Propofol's greatest attributes are its pharmacokinetic properties which result in a rapid, clear emergence and lack of cumulative effects even after prolonged administration. Compared with other iv anaesthetics, the induction dose of propofol has a relatively higher incidence of respiratory depression, short-lived apnoea and blood pressure reduction that may occasionally be marked. Possible mechanisms for the hypotension may relate to (1) its action on peripheral vasculature (vasodilatation), (2) decreased myocardial contractility, (3) resetting of the baroreflex activity and (4) inhibition of the sympathetic nervous system outflow. In vitro studies indicate that propofol depresses the immunological reaction to bacterial challenge as well as the chemotactic activity. Clinical studies, in cardiac surgery, have demonstrated that propofol, in association with an opioid, is a logical anaesthetic choice. Propofol is about to receive approval for continuous iv sedation. Comparative studies of propofol and midazolam have clearly demonstrated the superiority of propofol in terms of rapid recovery and precise control of the level of sedation.