Introduction: Currently, propofol is the most widely used intravenous anesthetic drug that is
able to provide a safe general anesthesia. Propofol can be administered by using different
techniques including target controlled infusion (TCI). The ability to maintain the
pharmacological conditions after achieving a predetermined clinical effect is one of the
major advantages of this technique. Although the use of TCI devices has increased in common
clinical practice, whether or not all patients are suitable for TCI remains unclear.
Pharmacological models were created based on information from healthy volunteers which may
not apply for specific clinical conditions resulting either in over- or sub-dosed when using
certain drugs.
It is not only individual variability in the pharmacokinetic (PK) parameters of the
anesthetic that is a clinical problem, but it is also the pharmacodynamic variability. A
previous study showed up to 6 times the inter-individual difference among young volunteers in
loss of consciousness (LOC) and return of consciousness (ROC). In addition, greater
differences may be found in the elderly.
Inaccurate general models require the anesthetic team to manually tailor medication
requirements for each individual based on the desired therapeutic effect.
The purpose of this study is to evaluate if a slow stepwise propofol TCI induction with Marsh
model (Ke0 0.26), assessed by clinical and electroencephalographic parameters, allows for an
accurate estimation of the effect concentration required for hypnosis titration and
maintenance of the general anesthesia, in adult populations older and younger than 65 years
of age.
General Objective
• To establish whether a guided slow stepwise guided propofol induction with TCI represents a
good correlation between the calculated Effect-Site Concentration (Ce) for the loss of
consciousness and the required Ce to maintain a bispectral index (BIS) value between 45 and
65 during anesthesia maintenance in both age populations
Specific Objectives
To determine the BIS value achieved with every propofol infusion based on the calculated
Ce for the time of loss of consciousness (TLOC)
To compare the drug infused per time unit required for the loss of consciousness in both
groups
To compare the time and Ce required to achieve loss of consciousness in both groups
To evaluate the impact of remifentanil during hypnosis by using the BIS index
Hypothesis
During a slow stepwise anesthetic induction with TCI using the Marsh Model 4.0, the
calculated Ce for the TLOC is comparable to the Ce required for the maintenance of the
hypnosis during the general anesthesia, overcoming the inter-individual variability.
Methods
Experimental study, prospective clinical trial, phase 4. Each subject will be assigned to the
propofol induction modality as described in the "intervention" section.
Once consciousness has been lost and maintenance target concentration has been established,
manual ventilation will be initiated. Remifentanil TCI 6 ng/ml and a neuromuscular relaxant
will be administered afterwards in order to perform endotracheal intubation. An infusion of
phenylephrine between 0,1 and 0,4 mcg/kg/min will be initiated in order to maintain blood
pressure values within 20% of the baseline value.
Continuous monitoring of BIS will be maintained after remifentanil infusion and intubation.
Three minutes after endotracheal intubation, surgery will be prepared following standard
procedures. BIS, spectrogram, and hemodynamics will be registered every 15 seconds,
continuously, and every 3 minutes during 10 minutes respectively.
Subsequently, propofol Ce at TLOC will be established (if any modifications were necessary
after TLOC) and it will be observed for another 30 minutes.
