The administration of intravenous anesthetics in the elderly population requires adequate
titration to avoid deleterious effects derived from overdosing or underdosing. Older
patients show greater sensitivity to similar doses of propofol compared to younger
patients. In addition, there is extensive interindividual variability among older
patients, which would also explain the different responses to the same dose of drugs.
This variability would be secondary to differences in comorbidities and physiological
age, in contrast to chronological age, which would not explain the differences found in
response to anesthetics in these patients.
One way in which an attempt has been made to make the doses of anesthetics in different
patients comparable is the use of models that predict what infusion rate is required to
maintain a given concentration at the site of drug action. The relationship between a
propofol effect site concentration (Ce) with a given effect can be represented by
pharmacodynamic (PD) models. Recently, Eleveld et al. created a
pharmacokinetic-pharmacodynamic (PKPD) model for the administration of intravenous
propofol in a population of wide ages, including neonates to older patients. However, the
pharmacodynamic parameter used in this model was the BIS index, which has been questioned
for its use in older adults. In addition, the creation of this PD model only included 3
patients older than 70 years, so the underrepresentation of this age group in the
construction of the model could affect its performance, making it even more difficult to
correctly predict the effect in this population.
Anesthetic drugs exert their desired hypnotic effect on the brain. Brain electrical
activity can be monitored non-invasively by recording electrical potential on the cranial
surface using electrodes. The electroencephalographic (EEG) changes observed with the
administration of anesthetics are usually systematic across different patients. These
have been described and have been used to identify different phases of anesthetic "depth"
or hypnosis. In addition, the representation of the EEG signal by means of a spectrogram
has facilitated the incorporation of this information into commercial EEG monitors that
previously only included highly processed indices such as the BIS.
Within the EEG patterns of the spectrogram described for anesthetic maintenance with
propofol, the alpha (8-12 Hz) and delta (1-4 Hz) oscillations stand out. However, the
power of alpha oscillations decreases with age and with other changes that are associated
with age, such as decreased cognitive ability, increased comorbidities and brain
vulnerability. Therefore, guiding our administration of propofol based on obtaining a
pattern of alpha predominance appears to be difficult in this aged population.
The general objective of this work is to build a PKPD model that uses the pharmacokinetic
parameters of the Eleveld model and new pharmacodynamic parameters derived from the
frontal EEG in a population older than 65 years. Our hypothesis is that the Eleveld PKPD
model, modified with this new pharmacodynamic parameter, will predict better the hypnotic
effect of propofol than the original Eleveld PKPD model, in adult patients older than 65
years.
The creation of a PKPD model of propofol for the population over 65 years of age would
allow a better titration of this drug to avoid possible deleterious effects secondary to
its under or overdosage.
