In previous posts, we discussed the synergy between propofol, remifentanil, and dexmedetomidine, and the impact of dexmedetomidine on alpha band power over time. The tendency that I have observed in my patients is a progressive decrease in alpha band power, which is more accentuated in fragile brains.
The big question remains as to why this happening?
Is this an indirect effect of dexmedetomidine on oscillatory states? or
This means that when the Cp of propofol decreases due to the synergistic effect of dexmedetomidine, the activation of GABAergic neurons in the anterior thalamic reticular nucleus promotes arousal from propofol.
Recently I read an article related to the topic, where they compared the perioperative EEG signatures, drug-induced changes, and neurocognitive outcomes between two anesthetic regimens in geriatric patients (Propofol-Remifentanil vs Propofol-Remifentanil-Dexmedetomidine), and at the end, they proposed the following question: “alpha band power per se is a valid predictor of frailty or is that only in the case of GABAergic anesthetics1.”
Two days ago, I had two 48-year-old patients. The first one was a female ASA I patient, under general anesthesia with Propofol-Remifentanil and Dexmedetomidine (0.2 mcg/kg/hour), with a typical DSA signature of propofol (“rail pattern”), adequate alpha power.
The second, female ASA II patient with history of breast cancer, autoimmune hypothyroidism being treated with tamoxifen and euthirox, ex-smoker, under general anesthesia with Propofol-Remifentanil and Dexmedetomidine (0.2 mcg/kg/hour), with a DSA typical of a fragil brain. After the first hour of anesthesia, the alpha band power decreased even more, with doses of propofol (5.5 mg/kg/hour and remifentanil (0.18 mcg/kg/hour). I decided to perform a 30 mg bolus of propofol at 12:35 (see DSA case 2), and a few seconds later, I recovered the alpha power that I had after LOC. The patient had adequate NMB, adequate analgesia, SEF trend towards 20 Hz, and after the bolus, it decreased to 16 Hz.
Although there is much left to know, I am still thinking that the most important thing is to titrate appropriately and not lose the power of alpha.
I have attached the DSAs processed with Python and the DSAs downloaded from the BIS monitor.
Reference
1.Mehler DM, Kreuzer M, Obert DP, Cardenas LF, Barra I, Zurita F, Lobo FA, Kratzer S, Schneider G, Sepúlveda PO. Electroencephalographic guided propofol-remifentanil TCI anesthesia with and without dexmedetomidine in a geriatric population: electroencephalographic signatures and clinical evaluation. J Clin Monit Comput. 2024 Mar 7. doi: 10.1007/s10877-024-01127-4. Epub ahead of print. PMID: 38451341.