During general anesthesia, monitoring of oxygen saturation, blood pressure, ECG, temperature, and other parameters is already routine. However, new types of monitoring are also emerging. One of them is brain monitoring. The brain is “no less important” than the heart. The brain also requires monitoring of what happens to it under the influence of general anesthetics. After all, the primary site of action of anesthetics is not the heart or the blood vessels, but the brain itself. Standard drug dosages are often unsuitable for each individual case, and dosing requires individualization through brain monitoring—monitoring the depth of anesthesia.
Some of the earliest studies in anesthesiology focused on senile dementia and cognitive impairment after general anesthesia. [1,2]Today, it is already considered an axiom that general anesthesia carries a risk of developing postoperative cognitive disorders (e.g., delirium), especially in elderly patients.
Probably one of the most unpleasant complications for a patient undergoing elective general anesthesia is intraoperative awareness. An entire national audit project in the United Kingdom, NAP5, was dedicated to this topic [6]. The estimated incidence of accidental awareness during general anesthesia was approximately ~1:19,000. However, this rate varies significantly across different settings. A wide range of patient experiences and psychological consequences has been reported (from none at all to life-changing effects). Long-term psychological effects were identified in about half of the patients who reported accidental awareness during general anesthesia.
One method of monitoring the depth of anesthesia is pEEG (processed EEG), which modern monitors use to calculate indices such as BIS. However, the isolated use of indices such as BIS—without the anesthesiologist’s ability to interpret the pEEG—does not guarantee the prevention of accidental awareness during anesthesia. In addition, indices often perform incorrectly with certain drugs, for example ketamine, and their use in children and in elderly patients is still not fully understood [3]. Using the Mindray BIS module, it is possible to display not only the numerical BIS value but also the pEEG waveform on the screen and analyze it, as recommended by anesthesia association guidelines. [4]
By continuously analyzing the pEEG waveform, an anesthesiologist can detect during general anesthesia a complication of anesthetic overdose known as Burst Suppression—periods of isoelectric activity on the pEEG alternating with sudden electrical activity. The presence of Burst Suppression may correlate with the development of postoperative delirium. [5]
Guidelines from the most well-known anesthesia associations worldwide recommend mandatory use of pEEG during total intravenous general anesthesia with neuromuscular blockade, and at the clinician’s discretion during inhalational anesthesia. [4] However, most cases of awareness during general anesthesia occur during the transition from intravenous to inhalational maintenance, for example after tracheal intubation [6]. Therefore, the use of pEEG during inhalational anesthesia is also justified and appropriate. There are many factors that influence changes in MAC for each patient. For example, factors that reduce MAC and therefore the required dose of an inhalational anesthetic include patient age, hypothermia, anemia, opioid drugs, and others. Therefore, selecting and individualizing anesthesia solely based on MAC (the percentage of anesthetic gas in exhaled air) is extremely subjective and requires the parallel use of pEEG.
So, what are the advantages of using pEEG during general anesthesia?
● monitoring the “state” of the brain in each individual patient
● “visualizing” anesthesia
● personalized anesthesia
● avoiding burst suppression and reducing the risk of postoperative cognitive impairment
● better cognitive recovery after general anesthesia
● minimizing the risk of awareness during general anesthesia
- BD Bedford Lancet 1955 Aug 6;269(6884):259-63
- N Kotekar eat al Indian J Anaesth 2014 May-Jun; 58(3): 263–268
- Tirel O eat al Br J Anaesth 2008; 100:82-7
- Recommendations for standards of monitoring during anaesthesia and recovery 2021. Guideline from Association of Anaesthetists.
- Niti Pawar et al Front Syst Neurosci 2021; 15: 767489
- 5th National Audit Project of the Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland.
