*Electroencephalography - From Basic Research to Clinical Applications*

**Figure 3.**

*Examples of raw recordings: (a) encephalopathy (ENC), (b) COVID-19, and (c) cardiorespiratory arrest (CRA). Right column shows mean spectra for channels. Red and blue lines indicate right and left hemispheres, respectively. Y-axis units in μV<sup>2</sup> /Hz [34].*

synchronization were highly different and are probably explained by symptomatology with quasi-normal EEG traces.

#### **5.3 Continuous EEG monitoring in ICU**

Long-term EEG monitoring in the ICU (cEEG) has been one of the main developing fields of electroencephalography in recent years. There are several methods used for EEG monitoring, and most of them share a similar philosophy: to identify the presence of seizure/status epilepticus to make the information of monitoring easy and fast. As stated above, we think that this reductionist approach impoverishes the scope of electroencephalography.

We systematically used qEEG during cEEG for the below indications:

• Monitoring the presence of ES/SE. More useful than identifying the presence of ES, qEEG is essential to discriminate between epileptic and non-epileptic patters, as we stated above.

*Necessity of Quantitative EEG for Daily Clinical Practice DOI: http://dx.doi.org/10.5772/intechopen.94549*

#### **Figure 4.**

*Box plots showing the comparison of EEG structures for different bands: (a) delta, (b) theta, (c) alpha, and (d) beta, (e) Se; (f) ρ. striped black box: ECN; striped red box: COVID-19; striped blue box: CRA; black asterisk: Difference between ENC and COVID-19; red asterisk: Difference between ENC and CRA; blue asterisk: Difference between COVID-19 and CRA.*

• Titration of sedation/anti-epileptic drugs (AEDs). Identifying changes in background from the variations in spectra or mean values of specific EEG bands is mandatory to increase/decrease the dose of sedation. Additionally, AEDs are adjusted with the help of qEEG, although *de visu* inspection of irritative activity is mandatory.

• Long-term recordings in patients with alterations of consciousness without sedo-analgesia to evaluate brain physiology. Severe encephalopathy can induce a low-consciousness level. These recordings typically lack irritative activity, and changes in the background are slow. However, these changes correlate with the level of consciousness and predict the outcome. Therefore, it is important identify changes to adjust treatment as soon as possible, especially to avoid unnecessary therapeutic actions.

In this way, we have performed more than 250 cEEG + qEEG in the ICU in the last five years. This is a time-consuming task (especially considering that every cEEG takes 1.4–4.3 days (inter-percentile 25–75 range)), but the clinical utiliy is clear because the demand increased from 1.0 0.2 cEEG/month in 2015 to 5.5 0.8 cEEG/month in 2019.

#### **5.4 Utility in dementia**

There are numerous articles in the literature showing that the initial phases of dementia can be detected by qEEG [59–63]. We have used our numerical method in patients with either minimum cognitive impairment (MCI) or aphasia. Obviously, the *de visu* analysis of raw recordings shows only a nearly normal aspect or lowvoltage. However, numerical analysis can show very relevant facts that are not observable by eye (**Figure 5**).

At this time, we are conducting a study to identify specific properties of different pathologies (sub-types of primary aphasia, Alzheimer disease, vascular dementia, etc). Although we have not yet defined different groups of features specific to each pathology, what is clear from the above figure is that connectivity is a magnitude that is affected early and consistently in most cognitive alterations.

## **5.5 Other examples of qEEG utility**

Finally, we provide two more representative examples of diagnosis highly aided by the use of qEEG.

Case 1. A 17-year-old male patient with severe cognitive and behavioral impairment, secondary to severe epileptic encephalopathy due to refractory epilepsy in childhood after a central nervous system infection. Daily seizure frequency, with countless seizures per day. In treatment with zonisamide (400 mg), valproic acid (1200 mg), oxcarbazepine (1400 mg), and clobazam (10 mg) daily. Rectal diazepam 10 mg if required. A video of EEG is performed in which it is observed that during sleep, the patient exhibits several episodes of lateral head movement and growls. *De visu* recordings (**Figure 6a**) can be described as global desynchronization. However, the dynamics of the EEG bands show a decrease (practically total) for all the bands (**Figure 6b**). As stated above, epilepsy is expected to be accompanied by an increase in cortical activity (α and β bands). Therefore, this event cannot be identified as epileptic.

Although the patient also presented true epileptic events, the number of these was substantially lowered and AED was adjusted according to the real number of ES. The final diagnosis for this event was a nonepileptic behavioral disorder, secondary to severe epileptic encephalopathy.

Case 2. A 22-year-old female diagnosed with epilepsy at the age of 14 years and with anxious-depressive illness from the age of 20 years. The applied treatment was lamotrigine (100 mg/day) and clonazepam (0.5 mg/8 h). Seizures occurred every 2–3 days, described as the perception of black dots in the visual field, weakness, loss of consciousness and muscle tone, loss of balance and falling to the ground. During

*Necessity of Quantitative EEG for Daily Clinical Practice DOI: http://dx.doi.org/10.5772/intechopen.94549*

#### **Figure 5.**

*Initial steps of dementia. (a) Example of a male with primary aphasia and (b) a female with MCI. Left column = raw recordings of both patients; middle column = connectogram for patients; right column = connectogram of a control volunteer of the same sex and age ( 5 years).*

telemetry, we recorded one episode of black dot perception followed by a loss of consciousness while in bed. *De visu* EEG recordings showed no significant changes (**Figure 7a**). However, the dynamic variation of EEG bands indicated a generalized decrease, except for the occipital α band, which increased after the eyes closed (**Figure 7b**).

The final diagnosis was psychogenic non-epileptic seizure (PNES), and the AEDs were slowly removed.

### **6. Discussion**

Numerous methods have been used for qEEG, although they are rarely used in daily clinical practice. There is, therefore, a huge gap between the promising (even spectacular) results obtained with qEEG and its practical usefulness. To the best of the knowledge of the authors, this issue has not been systematically addressed, although it has been said that electroencephalographers have poor trust in mathematical models [2, 17].

The degree of mathematical complexity and abstraction is quite different among the methods proposed. Not all of the mathematical models can be included in the same category, and it is of extreme importance that mathematical solutions be
