## 4 Discussion
\begin{table}
\begin{tabular}{c c} \hline \hline
**Patient** & **Most Important Findings on Density Spectral Array during Procedures** \\ \hline \multirow{2}{*}{**Horse A**} & Stable SEF during inhalant maintenance was observed \\  & Gradual changes of the level of low-frequency waves were observed \\  & Burst suppression as a sign of too-deep anesthesia was observed \\ \hline \multirow{2}{*}{**Horse B**} & Presence of waves of different frequencies was common \\ \hline \multirow{2}{*}{**Horse C**} & Changes only within the low-frequency waves \\ \hline \multirow{4}{*}{**Horse D**} & Artifacts impeded the observations \\  & High and changeable SEF \\  & Waves of different frequencies were observed \\  & Sudden jump of the frequency during recovery \\ \hline \multirow{2}{*}{**Horse E**} & Stable SEF \\  & Low-frequency waves were predominant \\ \hline \multirow{2}{*}{**Horse F**} & Stable frequency band power waves \\  & Very-low-frequency waves present during the procedure \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electroencephalography findings during anesthesia that were recorded in every patient. During field anesthesia, such as the case of Horse F, DSA might be especially helpful as in such cases there are limited possibilities of anesthesia monitoring compared to hospital conditions. Some modification of current monitors might be helpful. A comparison of Horse F and the other horses anesthetized with inhalant agent shows significant differences in the influence of the drugs on the Central Nervous System. Inhalants revealed the occurrence of various frequency waves, while total intravenous anesthesia seems to stabilize the waves on low and medium frequencies without significant changes. This also shows the complicated route of action of inhalant anesthetics, which has not been described until now. The vital signs monitored and recorded were not as responsive as the EEG changes during the surgical procedures. Heart rate changes were more likely to respond sooner to potential surgical pain than blood pressure. Neither eye movement/position nor muscle relaxation were indicative of pain during the levels of surgical anesthesia maintained in these horses. Comparing the changes between the phases of anesthesia can be a problem. The surface electrodes can be mounted before sedation in some horses, although during sedation there is not as much need for EEG monitoring as after induction of anesthesia. However, there is a need among the practitioners who perform standing surgery to be sure about the level of anesthesia in those procedures, so possibly the methodology of measurements in those cases should be improved. These kinds of surgeries are more and more widely used due to lower anesthetic risk. The recording of EEG during induction is still a challenge as the movement of the horse from the standing to the recumbent position interferes with measurements, which likely results in artifacts. However, from the observations, during inductions, the frequency of the waves drops, which is understandable. The most important readings are recorded during anesthetic maintenance, which can show significant changes in the wave frequencies, thus indicating inappropriate levels of anesthetic during surgery. There are some drawbacks to the method that was used in this research. There is still a need for better software for the EEG DSA machine, as the DSA can be saved only as a picture screenshot from the device during anesthesia but cannot be transferred to the computer and then mathematically analyzed. That is the reason that the study was based upon observations, rather than statistics. Moreover, making observations of the DSA and understanding the changes requires practice and the establishment of the relation to other parameters. From a physiological point of view there are different expected responses to medications selected in balanced anesthesia and analgesia. This was demonstrated in this study.