## 2 Materials and Methods  
Six horses were used for the study--an 11-month-old Arabian mare (A), a 9-year-old half-blood gelding (B), a 3-year-old half-blood stallion (C), a 3-year-old English blood stallion (D), a 7-year-old half-blood gelding (E), and a 12-year-old half-blood gelding (F). The types of procedures, positions of the horses, and types of anesthesia protocol, including drugs and their relevant doses, are shown in Table 1. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Patient** & **Procedure** & **Type of Anesthesia** & **Position** & **Anesthesia Protocol** \\ \hline
**Horse A** & \
\begin{tabular}{c} Computed \\ Tomography \\ \end{tabular} & Total inhalant & Left lateral &
\begin{tabular}{c} S: xylazine 1 mg/kg \\ I: ketamine 2.2 mg/kg, diazep 0.1 mg/kg \\ Mc: isoflurane \\ \end{tabular} \\ \hline
**Horse B** & \
\begin{tabular}{c} Colic \\ surgery \\ \end{tabular} & PIVA & Back &
\begin{tabular}{c} S: xylazine 1 mg/kg \\ I: ketamine 2.2 mg/kg, diazep 0.1 mg/kg \\ M: isoflurane, CRI xylazine 0.5 mg/kg/h + ketamine 1 \\ mg/kg/h \\ \end{tabular} + ketamine 1 \\ \hline
**Horse C** & \
\begin{tabular}{c} Castration \\ \end{tabular} & PIVA & Back &
\begin{tabular}{c} S: xylazine 1 mg/kg \\ I: ketamine 2.2 mg/kg, diazep 0.1 mg/kg \\ M: isoflurane, CRI xylazine 0.5 mg/kg/h + ketamine 1 \\ mg/kg/h \\ \end{tabular} \\ \hline
**Horse D** & \
\begin{tabular}{c} Sinusoscopy \\ \end{tabular} & Standing anesthesia & Standing &
\begin{tabular}{c} Loading dose: detomidine (0.02 mg/kg + butorphanol \\ 0.01 mg/kg \\ M: CRI detomidine 0.05 mg/kg \\ \end{tabular} \\ \hline
**Horse E** & Arthroscopy & PIVA & back &
\begin{tabular}{c} I: ketamine 2.2 mg/kg, diazep 0.1 mg/kg \\ M: isoflurane, CRI xylazine 0.5 mg/kg/h + ketamine 1 \\ mg/kg/kg/h \\ \end{tabular} \\ \hline
**Horse F** & \
\begin{tabular}{c} Removal of \\ hoof cancer \\ \end{tabular} & TIVA & Left lateral &
\begin{tabular}{c} S: detomidine (0.02 mg/kg + butorphanol 0.01 mg/kg \\ I: ketamine 2.2 mg/kg, diazep 0.1 mg/kg \\ M: Triple drip \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Description of patients, procedures, and types of anesthesia. S, sedation; I, induction; M, maintenance; PIVA, partial intravenous anesthesia; TIVA, total intravenous anesthesia; CRI, constant-rate infusion. In each case, electrodes were placed on the frontal part of the horse skull (according to [PERSON] 1996) with the use of gel and tape--two left (L1 and L2), two right (R1, R2), one ground electrode (GB) and one reference electrode (CT) in the center position. The placement area was not shaved. Once the electrodes were in place, the recording device (Root with Sedline(r), Masimo, Irvine CA, USA) was attached and the measurements commenced (Figure 1). On the monitor, the raw EEG waves from 4 channels (L1, L2, R1, R2), spectral edge frequency (SEF) of the left and right hemisphere, EMG (electromyography) of the muscles that could influence the measurements, Patient State Index (mathematical algorithm counted from raw EEG), burst suppression ratio (SR), and density spectral area (showing the power of waves in certain frequency bands) could be seen. The impedance was also measured, and when it exceeded the marginal acceptable level and interfered with the EEG measurement (indicated by the electrode color on the screen changing from green to yellow), the electrodes were pressed slightly and additional gel was applied between the electrode and the skin surface. For each procedure, a life parameter monitor (Datex Ohmeda Cardiocap 5 or Veterianian Patient Monitor Vs2000v) was attached for the measurement of pulse oximetry, ECG, capnography, breaths per minute count, and, in 3 cases, end tidal isoflurane and invasive blood pressure (Figure 2). These measurements were conducted during sedation (Case D), maintenance of anesthesia, and recovery (Cases A, B, C, E, and F). The results were recorded as numbers for hemodynamic parameters on the anesthesia record chart and compared in the time of recording during anesthesia with changes visible on the DSA.