because the instruments for collecting the SPI data from the monitor (S5 collector) could not be imported due to the manufacturer's problem.

Surgical plethysmography index (SPI) is a device that can noninvasively monitor the balance between the nociception and ant-nociception using pulse photoplethysmographic amplitude (PPGA) and heart rate obtained through an oxygen saturation measuring device. SPI has recently been studied as a useful tool to monitor the stress response of patients due to surgery or anesthesia and to guide the appropriate use of analgesics/anesthetics. However, these SPI devices have been developed for adults and have not been studied in pediatric patients with relatively high heart rates, and no direct effects on post-operative arousal excitability have been reported.

Inclusion Criteria:

• Pediatric patients aged 2-7 years with an American Society of Anaesthesiologists physical status (ASA PS) of 1 or 2, who were planned to undergo ophthalmology surgery requiring general anesthesia.

Exclusion Criteria:

• ASA PS 3 or 4
• Presence of developmental delays or neurological diseases
• History of allergies or contraindications to the use of ketamine (increased intracranial pressure, open-globe injury, or a psychiatric or seizure disorder)
• treatment with beta-receptor blockers, beta-receptor agonists or any other drug suspected to interact with the sympathovagal balance
• diseases with impairment of sensitivity (diabetes, polyneuropathy, peripheral arterial obstructive disease et etc)
• pacemaker therapy
• dermal diseases with the affection of the forearm/hand

Pediatric patients aged 2-7 years with an American Society of Anaesthesiologists physical status (ASA PS) of 1 or 2, who were planned to undergo ophthalmology surgery requiring general anesthesia.