The tethered spinal cord is a common pathology in pediatric neurosurgery. Intraoperative neurophysiologic monitoring (IOM) has gained popularity over the past two decades as a clinical discipline that uses neurophysiologic techniques to detect and prevent iatrogenic neurologic injuries. IOM techniques are extensively used in adult neurosurgery and, in their principles, can be applied to the pediatric population. Inhalational agents cause a dose-dependent reduction in MEPs and are arguably considered incompatible with effective neurophysiological monitoring(5) For this reason, total intravenous anesthesia (TIVA), using IV anesthetics (propofol or ketamine) and opioids (fentanyl or remifentanil), is commonly used in spinal surgeries under MEPs monitoring

A combination of ketamine and dexmeditomidine has several benefits in terms of hemodynamic stability, absence of respiratory depression, postoperative analgesia, and recovery. (11) ketamine could prevent the decrease of blood pressure and heart rate which had been observed with dexmedetomidine. In addition, dexmedetomidine could prevent the increase of blood pressure and heart rate, salivation, and physiological emergence reaction from ketamine. This combination was not previously used in this type of procedure except in a case report performed by Rozzana Penny who had used dexmedetomidine and ketamine infusion during scoliosis repair surgery with somatosensory and motor evoked potential monitoring in 15 years old female.(10) Evoked potentials are highly sensitive to fluctuations in physiological parameters such as peripheral and core body temperature, arterial blood pressure, hematocrit, etc. Keeping in view all the above factors we plan this study to compare the effect of the combinations of propofol and fentanyl versus the combination of ketamine and dexmedetomidine and fentanyl in producing a minimum effect on MEP amplitude and on hemodynamic stability during the surgery.

Inclusion Criteria:

• children with ASA I and II presented to Abu elreesh hospital for untethered spinal cord surgery.

Exclusion Criteria:

• Children with neuromuscular diseases or congenital scoliosis.
• Children with growing rod distraction surgery.
• Children with American Society of Anaesthesiologists (ASA) physical status III, IV
• Children with preoperative use of antidepressant or anticonvulsant medications.
• Children with a known history of drug allergies.

. The details of the series will be unknown to the investigators and the group assignment will be kept in a set of sealed envelopes, each bearing only the case number on the outside. a person who will prepare the drugs and data collector is not one of the trial investigators.