Adult patients undergoing awake Deep Brain Stimulation (DBS) surgery for movement disorders (e.g., Parkinson's Disease, Essential Tremor).

Study groups After approved by Local Institutional Ethics Committee and obtaining written informed consent ....pt Divided in two groups Group I (KD1): (n = 12) ....patients who will receive intravenous (I.V.) ketamine in a dose of 0.25 mg/kg diluted in 5 ml normal saline plus dexmetedomidine 0.25ug/kg followed by infusion of dexmedetomidine (Precedex, 100 μg/ml, Hospira, USA) in a rate of 0.1-0.5 ug/kg/hour and ketamine infusion 0.1mg / kg/hr until the .RASS 0 to -1.sedation score and BIS range of 50-70 was adjusted. Supplementary fentanyl 25 μg will be administered intravenously as rescue sedo-analgesic when required and recorded.

Group II (D2): (n =12 ) ......patients who received (I.V.) dexmedetomidine in a dose of 0.5 μg/ kg diluted in 5-ml. normal saline followed by continuous infusion of dexmedetomidine in a rate of 0.1-0.5 μg/kg/hour (Precedex, 100μg/ml, Hospira, USA) until Sedation Scorethe .RASS 0 to -1.sedation score and BIS range of 50-70 was adjusted.... and BIS range of 50-70 will be adjusted. Supplementary fentanyl 25 μg will be administered intravenously as rescue sedoanalgesic when required and recorded.

Anesthetic Protocol (Standardized) Monitoring Up on arrival to operating theatre, routine monitoring devices will be placed and baseline ECG, mean arterial pressure (MAP) and oxygen saturation (SpO2 ) will be recorded. Using Datexohmeda (GE Healthcare Co., USA) and continued till shifting out to the recovery room. The baseline values of H.R., mean arterial pressure (MAP), SPO2, and respiratory rate (RR) will be recorded.

• Bispectral index (BIS) monitoring throughout whole procedure
• Root Mean Square (RMS): The Root Mean Square (RMS) value of the recorded signal, often measured in volts, is a key parameter. A higher RMS value is often associated with entering the target nucleus, which is rich in neuronal activity.
• Normalized RMS (NRMS): To account for variations, the RMS is often normalized (NRMS) by dividing the RMS of a segment by the average RMS of a baseline segment (e.g., the first five stable sessions). A common indicator for good signal amplitude within the STN, for example, is an average NRMS greater than 2.0.

Following 8 hours period of fasting before the procedure, peripheral I.V. line established with a 20G cannula and lactated Ringer's will be infused At a rate of 6-8ml/kg/hour and oxygen 3 l/min will be administered through a nasal cannula. During the procedure, monitoring of HR, MAP, SPO2,and RR will be recorded every 2 min for the first 10 min, thereafter every 5 min until the end of the procedure.

Premedication: A standardized dose of midazolam (e.g., 0.02 mg/kg IV) Ondansterone 4 mg iv as antiemetic

Drug Administration:

Dexmedetomidine: A loading dose (e.g., 0.5 mcg/kg over 10-15 minutes) followed by a maintenance infusion ( 0.1 to 0.5 u g/kg/hour).

this dose not affecting MER Ketamine (in Group DK): A low-dose continuous infusion (0.05mg/kg/hr to 0.25 mg/kg/hour) this dose not affecting MER started concurrently with dexmedetomidine. SO the investigators will decrease the loading dose of dexmedotomidine to 0.25 mcg /kg in group Accounting for synergitic effect Local Anesthesia: Standardized scalp block and local infiltration (e.g., lidocaine with epinephrine).

Rescue Analgesia/Sedation: Fentanyl (e.g., 25-50 \mu g IV bolus) will be used as rescue analgesia for both groups, as needed.

If agitation is refractory, an unblinded investigator member may administer a rescue sedative (e.g., propofol), which must be recorded .

Titration: Infusions will be titrated based on the patient's sedation level, using a validated scale Following the bolus doses, sedation score was assessed by anesthesiologist unaware of regime used by the Richmond Agitation-Sedation Scale (RASS) Score Term Description

• 4 Combative Overtly combative or violent; immediate danger to staff.

• 3 Very Agitated Pulls on or removes tube(s) or catheter(s) or has aggressive behavior toward staff.

• 2 Agitated Frequent non-purposeful movement or patient-ventilator dyssynchrony.

• 1 Restless Anxious or apprehensive but movements not aggressive or vigorous. 0 Alert and Calm Spontaneously pays attention to caregiver.

  • 1 Drowsy Not fully alert, but has sustained (more than 10 seconds) awakening, with eye contact, to voice.
  • 2 Light Sedation Briefly (less than 10 seconds) awakens with eye contact to voice.
  • 3 Moderate Sedation Any movement (but no eye contact) to voice.
  • 4 Deep Sedation No response to voice, but any movement to physical stimulation.
  • 5 Unarousable No response to voice or physical stimulation.

Inclusion Criteria:

• Age 18-75 years.

  • American Society of Anesthesiologists (ASA) physical status I, II, or III.
  • Ability to give informed consent and cooperate with the procedure (e.g., follow commands, perform intraoperative tasks).

Exclusion Criteria:

• Contraindications to the study drugs (dexmedetomidine or ketamine).

  • Severe cardiac, respiratory, or hepatic disease.
  • Pre-existing psychological/psychiatric disorders that may interfere with intraoperative assessment (e.g., severe dementia, psychosis).
  • Allergy to local anesthetics.
  • Emergency surgery or previous DB
  • Electrocardiogram (ECG) showing heart block of any degree
  • heart failure,
  • liver cirrhosis, thrombocytopenia and coagulopathies,
  • severe bradycardia,