Group I :The patients will receive midazolam intravenously (i.v.) in a dose of 0.05 mg/kg diluted by 50ml saline over 10 minutes using syringe pump plus 1 mg/kg ketamine (iv).

Group II : The patients will receive Dexmedetomidine intravenously (i.v.) in a dose of 2mic/kg diluted by 50ml saline over 10 minutes using syringe pump plus 1 mg/kg ketamine (iv).

The objective of this study to evaluate the clinical effects, adverse effects and recovery time of two different sedative agents (midazolam and Dexmedetomidine) combined with ketamine during conscious sedation for child patient with haematological cancer undergoing BMA &biopsy.

Inclusion Criteria:

• All consecutive children with acute lymphoblastic leukemia undergoing bone marrow aspiration and biopsy.

Exclusion criteria:

• previous sensitization or anaphylactic reaction to Dexmedetomidine, ketamine,and midazolam;
• evidence of head injury,
• raised intracranial or intraocular tension;
• use of drugs known to interact with either study agent;
• an American Society of Anesthesiologists (ASA) physical status score greater than 2.
• Also Patients with cardiovascular, respiratory, hepatic diseases and epilepsy will be excluded.