The purpose of this randomized, double-blind and placebo-controlled pilot study is to investigate whether dexmedetomidine when used as an adjuvant to general anesthesia can decrease the harmful effects of anesthesia and surgery on intelligence development in pediatric patients undergoing craniotomy.

General anesthetics and sedatives are administered to millions of children each year to facilitate life-saving surgery and other essential surgical or medical procedures. In the past two decades, mounting evidence from animal and clinical studies have raised concerns that general anesthetics may produce harmful effects in the developing brain and lead to adverse neurodevelopmental outcomes. Factors that may influence the degree of injury include age at the time of drug exposure/surgery and cumulative anesthetic dose.

The Intelligence Quotients of pediatric patients with intracranial tumors are lower when compared with healthy children of same age. The investigators suppose that these patients are more sensitive to the neurotoxic effects of general anesthetics. Dexmedetomidine is an alpha 2-adrenoceptor agonist that provides sedation, anxiolysis, and analgesia, and has been shown to be safe to the brain in animal studies. In clinical studies, the use of dexmedetomidine decreases the consumption of anesthetics and opioids during general anesthesia and suppresses stress response induced by surgery. The investigators hypothesize that dexmedetomidine, when used as an adjuvant to general anesthesia, can reduce the neurotoxic effects of general anesthetics by decreasing anesthetic consumption and inhibiting stress response.

The purpose of this randomized, double-blind and placebo-controlled pilot study is to investigate whether dexmedetomidine, when used as an adjuvant to general anesthesia, can decrease the harmful effects of anesthesia and surgery on intelligence development of pediatric patients undergoing craniotomy.

Inclusion Criteria:

1. Age of 2 years or older, but no more than 12 years;
2. Plan to undergo selective craniotomy under general anesthesia for intracranial tumor resection;
3. Written informed consent signed by legal guardians.

Exclusion Criteria:

1. Refused to participate by the legal guardians;
2. Body weight lower than the 3rd percentile or higher than 97th percentile of the normal body weight reference;
3. American Society of Anesthesiologists physical classification of IV or higher;
4. Unable to complete preoperative intelligence assessment because of coma, dysnoesia, or language barrier;
5. Diagnosed pulmonary disease (including acute respiratory tract infection) or cardiovascular disease (including congenital heart disease, hypertension, hypotension, bradycardia, atrioventricular block, or cardiac insufficiency);
6. Abnormal liver or renal function (liver enzyme or creatinine higher than 1.5 times of the upper normal limit;
7. Other congenital diseases that may affect the development of the nervous system (such as Down's Syndrome);
8. Allergy to dexmedetomidine;
9. Other conditions that are considered unsuitable for study participation by the attending pediatricians or investigators.