We propose a double-blind randomized controlled trial to evaluate the effect of intravenously administered morphine at surgery conclusion on acute postoperative pain in patients recovering from craniotomy surgery. Participating adults having craniotomy surgery will be randomized in a 1:1 ratio to intraoperative intravenous administration of 0.08 mg/kg morphine at dura closure, or a matching placebo.

After confirming eligibility, patients will be approached by one of the study researchers for potential participation. After a thorough explanation, written informed consent will be obtained.

General anesthesia will be induced with propofol (2-3 mg/kg), and either remifentanil (1 mcg/kg) or fentanyl (2 mcg/kg). Lidocaine (1 mg/kg) and rocuronium (0.6 mg/kg) will be allowed and left to the discretion of the caregivers. Anesthesia will be maintained with infusions of propofol and remifentanil, and titrated to maintain hemodynamic goals and evaluation of anesthesia depth by somatosensory or motor evoked potentials according to clinical requirements. Ketamine and fentanyl administration will not be allowed at the maintenance phase. No additional IV opioids will be allowed during surgery. Other analgesics such as dipyrone and non-steroidal anti-inflammatory agents (such as diclofenac) will not be allowed during surgery or during PACU stay. At dura closure, patients will be randomized by a web-based randomization service in a 1:1 ratio. The intervention group will receive 0.08 mg/kg intravenous morphine (0.08 ml/kg), while the control group will receive 0.08 ml/kg 0.9% NaCl. The research solution (morphine/0.9% NaCl) will be administered via IV infusion over ten minutes. Randomization and study drug preparation will be performed by a research team-member, uninvolved in data collection, analysis, or patient care.

Both groups will receive acetaminophen (1 gr) at dura closure. Steroids and other anti-emetic medications will be allowed. Remifentanyl and propofol infusions will be discontinued at the end of the surgery during wound dressing. All patients will have orders for intravenous morphine administration in PACU for breakthrough pain as acceptable and according to the orders prescribed by anesthesiologist assigned for the case/the attending anesthesiologist in PACU. The research team/protocol does not interfere with morphine administration during PACU stay. All caregivers will be blinded to treatment allocation.

Patient's monitoring at the operating room and during transportation to the PACU will be done by the anesthesiologist assigned for the case. Patient's monitoring during PACU stay will be done by the PACU team and according to the patient's clinical status according to PACU protocol. Patients will be followed during PACU stay by a study team member blinded to the treatment allocation. The study team member will measure and record pain score (NRS), sedation score (Ramsay score) and PONV at admission to PACU and 30 minutes after admission to PACU. The research team, according the research hypothesis is interested in measuring pain (via NRS) while the patient is fully conscious and alert. Additional data regarding the surgery, anesthesia, recovering from anesthesia and PACU stay will be collected retroactively from computer system data (metavision, chameleon).

Demographic and clinical data will be collected on the day of surgery. Surgical and anesthetic data, laboratory results, details regarding side effects, time of first morphine requirement, total morphine consumption in PACU, and pain scores (NRS) at POD1 and POD2 will be collected from computerized patient files.

Inclusion Criteria:

• Informed consent.
• Scheduled for elective craniotomy for resection of supra-tentorial intracranial tumor that requires cranium sawing, dural opening and excision of tumor, under general anesthesia.
• Age 18 - 80 years.
• American Society of Anesthesiologists' physical status I-III.
• Body mass index (BMI) under 35 kg/m2.

Exclusion Criteria:

• Pregnant or current breastfeeding patients.
• Patients unable to provide informed consent or in need of a legal authorized representative.
• Patients with neurological disorders preventing a good understanding of the pain numerical reporting scale (NRS) before surgery.
• Patients with pre-operative aphasia.
• Patients with chronic pain or chronic use of opioids.
• Patients with current alcohol or drug abuse.
• Expected delayed extubation.
• Patients with documented allergy to opioids or acetaminophen.
• Preoperative Glasgow Coma Scale <15.