The study is performed in patients aged 5-18 years after thoracic surgery. The primary aim of this trial is to determine whether the use of gabapentin as a component of multimodal analgesic regiments reduces pain scores following thoracic surgery in pediatric patients. The secondary objective of the trial are to evaluate whether the use of gabapentin reduces postoperative anxiety scores and consumption of ropivacaine with fentanyl, decreases side-effects, and improves patient satisfaction.

The subjects are randomized to the Gabapentin or Placebo group. All patients receive preoperative gabapentin (15 mg/kg, treatment) or placebo, respectively and after surgery either gabapentin (7,5 mg/kg, treatment) or placebo 2 times per day for 3 days, respectively.

Patients are subjected to the same anaesthesia protocol. Postoperative analgesia are achieved with either continuous ropivacaine 0.2%/fentanyl 5.0 μg/ml infusion through a thoracic epidural catheter (N=40; Gabapentin n=20, Placebo n=20), or intravenous infusion of morphine (N=40; Gabapentin n=20, Placebo n=20). All patients receive acetaminophen and non-steroidal anti-inflammatory drugs, and metamizol as a "rescue drug"

The intravenous infusion of morphine grup was expanded on the basis of the bioethics commission's decision KB-125/2019 (N=64; Gabapentin n=32, Placebo n=32).

Inclusion Criteria:

• 5 - 18 years of age;
• surgery: lateral thoracotomy or Ravitch procedure;
• ASA 1-3;
• postoperative analgesia: thoracic epidural analgesia or intravenous infusion of morphine.

Exclusion Criteria:

• allergy or sensitivity to gabapentin;
• history of chronic pain or daily analgesic use;
• diagnosed with psychiatric disorders;
• treated oncologically;
• with impaired verbal communication;
• the lack of postoperative chest drainage.