Patients will be admitted in the intensive care unit after major abdominal surgery. All patients will receive 100 mg of tramadol intravenously every 6 hours. Pain will be assessed before and half an hour after tramadol administration by verbal Numeric Rating Scale.

To all patients included in the study from the blood sample taken prior to the operation the leukocytes counts, c-reactive protein (CRP), procalcitonin (PCT) and lactate level will be performed, as well as arterial blood gas analysis.

After admission to the intensive care unit, all patients will receive 100 mg of tramadol intravenously every 6 hours. Pain will be assessed before and half an hour after tramadol administration by verbal Numeric Rating Scale (NRS). Pain score will be compared between patients with and without systemic inflammation. Systemic inflammation is defined as fulfilling at least two of the following major criteria: fever > 38 oC or hypothermia < 36 oC, tachycardia > 90 beats/minute, pCO2 in arterial blood < 4.3 kPa and leukocytes > 12.000/mm3 or < 4.000/mm3. Also, preoperative values of CRP > 50 mg/L and PCT > 0.5 ng/ml was also considered systemic inflammation.

Inclusion Criteria:

• elective and emergency open abdominal surgery
• ICU admission

Exclusion Criteria:

• tramadol allergy
• surgery performed laparoscopically
• age younger of 18 years and older the 90 years

The study included patients admitted in the intensive care unit after major abdominal surgery performed with open laparotomy.

24 hours