The aim of this study is to investigate the efficacy of early postoperative enteral immunonutrition on immune response and outcomes in the low operative risk cardiac surgery population with low phase angle value measured by the bioelectrical impedance analysis.

Study enrolls a low operative risk cardiac surgery patients who undergo elective cardiac surgery with cardiopulmonary bypass (CPB). Patient is offered to take part in a study a day prior to surgery. Information is provided regarding protocol, aim and course of study. Only signing the consent form patients could be enrolled to the study.

Study consists of:

Primary assessment - information about study. Consent form. Assessment of patient according to predefined criteria. Phase angle evaluation by bioelectrical impedance. (Day prior to surgery). It is a specific cohort of patients basically governed by surgery risk and the status of patients' cells. Euroscore II value was used to evaluate the risk of surgery. Bioelectrical impedance analysis derived phase angle was used to evaluate patients' cells frailty and vitality.

First phase of blood sampling - blood samples were taken for evaluation immunological status (cellular and humoral) and inflammatory response (CRB, complete blood count) at the surgery day morning prior to surgery.

Surgery - evaluating the course of the surgery (see exclusion criteria). Randomization - the patients will randomly selected into intervention and control groups. The patients, physicians and investigators were separate from this process. The selection sequence was computer-generated and provided to the researchers by the statistician.

Intervention - patients in the intervention group received normal daily meals plus one sachet three times a day of immune nutrients ("Glutamine Plus" by Fresenius Kabi) for five days after the surgery. The control group was provided with normal daily meals. The patients were excluded from the study if they failed to intake all of the prescribed immunonutrients.

Second phase of blood sampling - repeated taking of blood samples for evaluation immunological status (cellular and humoral) and inflammatory response (CRB, complete blood count) at the sixth day morning after the surgery.

Data collection - data is recorded (demographic data of patients, co-morbidities, instrumental parameters, phase angle values, surgery course details, immunological assesment and laboratory tests, short term and long term outcomes).

Inclusion Criteria:

• Age ≥18 years;
• Elective cardiac surgery with cardiopulmonary bypass:
• coronary artery bypass grafting surgery (CABG);
• aortic valve replacement;
• mitral valve replacement;
• mitral valve repair;
• tricuspid valve repair;
• combined operations (CABG and valve surgery);
• Phase angle <5.5⁰ (phase angle was evaluated one day prior to surgery using bioelectrical impedance analysis (InbodyS10 device).

Exclusion Criteria:

Preoperative:

• previous cardiac surgery;
• left ventricle ejection fraction <40%;
• use of preoperative intra-aortic balloon pump (IABP);
• critical preoperative state;
• pulmonary artery mean pressure >55 mmHg;
• diagnosis of infectious endocarditis;
• pacemaker;

Operative:

• complicated intraoperative course (unplanned intervention or low cardiac output syndrome in the operating theatre: failure to wean from cardiopulmonary bypass (CPB) or intraoperative insertion of IABP or infusion of two or more inotropic medications with a cumulative dose of 0.2 mcg/kg/min);
• surgery time >6 h;
• unplanned intervention;

Postoperative:

• disturbance of dietary rules.