Immunonutrition in Cardiac Surgery

Objective To study the effect of two preoperative immune enhancing nutritional supplements compared with a control nutritional supplement in 'high risk' risk cardiac surgery patients

Introduction: Elderly patients and patients with a poor ventricular function undergoing cardiac operations with hypothermic cardiopulmonary bypass (CPB), have an increased postoperative morbidity and mortality. Host defence may be diminished due to nutritional deficiencies, hypoperfusion, anaesthesia and operative trauma. Immune function is additionally depressed by the use of CPB and hypothermia. It has been suggested that L-arginine can improve postoperative outcome in cardiac surgery patients, glycine may have a role in protecting tissues against insults such as ischemia-reperfusion and hypoxia, and omega-3 polyunsaturated fatty acids (omega3-PUFA's) can limit the postoperative generalised inflammatory response.

Experimental studies have shown that the use of nutritional supplements containing L-arginine, omega3-PUFA's or nucleotides, boost immune responsiveness after surgery or trauma. L-arginine is a semi-essential amino acid and precursor of nitrous oxide (NO), the most important endothelial vasodilator. In experimental studies, L-arginine improved wound healing, restored postoperative depressed macrophage function and lymphocyte responsiveness and augmented resistance to infections. Arginine protected against ischemia-reperfusion injury by increasing oxygen delivery upon reflow, thereby improving cardiac function. The intake of additional omega3-PUFA's alters cell membrane phospholipid content and prostaglandin synthesis. This might be an important factor in limiting the generalised inflammatory response and subsequent immunosuppression and capillary leakage following major surgery. Purines and pyrimidines are essential nutrients for rapidly dividing cells. The administration of nucleotides in the form of yeast-RNA has improved the host immune response to an infectious challenge. In experimental studies glycine has been proven cytoprotective in stomach, kidney, liver and cardiovascular system. The metabolic response to oral glycine is that it facilitates the uptake op glucose from the circulation.

The immunonutrients, arginine, omega3-PUFA's and yeast-RNA, have been combined into a single oral immune enhancing nutritional supplement (OIENS). In cancer surgery, trauma and critically ill patients 'post event' nutrition with this immune enhancing formula has improved immunocompetence, reduced infections and shortened length of stay in the hospital (LOSH). The onset of the effect of postoperative immune enhancing nutrition starts after 3 days and seems to be dose dependent. For this reason, it can be hypothesised that it may be beneficial to commence an oral immune enhancing nutritional supplement (OIENS) before surgery. A recent published clinical trail showed that the OIENS with these three immunonutrients in high risk cardiac surgery patients improves preoperative clinical relevant immunological parameters, reduced postoperative infectious morbidity and attenuated postoperative organ dysfunction. Recently, the three immunonutrients have been combined with glycine into a new single OIENS. Aim of the present study in 'high risk' cardiac surgery patients was to determine whether the intake of the new OIENS for minimally five days improves preoperative host defence and subsequently reduces postoperative infections and organ dysfunction.

Study design: A prospective randomized placebo-controlled three armed double blind study

Setting: Departments of cardiopulmonary surgery, anesthesiology and intensive care of the Academic Medical Center, Amsterdam, The Netherlands

Patients: Eligible patients will be included in the study after obtaining written informed consent Inclusion criteria: Patients who met one or more of the inclusion criteria: aged 70 years or more, undergoing cardiac surgery with the use of CPB, or patients with a poor left ventricular function (Ejection fraction < 0.40) or patients undergoing a mitral valve replacement.

Exclusion criteria: Age < 21 years, pregnancy, insulin dependent diabetes mellitus, hepatic cirrhosis, known malignancy, the use of chemotherapy, NSAIDs (excluding acetyl salic acid) or corticosteroids, schizophrenia, severe renal insufficiency (creatinine clearance < 25 mL/h), patients with an organ transplantation in the past

Randomization: 74 patients will be randomized by closed envelop method

Intervention: All patients will receive one of the three enteral nutritional supplements. A formula enriched with arginine, omega-3 PUFA's and nucleotides or the enriched formula further enriched with additional glycine or a control formula. Patients that needs postoperative enteral nutritional support will receive the same formula as preoperative. Patients that need no postoperative enteral nutrition nasogastric tube feeding will not receive the nutritional supplement

Endpoints: Patient compliance, infections, postperfusion phenomena, post-operative organ function (need of postoperative support e.g. inotropic, vasopressor support, fluids, myocardial infarction, ventilation parameters, renal function) time of recovery, mortality