Probiotics, prebiotics and synbiotics in critical illness

The interest in human intestinal microbiota in health and critical illness has increased in recent years. In critically ill patients, the gut ecology can be negatively affected by malnutrition, intestinal ischemia, impaired intestinal motility, and bacterial adherence. Trauma, surgical stress, surgical injury, antibiotic treatment, severe sepsis, vasoactive agents, hypovolemia, hypoxia, hypercarbia, electrolyte disorders and deep sedation can cause these conditions. Most clinical trials conducted to date focused on the effects of pre- and probiotic therapy in critical illness but there were potential confounders (single-center studies, small size, variable design, variable inclusion and endpoint criteria, variable pre- and probiotic treatment). The available meta-analyses suggest that probiotics were associated with lower rates of infection (including ventilator-associated pneumonia) and reduced Intensive Care Unit mortality, but no effect on hospital mortality, Intensive Care Unit or hospital stay were found. However, their use should be avoided in immunocompromised hosts and in patients with prosthetic vascular grafts or heart valves. In particular, Saccharomyces boulardii should not to be used in patients with indwelling central-line catheters.