The value of nutritional supplements in the critically ill

There are many nutritional additives which are hypothesized to improve host defenses by boosting immunity and are called by some immuno-nutrients [68]. A meta-analysis compared published studies using two different "immunologically enhanced" enteral feedings with standard enteral feeding mixtures. These two "enhanced" mixtures had increased amounts of arginine, omega-3 fatty acids and nucleotides when compared with standard feedings. One of the feeding mixtures had added glutamine as well [69]. All studies analyzed enrolled critically ill medical and surgical patients. Although there was no detectable mortality benefit to enhanced feedings, there was an overall reduction in infectious risk to 0.60 (p < 0.005). No statistically significant infectious benefit could be found if only medical patients were analyzed (p = 0.30).

When studies enrolling only cancer patients are analyzed, no significant benefit of enhanced enteral nutrition was found in reducing nosocomial pneumonia. Effects on other infections were not analyzed. There was no significant effect of enhanced feeding on length of hospital stay or mortality [70]. If the enhanced feedings were started 7 days before cancer surgery and continued after the surgery, there was evidence of an infectious benefit in 206 Italian patients [71]. The pneumonia rate was more than twice as high in those receiving non-enhanced nutrition and the overall infection in the standard nutrition group was 30% compared to 14% in the enhanced nutrition group (p = 0.009).

When a routine hospital diet feeding was compared with a diet supplemented with 22.5 grams of extra protein and extra calories, there was no infectious risk benefit for stroke patients. A large multinational trial involving 4,023 patients showed no difference in pneumonia or urinary tract infection rates. The rate of developing pressure ulcers was not altered by supplementation either [72].

An innovative form of nutritional supplement was given to Hungarian patients with pancreatitis [73]. Twenty-three control and 22 experimental patients received nasojejunal feedings for 7–10 days. The control group also received 10 grams of oat fiber twice a day as well as 10 billion heat-killed Lactobacillus plantarum. The experimental group received the oat fiber and living bacteria. Seven control patients and only 1 experimental patient had a positive pancreatic aspiration culture (p = 0.05). Seven control patients required surgery to control sepsis compared to one experimental patient. The hypothesis that the composition of the enteral flora affects the rate of sepsis is supported by this study.

There is considerable literature regarding the amino acid glutamine's ability to preserve enterocyte integrity and reduce bacterial translocation from the gut [74]. When Dutch trauma patients received enteral nutrition or glutamine-supplemented enteral nutrition (which was iso-nitrogenous and iso-caloric), the glutamine supplemented group showed a definite infectious benefit [75]. There were fewer pneumonias (17% vs 43%) and bacteremias (9% vs 38%). A study of Spanish ICU patients with systemic inflammatory response syndrome yielded similar results for enteral glutamine supplementation [76]. The pneumonia incidence was about halved in the glutamine group (p = 0.04), although the incidence of bacteremia was unaffected by glutamine supplementation.

Glutamine need not apparently be given enterally to detect an infectious benefit. Burn patients receiving intravenous glutamine were compared with those receiving an iso-nitrogenous amino acid mixture. Only 1 of 12 glutamine patients had a Gram-negative bacteremia compared to 6 of 14 control patients (p = 0.04). The Gram-positive bacteremia and fungemia rates were unaffected by glutamine infusion [77]. Intravenous supplementation glutamine decreased bacteremias in bone marrow transplant patients when compared with parenteral nutrition without glutamine supplementation [78].

Table 2 summarizes the effect of various nutritional interventions on infections in hospitalized patients.