Fish oil in critical illness

Enteral omega-3 in acute respiratory distress syndrome

PURPOSE OF REVIEW

The acute respiratory distress syndrome (ARDS) is a severe illness that is often the cause of death in ICU patients. A safe and effective intervention for this condition is lacking. Fish oil-based enteral nutrition [rich in n-3 polyunsaturated fatty acids (PUFAs) and antioxidants] improved clinical outcomes in a previous trial on ARDS patients but was ineffective, or even harmful in other studies utilizing different fish oil formulae (rich in n-3 PUFAs and arginine) in severely ill ICU patients. Until most recently, consistent evidence that enteral n-3 PUFA is therapeutic in ARDS was lacking.

RECENT FINDINGS

In ARDS, an overwhelming inflammatory response damages the endothelial-alveolar units, reducing oxygen diffusion and increasing pulmonary workload. n-3 PUFA targets this inflammatory response. In two recent randomized, controlled studies, the fish oil formula that was previously shown to be effective was administered to patients with ARDS/acute lung injury (in which hypoxia is less severe) and to patients with severe sepsis and hypoxia, respectively. n-3 PUFA feeding improved oxygenation, and a meta-analysis of the three studies demonstrated that enteral fish oil reduces mortality, complications and length of ICU stay.

SUMMARY

Enteral administration of fish oil, antioxidants and physiologic amounts of arginine improve oxygenation and clinical outcomes in ICU patients with impaired oxygenation. Whether n-3 PUFA per se produces such benefit is the subject of an ongoing clinical study.

Acute lung injury is reduced in fat-1 mice endogenously synthesizing n-3 fatty acids

RATIONALE

Acute lung injury (ALI) remains an important cause of mortality in intensive care units. Inflammation is controlled by cytokines and eicosanoids derived from the n-6 fatty acid (FA) arachidonic acid (AA). The n-3 FA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and mediators derived from EPA and DHA possess reduced inflammatory potency.

OBJECTIVES

To determine whether the ability of fat-1 mice to endogenously convert n-6 to n-3 FA, and thus generate an increased ratio of n-3 to n-6 FA, impacts experimental ALI.

METHODS

We investigated ALI induced by intratracheal instillation of endotoxin in fat-1 and wild-type (WT) mice, assessing leukocyte numbers, protein concentration, and prostaglandin and cytokine levels in bronchoalveolar lavage fluid, as well as free FA in plasma, and lung ventilator compliance. Body temperature and motor activity of mice--markers of sickness behavior--were also recorded.

MEASUREMENTS AND MAIN RESULTS

In ALI, fat-1 mice exhibited significantly reduced leukocyte invasion, protein leakage, and macrophage inflammatory protein-2 and thromboxane B(2) levels in lavage fluid compared with WT mice. Free AA levels were increased in the plasma of WT mice in response to endotoxin, whereas EPA and DHA were increased in the fat-1 group. Ventilator compliance was significantly improved in fat-1 mice. Body temperature and motor activity were decreased in ALI. fat-1 Mice recovered body temperature and motor activity faster.

CONCLUSIONS

fat-1 Mice exhibited reduced features of ALI and sickness behavior. Increasing the availability of n-3 FA may thus be beneficial in critically ill patients with ALI.

Immunonutrition in critically ill patients: a systematic review and analysis of the literature

BACKGROUND

The role of immuno-modulating diets (IMDs) in critically ill patients is controversial.

OBJECTIVE

The goal of this meta-analysis was to determine the impact of IMD's on hospital mortality, nosocomial infections and length of stay (LOS) in critically ill patients. Outcome was stratified according to type of IMD and patient setting.

DATA SOURCES

MEDLINE, Embase, Cochrane Register of Controlled Trials.

STUDY SELECTION

RCT's that compared the outcome of critically ill patients randomized to an IMD or a control diet.

DATA SYNTHESIS

Twenty-four studies (with a total of 3013 patients) were included in the meta-analysis; 12 studies included ICU patients, 5 burn patients and 7 trauma patients. Four of the studies used formulas supplemented with arginine, two with arginine and glutamine, nine with arginine and fish oil (FO), two with arginine, glutamine and FO, six with glutamine alone and three studies used a formula supplemented with FO alone. Overall IMD's had no effect on mortality or LOS, but reduced the number of infections (OR 0.63; 95% CI 0.47-0.86, P = 0.004, I(2) = 49%). Mortality, infections and LOS were significantly lower only in the ICU patients receiving the FO IMD (OR 0.42, 95% CI 0.26-0.68; OR 0.45, 95% CI 0.25-0.79 and WMD -6.28 days, 95% CI -9.92 to -2.64, respectively).

CONCLUSIONS

An IMD supplemented with FO improved the outcome of medical ICU patients (with SIRS/sepsis/ARDS). IMDs supplemented with arginine with/without additional glutamine or FO do not appear to offer an advantage over standard enteral formulas in ICU, trauma and burn patients.

Immunonutrition in critically ill patients: a systematic review and analysis of the literature

BACKGROUND

The role of immuno-modulating diets (IMDs) in critically ill patients is controversial.

OBJECTIVE

The goal of this meta-analysis was to determine the impact of IMD's on hospital mortality, nosocomial infections and length of stay (LOS) in critically ill patients. Outcome was stratified according to type of IMD and patient setting.

DATA SOURCES

MEDLINE, Embase, Cochrane Register of Controlled Trials.

STUDY SELECTION

RCT's that compared the outcome of critically ill patients randomized to an IMD or a control diet.

DATA SYNTHESIS

Twenty-four studies (with a total of 3013 patients) were included in the meta-analysis; 12 studies included ICU patients, 5 burn patients and 7 trauma patients. Four of the studies used formulas supplemented with arginine, two with arginine and glutamine, nine with arginine and fish oil (FO), two with arginine, glutamine and FO, six with glutamine alone and three studies used a formula supplemented with FO alone. Overall IMD's had no effect on mortality or LOS, but reduced the number of infections (OR 0.63; 95% CI 0.47-0.86, P = 0.004, I(2) = 49%). Mortality, infections and LOS were significantly lower only in the ICU patients receiving the FO IMD (OR 0.42, 95% CI 0.26-0.68; OR 0.45, 95% CI 0.25-0.79 and WMD -6.28 days, 95% CI -9.92 to -2.64, respectively).

CONCLUSIONS

An IMD supplemented with FO improved the outcome of medical ICU patients (with SIRS/sepsis/ARDS). IMDs supplemented with arginine with/without additional glutamine or FO do not appear to offer an advantage over standard enteral formulas in ICU, trauma and burn patients.