Fish Oil–Containing Lipid Emulsions in PN: Review Reports on Immunomodulation and ICU Outcomes

A narrative review in Nutrients examines fish oil–containing injectable lipid emulsions used in parenteral nutrition, focusing on how intravenous omega-3 fatty acids (EPA and DHA) are framed as influencing inflammatory and immune biology in critical illness. Alongside this mechanistic rationale, the authors compile clinical signals across critical care and selected other settings, emphasizing infectious complications and sepsis as well as resource-use measures and survival. Infections/sepsis, length of stay, mechanical ventilation, and mortality recur as the main outcome domains used to structure the clinical narrative. The piece ultimately presents what the authors describe as a biologically plausible pathway from lipid composition to observed clinical endpoints.

The review describes modern injectable lipid emulsions as mixed formulations that may combine soybean oil–derived long-chain triglycerides with medium-chain triglycerides, olive oil, and fish oil, framing composition as a determinant of downstream biologic activity rather than energy delivery alone. Within that framework, the authors attribute several connected immunomodulatory mechanisms to intravenously delivered EPA and DHA. They describe incorporation of these fatty acids into membrane phospholipids, with downstream changes in membrane characteristics and signaling that may extend to altered gene-expression patterns relevant to inflammatory and immune responses. They also outline competition with arachidonic acid in cyclooxygenase and lipoxygenase pathways, shifting the profile of eicosanoids generated from membrane substrates. In addition, they highlight EPA/DHA as precursors for specialized pro-resolving mediators—resolvins, protectins, and maresins—positioned as contributors to active resolution biology. In parts of the cited literature, the authors discuss inflammatory markers and cytokine readouts (such as CRP and IL-6) as bridging measures. Together, these mechanistic themes are presented as the biologic backdrop for the clinical outcomes summarized later in the review.

Clinical evidence is summarized across the narrative review’s summary of randomized trials and meta-analyses comparing fish oil–containing emulsions with conventional soybean oil–based emulsions in parenteral nutrition. As characterized by the authors, the most consistent direction of findings is toward lower risk of infections and sepsis and shorter hospital length of stay with fish oil–containing formulations. The review also notes that selected analyses report shorter ICU length of stay and reduced duration of mechanical ventilation, particularly in sepsis-focused datasets. For in-hospital mortality, the authors describe a signal favoring fish oil–containing emulsions while also emphasizing uncertainty, including interval estimates that allow for no difference. Overall, the review presents these results as summarized associations and signals rather than definitive effects across all settings.

Guideline context is incorporated through the review’s discussion of ESPEN 2023 recommendations, which suggest using mixed injectable lipid emulsions containing MCTs, omega-9 fatty acids, and omega-3 fatty acids within parenteral nutrition formulations.

Within that same guideline framing, the review notes a lipid-intake ceiling described as not exceeding 1.5 g/kg/day, presented as part of dose and tolerance considerations. Beyond general ICU populations, the review uses condition-specific sections to illustrate where fish oil–containing emulsions and omega-3 delivery have been evaluated, including acute pancreatitis, COVID-19, delirium in critical illness, and postoperative delayed gastric emptying. These sections are presented as examples of how the broader mechanistic and outcomes narrative has been applied to specific clinical contexts. The overall synthesis places guideline statements and condition-focused evidence side by side as complementary strands of the authors’ summary.

Evidence gaps highlighted by the authors center on heterogeneity: differences in patient populations, illness categories, and baseline risk; variation in dosing regimens, omega-3 exposure, and emulsion composition; and inconsistency in how endpoints are defined and measured across studies. The review also points to variability across meta-analyses and emphasizes that narrative syntheses must reconcile mixed designs and differing analytic choices, which can affect how consistently signals appear. The authors characterize the current evidence base as supportive of further clarification rather than fully settled, and they return to the need for additional well-designed randomized trials to better define dosing approaches and reduce uncertainty across outcomes. The review closes by positioning remaining questions as largely methodological and population-specific rather than purely mechanistic.

Key Takeaways:

• The review summarizes signals from comparative studies in which fish oil–containing emulsions were associated with fewer infectious complications/sepsis and shorter hospital stay versus soybean oil–based emulsions.
• Mechanistic themes emphasized include EPA/DHA incorporation into membranes, competition with arachidonic acid in eicosanoid pathways, and provision of substrates for specialized pro-resolving mediators.
• The authors cite ESPEN 2023 guideline context (including a lipid-intake limit) and highlight heterogeneity across populations and regimens, with further randomized trials described as needed to reduce uncertainty.