C-reactive protein rise in response to macronutrient deficit early in critical illness: sign of inflammation or mediator of infection prevention and recovery

PURPOSE

Withholding parenteral nutrition (PN) early in critical illness, late-PN, has shown to prevent infections despite a higher peak C-reactive protein (CRP). We investigated whether the accentuated CRP rise was caused by a systemic inflammatory effect mediated by cytokines or arose as a consequence of the different feeding regimens, and whether it related to improved outcome with late-PN.

METHODS

This secondary analysis of the EPaNIC-RCT first investigated, with multivariable linear regression analyses, determinants of late-PN-induced CRP rise and its association with cytokine responses (IL-6, IL-10, TNF-α) in matched early-PN and late-PN patients requiring intensive care for ≥ 3 days. Secondly, with multivariable logistic regression and Cox proportional-hazard analyses, we investigated whether late-PN-induced CRP rises mediated infection prevention and enhanced recovery or reflected an adverse effect counteracting such benefits of late-PN.

RESULTS

CRP peaked on day 3, higher with late-PN [216(152-274)mg/l] (n = 946) than with early-PN [181(122-239)mg/l] (n = 946) (p < 0.0001). Independent determinants of higher CRP rise were lower carbohydrate and protein intakes (p ≤ 0.04) with late-PN, besides higher blood glucose and serum insulin concentrations (p ≤ 0.01). Late-PN did not affect cytokines. Higher CRP rises were independently associated with more infections and lower likelihood of early ICU discharge (p ≤ 0.002), and the effect size of late-PN versus early-PN on these outcomes was increased rather than reduced after adjusting for CRP rise, not confirming a mediating role.

CONCLUSIONS

The higher CRP rise with late-PN, explained by the early macronutrient deficits, did not relate to cytokine responses and thus did not reflect more systemic inflammation. Instead of mediating clinical benefit on infection or recovery, the accentuated CRP rise appeared an adverse effect reducing such late-PN benefits.

Glucose homeostasis, nutrition and infections during critical illness

Critical illness is a complex life-threatening disease characterized by profound endocrine and metabolic alterations and by a dysregulated immune response, together contributing to the susceptibility for nosocomial infections and sepsis. Hitherto, two metabolic strategies have been shown to reduce nosocomial infections in the critically ill, namely tight blood glucose control and early macronutrient restriction. Hyperglycaemia, as part of the endocrine-metabolic responses to stress, is present in virtually all critically ill patients and is associated with poor outcome. Maintaining normoglycaemia with intensive insulin therapy has been shown to reduce morbidity and mortality, by prevention of vital organ dysfunction and prevention of new severe infections. The favourable effects of this intervention were attributed to the avoidance of glucose toxicity and mitochondrial damage in cells of vital organs and in immune cells. Hyperglycaemia was shown to impair macrophage phagocytosis and oxidative burst capacity, which could be restored by targeting normoglycaemia. An anti-inflammatory effect of insulin may have contributed to prevention of collateral damage to host tissues. Not using parenteral nutrition during the first week in intensive care units, and so accepting a large macronutrient deficit, also resulted in fewer secondary infections, less weakness and accelerated recovery. This was at least partially explained by a suppressive effect of early parenteral nutrition on autophagic processes, which may have jeopardized crucial antimicrobial defences and cell damage removal. The beneficial impact of these two metabolic strategies has opened a new field of research that will allow us to improve the understanding of the determinants of nosocomial infections, sepsis and organ failure in the critically ill.