In critically ill patients, should nutrition support prescription be individualised to their mortality risk and nutritional status?

Author: Chin Han Lew

Lew, Charles Chin Han , 2019 In critically ill patients, should nutrition support prescription be individualised to their mortality risk and nutritional status?, Flinders University, College of Nursing and Health Sciences

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Abstract

Optimising nutritional status is traditionally associated with aggressive nutrition support designed to provide higher energy and protein intakes. However, in the critical care arena, this issue has become controversial. While several studies demonstrated that higher intakes resulted in lower mortality and infection risk, others showed otherwise. In an effort to identify patients who would derive the most benefit from higher energy and protein intakes, a systematic approach was undertaken with the aim of developing a prognostic model, namely the Global Index of Mortality Probability in the Severely ill (GLIMPSE). This work hypothesized that the integration of key factors such as baseline nutritional status and disease severity could better: 1) prognosticate mortality, and 2) identify patients who would derive the most benefit from aggressive nutrition support in the critical care setting.

To identify nutrition assessment tools that have good prognostic validity for worsened clinical outcomes in critically ill patients, two systematic reviews and an original study were conducted. The first systematic review [1] coupled with an original study [2] concluded that the 7-point Subjective Global Assessment (7-point SGA) has good prognostic validity but that this was not the case for the thickness of the adductor pollicis muscle [3].

To identify tools that quantify disease severity, two original studies were conducted. The first study concluded that the Acute Physiologic Assessment and Chronic Health Evaluation II (APACHE II) has limited prognostic accuracy and that more predictors are required to improve performance [4]. The second study showed that the modified Nutrition Risk in Critically Ill score (mNUTRIC) is a valid disease severity score with consistent and robust mortality prognostic value [5].

The above key findings led to the development of GLIMPSE, in which baseline nutritional status (measured by the 7-point SGA) and disease severity (measured by mNUTRIC) were integrated into a logistic model, and a robust validation study demonstrated that GLIMPSE has good discrimination and calibration accuracy for 28-day mortality. However, GLIMPSE was unable to identify patients who would benefit from aggressive nutrition support as high-energy and protein intakes are positive and inversely associated with 28-day mortality in patients with identical mortality risk. In other words, in malnourished and severely ill patients, aggressive nutrition support was associated with higher mortality risk in some patients whereas the converse was observed in others, and GLIMPSE was unable to differentiate between them.

A review of recent evidence suggests that energy and protein metabolism during the early phase of critical illness differ across patients, and this determines how aggressive nutrition support can affect clinical outcomes. Some literature also claims that aggressive nutrition support provided at the later phase of critical illness may be more effective. Taken together, in critically ill patients with high mortality risk, it appears that it is not so much “who” requires aggressive nutrition support as “when” it should be provided.

In conclusion, it takes more than baseline nutritional status and disease severity to determine energy and protein needs in the early phase of critical illness. More work is needed to elucidate the complex interactions between metabolic processes during the early phase of critical illness so that individualised nutrition therapy can be provided in order to bring about the best clinical outcomes.

Keywords: Critical care, nutrition support, nutrition assessment, malnutrition, prognostication, subjective global assessment, acute physiology and chronic health evaluation II

Subject: Nutrition thesis, Nutrition and Dietetics thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Nursing and Health Sciences
Supervisor: Michelle Miller