Nutrition in the Critically Ill Surgical Patient

Purpose of Review

The aim of this study was to discuss recent findings related to providing adequate and well tolerated nutrition to the critically ill surgical patient.

Recent Findings

The majority of nutritional studies in the critically ill have been performed on well nourished patients, but validated scoring systems can now identify high nutrition risk patients. Although it remains well accepted that early enteral nutrition with protein supplementation is key, mechanistic data suggest that hypocaloric feeding in septic patients may be beneficial. For critically ill patients unable to tolerate enteral nutrition, randomized pilot data demonstrate improved functional outcomes with early supplemental parenteral nutrition. Current guidelines also recommend early total parenteral nutrition in high nutrition risk patients with contraindications to enteral nutrition.

When critically ill patients require low or moderate-dose vasopressors, enteral feeding appears well tolerated based on a large database study, while randomized prospective data showed worse outcomes in patients receiving high-dose vasopressors.

Summary

Current evidence suggests early enteral nutrition with protein supplementation in critically ill surgical patients with consideration of early parenteral nutrition in high nutrition risk patients unable to achieve nutrition goals enterally. Despite established guidelines for nutritional therapy, the paucity of data to support these recommendations illustrates the critical need for additional studies.

Malnutrition is prevalent in the critically ill and it has been associated with poor outcomes including clinical complications, longer hospital stays, and increased mortality [3]. A prospective randomized trial by Schuetz et al. [4] investigated this association and showed malnutrition to be a modifiable risk factor for poor outcomes. The authors illustrated that when identified and treated early, modifying malnutrition can substantially improve functional status and survival [4]. Despite recognition of its prevalence and potential impact to patient care when recognized early, there continues to be no universally accepted approach to the diagnosis and documentation of adult malnutrition [5].

There have been many screening and assessment tools created to evaluate nutritional status including: Mini Nutritional Assessment. Approximately 4 million patients are admitted to ICUs annually in this country, many for treatment of surgical diseases (https://healthpolicy. ucsf. edu/ icu-outcomes). Although the benefits of early nutritional supplementation are well recognized, critically ill patients receive on average only 40–50% of their prescribed goal nutritional requirements for prolonged periods following ICU admission [1,2]. In this review, we discuss recent literature and guidelines related to the institution and advancement of optimal nutrition in the critically ill patient and address challenges to its adequate delivery (Fig. 1).

As most literature does not focus on surgical patients, assumptions must be made to their generalizability, identifying a gap in our current knowledge and focus for future studies.

• The two scoring systems most often utilized, but not universally accepted, to diagnose malnutrition in the critically ill are the NRS-2002 and NUTRIC systems.
• In haemodynamically stable critically ill patients not on vasopressors, early and progressive enteral nutrition is recommended.
• In the setting of critical illness, protein is touted as the most important macronutrient for healing wounds, supporting immune function and maintaining lean body mass.
• When parenteral nutrition is used, omega-3 fatty acids are the preferred lipid emulsion.
• Low and medium-dose vasopressor use in patients receiving enteral nutrition is generally well tolerated. Universal Screening Tool, the Short Nutritional Assessment Questionnaire, the Subjective Global Assessment (SGA), the Nutrition Risk Screening Score (NRS-2002) and the Nutrition Risk in Critically ill (NUTRIC), but not all are applicable to the critically ill [6 ,7,8]. Some scoring systems are prone to error in the critically ill due to fluid shifts that can affect BMI calculations and the acute-phase response, which can affect protein markers [6]. The two scoring systems most often utilized, but not universally accepted, in the critically ill are the NRS-2002 and NUTRIC systems. & & The NRS-2002 was originally described in 2003 and is based on BMI, percentage recent weight loss and recent change in food intake [9]. Its ability to predict clinical outcomes including mortality has been studied in several different patient populations and its efficacy was recently supported by a retrospective study of 5698 medical patients [10]. In addition, it was recently validated by a secondary analysis of a prospective randomized trial of 2028 medical patients. Both these studies excluded ICU patients and recent European Society for Clinical Nutrition and Metabolism (ESPEN) guidelines recommend it should not be applied to ICU patients until further studies validate its use in this population [6]. This is in contrast to the Society of Critical Care Medicine (SCCM)/American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines, which recommend determination of NRS-2002 for all patients admitted to ICU and cite its application to ICU patients in several prospective studies as evidence of its utility in this population [7]. & &

Despite the known benefits of early enteral nutrition, surgical patients pose a number of challenges that can impede delivery of adequate enteral nutrition such as delayed initiation with ongoing resuscitation, open abdomens from damage control surgeries and frequent surgeries with nil per os feeding prior to planned surgical procedures. Some of these can be overcome by targeted feeding strategies that focus on the early initiation of enteral nutrition, volume-based feeding protocols and multidisciplinary protocols to allow feeding to continue until the time of surgery [15].

Nutrition is a critical component in the management of sepsis, but as with all critically ill patients, haemodynamic status and vasopressor requirements influence nutritional supplementation. For haemodynamically stable septic patients, the most recent ESPEN, SCCM/ASPEN and Surviving Sepsis guidelines agree that early and progressive enteral nutrition is recommended [6 ,7,16]. Enteral nutrition in these patients is considered to be the ideal form, as it has potential physiologic advantages to parental nutrition with regards to maintenance of gut integrity, dampening of the inflammatory response and modulation of metabolic responses that may reduce insulin resistance [16].

Underfeeding in sepsis

The recommendation for early full enteral nutrition in patients with sepsis has recently been drawn into question by some who point out that these recommendations are based on expert consensus with a lack of high-quality clinical trials on the efficacy of www. co-criticalcare. com & permissive underfeeding in sepsis [17]. The concept of hypocaloric therapy in sepsis has been supported by mechanistic studies of autophagy. This is a cellular repair process that is inhibited by full nutrition and thought to be responsible for worse outcomes seen in some studies [18].

A Cochrane review to evaluate hypocaloric nutritional support identified 15 trials with 3219 patients, but unfortunately due to clinical and statistical heterogeneity, pooled estimates of the primary and secondary outcomes were unable to be made. Authors concluded there was currently very low-quality evidence to support hypocaloric therapy and larger prospective trials were needed [19].

In the setting of critical illness, protein is touted as the key macronutrient for wound healing, immune function and maintenance of lean body mass [7]. As previously discussed, enteral is the preferred method for nutrition in the critically ill but optimal protein amount, timing and type of formulation have been topics of debate [2,10 ].

Protein amount

The 2019 the ESPEN guideline on clinical nutrition in the ICU recommended 1. 3 g/kg protein equivalents per day [6]. This is similar to the SCCM/ASPEN guideline, which recommends daily intake with goals of 1. 2–2. 0 g/kg actual body weight per day and possibly higher in trauma and burn patients [7]. These higher dose recommendations are supported by several prospective studies. Weijs et al. [21] performed a prospective observational study that demonstrated high protein (1. 3 g/kg protein) was associated with 50% decrease in 28-day mortality when compared with low protein (0. 8 g/kg/day). Meeting caloric targets without meeting protein demands did not confer the same mortality reduction as when protein targets were also reached [21].

A later prospective study by the same group again comparing low protein (0. 8 g/kg/day) to high protein (0. 8 g/kg/day) diets in nonseptic patients revealed an almost linear association with mortality reduction as protein intake increased [22]. In a similar prospective observational cohort study of 113 ICU patients administered a 1. 2–1. 5 g/kg/day protein enteral regimen, mortality was decreased in comparison to a lower protein regimen [23].

Protein timing

The initial phase of critical illness is catabolic in nature and results in acute muscle wasting [6].

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