Chapter 32: Nutrition

INTRODUCTION

Critical illness is associated with a systemic inflammatory response and catabolic state that leads to increased infections, multiorgan dysfunction, prolonged hospitalization, and death. The individual’s adaptive response aims to increase energy provision to vital organs by increasing release of pituitary hormones, increasing sympathetic nervous system stimulation, and increasing peripheral resistance to anabolic hormones. Society of Critical Care Medicine (SCCM) and American Society of Parenteral and Enteral Nutrition (ASPEN)’s approach to nutritional is designed to preserve lean body mass, attenuate stress response, prevent oxidative injury, and modulate immune response.¹ The current nutritional bundle includes (1) assess patients for nutritional risk and calculate energy and protein requirements to determine goals; (2) initiate enteral nutrition (EN) within 24 to 48 hours after the onset of critical illness and admission to the intensive care unit (ICU) and increase to goal within the first week of the ICU stay; (3) reduce the risk of aspiration or improve tolerance to gastric feeding with the use of prokinetic agents, continuous infusion, chlorhexidine mouthwash, elevation of the head of the bed, and diverted level of feeding in the gastrointestinal (GI) tract; (4) implement enteral feeding protocols with institution-specific strategies to promote delivery of enteral nutrition; (5) do not use gastric residual volumes as part of routine care to monitor ICU patients on EN; and (6) start parenteral nutrition (PN) early when EN is not feasible or sufficient in high-risk poorly nourished patients.¹

NUTRITIONAL ASSESSMENT

The patient population in the ICU is heterogeneous, and objective markers such as albumin, prealbumin, transferrin, and retinol binding protein participate in the acute phase response and do not accurately reflect the nutritional status of a critically ill patient.¹ Other markers are still under investigation; these include calcitonin, C-reactive protein, interleukin-1, interleukin-6, citrulline, ultrasound with measurement of muscle mass, and computed tomography.¹ Nutritional risk assessment such as the Nutritional Risk Score (NRS-2002) helps to identify patients who will likely benefit from early enteral therapy because they will reduce nosocomial infection, complications, and mortality risk.¹ Patients with an NRS-2002 greater than 3 are at risk, and those with scores of 5 or greater are at high nutritional risk.^1-4

Energy needs are determined via indirect calorimetry (low evidence), but when this is unavailable, a weight-based equation of 25 to 30 kcal/kg/d can be used.¹ The accuracy of this equation varies from 40% to 75% and becomes less accurate with obese and underweight patients.¹ Other considerations for this calculation include using dry weight and including energy provided by dextrose-containing fluids and lipid-based medications.¹ Because of protein’s role in wound healing, immune function, and maintaining lean body mass, protein requirements are higher in critically ill patients, and most EN has a high ratio of nonprotein calorie to nitrogen.¹ When nitrogen balance studies are not available, 1.2 to 2 g/kg/d can be used to monitor adequate protein provision, although ...