Nutrition assessment and nutritional requirements

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The first step before delivering nutrition support therapy is to perform a nutritional assessment and determine nutrient requirements based on the patient's nutritional status and clinical conditions. Subjective and objective data of dietary intake, functional capacity, anthropometrics, weight changes, GI function, medical history, medication therapy, and laboratory data are collected to determine a patient's nutritional status, identify patients with malnutrition or at risk for malnutrition, and to identify risk factors that may put a patient at risk for nutrition-related problems.1 A nutrition assessment should include:1,19

• Patient history

• Physical assessment including height, weight, ideal body weight (IBW), body mass index (BMI = weight [kg]/height [m ]), and recent weight loss (intentional or unintentional). BMI relates a person's body weight to their height and is a vague indicator of total body fat mass in adults. BMI categories do not account for frame size, muscle mass, bone, and water weight. Classifications of weight status in relation to

22 BMI are: underweight less than 18.5 kg/m ; normal 18.5 to 24.9 kg/m ; overweight

22 25 to 29.9 kg/m ; obese greater than or equal to 30 kg/m

• Physical examination of the musculoskeletal system (e.g., biceps, triceps, quadriceps, temporalis, deltoid, and interosseus muscles) for loss of muscle mass, and examination of the skin and mucous membranes for abnormalities (e.g., noting dry or flaky skin, bruising, edema, ascites, poorly healing wounds) and loss of subcutaneous fat (e.g., triceps, chest)

• Changes in eating habits and GI function, and associated GI symptoms

• Presence and severity of underlying and concurrent disease(s)

• Serum visceral protein concentrations (e.g., albumin, prealbumin). Hypoalbu-minemia at baseline or prior to hospitalization may be indicative of malnutrition, and severe hypoalbuminemia may be associated with poor patient outcome. Serum albumin and prealbumin concentrations are not sensitive and specific markers of nutritional status and protein stores in hospitalized patients under metabolic stress (e.g., postsurgery, organ failure, severe burns, trauma, and sepsis). Albumin and prealbumin are negative acute phase proteins. Their liver synthesis is decreased under stress and they are sensitive to non-nutritional factors including hydration status, and kidney and liver functions. Because prealbumin has a shorter half-life (approximately 2 days) than albumin (approximately 20 days), serum prealbumin concentrations are measured usually once weekly to help evaluate the net anabolism in response to nutrition support therapy.

• Serum concentrations of vitamins, trace elements, and iron as indicated

There are several methods to conducting a nutrition assessment, but one approach that has been validated is the Subjective Global Assessment (SGA).1 Application of the SGA requires gathering the data listed above and assessing these parameters (i.e., weight change, dietary changes, GI symptoms, functional capacity, and physical examination) and then assigning a subjective rating (A = well nourished; B = moderately malnourished or suspected of being malnourished; C = severely malnour-ished).19

After performing a nutrition assessment, estimate the patient's daily energy and protein requirements (Table 100-4). Indirect calorimetry involves measuring the volumes of oxygen consumption (VO2) and carbon dioxide production (VCO2) to determine the resting metabolic rate (RMR) or resting energy expenditure (REE) and respiratory quotient (RQ = VCO2/VO2). The REE or RMR is the amount of calories required during 24 hours by the body in a nonactive state, and is approximately 10% higher than the basal energy expenditure (BEE, metabolic activity required to maintain life) as it adjusts for the thermic effect of food and awake state. Because critically ill patients may have variable energy expenditure, indirect calorimetry is a valuable tool in assessing energy expenditure in mechanically ventilated patients with multiple and changing clinical conditions. Indirect calorimetry requires expensive equipment and trained personnel to use, and therefore is not feasible in all institutions. Over 200 equations have been developed to determine energy expenditure (EE) for adults. The Harris-Benedict equations, Penn State equations (for nonobese critically ill patients), and the Mifflin St. Jeor equations (for obese noncritically ill patients) are some of the most widely used. Harris-Benedict equations take into account a patient's sex, weight, height, and age to determine the BEE. A "stress" or "injury" factor is then applied to estimate the daily total EE (TEE). Daily energy requirements are about 100% to 130% of the RMR with adequate protein intake. Alternatively, EE can be estimated based on EE per body weight (i.e., kilocalories per kilogram). However, dry weight or admission weight should be used, and this estimation may not be appropriate in patients who are obese or in elderly patients. There is debate over the best method to estimate energy requirements for obese patients. Several equations have been developed to estimate EE in obese patients. Although there is no consensus on the weight used to estimate EE in obese patients, it is reasonable to use an adjusted body weight (AdjBW) in obese patients to avoid overfeeding. Adjusted body weight can be calculated with 25% to 50% of the difference between the actual weight and IBW added to the IBW. Using a 25% difference in calculating the adjusted body weight further avoids overfeeding when estimating energy requirements:

Table 100-4 Estimating Daily Energy and Amino Acid Requirements in Adults

0*teririlnlng En« ay tuptudllait

Men: E£E = t6A2 t- 1575 m + 5 (H) - tJS(A) Women: BEE - 655.1 ¥ 9jfiS (W) * 1.85 (W - 4« MJ W ivett^ifl In kijLH = lniitjhl in im.fl jye in jnim

Lnoigytipwidiiuieiiicrtihoirt) btinuiiiiiied by a sirfwfatiw lotstimate (hi total energy expendiltiie (TIE): Bed rat - 12 x BEE Ambulatory*: UxBil Anjbefc ^l.ifiSEE

Erwyy requRwwKS si*)ukJ jiw bo inci^Hd with 11 m ¡n fi^iTt ■ltx*** paefF).

= ««[')+ (31XV,) K17JnT_J.ft.4JJ RWIfi - 0MH1] + (Jl if V,] + (l&J w TJ -

fit E oilciJiaDed thing Hjnfe^enedlci;: Bwfl caksrtaned umi*) iffihhSt Jwr «jiHtkim v. -minute ventilation in liteis per mimHeiTma* maximum body tempeiatuip in degrees ciiiul

SMfl - fcyJldl mcUUiic rjli.'. w ■■ Wfigtvi {kyO; H ■ height Oc ro): A .igc (jvii Jiangs of "20-30 fccalfligAfcy, possibly up to 35 fecalvkgrtiay MaiHenance -2Q-2S ka1/hjyay ktpft(kwiKiiii^jc*aiivo\vyuryj heillng, «Hal illrvw. stcsi4-«v(TtiJaijrrij. stuerc bums -?S-JO Kil/k^Aisy, pcssWy vp to Ji fcal/kg/diy

Determining Amino Acid Requirement)

P.mVnl Llij-iitil Cnr.dilinn

Dai ly Amino Acid Rcnuirrrm'nli- (ql t'jl





Tiauma, burns, sepahv cjHkral iltiess


1 Hepatic Inline fjiih, fnrrprulopallfy


Acult kiJnt.'v injury, PrcJijIyvi


Acule kdnfy Injury receiving Inlermrltenl



Chronic kidney disease iccelvirig


HUflirniiKH jrftbuldlDry [vrikirnyl

cli.vysr; (t AH30

Acult1 kiJiwy dwinc KCCiVlnQ tontinuous


renal replacement therapy |l iirll)

-Amino.yId iL^uliMihwrKi. .qrl■ based an .viuil body weight for norrrviE borty M/Pilor malnomKhfti .yjuli patie*\ii mJno Ideal ludyiMight (IBWor obese pdlKfris.

-Amino.yId iL^uliMihwrKi. .qrl■ based an .viuil body weight for norrrviE borty M/Pilor malnomKhfti .yjuli patie*\ii mJno Ideal ludyiMight (IBWor obese pdlKfris.

Amino acid requirements are based on the patient's nutritional status, clinical condition^), and kidney and liver function. There are no evidence-based data on what body weight (actual, ideal, or adjusted) should be used for dosing amino acids in adult patients. It is however suggested to dose amino acids based on actual body weight for normal body sized or malnourished adult patients and based on IBW for obese patients. Amino acids are needed in adequate amounts to facilitate anabolism, restore lean body mass, or promote wound healing while avoiding adverse effects from excessive amino acid loading (e.g., azotemia). Actual body weight is used for amino acid dosing in adult patients with severe malnutrition when their body weight is at or below the IBW.

Hypocal2oric nutrition support therapy for obese patients (BMI greater than or equal to 30 kg/m or actual weight greater than 150% of IBW) is a promising approach. Hy-pocaloric feeding involves providing high amounts of proteins (approximately 2 g/kg IBW/day) to support anabolism with lower amounts of total calories (average approximately 11-14 kcal/kg [46-59 kJ/kg] actual weight/day, or approximately 22-25 kcal/ kg [92-105 kJ/kg] IBW/day) with primary goals to promote net anabolism and avoid hyperglycemia or exacerbation of metabolic stress in critically ill patients.20 Secondary benefits of hypocaloric feeding could be avoiding fat weight gain or possibly promoting fat weight loss. The role of hypocaloric feeding in patients with acute kidney injury or chronic kidney disease, or in patients with end-stage liver disease and hepatic encephalopathy is unknown. Also, the optimal safe duration of hypocaloric feeding in critically ill obese patients is unknown.

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