Clinical assessment and monitoring of nutrition support in adult surgical patients

INTRODUCTION — Nutrition support represents one of the most important cornerstones in the management of surgical patients. An assessment of nutritional status must be conducted to identify patients in need of nutrition support. Nutritional status is considered so vital to patient outcomes that the Joint Commission mandates nutrition screening within 24 hours of hospital admission [1]. In a surgical population, the goal of the assessment is to identify patients at high nutritional risk secondary to their primary surgical disease, comorbidities, or planned procedures [2,3].

Clinical monitoring is the key tool for assessing the adequacy of ongoing nutrition support. Laboratory markers for immune response, indirect calorimetry, and body weight and composition can also be used.

The initial clinical evaluation and ongoing assessment/clinical monitoring of nutrition support in surgical patients is reviewed. Indications for nutrition support, timing, delivery, and types of nutrition support are discussed separately. (See "Overview of perioperative nutrition support".)

INITIAL ASSESSMENT OF NUTRITIONAL STATUS — The first task when considering nutrition support is to assess whether the patient has malnutrition. Many studies have been conducted to examine the best ways to determine the presence of malnutrition in surgical and other hospitalized patients. These include unintentional weight loss, ideal body weight (IBW), body mass index (BMI), weight index, subjective global assessment (SGA), mid-arm muscle circumference (MAMC), triceps skinfold thickness (TSF), mid-arm circumference (MAC), mid-arm muscle area (MAMA), subscapular skinfold thickness (SSF), serum albumin, transferrin, transthyretin, and retinol-binding protein [4]. Important aspects of nutritional assessment that pertain to surgical patients are reviewed below.

Based upon expert consensus, a diagnosis of malnutrition requires that the patient exhibit two or more of the following [2,5-7]:

●Insufficient energy intake

●Weight loss

●Loss of muscle mass

●Loss of subcutaneous fat

●Localized or generalized fluid accumulation that may sometimes mask weight loss

●Diminished functional status as measured by handgrip strength

To determine if the above criteria are present, the following tools for diagnosis are used:

History and physical — Several aspects of the past medical history are of particular importance. These include a history of chronic diseases (eg, diabetes, anorexia, cancer, other conditions that might interfere with a patient's ability to achieve adequate intake), infection, recent hospitalization, and prior surgery (particularly gastrointestinal surgery).

On review of systems, a history of weight loss or gain is important. Any recent losses or gains (and whether they were purposeful or not) prior to the hospital stay should be assessed (figure 1). The details of the current hospitalization also play a central role. Newly admitted trauma patients who are otherwise well likely have very different needs from patients who have had surgery several weeks in the past but have remained hospitalized due to complications.

In addition to collecting information on current medications, nonprescription medicines and other supplements, particularly vitamin and herbal products that may interfere with coagulation and other medications, should be noted. The intake of calorie supplements such as protein shakes should also be determined. Lastly, any allergies or food intolerances should also be noted. A diet history should be collected from the patient, family or other caregivers, or from care facility. Although there are several methods of dietary assessment, the most useful and straightforward may be to assess the usual intake on an average day before hospitalization or before the onset of the current illness [8]. (See "Overview of herbal medicine and dietary supplements".)

In addition to vital signs and a general physical examination, the following should be noted:

●Height and weight (calculate body mass index [BMI] using weight in kg divided by height in meters squared (calculator 1), or using a nomogram) (figure 2)

●General: Loss of subcutaneous fat, any generalized fluid accumulation

●Head and neck exam: Hair loss, bitemporal wasting, conjunctival pallor, xerosis, glossitis, bleeding or sores on the gums and oral mucosa, angular cheilosis or stomatitis, dentition

●Cardiovascular: Evidence of heart failure or high-output state

●Neck: Thyromegaly

●Extremities: Edema, loss of muscle mass

●Neurologic: Evidence of peripheral neuropathy, reflexes, tetany, mental status, handgrip strength

●Skin: Ecchymoses, petechiae, pallor, pressure ulcers, assessment of surgical wound healing and signs of surgical site infection (if postoperative)

●Anthropometric data: MAMC, TSF, MAC, MAMA, SSF [4,9]

Signs of specific nutritional deficiencies should also be sought. Some of these are given in the table (table 1). Appropriate micronutrient levels should be investigated depending on clinical exam findings.

Nutritional risk screening tools — Several clinical tools are available to quickly assess and score nutrition status. One of these tools should be used in all patients who are hospitalized [10] and who are undergoing elective surgery [11].

●The Subjective Global Assessment of Nutritional Status is a brief tool that includes history and physical examination findings and allows standardized assessment [12]. (See 'History and physical' above.)

●The Nutritional Risk Screening tool (NRS 2002) can be applied rapidly and used to screen for poor baseline nutritional status [13,14]. A study that assessed the ability of the NRS 2002 score to predict the incidence and severity of postoperative complications found the overall incidence of nutritional risk was 14 percent among 608 patients undergoing gastrointestinal surgery [15]. A significantly higher overall complication rate was found in patients at nutritional risk compared with those with a normal NRS 2002 risk score (40 versus 15 percent). Severe complications were also significantly higher in patients at nutritional risk (54 versus 15 percent) [16,17].

●The Nutrition Risk Index (NRI) was developed by the Veterans Affairs Total Parenteral Nutrition Cooperative Study Group originally for cancer populations [18]. It is derived from the serum albumin concentration and the ratio of the actual to usual body weight.

•The following risk groups were used:

-Not at risk: NRI >00

-Mild risk: NRI between 97.5 and 100

-Moderate risk: NRI between 83.5 and 97.5

-Sever risk: NRI <83.5

Assessing protein status — Assessing initial protein status is particularly important in the surgical patient because protein status predicts wound healing and surgical complications [19-22]. Protein status is affected by previous intake, muscle mass, duration of current illness, blood loss, wound healing, infections, and gastrointestinal absorption. Although decreased levels of three serum protein markers correlate with adverse outcomes, improvements in these markers with nutritional supplementation are not reliably associated with a clinical benefit [23]. (See "Overview of perioperative nutrition support", section on 'Consequences of malnutrition in surgical patients' and "Risk factors for impaired wound healing and wound complications".)

●Serum albumin has the longest half-life at 18 to 20 days and is the most extensively used parameter. Low serum albumin (<2.2 g/dL) is a marker of a negative catabolic state and a predictor of poor outcome [24]. Surgical stress, burns, infection, other acute stresses, hepatic disease, and renal disease decrease serum albumin levels [25]. Neither starvation nor supplementation has any impact on levels [26].

●Serum transferrin has an intermediate half-life of eight to nine days and is reflective of recent systemic inflammatory response. Transferrin also reflects iron status, and low transferrin should be considered an indicator of protein status only in the setting of normal serum iron.

●Serum prealbumin (transthyretin) has the shortest half-life at two to three days. Prealbumin responds quickly to the onset of catabolism or inflammation and rises rapidly when it resolves. In general, inflammatory cytokines reduce the level of prealbumin synthesis by the liver, and it can also be reduced with renal and hepatic disease but, like all "negative acute phase reactants," is likely lowered via capillary leak.

●C-reactive protein is an acute phase reactant. It can be used to help determine whether albumin, transferrin, and prealbumin are reduced due to an inflammatory process or due to malnutrition.

Other laboratory studies — In addition to assessing protein status, a few other laboratory studies may be helpful in assessing initial nutritional status. Electrolytes, glucose, and blood urea nitrogen (BUN)/creatinine help assess overall clinical and fluid volume status and need to be obtained if parenteral (intravenous) nutrition will be instituted. Additionally, BUN, in studies of the effects of bed rest, has been found indicative of muscle mass changes [27]. A reduction in muscle mass can increase urea generation due to the high protein content of muscle tissue and urea as the final catabolite of endogenous protein breakdown [28]. In addition, if a patient is likely to need parenteral nutrition, a baseline triglycerides level should be obtained [29]. Liver function tests are useful to check during nutrition assessment since the liver is responsible for the synthesis of albumin and prealbumin as well as the fact that elevated liver enzymes may preclude some forms of nutrition support [25].

Iron levels should be measured in the setting of unexplained anemia, as should specific vitamin levels if clinically indicated. (See "Diagnostic approach to anemia in adults" and "Overview of water-soluble vitamins" and "Overview of vitamin A" and "Overview of vitamin D" and "Overview of vitamin E" and "Overview of vitamin K".)

Serum calcium, magnesium, and phosphorous should also be assessed periodically, particularly in the setting of poor oral intake or diarrhea [30]. (See "Overview of postoperative electrolyte abnormalities".)

Specific populations

Burns — Burn patients pose a particular challenge in assessing and managing nutrition. Adequate nutrition is vital to all patients with a burn injury, but not all of them require nutrition support. The key is to identify patients who require coordinated nutrition support. Initial assessment of nutritional status of a burn patient is similar to other hospitalized patients as described above. However, patients have a heterogeneous metabolic response to burn, which makes it challenging to determine which patients need supplementation. Due to the hypermetabolism of a burn injury, the combined Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines suggest based on expert consensus that very early initiation of enteral feeds should be targeted in patients with burn injury [31]. Burn patients who are not expected to initiate an oral diet within 6 to 12 hours of sustaining the burn injury are started on nutrition support [32]. (See "Overview of nutrition support in burn patients", section on 'Timing of nutrition support'.)

In burn injured patients, the metabolic rate increases proportionally to burn size with a burn larger than 15 to 25 percent total body surface area (TBSA) initiating a catabolic response [33]. Patients with burns greater than 40 percent TBSA consistently experience hypermetabolism and often cannot consume enough calories to maintain lean body mass (LBM) [34,35]. (See "Hypermetabolic response to moderate-to-severe burn injury and management".)

Nutrition support is used selectively in patients with less extensive burn injury (<20 percent) burn injury. Patient groups that may benefit include children, older adults, and patients with obesity. (See "Overview of nutrition support in burn patients", section on 'Selected patients with less severe burns'.)

Nutritional assessment on admission can help determine which patients with smaller burns may benefit from nutritional supplementation. Despite nutrition support, it is unlikely that preexisting malnutrition can be corrected following a burn injury, but one can hope to keep up with the metabolic demands of the burn [36].

Trauma/surgical critical care — Adequate nutrition is important in the management of both trauma and surgical critical care patients [37,38]. All trauma and critical care patients should undergo a full assessment of nutritional risk within 48 hours of admission [33]. The NRS 2000 and the Nutrition Risk in the Critically Ill (NUTRIC) score are especially suited to use in the trauma and critical care population as they are capable of determining nutritional status and disease severity. The NUTRIC score links starvation, inflammation, nutritional status, and outcomes [39]. In this scale, low scores indicate a low risk of malnutrition and high scores indicate a high risk of malnutrition and an association with increased ventilator duration and mortality. (See "Overview of inpatient management of the adult trauma patient", section on 'Fluid therapy and nutrition support' and "Nutrition support in intubated critically ill adult patients: Initial evaluation and prescription".)

Malignancy — Patients with cancer are prone to weight loss and may not have adequate calorie consumption [40]. If the patient is a candidate for surgical resection, malnutrition can cause significant problems and increase the risk of perioperative morbidity and mortality [41]. Nutrition support has become an essential part of preoperative care in malnourished cancer patients as it was found that it could reduce the rate of postoperative complications by 10 percent [30]. As an example, patients with esophageal cancer may benefit from enteral nutrition during neoadjuvant therapy prior to surgery, and in general patients with better nutritional status have fewer complications following surgery [42]. Specifically, patients unable to tolerate full liquids or those with severe malnutrition identified at their initial office visit benefit from placement of a feeding jejunostomy to improve their nutritional status during neoadjuvant therapy. (See "Overview of perioperative nutrition support", section on 'Preoperative nutrition support' and "The role of parenteral and enteral/oral nutritional support in patients with cancer".)

Standard nutritional assessment including dietary assessment, physical examination, laboratory examination, Nutritional Index, anthropometric and body composition measurements, and bioelectrical impedance analysis are all part of the assessment of the nutritional status of a cancer patient. In addition, a cancer-specific assessment has been developed. The Oncology Nutrition Dietetic Practice Group of the American Dietetic Association created the patient-generated subjective global assessment (PG-SGA), which was specifically designed for cancer patients and has become the standard assessment for cancer patients [43,44].

Patients with obesity — Patients with obesity who undergo surgery provide a particular nutrition assessment challenge. While it is tempting to assume that patients with obesity are well nourished due to their weight, this not necessarily the case, and often the opposite is true. Studies have found that patients with obesity can have extremely high rates of critical malnutrition, suggesting that all should be screened for malnutrition prior to surgery. Sarcopenic obesity is present when a patient has markedly low lean body mass (LBM), despite their extensive fat stores [45,46]. Patients with sarcopenic obesity have morbidity and mortality rates following surgery that are more in line with their LBM measurements then with their actual or ideal body weight. Patients with obesity typically have decreased visceral protein stores and muscle mass, and the hormonal response of hypermetabolism limits the body's ability to use fat stores as an energy source [36]. This can complicate the practitioner's ability to calculate their caloric needs. (See "Preanesthesia medical evaluation of the patient with obesity", section on 'Metabolic syndrome' and "Metabolic syndrome (insulin resistance syndrome or syndrome X)".)

Comorbidities — Other comorbid conditions can affect nutrition assessment in surgical patients. These include aging, chronic kidney disease, and chronic liver disease and are discussed separately.

●Advanced age (see "Geriatric nutrition: Nutritional issues in older adults")

●Chronic kidney disease (see "Assessment of nutritional status in patients on hemodialysis" and "Nutritional status and protein intake in patients on peritoneal dialysis")

●Chronic liver disease (see "Nutritional issues in adult patients with cirrhosis")

MONITORING NUTRITION SUPPORT — Although the initial assessment of nutritional status is critical, it is also important to monitor the effects of our interventions. Adequate nutrition means meeting the energy demands of the metabolic process that has led to hospitalization, maintaining core body temperature, and supporting healing, to reduce recovery time and complications [47]. A variety of methods can be used to monitor whether a patient's nutritional needs are being maintained.

Clinical status — The adequacy of nutrition support is best monitored by assessing the patient's clinical course and wound healing [48]. Trends, rather than single measurements or point estimates, should be monitored. Parameters used to evaluate the clinical course include:

●Hemodynamic stability

●Respiratory status

●Functional status

●Evidence of infection or sepsis

●Tolerating diet

Adequate wound healing — An experienced clinician should evaluate the patient's wounds daily. Assessment of the wound includes recording size, depth, condition of the base, and pain [49]. This examination allows for early identification of delayed or inadequate wound healing, both of which may indicate inadequate nutrition [19].

Changes in body weight/mass — Changes in total body weight (TBW) and in lean body mass (LBM) are some of the few objective measures available for monitoring nutritional status. TBW is easiest to obtain and therefore is easiest to follow; however, surgical patients may have received a large volume of resuscitation and may be above their prehospitalization TBW before it can be measured for the first time [50]. LBM can be useful for accounting for the large volume of resuscitation some patients require, and for ensuring that patients are not losing muscle mass. Multiple methods are used for measuring TBW and LBM in surgical patients.

Total body weight — TBW measures two components: lean weight (muscles, bones, tendons, ligaments, and water) and fat weight. However, for patients who require a significant volume of fluid for resuscitation (eg, burns, multiple trauma), measurements of TBW may not be particularly useful or indicative of prehospitalization weight or nutritional status. Due to ease of measurement, TBW serves as one indicator for monitoring and evaluating nutritional status [51]. Because of the limited utility of body weight for monitoring nutritional status in acute injury, TBW should only be measured weekly to allow assessment of trends in all surgical patients [50]. Trends in TBW are more helpful as an indicator of nutritional status once patients enter the rehabilitative phase [52].

Lean body mass — Maintenance of LBM represents one of the central tenets of nutrition support, and accurate measurement can assist with determining protein needs as well as with drug dosing in some cases [53]. There are many methods for measuring LBM that can theoretically be used in clinical practice (dual X-ray absorptiometry [DEXA] scanning, radioactive total body potassium determination [⁴⁰K Counter], bioimpedance analysis [BIA], computed tomography [CT] measurement, and musculoskeletal ultrasound), but many of these are not practical for repeated or routine use. In particular, DEXA and ⁴⁰K Counter are not routinely used for LBM measurement in hospitalized surgical patients, as they cannot be done at the bedside; these have been used more for long-term follow-up [54,55].

CT scan analysis, musculoskeletal ultrasound, and BIA are increasingly being used in the intensive care unit (ICU) for determination of LBM in surgical patients [53]. Ultrasound and BIA are inexpensive, well tolerated, and able to be done at the bedside; however, there are concerns about the validity and reproducibility of these measurements. To alleviate these concerns, standardized protocols are needed to improve their use in routine clinical practice. CT scan analysis is more reliable and less dependent on technical skill and can be performed on scans made for other reasons (trauma, staging for cancer, etc), but it is not useful for longitudinal monitoring and is not readily available in all patients.

For patients who sustained burns or trauma, body composition assessment may not be reliably used as a means to monitor nutritional status after initial assessment because of the edema and fluid shifts associated with the inflammatory response to injury. As patients recover, and their fluid status returns to normal, these measurements once again become more reliable.

Indirect calorimetry — While not strictly used to monitor nutritional status, indirect calorimetry (IC) can be used to determine the nutritional requirements and does have the ability to serve as an indicator of response to nutrition support, particularly in the difficult-to-manage patient (burn patients in particular) [56]. However, one of the greatest limitations of IC is that energy expenditure fluctuates with activity, and the utility of IC as a single measurement point is questionable [52,57,58]. (See "Nutritional demands and enteral formulas for adult surgical patients", section on 'Determining caloric requirements'.)

Trends in IC are more reliable estimates of adequate nutrition support rather than a single measurement. IC is monitored weekly, and adjustments in nutrition support are made based upon IC calculation, nitrogen balance, and clinical progress. Two thirds of responding burn center dieticians have indicated that they used IC to assess energy demands in adult patients [51].

Nitrogen balance — The assessment of adequate nutrition support must address both energy requirements and protein demands of surgical patients. Nitrogen balance, therefore, plays an important role in assessing nutritional adequacy. Measuring urinary urea nitrogen (UUN) and calculating nitrogen balance on a weekly basis allows approximation of the trend in nitrogen breakdown and appropriate adjustment of protein goals, particularly when used in conjunction with clinical monitoring methods in injured surgical patients (burn and trauma) [52,59,60]. (See 'Clinical status' above.)

Laboratory examination — A variety of acute phase reactants have been examined as laboratory markers that assess the efficacy of nutrition support. However, the physiologic changes that accompany the surgical stress response make interpretation of these markers difficult. Some markers may correlate with compromised nutritional status, but they do not provide a meaningful measure of overall trends and should only be used in conjunction with the assessment of the clinical status [52,59]. (See 'Assessing protein status' above and 'Other laboratory studies' above and 'Clinical status' above.)

The use of these markers is not uniform across surgical disciplines. As an example, in burn patients, it is not general practice to use visceral proteins (eg, albumin) or other protein markers (transthyretin, transferrin, retinol-binding protein, and C-reactive protein) to monitor nutritional status, as they are not generally thought to be reliable on their own. Serum albumin does not correlate with nitrogen balance. Serum albumin levels decrease dramatically with burn injury and remain chronically low, even when other indicators, including nitrogen balance, suggest adequate nutrition support [61].

For trauma patients, prealbumin correlates well with nitrogen balance while albumin and transferrin levels do not [60]. In addition, serial determinations of serum levels of acute phase reactants (C-reactive protein, fibrinogen, alpha-1-glycoprotein, etc) may improve the value prealbumin as a nutritional monitoring tool. Serum albumin and prealbumin can be useful as predictors of outcome for patients with traumatic brain injury (TBI), but in general, albumin is a better predictor of poor outcome [62,63]. In patients of severe TBI (GCS ≤8), serum albumin is an independent predictor of poor outcome, while prealbumin does not have predictive value in this group.

For other hospitalized patients (including surgical patients), the National Institute for Health and Care Excellence (NICE) clinical guidelines recommend measuring albumin weekly and C-reactive protein every two to three days until stable [64].

For patients who require parenteral nutrition with the use of injectable lipids, a serum triglyceride level should be measured at baseline and periodically while injectable lipids are a part of their parenteral nutrition regimen. For short-term parenteral nutrition, a weekly triglyceride level is appropriate, while patients receiving long-term nutrition should be monitored monthly [65].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nutrition support (parenteral and enteral nutrition) in adults".)

SUMMARY AND RECOMMENDATIONS

●Initial nutrition assessment – Nutrition support represents one of the most important cornerstones in the management of surgical patients. When evaluating a patient for surgery or other intervention, nutritional status should be assessed by performing a history and physical examination, making use of nutritional risk and screening tools. Judicious use of laboratory tests aimed at assessing protein status is useful for determining prognosis but does not reflect protein intake. Decreased levels of serum protein markers correlate with adverse outcomes, but improvements in these markers with nutritional supplementation are not reliably associated with a clinical benefit. (See 'Initial assessment of nutritional status' above.)

●Specific populations – Special considerations need to be addressed in the initial assessment of specific populations (burn, trauma/critical care, cancer, obesity). (See 'Specific populations' above.)

●Monitoring nutrition support – The adequacy of ongoing nutrition support in surgical patients is best assessed by the clinical course and wound healing. When used in conjunction with daily clinical assessment, evaluating trends in total body weight, indirect calorimetry, and laboratory results can be helpful in assessing adequacy of nutrition support. Single or random measurements are not useful. (See 'Monitoring nutrition support' above.)

•The long-term trend in total body weight (TBW) is a helpful indicator of nutritional status when patients enter the rehabilitative phase following surgery. (See 'Total body weight' above.)

•Maintenance of lean body mass (LBM) is one of the central tenets of nutrition support, but there is no proven method for accurate assessment of LBM. (See 'Lean body mass' above.)

•Adjustments in nutrition support should be made no more than twice per week based upon trends in indirect calorimetry, urinary urea nitrogen, and clinical findings. (See 'Indirect calorimetry' above and 'Nitrogen balance' above.)

•Laboratory tests are difficult to accurately interpret in the surgical patients. If laboratory tests are used to assess nutritional status, they should be used in conjunction with the assessment of the overall clinical course and wound healing. (See 'Laboratory examination' above.)