Nutritional Support and the Surgical Patient

Yvonne Huckleberry

Disclosures

Am J Health Syst Pharm. 2004;61(7) 

In This Article

Plasma Proteins

Albumin has long been criticized as a player in nutritional assessment due to its lack of specificity and long half-life (appromately 20 days).[40,41] Albumin is synthesized in and catabolized by the liver. The normal range for serum albumin is 3.5-5 g/dL. Levels of this visceral protein may decline in the setting of acute injury and illness as the liver reprioritizes protein synthesis from visceral proteins to acute-phase reactant proteins. Synthesis also declines with hepatic insufficiency or failure. Renal losses of albumin can occur with nephrotic syndrome; enteropathies can result in losses via the GI tract. Systemic inflammation not only reduces albumin synthesis but can increase its degradation and promote transcapillary leakage of albumin. Fluid overload dilutes serum albumin, whereas dehydration or intravenous albumin infusion can temporarily raise levels.[39,40,41]

Despite the numerous factors that can skew the interpretation of postoperative albumin in relation to nutritional status, several studies have found this protein to be an excellent predictor of surgical outcomes when evaluated preoperatively.[42,43,44,45] Gibbs and colleagues[44] published the largest prospective trial, with 54,215 patients undergoing major noncardiac surgeries. Preoperative serum albumin was evaluated in relation to 30-day postoperative morbidity and mortality. Compared with nine other risk variables, serum albumin was ranked as the strongest predictor of surgical outcomes, with an inverse relationship between postoperative morbidity and mortality compared with preoperative serum albumin levels. A more recent study confirmed these results and added evidence that preoperative albumin could be found in approximately 75% of the medical records of patients undergoing elective surgery.[45] Whether the hypoalbuminemia was due to undernutrition or advanced disease was not specified in these trials. However, it appears that preoperative serum albumin, although often available, is an underutilized prognostic indicator of surgical outcomes.

Prealbumin, also referred to as transthyretin, is a transport protein for thyroid hormone.[37,40,41] It is synthesized by the liver and partly catabolized by the kidneys. Normal serum prealbumin concentrations range from 16 to 40 mg/dL; values of <16 mg/dL are associated with malnutrition.[40] Levels may be increased in the setting of renal dysfunction, corticosteroid therapy, or dehydration, whereas physiological stress, infection, liver dysfunction, and over-hydration can decrease prealbumin levels.[8,30,37]

The half-life of prealbumin (two to three days) is much shorter than that of albumin,[37,40,41] making it a more favorable marker of acute change in nutritional status. A baseline prealbumin is useful as part of the initial nutritional assessment if routine monitoring with NS is planned. However, this test may be more expensive than the test for albumin and may not be available in all institutions.

If prealbumin is used to monitor the acute changes in nutritional status for patients receiving NS, a reasonable goal would be to increase prealbumin by 3-5 mg/dL/wk until values are within normal limits.[40] This goal would be valid only in the absence of other factors that can influence prealbumin. For example, one common influence that has been previously mentioned is physiological stress that occurs with tissue injury or infection. It has been suggested that acute-phase reactants, such as C-reactive protein, may be used in the detection and management of postoperative infections. This nonspecific marker of inflammation and infection can increase up to a thousandfold early in the acute-phase response.[41] Elevated concentrations of C-reactive protein (>10 mg/dL) suggest physiological stress that requires continued hepatic synthesis of acute-phase reactants and delays production of markers of nutritional rehabilitation, such as prealbumin.[46] Until this stress response subsides, practitioners may not see improvement in prealbumin levels no matter how much nutrition is being provided. Routine measurement of C-reactive protein is not recommended at this time; the test can be expensive, and its role in assessing postoperative inflammation has not been defined. Further study is warranted.

Transferrin has also been used as a marker of nutritional status. This acute-phase reactant is a transport protein for iron; normal concentrations range from 200 to 360 mg/dL. Transferrin has a relatively long half-life (8-10 days) and is influenced by several factors, including liver disease, fluid status, stress, and ill-ness.[36,37] Levels decrease in the setting of severe malnutrition, but this marker is unreliable in the assessment of mild malnutrition, and its response to nutrition intervention is unpredictable.[41] Transferrin has not been studied as extensively as albumin and prealbumin in relation to nutritional status, and the test can be expensive.[27,37] For these reasons, this variable is less commonly used in routine nutritional assessments performed in acute care settings.

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