Clinical nutrition is somewhat complex. Much of clinical practice is based on observation or on flawed, biased, or severely underpowered studies. Furthermore, terminology related to malnutrition is extremely confusing; incorporating terms referring to problems attributable to alterations in nutritional intake intermixed with those secondary to inflammatory illness, which are not responsive to changes in nutrition intake.
Many excellent clinical publications1,2 review general and specific nutritional concepts. This chapter focuses on newly proposed definitions for malnutrition and on the clinical challenges specific to selected pulmonary diseases and acute respiratory failure and the critical care setting. Chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) serve as the prototypes for nutrition-related issues encountered in chronic pulmonary disease.
Malnutrition has long been known to be associated with poor outcomes in medical and surgical patients.3 However, for decades the terminology describing malnutrition has created great confusion. While new efforts focus on defining malnutrition based on etiology,4 clinical parameters unrelated and unresponsive to nutrient intake5,6 remain entrenched.
The new definition of malnutrition (Table 149-1) describes two forms: malnutrition due to nutrient imbalance or malnourishment (e.g., starvation, marasmus, obesity), and that which occurs due to systemic illness (e.g., catabolism, cachexia).4 Only malnutrition due to nutrient imbalance resulting from alterations in intake or uptake can be treated by alterations in nourishment.
Table 149-1Findings in the New Definition of Malnutrition ||Download (.pdf) Table 149-1Findings in the New Definition of Malnutrition
| ||Starvation-Related Malnutrition (Malnourishment) ||Disease-Related Malnutrition |
|Starvation ||X ||X |
|Fat wasting ||X ||+/– |
|Muscle wasting ||X ||X |
|Hypoproteinemia || ||X |
|Elevated inflammatory markers || ||X |
The belief that most traditional markers of malnutrition (e.g., albumin, prealbumin [transthyretin], measures of immune function) reflect adequacy of nourishment has been disproved,5,6 and some of these elements have been removed from the new definition.4
Confusion will likely continue, however, because remaining in the definition are clinical findings, such as loss of lean body mass, which may be caused by starvation, systemic inflammation, or both. The etiology of these signs may be difficult, if not impossible, to distinguish clinically; furthermore, lean body mass loss due to inflammation, for example, does not respond to stand-alone nourishment strategies when inflammation is present. Patients with “malnutrition” may or may not be “malnourished.” Well-nourished patients (e.g. receiving tube feeding or eating well) with disease-related muscle wasting are “cachectic.”
While it still comes as a “surprise” to many clinicians that so-called nutritional markers are, in truth, markers of systemic inflammation, this is far from a new finding.7,8 Discussion of alterations in serum albumin and other parameters as arising from systemic inflammation has appeared in physiology and biology texts for decades.9 By the same token, these “nutritional” ...