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. Author manuscript; available in PMC: 2012 Apr 25.
Published in final edited form as: Am J Crit Care. 2006 Mar;15(2):166–177.

Assessing Nutritional Status in Chronically Critically Ill Adult Patients

Patricia A Higgins 1, Barbara J Daly 1, Amy R Lipson 1, Su-Er Guo 1
PMCID: PMC3336201  NIHMSID: NIHMS9218  PMID: 16501136

Abstract

Background

Numerous methods are used to measure and assess nutritional status of chronically critically ill patients.

Objectives

To discuss the multiple methods used to assess nutritional status in chronically critically ill patients, describe the nutritional status of chronically critically ill patients, and assess the relationship between nutritional indicators and outcomes of mechanical ventilation.

Methods

A descriptive, longitudinal design was used to collect weekly data on 360 adult patients who required more than 72 hours of mechanical ventilation and had a hospital stay of 7 days or more. Data on body mass index and biochemical markers of nutritional status were collected. Patients’ nutritional intake compared with physicians’ orders, dieticians’ recommendations, and indirect calorimetry and physicians’ orders compared with dieticians’ recommendations were used to assess nutritional status. Relationships between nutritional indicators and variables of mechanical ventilation were determined.

Results

Inconsistencies among nurses’ implementation, physicians’ orders, and dieticians’ recommendations resulted in wide variations in patients’ calculated nutritional adequacy. Patients received a mean of 83% of the energy intake ordered by their physicians (SD 33%, range 0%–200%). Patients who required partial or total ventilator support upon discharge had a lower body mass index at admission than did patients with spontaneous respirations (Mann-Whitney U = 8441, P = .001).

Conclusions

In this sample, the variability in weaning progression and outcomes most likely reflects illness severity and complexity rather than nutritional status or nutritional therapies. Further studies are needed to determine the best methods to define nutritional adequacy and to evaluate nutritional status.

Although severity of illness is the single most important predictor of survival in critically ill patients,1 many questions exist about the contribution of other factors to patients’ outcomes. Two factors are the role of nutritional status and the role of nutritional supplementation. Many critically ill patients are hypermetabolic and have increased nutritional needs, yet research on nutritional supplementation and the relationship of supplementation to clinical outcomes has produced mixed findings.2–4 Consequently, although researchers and clinicians generally agree that nutritional status is important in critically ill patients, current guidelines5 are fairly broad, and the timing, type, and amount of supplemental feeding can vary considerably because of the range of underlying disease processes, the wide variation in patients’ responses to the same disease, and/or clinicians’ preferences.

The relationship between nutritional status and patients’ outcomes is of particular interest in chronically critically ill patients, that is, patients who survive the life-threatening phase of critical illness but have prolonged hospitalizations because of their dependence on critical care support services.6 Even after the clinical and hemodynamic conditions of these patients become stable, poor functional status, primarily manifested by dependence on mechanical ventilation, suggests that the patients may also experience adult failure-to-thrive syndrome, which is defined as a lower than expected level of functioning associated with nutritional deficits. Although this syndrome has been discussed primarily in relation to the elderly,7–10 it most likely exists in other populations of adults. Thus, factors such as nutritional supplementation have the potential to influence recovery and outcomes, but relatively little is known about the nutritional status of chronically critically ill patients. Complicating the challenge of understanding the relationship between nutrition and outcomes in chronically critically ill patients is the variation in methods of measuring both nutritional status and nutritional therapies. In this article, we discuss the multiple methods used to assess nutritional status in chronically critically ill adult patients, provide a description of the nutritional status of such patients, and assess the relationship between nutritional indicators and the outcomes of mechanical ventilation.

Assessment of Nutritional Status

Malnutrition in patients receiving mechanical ventilation has an adverse effect on all physiological processes. It increases the risk for infection and pulmonary edema, decreases phosphorus levels needed for cellular energy (adenosine triphosphate or ATP) production, reduces ventilatory drive, and impairs production of surfactant.3 Patients who are undernourished are prone to the complications of a prolonged and difficult course of weaning because of muscle fatigue caused by diaphragmatic and skeletal muscle weakness and/or reduced muscle endurance.4

Nutritional status is a multidimensional phenomenon that requires several methods of assessment, including nutrition-related health indicators, nutritional intake, and energy expenditure.2,11

Nutrition-Related Health Indicators

Nutrition-related health indicators include body mass index (BMI) and serum levels of albumin, prealbumin, hemoglobin, magnesium, and phosphorus.

Body weight is used to calculate BMI, a common anthropometric measure of nutritional status12–14 that is used in the diagnosis of obesity12,15,16 and undernutrition associated with clinical conditions.15

The most common measure of protein nutritional status in critically ill patients is the serum level of albumin. Supplemental feedings for chronically critically ill patients receiving long-term ventilation are now routine clinical interventions,17 yet studies continue to indicate that these patients have low albumin values during hospitalization.18 The low levels most likely reflect both nutritional status and prolonged physiological stress associated with the illness process and/or weaning. Critical illness decreases synthesis of albumin, causes a shift in the distribution of albumin from the vascular space to the interstitial space, and releases hormones that increase the metabolic destruction of albumin.19–22 Thus, albumin levels in critically ill patients must be considered an indicator of severity of illness as well as an indicator of protein nutritional status.

Low levels of albumin (<35 g/L) in an acutely ill patient indicate a depletion of body protein that results in protein catabolism and/or decreased sources of amino acids.23 Research has indicated a tentative relationship between protein nutritional status and the physical functioning of patients receiving mechanical ventilation. In 3 studies,24–26 differences in albumin levels between patients who died or remained ventilator dependent and patients who were successfully weaned were statistically significant. Conversely, however, Gluck27 found that albumin levels were not predictive of weaning success, and Sapijaszko et al28 found that albumin values at the time of admission to the intensive care unit (ICU) were not predictive of the duration of mechanical ventilation. Serum levels of prealbumin, which has a half-life of 5 days, are a more immediate indicator of physiological stress and nutrition during hospitalization but are less frequently monitored than are albumin levels in chronically critically ill patients. Decreases in the concentrations of prealbumin and albumin are mediated by the same mechanisms.22

Serum levels of hemoglobin and the trace elements magnesium and phosphorus are 3 additional biochemical indicators routinely used by clinicians to monitor nutritional status in chronically critically ill patients. The protein hemoglobin is used as an indicator of the blood’s oxygen-carrying capacity. Magnesium deficiency can be associated with acute diarrhea,29 a common occurrence in patients given enteral feedings, and magnesium and phosphorus are important in energy synthesis and wound healing. Abnormal levels of either magnesium or phosphorus can cause cardiac, neurological, and neuromuscular disorders.30–33

Nutritional Intake and Nutritional Adequacy

For chronically critically ill patients, nutritional intake to ensure nutritional adequacy is most often provided as nutritional supplementation through enteral or parenteral feedings. Researchers have examined types of feedings and problems and barriers associated with supplemental nutrition.

In a study34 of patients in long-term acute care facilities who were receiving mechanical ventilation, nutritional adequacy was defined as energy intake (kilocalories received on the basis of physician’ orders) divided by energy required (determined by indirect calorimetry). In this sample,34 25% of the patients received their required energy intake (90%–110% of requirements), 58% were overfed (>110% of requirements), and 12% were underfed (<90% of requirements). In 2 other studies,35,36 nutritional adequacy was defined as energy intake divided by energy requirements (in kilocalories) as indicated by physicians’ orders. In the first study,35 which involved patients in a medical ICU/coronary care unit who were receiving enteral tube feedings, 51.6% of the patients received their energy goal requirements. In the second study,36 which was an investigation of guidelines for nutritional support of patients receiving mechanical ventilation, patients in the sample received 44.6% of prescribed energy intake (kilocalories). In all 3 studies,34–36 under-ordering by physicians, amount of dietician support, and repeated interruptions of feedings contributed to insufficient delivery of supplemental feedings.

In a recent study, O’Leary-Kelley et al37 investigated nutritional adequacy in 60 patients receiving enteral feedings at prescribed rates. Nutritional adequacy (energy requirement) was defined as the amount of energy consumed divided by the amount required as calculated by the Harris-Benedict equation. Indirect calorimetry was used in a subset of 25 patients. During the 3-day period of data collection, 30% of the patients received their required energy, 2% were overfed, and 68% were underfed. The difference between the mean estimated energy requirements and the mean daily energy intake were significant, but no difference was found between estimated requirements and energy requirements as determined by indirect calorimetry. Five variables (number of episodes of diarrhea, episodes of emesis, feeding tube replacements, mean gastric residual volume, and the number of minutes tube feedings were withheld) accounted for more than 70% of the variance in the adequacy of enteral nutritional intake received (P <.001).

The relationship between supplemental feedings and clinical outcomes has also been investigated, although not in chronically critically ill patients. Here, too, the results were mixed. For patients who underwent liver transplantation, early tube feedings were associated with a reduction in overall infection rates but not with reductions in hospital costs, number of hours of mechanical ventilation, or number of days hospitalized.38 Using data from the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments, Borum et al39 found that coma patients who received enteral or parenteral types of supplemental feedings had improved survival rates 6 months after hospitalization. However, both enteral and parenteral feedings were associated with decreased survival in patients with adult respiratory failure or multiorgan system failure with sepsis.

Energy Expenditure

In the ICU, the energy needs of chronically critically ill patients can be determined through estimates based on a variety of guidelines. Energy demand is a function of multiple parameters, including body size and composition, age, and sex. A number of formulas have been used to calculate energy demand. The most well known of these is the Harris-Benedict equation.11,40 More recently, formulas have been developed to take into account abnormal physiological states, such as trauma, burns, and mechanical ventilation, that would markedly affect metabolic demand.41 However, although theoretically valid for large groups, all of these formulas have unpredictable errors when used to estimate energy demand in individual subjects.42,43

Indirect calorimetry is currently the recommended method of measurement of resting energy expenditure in critically ill patients.42,44 This method is an indirect measure of heat production; oxygen consumption and carbon dioxide production are measured directly,11,45 and the values are used in a standard equation to yield energy expenditure in kilocalories. Absolutely precise measurement of resting energy expenditure requires measurement in a thermoneutral environment; subjects must have been at rest for more than 30 minutes and without food for 2 hours. When applied to hospitalized patients receiving nutritional support, values provided by calorimetry reflect both energy requirements of the disease state and nutrient-induced thermogenesis.44

Methods

Setting and Sample

This natural history study was conducted at University Hospitals of Cleveland, Cleveland, Ohio, a 900-bed academic medical center with 70 beds for critical care of adults. The convenience sample of 360 chronically critically ill subjects was consecutively enrolled during a period of 14 months. All subjects in this sample were enrolled in a federally funded study. Patients were included if they were 18 years or older, had been receiving mechanical ventilation for more than 72 hours, had been hospitalized 7 days or more, had not been dependent on mechanical ventilation before admission, and had no neuromuscular condition that precluded weaning from mechanical ventilation. All patients had been admitted at least once to an ICU (cardiac, neuroscience, medical, or surgical). With the exception of the cardiac unit, all units were staffed by full-time physician intensivists.

Procedure

This study was approved by the hospital’s human subjects review board. All nutritional data were abstracted from patients’ records. A prospective, longitudinal design was used. For each patient, weekly data collection began on the day of enrollment in the study and continued for every 7th day until the patient died or was discharged from the hospital. Enrollment occurred after the patient had been receiving mechanical ventilation for more than 72 hours, and consent was obtained from the patient’s physician.

Clinical Management of Nutrition

At University Hospitals of Cleveland, 5 hospital dieticians provide services to adult patients. None of the dieticians works exclusively in the critical care units, and all function in a consultative role. Physicians and nurses routinely initiate nutrition referrals for ICU patients. Nutritional and dietary recommendations, along with periodic evaluations, are a permanent part of each patient’s record. Hospital policy also mandates nutritional assessment for certain patients, as required by the Joint Commission on Accreditation of Healthcare Organizations.

Every 7 days of the patient’s hospitalization, we collected nutritional status data for a continuous 24-hour period. Because critically ill patients often have their enteral or parenteral feedings interrupted, some patients did not receive their ordered feedings because of clinical, diagnostic, and/or surgical reasons. These patients were included in the analysis of data obtained at that weekly data collection point. However, if there was a physician’s order to withhold food and fluids, or the patient was able to take feedings orally, the patient was excluded from the data analysis for that weekly data collection point. Additionally, all dieticians’ recommendations were recorded weekly, but if no new or revised goals were recorded, a patient’s goals were assumed to be the same as those of the previous week or weeks.

The algorithms used by the dieticians were consistent with the guidelines5 recommended by the American College of Chest Physicians for calculating total energy need per 24 hours: 105 to 126 kJ (25–30 kcal) per kilogram of body weight for mild to moderate stress and 126 to 146 kJ (30–35 kcal) per kilogram of body weight for catabolic injury (eg, sepsis, trauma). The study variables were nutrition-related health indicators, nutritional intake, nutritional adequacy, and energy expenditure.

Nutrition-related health indicators were BMI (calculated as weight in kilograms divided by the square of height in meters) at the time of hospital admission and at discharge and serum levels of albumin, prealbumin, hemoglobin, magnesium, and phosphorus. All indicators were measured as part of routine clinical care. For chronically critically ill patients who received nutritional supplementation (enteral and/or parenteral feedings), nutritional intake (24-hour energy intake) was measured both as physicians’ feeding orders and as patients’ intake.

Nutritional adequacy was assessed by using calculations of 4 ratios: patients’ intake compared with physicians’ orders, patients’ intake compared with dieticians’ recommendations, physicians’ orders compared with dieticians’ recommendations, and patients’ intake compared with values determined by using indirect calorimetry. Nutritionist Pro software (2004 version, First DataBank, Inc, San Bruno, Calif) was used to calculate energy intake provided by enteral and parenteral feedings.

Energy expenditure was measured by using indirect calorimetry while the patients were receiving mechanical ventilation. All tests were conducted by licensed respiratory therapists using the Puritan Bennett 7250 Metabolic Monitor (Puritan Bennett, Pleasanton, Calif). The measurement was obtained by calculating the mean of 7 readings gathered in 5-minute intervals during a period of 30 minutes. Although indirect calorimetry is available as a clinical assessment tool, it is not widely used in the critical care units at University Hospitals of Cleveland. In addition to the availability of respiratory therapists, several factors related to patients precluded use of indirect calorimetry: high levels of nitric oxide, need for high fractions of inspired oxygen or high levels of positive end-expiratory pressure, weaning status, rapid extubation, and dialysis.

Missing Data

The use of chart review allowed collection of data on a large number of subjects, but one of its primary limitations, missing data, was a factor in this study. This limitation was an issue for the information on variables collected on a weekly basis even though data collection included a 72-hour window around the designated weekly date. Although this interval may seem lengthy, an extended window of time reflects the clinical reality of chronically critical ill patients, because laboratory work often is not done on a daily basis.46

Data Analysis

With data collection dependent on patients’ length of stay, the number of times data were collected for each patient varied widely, from 1 to 12 times (mean 2.7, mode 1). Nutritional data for the first 8 data collection points are reported here because only 5 patients had data collected for 9 weeks and only 1 patient had 12 data collection points. Three team members collected study data. Inter-rater reliability for data collection was evaluated quarterly and was always greater than 90%. Multivariate analyses were conducted by using SPSS software, version 11.5 (SPSS Inc, Chicago, Ill), with the significance level set at .05.

Results

Characteristics of the Sample

The characteristics of the sample are given in Table 1. Dieticians were consulted for 83% of all patients in the study (91% of the survivors). Of the patients who received supplemental nutrition, most (85%) received enteral feedings only.

Table 1.

Demographic and illness-related characteristics of the sample

Variable Mean (SD) Median Range No. of patients
Age, y 62.3 (16.4) 63.0 18–96 360
Score on Acute Physiology and Chronic Health Evaluation III 75.5 (28.9) 74.0 20–177 360
Episodes of mechanical ventilation 1.3 (0.6) 1.0 1–5 360
Duration of mechanical ventilation, days 12.6 (9.8) 9.0 3–53 360
Length of hospital stay, days 24.2 (16.9) 19.0 7–111 360
Length of intensive care unit stay, days 17.6 (14.2) 13.0 3–95 359
No. of medications taken before admission to the hospital 5.1 (3.8) 5.0 0–18 340
No. of preexisting conditions 5.8 (3.4) 5.0 0–20 360
Duration of mechanical ventilation before attempts at weaning, days 6.6 (7.6) 4.0 0–47 360
Time required for weaning, days 3.8 (6.0) 1.0 0–44 360
Variable No. of patients %
Sex
 Female 202 56
 Male 158 44
Living status before hospitalization
 Home 325 90
 Nursing home, hospital, rehabilitation facility, assisted living facility 35 10
Type of admission
 Planned 51 14
 Unplanned 308 86
Primary diagnostic classification*
 Neurological 85 24
 Respiratory 73 20
 Cardiologic 60 17
 Gastrointestinal 52 14
 Genitourinary, hematologic, metabolic, trauma 35 10
 Infectious disease 31 9
 Miscellaneous (eg, overdose, obstetric complications) 24 7
Weaning outcome
 Spontaneous respiration 229 64
 Total or partial ventilator support 131 36
Disposition
 Died 119 33
 Long-term care 193 54
 Home 48 13
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*

Percentages total more than 100 because of rounding.

Health-Related Indicators

According to BMI data collected at the time of admission, 40% (124/312) of the patients were obese (BMI ≥ 30) and remained so throughout their hospitalization (Table 2). A total of 5% (16/312) had a BMI less than 18.5. Values at the time of admission and discharge and mean values during hospitalization were calculated for all biochemical indicators. Mean albumin and hemoglobin values were low at the time of admission and remained low throughout hospitalization. Mean prealbumin values were less than normal throughout hospitalization but tended to increase. Levels of magnesium and phosphorus were within the normal reference range and were stable throughout hospitalization.

Table 2.

Admission, in-hospital, and discharge nutrition data

Variable* Mean (SD) Median Range No. of patients
Body mass index†
 Admission 30.0 (9.7) 28.1 14–78 312
 Discharge 30.8 (9.6) 28.7 15–71 192
Serum albumin, g/L
Reference range, 34–50
 First time point 30 (7) 29 10–63 280
 Mean‡ 27 (10) 26 9–87 218
 Discharge 26 (6) 25 15–45 103
Hemoglobin, mg/dL
Reference range: men 12.0–16.0, women 13.5–17.5
 First time point 10.4 (1.7) 10.4 2.7–17.7 358
 Mean‡ 10.4 (1.5) 10.3 3.3–18.3 358
 Discharge 10.5 (1.6) 10.4 3.3–18.8 358
Magnesium, mmol/L
Reference range, 0.7–1.05
 First time point 0.9 (0.14) 0.9 0.55–1.45 352
 Mean‡ 0.9 (0.15) 0.9 0.6–1.3 354
 Discharge 0.9 (0.17) 0.9 0.6–1.2 354
Magnesium, mEq/L
Reference range, 1.4–2.1
 First time point 1.8 (0.27) 1.8 1.1–2.9 352
 Mean‡ 1.8 (0.24) 1.8 1.2–2.6 354
 Discharge 1.8 (0.33) 1.8 1.2–2.4 354
Phosphorus, mmol/L
Reference range, 0.81–1.45
 First time point 1.10 (0.45) 1.00 0.16–3.29 334
 Mean‡ 1.13 (0.36) 1.10 0.45–2.68 345
 Discharge 1.16 (0.45) 1.10 0.42–3.49 345
Phosphorus, mg/dL
Reference range, 2.5–4.5
 First time point 3.4 (1.4) 3.1 0.5–10.2 334
 Mean‡ 3.5 (1.1) 3.4 1.4–8.3 345
 Discharge 3.6 (1.4) 3.4 1.3–10.8 345
Prealbumin, g/L
Reference range, 180–400
 First time point 104 (62) 91 30–303 103
 Mean‡ 145 (70) 139 30–379 196
 Discharge 158 (79) 146 30–382 195
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*

Values for albumin and prealbumin are reported in SI units. To convent to conventional units (g/dL), divide by 10. Hemoglobin is reported in conventional units. Magnesium and phosphorus are dually reported in both SI units and conventional units.

†

Body mass index was calculated as weight in kilograms divided by the square of height in meters. Categories are underweight, <18.5, normal weight 18.5–24.9, overweight 25–29.9, and obesity ≥30.16

‡

Mean of all laboratory values during hospitalization.

At the time of admission to the study, the majority of the patients (272/347, 78%) had orders for supple-mental nutritional feedings, 59 (17%) were not allowed anything by mouth, and 14 (4%) were able to take feedings orally. Of the 272, 11 did not receive any of their physician-ordered supplemental feedings; the remainder received all or part of the ordered feeding (mean 83%, SD 33%, range 0%–200%). Eight different types of formula were used for enteral feedings; the majority of the patients (75%) received general-use, renal, or pulmonary formulas.

Nutritional Adequacy

Using 3 nutritional designations, underfeeding (<90% of energy requirements), appropriate feeding (90%–110% of energy requirements), and overfeeding (>110% of energy requirements),34 we calculated the percentage of patients in each category and compared patients’ intake, physicians’ orders, and dieticians’ recommendations for the 8 weekly time points. Figure 1 compares patients’ intake with physicians’ orders; Figure 2, patients’ intake with dieticians’ recommendations; Figure 3, physicians’ orders with dieticians’ recommendations; and Figure 4, patients’ intake with results of indirect calorimetry.

Figure 1.

Figure 1

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Comparison of patients’ energy intake with intake ordered by physicians.

Figure 2.

Figure 2

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Comparison of patients’ energy intake with intake recommended by dieticians.

Figure 3.

Figure 3

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Comparison of patients’ energy intake ordered by physicians with intake recommended by dieticians.

Figure 4.

Figure 4

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Comparison of patients’ energy intake with intake indicated by indirect calorimetry.

For the entire 738 patient days that patients had orders for supplemental nutrition, the patients received a mean of 83% of the energy intake ordered by their physicians (SD 27%, range 0%–163%) and 68% of the dieticians’ recommended intake (SD 33%, range 0%–219%). However, according to indirect calorimetry, the patients received 105% (SD 96%, range 24%–614%) of their energy requirements. On average, the amounts the physicians ordered were 84% (SD 31%, range 9%–219%) of the intake recommended by dieticians.

Nutritional Status and Mechanical Ventilation

In the final level of analyses, we investigated relationships between indicators of nutritional status and 4 clinical variables related to mechanical ventilation: time required for weaning, duration of mechanical ventilation, number of episodes of mechanical ventilation, and weaning outcome. We found few clinically or statistically significant relationships between variables for nutritional status and variables for mechanical ventilation.

Of the nutritional indicators in Table 2, we detected positive relationships between duration of mechanical ventilation and (1) mean levels of phosphorus (r = 0.12, P = .03) during hospitalization and (2) levels of prealbumin (r = 0.25, P < .001) at the time of discharge. We detected inverse relationships between duration of mechanical ventilation and (1) levels of albumin (r = −0.14, P=.02) at the time of admission, (2) mean levels of hemoglobin during hospitalization (r= −0.12, P= .03), and (3) levels of hemoglobin (r = −0.12, P = .05) at the time of discharge. For time required for weaning, we detected statistically significant relationships with (1) mean levels of albumin (r = 0.13, P = .05) during hospitalization and (2) levels of prealbumin (r=0.15, P=.03) at the time of discharge. Interestingly, duration of mechanical ventilation was not related to age or to scores on the Acute Physiology and Chronic Health Evaluation III but was related to the number of preexisting medical conditions (r = 0.14, P = .01). We also detected no statistically significant differences in duration of mechanical ventilation among the 3 nutritional designations (underfeeding, appropriate feeding, and overfeeding).

The 43 patients who were treated with mechanical ventilation more than once received a greater percentage of ordered energy intake throughout their hospitalization than did patients who were treated with mechanical ventilation only once (90% vs 80%; Mann-Whitney U = 5436, P = .05). Patients who required partial or total ventilator support at the time of discharge (n = 131) had lower admission BMI values than did patients with spontaneous respirations at the time of discharge (27.4 vs 31.4; Mann-Whitney U=8441, P=.001).

Discussion

Our study had 3 primary purposes: to discuss the multiple methods used to assess nutritional status in chronically critically ill patients, describe the nutritional status of chronically critically ill patients, and assess the relationship between nutritional indicators and outcomes of mechanical ventilation. The nutritional practice patterns reported here are from a single academic tertiary medical center with a mixed medical-surgical population. The findings are not generalizable to community-based ICUs, where Heyland et al47 found that different nutritional practices can result in later initiation of feedings and/or provision of less than prescribed energy requirements from enteral feedings. The limitations of that study47 include its convenience sample and the dependence on chart abstraction. The strength of our study, however, is that its longitudinal design includes weekly data points across each patient’s hospitalization and multiple indicators of clinical practice and outcomes.

Investigations designed to determine if patients with extremely low or extremely high body weights have different nutritional requirements than do patients with normal body weights are needed. In contrast to the BMI statistics, the laboratory data indicate that at the time of admission or early in their hospital stay, most of the patients in our study had considerable deficits in albumin, prealbumin, and hemoglobin. One explanation for this finding is the source of the admission: 48% of our patients were transferred from other institutions and 36% were admitted from the hospital’s emergency department. A second explanation is related to severity of illness. Typically, mean scores on the Acute Physiology and Chronic Health Evaluation III for all patients admitted to an ICU are 46.9 (SD 27.6) regionally48 and 34.2 (SD 24.6) nationally,49 whereas the mean score in our study was 77. The mean laboratory values during hospitalization and at discharge also reveal, however, that many of the survivors in our study never recovered from these deficits despite aggressive medical treatment that included supplemental nutrition.

Implementing nutritional supplementation in chronically critical ill patients produces unique challenges for critical care clinicians. No known guidelines specifically address the nutritional needs of chronically critically ill patients; however, the American College of Chest Physicians suggests that written recommendations for management of nutritional supplementation of all critically ill patients include the following5

  • Total energy intake required should be measured directly or estimated.

  • A total of 105 kJ (25 kcal) per kilogram of usual body weight per day is adequate for most patients.

  • Nutritional status should be monitored routinely.

  • The enteral route is the preferred route of feeding.

  • An anabolic state should be maintained, but overfeeding should be avoided.

The precise time frame for initiating feedings is unknown; however, supplemental feedings are recommended for patients who are not likely to resume oral feedings within 7 to 10 days.50

Our data indicate that 4 of the 5 criteria of the American College of Chest Physicians were fulfilled in a timely fashion in the majority of our patients. The patients had written estimations of required energy intake well within the first week of intubation, and the dieticians’ recommendations followed the suggested algorithm for calculation of energy needs. The majority of the patients were receiving supplemental nutrition by day 7, all patients had routine monitoring of their nutritional status, and the enteral route was the preferred route of feeding.

The subject of nutritional adequacy also is clouded by the numerous methods used to determine optimal energy needs and lacks consensus among experts. Although measuring energy expenditure by using indirect calorimetry is considered the gold standard, often use of this method is not possible because of lack of resources and/or complicating clinical factors. In our sample, indirect calorimetry was not part of routine clinical care, and we obtained only 50 indirect calorimetry measurements in a sample of 360 subjects. McClave et al34 used energy received divided by energy required (measured via indirect calorimetry) to define nutritional adequacy, and in 2 other studies,35,36 nutritional adequacy was defined as patient’s energy intake divided by energy intake ordered by physicians. O’Leary-Kelley et al37 defined nutritional adequacy as the amount of energy consumed by the amount required as measured by the Harris-Benedict equation.

On the basis of the 3 designations of nutritional adequacy of McClave et al,34 56% of our patients were underfed, 30% were overfed, and 14% received feeding within 10% of required energy intake. The percentage of patients overfed is markedly less than the percentage of patients (58.2%) who were overfed in the study by McClave et al34 of patients receiving mechanical ventilation in 32 long-term acute care hospitals. In addition to variation in physicians’ orders, a potential reason for this discrepancy is severity of illness in the hospitalized setting.

Clinicians need better information about organizational factors that affect nutrition management and the effect of nutritional adequacy on hospital outcomes related to mechanical ventilation and discharge disposition. This increased understanding is crucial for chronically critically ill patients who survive hospitalization but continue their recovery in extended care facilities. In our sample of chronically critically ill patients, the variability in weaning progression and outcomes most likely reflects illness severity and complexity rather than patients’ age, nutritional status, or nutritional therapies. Therefore, further studies are needed to determine the best methods to define nutritional adequacy and to evaluate the nutritional status of patients, because little evidence indicates that underfeeding contributes to inferior outcomes more than standard nutritional management does.51 In addition, a continuing need exists for well-designed clinical trials related to management of all aspects of nutritional supplementation.50,52

Acknowledgments

This research was done at Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio. Support was provided by grant NINR-05005 from the National Institutes of Health.

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