Should indirect calorimetry be used as part of nutritional assessment?

The use of indirect calorimetry in the design of nutritional support regimens is poorly appreciated by clinicians, who fail to recognize the importance of providing a sufficient volume of enteral feeding to critically ill patients. In contrast to the overfeeding that routinely occurred in the past with the provision of total parenteral nutrition, patients placed on the enteral route of support tend to be underfed because of problems with intolerance and frequent cessation. Clearly identifying and coming as close as possible to the caloric goal may be required to achieve the therapeutic endpoints of enteral tube feeding (which include maintenance of gut integrity, attenuation of the stress response, prophylaxis against stress-induced gastropathy, and stimulation of immune function). Indirect calorimetry is a convenient, accessible, and highly accurate instrument for the measurement of caloric requirements and is a valuable tool for the optimization of nutritional support in the intensive care unit.

Dissecting the energy needs of the body.

The majority of the resting energy expenditure can be explained by the energy needs of a few highly metabolic organs, making up a small percentage of the body by weight. The relationship of the specific size, individual metabolism, and proportional contribution to the actual body weight and total energy expenditure for each of these organs is a dynamic process throughout growth and development, the onset of disease, and changes in nutritional status. Defining the energy needs of the individual tissues and organ systems immeasurably enhances our understanding of the body's response to these clinical processes, which otherwise could not easily be evaluated by focusing solely on total energy expenditure, fat-free mass, nitrogen imbalance, or actual body weight. Recently reported studies have served mainly to reinforce concepts described previously, and clarify some areas of controversy.

Infusion protocol improves delivery of enteral tube feeding in the critical care unit.

BACKGROUND: Numerous factors may impede the delivery of enteral tube feedings (ETF) in the intensive care unit (ICU). We designed a prospective study to determine whether the use of an infusion protocol could improve the delivery of ETF in the ICU. METHODS: In a prior prospective study, we monitored all patients admitted to the medical intensive care unit (MICU) or cardiac care unit (CCU) who were made nil per os and placed on ETF (control group). We found that critically ill patients received only 52% of their goal calories, primarily due to physician underordering (66% of goal), frequent cessations of ETF (22% of the time), and slow advancement (14% at goal by 72 hours). Based on these findings, we developed an ETF protocol that incorporated standardized physician ordering and nursing procedures, rapid advancement, and limited ETF interruption. After extensive educational sessions, the ETF protocol was begun. Again, all patients admitted to the MICU or CCU who were made nil per os and placed on ETF were prospectively followed (protocol group). RESULTS: Thirty-one patients in the protocol group were followed during 312 days of ETF and compared with the control group (44 patients with 339 days of ETF). Despite efforts by the nutritional support team, the infusion protocol was used in only 18 patients (58%). The main reasons for noncompliance with the protocol were physician preference and system failure (ETF order sheet not placed in chart). When used, the infusion protocol improved physician ordering (control 66% of goal volume, noncompliant 68%, compliant 82%, p < .05); delivery of calories (control 52% of goal, noncompliant 55%, compliant 68%, p < .05); and advancement of ETF (control 14% at goal by 72 hours, noncompliant 31%, compliant 56%, p < .05). Although significant reduction in ETF cessation due to nursing care was noted, it represented only a fraction of the total time ETF were stopped. Cessation due to residual volumes, patient tolerance, and procedure continued to be a frequent occurrence and was often avoidable. CONCLUSIONS: An evidence-based infusion protocol improved the delivery of ETF in the ICU, primarily because of better physician ordering and more rapid advancement. The nursing staff rapidly assimilated these changes. However, physicians' reluctance to use the protocol limited its efficacy and will need continued educational efforts.

Enteral tube feeding in the intensive care unit: factors impeding adequate delivery.

OBJECTIVE: To evaluate those factors that impact on the delivery of enteral tube feeding. DESIGN: Prospective study. SETTING: Medical intensive care units (ICU) and coronary care units at two university-based hospitals. PATIENTS: Forty-four medical ICU/coronary care unit patients (mean age, 57.8 yrs; 70% male) who were to receive nothing by mouth and were placed on enteral tube feeding. INTERVENTIONS: Rate of enteral tube feeding ordered, actual volume delivered, patient position, residual volume, flush volume, presence of blue food coloring in oropharynx, and stool frequency were recorded every 4 hrs. Duration and reason for cessation of enteral tube feeding were documented. MEASUREMENTS AND MAIN RESULTS: Physicians ordered a daily mean volume of enteral tube feeding that was 65.6% of goal requirements, but an average of only 78.1% of the volume ordered was actually infused. Thus, patients received a mean volume of enteral tube feeding for all 339 days of infusion that was 51.6% of goal (range, 15.1% to 87.1%). Only 14% of patients reached > or = 90% of goal feeding (for a single day) within 72 hrs of the start of enteral tube feeding infusion. Of 24 patients weighed before and after, 54% were noted to lose weight on enteral tube feeding. Declining albumin levels through the enteral tube feeding period correlated significantly with decreasing percent of goal calories infused (p = .042; r2 = .13). Diarrhea occurred in 23 patients (52.3%) for a mean 38.2% of enteral tube feeding days. In >1490 bedside evaluations, patients were observed to be in the supine position only 0.45%, residual volume of >200 mL was found 2.8%, and blue food coloring was found in the oropharynx 5.1% of the time. Despite this, cessation of enteral tube feeding occurred in 83.7% of patients for a mean 19.6% of the potential infusion time. Sixty-six percent of the enteral tube feeding cessations was judged to be attributable to avoidable causes. CONCLUSIONS: The current manner in which enteral tube feeding is delivered in the ICU results in grossly inadequate nutritional support. Barely one half of patient caloric requirements are met because of underordering by physicians and reduced delivery through frequent and often inappropriate cessation of feedings.

Preoperative issues in clinical nutrition.

Allowing a patient's nutritional state to deteriorate through the perioperative period adversely affects measureable outcome related to nosocomial infection, multiple organ dysfunction, wound healing, and functional recovery. Careful preoperative nutritional assessment should include a determination of the level of stress, an evaluation of the status of the GI tract, and the development of specific plans for securing enteral access. Patients already demonstrating compromise of nutritional status (defined by > 10% weight loss and serum albumin level < 2.5 g/dL) should be considered for a minimum of 7 to 10 days of nutritional repletion prior to surgery. Widespread use of total parenteral nutrition in unselected patients is unwarranted, may actually worsen outcome, and should be reserved for preoperative nutritional support only in severely malnourished patients in whom the GI tract is unavailable. Compared with the parenteral route, use of perioperative enteral feeding has been shown to provide more consistent and beneficial results, and can be expected to promote specific advantages in long-term morbidity and mortality.

Nutritional management in acute and chronic pancreatitis.

Patients with severe pancreatitis, characterized by multiple organ failure and pancreatic necrosis on CT scan (identified by an Acute Physiology and Chronic Health Evaluation II score of > or = 10 with > or = 3 Ranson criteria), most likely require aggressive nutritional support. Use of the enteral route of feeding may help contain the hypermetabolic stress response, reduce morphologic change and atrophy of the gut, and theoretically decrease late complications of nosocomial infection and organ failure. Evidence that decreasing degrees of stimulation of the pancreas occur as the site of feeding descends in the gastrointestinal tract and evidence from perspective, randomized trials suggest that jejunal feeding appears at least as safe and well tolerated as total parenteral nutrition in acute pancreatitis.

Comparison of the safety of early enteral vs parenteral nutrition in mild acute pancreatitis.

BACKGROUND: This prospective study was designed to compare the safety, efficacy, cost, and impact on patient outcome of early total enteral nutrition (TEN) vs total parenteral nutrition (TPN) in acute pancreatitis. METHODS: Patients admitted with acute pancreatitis or an acute flare of chronic pancreatitis, characterized by abdominal pain and elevated serum amylase and lipase, were randomized to receive either isocaloric and isonitrogenous TEN (via a nasojejunal feeding tube placed endoscopically) or TPN (via a central or peripheral line) started within 48 hours of admission. RESULTS: Thirty patients were studied over 32 admissions (TEN given on 16 and TPN on 16) for acute pancreatitis. There were no differences on admission in mean age, Ranson criteria, multiple organ failure score (MOF), or APACHE III score between TEN and TPN groups. Although slower to approach goal feeding over the first 72 hours of admission, TEN patients received 71.3% goal calories by day 4 vs 85.2% for TPN patients (not significant). There were no deaths and no differences between groups in serial pain scores, days to normalization of amylase, days to diet by mouth, serum albumin levels, or percent nosocomial infection. However, the mean cost of TPN per patient was over four times greater than that for TEN ($3294 vs $761, respectively, p < .001). Mean serial Ranson criteria, APACHE III, and MOF scores recorded every 2 to 3 days decreased in the TEN group, whereas those in the TPN group increased. Only the difference in the third Ranson criteria (mean 6.3 days after admission) for the TEN and TPN groups (0.5 vs 2.8, respectively) reached statistical significance (p = .002). Stress-induced hyperglycemia was worse in the TPN group, as serum glucose levels increased significantly over the first 5 days of hospitalization (p < .02), whereas those in the TEN group showed no significant change. An exacerbation of pancreatitis, occurring in one TEN patient when the nasojejunal tube was dislodged into the stomach, resolved after placement back in the jejunum. Three patients who became asymptomatic and normalized amylase on TEN flared upon advancing to diet by mouth. CONCLUSIONS: TEN for acute pancreatitis is as safe and effective, but is significantly less costly than TPN. Compared with TPN, TEN may promote more rapid resolution of the toxicity and stress response to pancreatitis. TEN via jejunal feeding should be used preferentially in this disease setting.

Understanding the metabolic response to critical illness: factors that cause patients to deviate from the expected pattern of hypermetabolism.

Resting energy expenditure is comprised by the sum of the metabolic needs of the peripheral tissues and individual organ systems, influenced by an interaction between thyroid hormone and the sympathetic nervous system. Multiple primary, secondary, and tertiary factors affect this sum to generate the total energy expenditure. Disease processes may increase energy expenditure through direct (stimulating the sympathetic nervous system, increasing oxygen delivery, raising body temperature, increasing motor activity) or indirect processes (uncoupling effect, inefficient metabolism, release of cytokine mediators). Not all patients demonstrate the classic hypermetabolic response. A number of factors involving treatment, weight, choice of predictive formula, timing of the metabolic study, nutritional support, and level of consciousness may contribute in a factitious manner to a hypometabolic response. In some patients, a true serial progressive pattern of inappropriate low metabolism may imply impending septic shock and identifies that patient at risk for organ failure and increased mortality. Serial indirect calorimetric studies may be needed in the intensive care setting to adequately establish patterns of response to critical illness.

Primary spontaneous pneumothorax. Therapeutic considerations.

Primary pneumothorax represents the single most frequent cause of admission of young adults to a hospital's thoracic service. However, the best management of these patients with rupture of subpleural blebs in the apical region remains controversial. In a retrospective analysis of 108 consecutive patients with spontaneous primary pneumothorax treated at a university hospital over a 5-year period, we were able to examine the risks and benefits of various treatment approaches. Interestingly, although male patients outnumbered female patients approximately 2:1, female patients were statistically more likely to undergo operative intervention.

Use of indirect calorimetry in clinical nutrition.

The tremendous variability in resting energy expenditure makes efforts to predict caloric requirements difficult. Indirect calorimetry has provided a valuable tool in assessing energy expenditure, evaluating the way in which the body uses nutrient fuel, and designing nutritional regimens that best fit the clinical condition of the patient. The many indirect calorimetric instruments available vary in their application to clinical nutrition. The best metabolic studies are achieved by controlling the testing environment, accounting for the many clinical factors that may affect measurements, and eliminating potential sources for error. Although indirect calorimetry would seem to reduce the likelihood of complications from overfeeding, its greatest effect may be in cost savings by avoiding unnecessary nutritional support and in providing a means for clinical research.

Immunonutrition and enteral hyperalimentation of critically ill patients.

Physicians need to be maximally aggressive in their use of total enteral nutrition (TEN) in the critically ill patient, due to its lower cost, better physiology, and lower complication rate when compared to parenteral therapy. Various components in TEN such as glutamine, arginine, RNA nucleotides, omega-3 fish oils, and fiber, may have important roles in immunonutrition by maintaining gut integrity, stimulating the immune system, and preventing bacterial translocation from the gut. For each patient, the physician must choose the optimal enteral formula for that particular disease or organ failure state to maximize nutrient substrate assimilation and tolerance. Total parenteral nutrition (TPN) should be used only when a true contraindication to enteral feedings exists or as adjunctive therapy when full nutritional requirements cannot be met by TEN alone.

Use of residual volume as a marker for enteral feeding intolerance: prospective blinded comparison with physical examination and radiographic findings.

High gastric residual volumes (RVs) are a frequent cause for cessation of total enteral nutrition (TEN). This study was designed to determine the RV that indicates intolerance or inadequate gastric emptying and to compare the RV findings in a blinded fashion with those findings obtained on physical examination and radiography. Twenty healthy normal volunteers (HNV), 8 stable patients with gastrostomy tubes (GTP), and 10 critically ill patients (CIP) were evaluated prospectively for 8 hours while receiving TEN. No subjects were clearly intolerant (ie, vomiting, aspiration). Of the total RVs recorded, 13.1% were greater than or equal to 150 mL in the CIP group, whereas only 2.4% of the RVs were greater than or equal to 150 mL in the HNV group. None of the RVs in the GTP group were greater than or equal to 150 mL. Objective scores on physical examination failed to correlate with RV (p = .397), as did objective scores on radiography (p = .742). However, objective scores on physical examination were significantly related to scores on radiography (p = .016). Abnormal physical examination findings were found in 4 out of 11 patients (GTP + CIP) with RVs less than 100 mL and in 6 out of 7 with RVs greater than or equal to 100 mL. Abnormal radiographic results were found in 6 out of 11 patients with RVs less than 100 mL, in 7 out of 7 patients with RVs greater than or equal to 100 mL, and in 4 out of 20 HNVs. There was no difference in RVs obtained from the supine or right lateral decubitus positions.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of an aldose reductase inhibitor on cardiovascular performance in patients with diabetes mellitus.

Because some aldose reductase inhibitor studies have demonstrated clinical improvement in scored neurological signs and symptoms of diabetic neuropathy, a prospective study of the effect on cardiovascular performance of sorbinil 250 mg/day for 12 months was conducted on patients with diabetic autonomic neuropathy who were free of atherosclerotic coronary artery disease and/or cardiomyopathy. After 1 year of treatment, the study group (n = 14) demonstrated significant improvement in both the resting cardiac output (P = 0.02), and the maximal cardiac output (P = 0.03). This observation suggests that the use of an aldose reductase inhibitor may be useful in treating suboptimal cardiovascular performance in patients with diabetic cardiac autonomic neuropathy.

Pulmonary complications after tricyclic antidepressant overdose.

We studied 82 consecutive patients admitted to the ICU with predominant tricyclic antidepressant overdose (mean plasma tricyclic level, 1,025 ng/ml) to determine the nature and incidence of respiratory complications. The majority of patients (80.4 percent) had a decreased arterial to alveolar oxygen tension ratio (PaO2/PAO2) on initial emergency room arterial blood gas analysis (mean, 0.56). Mechanical ventilation was required in 76.8 percent of the patients for a mean duration of 46.2 h. Chest radiograph abnormalities developed during the first 48 h in 32/82 patients (39 percent). The group with radiographic abnormalities had higher mean drug levels than the group without (p less than 0.05). Of 82 patients, nine (11 percent) developed radiographic evidence of bilateral alveolar infiltrates suggestive of acute lung injury. This group had significantly higher mean drug levels than the groups with other types of radiographic abnormalities (p less than 0.001). Charcoal was recovered from the airway of 18/72 patients who received activated charcoal slurry by nasogastric tube in the emergency room after endotracheal intubation. The group who aspirated did not show statistically significant difference in the incidence of chest radiograph abnormalities, gas exchange, or survival compared with the group that did not aspirate.

Autonomic influence on cardiovascular performance in diabetic subjects.

PURPOSE: Cardiomyopathy, coronary artery atherosclerosis, or autonomic neuropathy may affect the cardiovascular performance of the diabetic patient. To evaluate the role of parasympathetic nervous system activity on cardiovascular performance, 25 diabetic subjects who lacked symptoms, signs, or objective measurements of ischemia or cardiomyopathy were studied. PATIENTS AND METHODS: Diabetic subjects were classified according to their RR variation, an index of cardiac parasympathetic nervous system activity. Fourteen diabetic subjects had a normal RR variation of greater than 30 (D-NOR), and 11 diabetic patients had an abnormal RR variation of less than 20 (D-ABN). Fifteen age- and weight-matched, healthy, nondiabetic subjects (NOR) constituted the control group. All subjects had oxygen consumption, multigated acquisition determination of cardiac output, and work product measured before and during supine bicycle maximum exercise testing. RESULTS: There was no difference in the resting cardiac output among the groups. Resting work product, however, was greatest in the D-ABN group when compared with performance in the other two groups (D-ABN: 11,500 +/- 800; D-NOR: 9,000 +/- 600; NOR: 8,700 +/- 400; p less than 0.0025). This was due to an increase in both heart rate (p less than 0.025) and systolic blood pressure (p less than 0.015). In the diabetic subjects, there was an inverse relationship between the RR variation and resting work product (r = 0.47, n = 25, p less than 0.005). In response to exercise, the percent increase in cardiac output at matched percent maximum oxygen uptake was greatest in the NOR, D-NOR, and D-ABN groups, respectively (analysis of variance, p less than 0.01). In the diabetic subjects, there was a significant relationship between the RR variation and the maximum percent change in cardiac output (r = 0.41, n = 25, p less than 0.02). Compared with the NOR group, the maximum increase in work product was impaired in diabetic subjects (p less than 0.002) and not different between the D-NOR and D-ABN groups. CONCLUSIONS: The increase in resting work product and the poor cardiac output responses to exercise in the D-ABN group are due to a decrease in cardiac parasympathetic nervous system activity and can be suggested by an abnormal RR variation. This index of parasympathetic nervous system activity can help the physician identify that subset of diabetic patients that may need special consideration when exercise training is prescribed.

Cigarette smoking and federal black lung benefits in bituminous coal miners.

The records of 1000 consecutive coal miners applying for benefits under the Federal Coal Mine Health and Safety Act were examined to determine the contribution of age, dust accumulation, and cigarette smoking to the profile of the miner who satisfies the current pulmonary criteria for disability. Using the presence of pneumoconiosis on chest radiograph as the indication of significant coal dust accumulation, the miners were separated into Group A--those without pneumoconiosis (n = 316) and Group B--those with pneumoconiosis (n = 684). The federal spirometric criteria for disability identified 55/316 miners in Group A (14.5%) and 99/684 miners in Group B (17.4%) potentially eligible for an award (P = .27). The mean ages of miners in both groups did not differ significantly, nor was there difference in the mean ages of groups that did or did not meet the federal criteria. In both groups, those miners potentially eligible for a financial award smoked more cigarettes than did their counterparts (Group A, 31.0 v 18.5 pack-years, P less than .001; Group B, 31.3 v 23.6 pack-years, P less than .001). There was no difference in the smoking histories of the miners from either group who met the federal criteria. Our data indicate that, in the case of bituminous coal miners, the present federal legislation intended to identify and remunerate those who suffer lung impairment from chronic occupational exposure to coal dust is biased in favor of those who sustain additional damage to their ventilatory capacity by smoking cigarettes.

Resting gas exchange in nonsmoking bituminous-coal miners with simple pneumoconiosis.

Gas exchange at rest under normoxic conditions was studied in 2,297 nonsmoking bituminous-coal miners with and without simple coal workers' pneumoconiosis (CWP). Measurements of arterial oxygen tension (Pao2) and arterial carbon dioxide tension (Paco2) from blood gas samples obtained at rest in the seated position were used to calculate the alveolar-arterial oxygen tension difference, (A-a)Do2, using the classic alveolar-air equation. We then recalculated the (A-a)Do2 using the age-predicted Pao2 for each miner. The difference between the actual and the predicted (A-a)Do2 was measured and the mean difference for each category of simple CWP was analyzed. We found no evidence that the resting gas exchange differs significantly from the age-predicted (A-a)Do2 in the nonsmoking bituminous-coal minor with simple CWP. Likewise, there is no significant change in (A-a)Do2 with change in the category of simple CWP.