Basic Principles of Intravenous Nutritional Support

Standard Equations Are Not Accurate in Assessing Resting Energy Expenditure in Patients With Amyotrophic Lateral Sclerosis

OBJECTIVE

To assess the utility of standard equations for calculating caloric requirements in patients with amyotrophic lateral sclerosis (ALS).

BACKGROUND

Malnutrition substantially increases the risk of death in ALS. Weight loss can be stabilized and survival prolonged with early gastrostomy feeding. However the use of standard nutrition equations has not been validated in this population. We therefore compared measured caloric expenditure to 2 predictive equations in patients with varying stages of ALS.

METHODS

Thirty-four patients were studied. Caloric expenditure and respiratory quotient (R) were measured using indirect calorimetry. Results were compared with the Harris-Benedict equation.

RESULTS

The prediction error for the Harris-Benedict equation was 18.6 + 14.9%. Limits of agreement showed this equation could overestimate caloric expenditure by 591 kcal/d and underestimate requirements by 677 kcal/d. R was >0.86 in 11 patients, suggesting overfeeding, and <0.8 in 15 patients, suggesting underfeeding. The difference between predicted and measured caloric expenditure did not correlate with disease severity, disease duration, or body mass index. Mechanically ventilated patients had higher than predicted energy expenditure.

CONCLUSIONS

We found that standard equations used to calculate energy expenditure were not valid for patients with ALS. Moreover, the majority of our patients were either overfed or underfed. As underfeeding can cause diaphragm impairment, and overfeeding can increase ventilatory load, indirect calorimetry should be considered in ALS patients to determine optimal caloric requirement.

A predictive equation for determination of resting energy expenditure in mechanically ventilated patients

STUDY OBJECTIVE

To evaluate an equation that estimates resting energy expenditure from two easily obtained measurements--expired carbon dioxide and minute ventilation, and compare the results of this equation with standard methods of estimating and measuring caloric expenditure in mechanically ventilated patients.

DESIGN

Prospective evaluation in a consecutive, unselected cohort.

SETTING

Medical, surgical, and coronary intensive care units in a university hospital.

PATIENTS

Twenty-five patients (16 to 79 years of age) receiving mechanical ventilation.

INTERVENTION

Indirect calorimetry (IC), minute ventilation (VE), and partial pressure of expired carbon dioxide (PECO2) were obtained on all patients. Harris-Benedict equations were calculated and corrected for known stress factors (HBc). Calculated energy expenditure (CEE) was determined using the following equation: CEE = 9.27 x VE x PECO2 CEE was then compared with IC and HBc.

MEASUREMENTS AND RESULTS

The IC was interpretable in 22 of 25 patients, and CEE was significantly better at estimating caloric requirements than HBc. The mean absolute difference between CEE and IC was significantly less than between HBc and IC (118 +/- 96 vs 302 +/- 269, p < .003). CEE estimated caloric requirements to within 200 kcal of IC in 16 of 22 (72 percent); HBc estimated within 200 kcal of IC in 9 of 22 (41 percent).

CONCLUSIONS

Minute ventilation and expired carbon dioxide measurements are easily and inexpensively obtainable. Energy expenditures calculated from these measurements (CEE) compare favorably with values obtained from a metabolic cart and are significantly more accurate than HBc.

Nutritional support of hospitalized patients

Effective nutritional support requires sound knowledge of both basic and clinical nutrition of dogs and cats as well as familiarity with products and delivery systems. Case management includes assessment of nutritional status and estimation of fuel sources. Most starved or stressed patients use fatty acids for over 70 per cent kcalME and protein for over 20 per cent kcalME. Approximate kcal needs are calculated from maintenance energy equations. Most patients respond best to enteral nutrition. Meat-based pet foods, liquid enteral products, and nutrient modules are offered in slurries or are tube-fed. Management includes careful monitoring of patients and gradual transitions to diets with more complex nutrient sources.