A method for estimating respiratory muscle efficiency using an automated metabolic cart

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.