Asssessing Energy Requirements of Patients on Respirators

Abstract

This report documents a specific situation in which indirect calorimetry produced large overestimations of oxygen consumption and energy expenditure of a patient on a respirator. High positive-end expiratory pressures combined with high fractional concentrations of O2 led to perforation of lung parenchyma with considerable loss of O₂, which produced subcutaneous emphysema and recurrent pneumothoraces. Typical calculations for determining energy expenditure from O2 consumption, therefore, could not be employed. Calculations utilizing the volume of CO₂ expired, however, were less sensitive and variable during this time period. Resting energy expenditures were calculated from the volume of CO₂ expired by using 5.52 kcal/1 as the caloric equivalent of CO₂. This procedure does not overestimate energy needs when a physiological gas leak exists (high positive-end expiratory pressures and high fractional concentrations of O2 or chest tube). This is very important in the ventilatory patient as excess carbohydrate can further stress the compromised pulmonary status.