Effects of ventilator resetting on indirect calorimetry measurement--the importance of patience

Mechanical ventilation mode (volume × pressure) does not change the variables obtained by indirect calorimetry in critically ill patients

PURPOSE

The aim of the study was to analyze the difference between the results obtained by indirect calorimetry (IC) using volume-controlled and pressure-controlled mechanical ventilation in 2 different ventilators and to characterize the variables achieved by IC after well-defined changes in minute volume (Vm).

MATERIALS AND METHODS

Prospective study of 20 critically ill patients under volume-controlled (n = 15) or pressure-controlled (n = 5) mechanical ventilation. Three IC measurements of 45 minutes each were taken; values of oxygen consumption (Vo(2)), carbon dioxide production (Vco(2)), Vm, resting energy expenditure (REE), and respiratory quotient (RQ) were obtained. For the last measurement, Vm was set at 20% above the baseline.

RESULTS

There were no differences between the results obtained by IC during volume-controlled and pressure-controlled mechanical ventilation. The most relevant changes in the variables obtained by IC before and after intervention in Vm were a significant increase in Vco(2) (from 165 to 177 mL·min(-1); P < .01), a decrease in Paco(2) (from 38.49 to 28.46 mm Hg; P < .01), and a rise in pH (from 7.41 to 7.49; P < .01). There were no alterations in Vo(2), REE, or RQ.

CONCLUSIONS

Ventilators and ventilation modes do not influence the IC measurements. The observed changes have no clinical effects and are reversible, provided that increased Vm is maintained for no longer than 45 minutes.