Correlação entre o consumo de oxigênio obtido pelo método de Fick e pela calorimetria indireta no paciente grave

OBJECTIVE: To compare the oxygen consumption index measured by using indirect calorimetry (VO2IDelta) with a portable metabolic cart and calculated according to Fick's principle (VO2 IFick) in critically ill patients. METHODS: Fourteen patients (10 men and 4 women, mean age 39.4 ± 5.4 years) were analyzed, 5 of them trauma victims and 9 sepsis victims. The following mean scores were obtained for these patients: APACHE II = 21.3±1.8, ISS = 24.8±6, and sepsis score = 19.6±2.3. The mortality risk (odds ratio), calculated from APACHE II, was 41.9±7.1%. All patients underwent mechanical ventilation and invasive hemodynamic monitoring with a Swan-Ganz catheter. VO2 was obtained using the 2 methods (VO2IDelta and VO2IFick) at 4 different times (T1-T4). RESULTS: A good correlation was found between the 2 methods (r=0.77) for the mean of the 4 serial measurements. No statistically significant differences were observed between indirect calorimetry and Fick's equation at T1 (VO2I Delta = 138±28 and VO2IFick = 59±38 mL.min-2.m-2, P=0.10) and T3 (VO2IDelta = 144±26 and VO2IFick = 158±35 mL.min-2.m-2, P=0.14), but a significant difference was observed at T2 (VO2IDelta = 141±27 and VO2IFick = 155±26 mL.min-2.m-2, P=0.03) and T4 (VO2IDelta = 145±24 and VO2IFick = 162±26 mL.min-2.m-2, P=0.01). CONCLUSION: We may state that indirect calorimetry can be used for oxygen consumption analysis in critically ill patients and is as efficient as Fick's reverse equation, with the benefit of being a noninvasive and risk-free procedure.