Comparison of oxygen consumption calculated by Fick’s principle (using a central venous catheter) and measured by indirect calorimetry

We investigated the clinical usefulness of the Fick method using central venous oxygen saturation \( Scv_{O_2 } \) and cardiac output (CO) measured by pulse dye densitometry (PDD) for monitoring oxygen consumption (\( \dot V_{O_2 } \)). This prospective clinical study was performed in 28 mechanically ventilated postoperative patients after major abdominal surgery. \( \dot V_{O_2 } \) was determined by two methods, i.e., the Fick method and indirect calorimetry. The Fick method was employed using CO measured by PDD and \( Scv_{O_2 } \) obtained from a central venous catheter (CVC). \( \dot V_{O_2 } \) measured by indirect calorimetry was averaged for 15 min. Fifty-six sets of measurements were performed. \( \dot V_{O_2 } \) values determined by the Fick method were significantly lower than those measured by indirect calorimetry (110 ± 29 vs 148 ± 28 ml·min−1·m−2; P < 0.01). Bland and Altma analysis showed that the mean bias and precision were 33 ml·min−1·m−2 and 32 ml·min−1 −2, respectively. The correlat between the two measurements of \( \dot V_{O_2 } \) was weak (r 2 = 0.145; P = 0.0038), indicating that the Fick method using PDD and \( Scv_{O_2 } \) is not clinically acceptable for the monitoring of \( \dot V_{O_2 } \).