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Abstract

Monitoring of oxygen uptake during general anesthesia would have several benefits, but unfortunately, this is usually not available in the clinical routine situation. The herein proposed formula to calculate oxygen uptake (.VO2) necessitates only the accurate measurement of FIO2 as well as fresh gas flow and composition. Additionally, this method is not affected by the presence of anesthetic gases. The calculation uses the difference in oxygen content between the delivered fresh gas and the resulting FIO2 in the anesthesia circle system. This gap originates from oxygen uptake (that is mainly caused by metabolic oxygen consumption) and is more pronounced if low fresh gas flows are administered. In order to obtain representative results, calculation of .VO2 should be performed only after achievement of respiratory steady state conditions. Due to its simplicity and wide availability, it has the potential to become a valuable extension in anesthesia monitoring during the performance of routine general anesthesia.

The Relation Between Oxygen Consumption and the Equilibrated Inspired Oxygen Fraction in an Anesthetic Circle Breathing System: A Mathematic Formulation & Laboratory Simulations

“…Despite that, Biro used a modified Foldes equation to calculate _ VO 2 during low flow anesthesia in a circle breathing system. 3 Biro's equation is simple, but does not correlate well with data obtained from patients and laboratory simulations. 10,12 We think that Foldes-Biro equation is an over-simplified description of a circle breathing system.…”

“…1,3,7 Foldes and colleagues recognized the difference between F I O 2 and F FG O 2 in a circle breathing system in 1956, 7 and presented an equation to describe the relation between F I O 2 , F FG O 2 , fresh gas flow, and…”

Continuous indirect calorimetry—a laboratory simulation of a new method for non-invasive metabolic monitoring of patients under anaesthesia or in critical care

“…For instance, the electronic fresh gas flowmeters seen on the latest types of anaesthesia delivery units would obviate the need for manual fresh gas flow data entry, such as we performed in our prototype system, and would allow full automation of the calibration routine. This method for the non-invasive measurement of V O 2 is similar in aim to that proposed by Biro (1998), which was based on a formula by Foldes et al (1952). Biro's method was tested in a clinical study against the reverse Fick method by Leonard et al who found poor agreement with a substantial negative bias in the order of 40-50% (Leonard et al 2002).…”

Perioperative estimations of oxygen consumption from LiDCO™plus-derived cardiac output and Ca-cvO2 difference: Relationship with measurements by indirect calorimetry in elderly patients undergoing major abdominal surgery

“…Available techniques, by pulmonary artery catheterisation or indirect calorimetry, are either deemed too invasive or difficult to manage in a clinical study setting during non-cardiac surgery. Using oxygen uptake calculated from fractions of inspiratory and expiratory oxygen in the closed breathing circuit during low-flow anaesthesia [ 7 ] has not demonstrated agreement when compared to standard methods [ 8 ]. Importantly, it can not be used in awake patients in the postoperative period.…”