Association between Oxygen Delivery and Consumption in Patients Undergoing Cardiac Surgery. is There Supply Dependence?

Abstract

We studied the relationship between oxygen delivery (DO2) and consumption (VO2) in twenty patients undergoing cardiac surgery, in order to determine if VO2 was dependent on DO2 (pathological oxygen supply dependence). We measured VO2 from expired gas analysis (VO2G) and compared this to that calculated using the reverse Fick method (VO2F). Both VO2G and VO2F increased after cardiopulmonary bypass (P<0.001), without change in DO2 (i.e. oxygen extraction ratio increased). There was a significant relationship between changes in DO2 and VO2F, both before bypass (r=0.74, P < 0.001) and after bypass (r=0.69, P < 0.001), while changes in DO2 and VO2G had no such relationship (pre-bypass: r=0.38, P=0.094; post-bypass: r=0.10, P=0.68). There was poor agreement between VO2F and VO2G perioperatively. We could not demonstrate supply dependence in elective cardiac surgical patients.

Perioperative red cell, plasma, and blood volume change in patients undergoing cardiac surgery

“…Indeed, the much described oxygen debt theory after cardiac surgery has now become increasingly questioned. [9][10][11] In addition to the above, work by our unit (R.D. Slight and colleagues) has suggested that several patient and operative variables, normally associated with an increase in transfusion requirement, are not associated with an increase in RCV lost.…”

“…Such results suggest that oxygen delivery remains adequate during times of acute stress despite a lowering of Hb concentration. Indeed, the much described oxygen debt theory after cardiac surgery has now become increasingly questioned 9‐11 …”

Factors predicting loss and gain of red cell volume in cardiac surgery patients

“…The possibility of such a RCV‐based system for transfusion is also supported by recent evidence that circulating RCV is relatively preserved in peri‐operative surgical patients (Orth et al ., 1998; Fransen et al ., 2001). Furthermore, the oxygen debt theory following cardiac surgery, which has long been used as an argument for a higher haemoglobin concentration, has now come under increasing scrutiny as to its likelihood (Hinds & Watson, 1995; Myles et al ., 1996; Ganushchak et al ., 2002).…”

Measurement of systemic oxygen uptake during low‐flow anaesthesia with a standard technique vs. a novel method

“…Although no gold standard for measurement of has been established, the most frequently used methods have been the Fick‐derived method and indirect calorimetry [4, 7–9]. Calorimetry, which has been used extensively for research purposes in the critical care setting, is not widely available in clinical anaesthesia practice.…”

“…Calorimetry, which has been used extensively for research purposes in the critical care setting, is not widely available in clinical anaesthesia practice. The Fick‐derived method [3], based on the arteriovenous oxygen content difference, is an established technique and is a more generally available method for measurement of during anaesthesia [7, 8].…”