Intramucosal–arterial PCO2 gap does reflect tissue dysoxia – authors' response

Although the reduction in oxygen transport was greater in ischaemic hypoxia (IH), there were comparable falls in systemic and intestinal oxygen consumption in HH. We agree with Gutierrez and Turkan that oxygen supply dependence is not an infallible marker of anaerobic metabolism. However, the occurrence of compensatory mechanisms to lower tissue metabolic rate and to decrease oxygen consumption (VO2) in response to hypoxaemia in an acute setting seems unlikely. Consequently, we consider the fall in VO2, as well as the metabolic response, to represent evidence of anaerobic metabolism [3].As was pointed out by Gutierrez and Turkan [1], another parameter that may be used to determine the onset of anaerobiosis is the presence of increased H+ concentration in tissues and blood. Nevertheless, we do not agree with their explanation of the lack of change in bicarbonate in HH. We believe that, in HH, bicarbonate remains unchanged because of concomitant increase in arterial PCO2 and subsequent buffer titration. Additionally, base excess, a better indicator of metabolic state, had a similar reduction of approximately 10 mmol/l (data not shown in the study) in both groups. Thus, the magnitude of metabolic acidosis, as marker of tissue hypoxia, was comparable in the groups.Despite the fact that systemic and intestinal oxygen extraction ratios were lower in the HH group (64% and 56%, respectively) than in the IH group (87% and 78%, respectively) in the last step of decreasing oxygen transport, this does not necessarily mean that there is a greater oxygen debt in IH. This finding has previously been reported by other researchers [4]. It could indicate an alteration in oxygen extraction capacity in HH. It could also explain the finding that VO2 decrease and metabolic acidosis were similar in the groups, even though oxygen transport was somewhat higher in the HH group.We have some concerns about calculation of respiratory quotient (RQ) relating to multiple propagation of errors. In