Are supranormal values of DO₂ defined well?

Introduction

The physiological assumption of oxygen debt elimination is a spontaneous or therapeutically induced increase of DO₂ in relation to the values of DO₂ recorded before the occurrence that led to the oxygen debt formation. The target of this research was to analyse the relation between post-operative achievement of DO₂I >600 ml/min/m² and the dynamics of changes of DO₂ during the perioperative period and in that way to give an answer to the question if the achievement of so called `supranormal values' of DO₂ is equal to the physiological principle of oxygen debt elimination.

Methods

There were included 36 high-risk surgical patients in the prospective research (age 53 ± 1.5 years, 28 male and 8 female, 58% extensive ablative surgery for carcinoma). PA catheter and arterial catheter were inserted 12 h before surgery in the average. The target of therapeutical approach was to reach DO₂I>600 ml/min/m² within 12 h from the end of surgery in every patient and then to keep these values during following 36 h. Haemodynamic measurements and laboratory analyses of blood samples, including arterial lactate, were analysed during the first 48 h after an interval of 6 h. While the data were analysed, we were comparing the dynamics of changes of DO₂ and arterial lactate in the peri-perative period in relation to the real achievement of the therapeutical target (DO₂I>600 ml/min/m² within 12 h after the end of surgery) and the survival rate of the patients.

Results

The 28-day mortality was in the whole group of patients 31% (11/36). We achieved therapeutical target in 22 patients (61%). The mortality was 23% (5/22) in this group which was not statistically lower compared to the group of patients where the target was not achieved (43%, 6/14). When we compared the dynamics of changes of DO₂ and arterial lactate during the peri-operative period in relation to the real achievement of the therapeutical target and surviving of patients, we found out in group of patients which achieved target the results which are demonstrated on the following figures. The results which were found out in group of patients which did not achieve target were the same.

Conclusion

Regardless of post-operative achievement of DO₂I>600 ml/min/m², in survived patients there was observed that they were achieving statistically higher values of DO₂ in comparison with pre-operative values of DO₂ and this process was accompanied by a decrease of arterial lactate level. We suppose that supra-normal values of DO₂ should be define in relation to the pre-operative (i.e. normal) values of DO₂ and not in relation to the `magic number' 600 ml/min/m².

Figure 1.

Perioperative oxygen delivery.

Figure 2.

Postoperative arterial lactate.