Different dosages of dobutamine in septic shock patients: determining oxygen consumption with a metabolic monitor integrated in a ventilator

Abstract

With a metabolic monitor integrated in a ventilator it was possible to carry out continuous monitoring of calorimetric data under clinical conditions. In contrast to previous studies using indirect calorimetry, this study showed a moderate correlation between VO2 and DO2 in septic patients using either method. The clinical relevance of this finding requires further investigation. Different factors (e. g. injectant temperature, pulmonary VO2) produced substantial differences between VO2,IC and VO2,Fick as previously shown.

VO2/DO2 relationship: how to get rid of methodological pitfalls?

“…In the second patient DO 2 increases by 300 ml min ±1 M ±2 with a 10 % slope, which suggests VO 2 /DO 2 independence. VO 2 was significantly increased in the patients investigated by Schaffartzik et al [5], from 173 to 188 ml min ±1 M ±2 , which could suggest VO 2 /DO 2 dependence. However, these patients had been in a stable hemodynamic condition for more than 6 h, so that VO 2 /DO 2 dependence was very unlikely.…”

“…Fourth, various studies have shown good agreement between calculation of VO 2 using the Fick principle and indirect calorimetry [14,15]. In this issue, Schaffartzik et al [5] report that agreement between the two methods of approx. 20 %.…”

“…Constructing VO 2 /DO 2 relationships using more than two points is another possibility for limiting the effects of random errors. The study by De Backer et al [14] and the current study by Schaffartzik et al [5] used this methodology and reported that VO 2 calculated from the Fick equation and VO 2 measured by indirect calorimetry were similar. Third, several studies have observed that VO 2 /DO 2 dependence can occur in one group of patients but not in others, despite similar changes in DO 2 [2,3].…”

“…However, the methodology of some of these studies was questioned, and this led to a controversy about the reality of VO 2 /DO 2 dependence in critically ill patients. In this issue, the article by Schaffartzik et al [5] sheds new light in a very foggy area.The relationship between VO 2 and DO 2 is complex. When oxygen demand is stable, VO 2 remains unaffected by changes in DO 2 under normal conditions since changes in oxygen extraction (EO 2 ) by the tissues compensate the decrease in DO 2 .…”

“…However, the methodology of some of these studies was questioned, and this led to a controversy about the reality of VO 2 /DO 2 dependence in critically ill patients. In this issue, the article by Schaffartzik et al [5] sheds new light in a very foggy area.…”