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. 2020 Jan;48(1):300060519854633.
doi: 10.1177/0300060519854633. Epub 2019 Jul 1.

Relationship of relevant factors to P(v-a)CO2/C(a-v)O2 ratio in critically ill patients

Huaiwu He  1 , Yun Long  1 , Dawei Liu  1 , Bo Tang  1 , Can Ince  2
Affiliations

Relationship of relevant factors to P(v-a)CO2/C(a-v)O2 ratio in critically ill patients

Huaiwu He et al. J Int Med Res. 2020 Jan.

Abstract

Objective: This study investigated the factors related to the ratio of the venoarterial carbon dioxide tension difference [P(v-a)CO2] to the arteriovenous oxygen content difference [C(a-v)O2] (hereafter termed “Ratio”).

Methods: We retrospectively studied 1294 pairs of arterial and central venous blood gas measurements in 352 critically ill patients. A high Ratio was defined as > 1.68 based on published literature. Measurements were divided into four groups: Group I [P(v-a)CO2 ≤ 6 mmHg/central venous oxygen saturation (ScvO2) < 70%], Group II [P(v-a)CO2 ≤ 6 mmHg/ScvO2 ≥ 70%], Group III [P(v-a)CO2 > 6 mmHg/ScvO2 ≥ 70%], and Group IV [P(v-a)CO2 > 6 mmHg/ScvO2 < 70%].

Results: The Ratio’s strongest correlation was with P(v-a)CO2 when compared with ScvO2 and hemoglobin in all data. The P(v-a)CO2 and ScvO2 were significantly higher and the hemoglobin and arterial oxygen saturation were significantly lower in the high Ratio measurements (>1.68) than low Ratio measurements (≤1.68). The P(v-a)CO2 was best for predicting a high Ratio. A P(v-a)CO2 threshold of 7 mmHg was associated with a sensitivity of 41.77% and specificity of 90.62% for predicting a high Ratio.

Conclusions: A high P(v-a)CO2 is the most relevant contributor to a high Ratio among all related factors in critically ill patients.

Keywords: P(v-a)CO2; P(v-a)CO2/C(a-v)O2 ratio; ScvO2; intensive care unit; oxygen consumption (VO2); oxygen delivery (DO2).

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Figures

Figure 1.
Figure 1.
Flow diagram.
Figure 2.
Figure 2.
Difference in (a) hemoglobin, (b) P(v-a)CO2, (c) ScvO2, and (d) SaO2 between high and low P(v-a)CO2/C(a-v)O2 ratio measurements. *P <0.05. P(v-a)CO2, venoarterial carbon dioxide tension difference; ScvO2, central venous oxygen saturation; SaO2, arterial oxygen saturation; C(a-v)O2, arteriovenous oxygen content difference.
Figure 3.
Figure 3.
Receiving operating characteristic curves showing the ability of ScvO2, P(v-a)CO2, and hemoglobin to predict a high P(v-a)CO2/C(a-v)O2 ratio of >1.68. ScvO2, central venous oxygen saturation; P(v-a)CO2, venoarterial carbon dioxide tension difference; C(a-v)O2, arteriovenous oxygen content difference.
Figure 4.
Figure 4.
Percentages of a high P(v-a)CO2/C(a-v)O2 ratio (>1.68) in different groups based on the cutoffs of ScvO2 (70%) and P(v-a)CO2 (6 mmHg). *P <0.05. P(v-a)CO2, venoarterial carbon dioxide tension difference; C(a-v)O2, arteriovenous oxygen content difference; ScvO2, central venous oxygen saturation.
Figure 5.
Figure 5.
EO2 in different groups based on the cutoffs of ScvO2 (70%) and P(v-a)CO2 (6 mmHg). *Group I vs. Groups II, III, and IV; P <0.05. Group IV vs. Groups II and III; P <0.05. EO2, oxygen extraction percentage; ScvO2, central venous oxygen saturation; P(v-a)CO2, venoarterial carbon dioxide tension difference.
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