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Journal of Clinical Monitoring and Computing

, Volume 31, Issue 6, pp 1203–1211 | Cite as

Central venous-to-arterial carbon dioxide difference and the effect of venous hyperoxia: A limiting factor, or an additional marker of severity in shock?

  • P. Saludes
  • L. Proença
  • G. Gruartmoner
  • L. Enseñat
  • A. Pérez-Madrigal
  • C. Espinal
  • J. Mesquida
Original Research

Abstract

Central venous-to-arterial carbon dioxide difference (PcvaCO2) has demonstrated its prognostic value in critically ill patients suffering from shock, and current expert recommendations advocate for further resuscitation interventions when PcvaCO2 is elevated. PcvaCO2 combination with arterial–venous oxygen content difference (PcvaCO2/CavO2) seems to enhance its performance when assessing anaerobic metabolism. However, the fact that PCO2 values might be altered by changes in blood O2 content (the Haldane effect), has been presented as a limitation of PCO2-derived variables. The present study aimed at exploring the impact of hyperoxia on PcvaCO2 and PcvaCO2/CavO2 during the early phase of shock. Prospective interventional study. Ventilated patients suffering from shock within the first 24 h of ICU admission. Patients requiring FiO2 ≥ 0.5 were excluded. At inclusion, simultaneous arterial and central venous blood samples were collected. Patients underwent a hyperoxygenation test (5 min of FiO2 100%), and arterial and central venous blood samples were repeated. Oxygenation and CO2 variables were calculated at both time points. Twenty patients were studied. The main cause of shock was septic shock (70%). The hyperoxygenation trial increased oxygenation parameters in arterial and venous blood, whereas PCO2 only changed at the venous site. Resulting PcvaCO2 and PcvaCO2/CavO2 significantly increased [6.8 (4.9, 8.1) vs. 7.6 (6.7, 8.5) mmHg, p 0.001; and 1.9 (1.4, 2.2) vs. 2.3 (1.8, 3), p < 0.001, respectively]. Baseline PcvaCO2, PcvaCO2/CavO2 and ScvO2 correlated with the magnitude of PO2 augmentation at the venous site within the trial (ρ −0.46, p 0.04; ρ 0.6, p < 0.01; and ρ 0.7, p < 0.001, respectively). Increased PcvaCO2/CavO2 values were associated with higher mortality in our sample [1.46 (1.21, 1.89) survivors vs. 2.23 (1.86, 2.8) non-survivors, p < 0.01]. PcvaCO2 and PcvaCO2/CavO2 are influenced by oxygenation changes not related to flow. Elevated PcvaCO2 and PcvaCO2/CavO2 values might not only derive from cardiac output inadequacy, but also from venous hyperoxia. Elevated PcvaCO2/CavO2 values were associated with higher PO2 transmission to the venous compartment, suggesting higher shunting phenomena.

Keywords

Venous-to-arterial carbon dioxide difference Circulatory shock Hemodynamic monitoring Tissue hypoxia 

Abbreviations

CaO2

Arterial oxygen content

CavO2

Arterial-to-venous oxygen content difference

CvO2

Central venous oxygen content

CvaCO2

Central venous-to-arterial carbon dioxide content difference

CvaCO2/CavO2

Respiratory quotient

DO2

Global oxygen delivery

Hb

Hemoglobin

MAP

Mean arterial pressure

PaO2

Arterial oxygen tension

PaCO2

Arterial carbon dioxide tension

PcvO2

Central venous oxygen tension

PcvCO2

Central venous carbon dioxide tension

PcvaCO2

Central venous-to-arterial carbon dioxide difference

PcvaCO2/CavO2

Central venous-to-arterial carbon dioxide difference/arterial–venous oxygen content difference ratio

SaO2

Arterial oxygen saturation

ScvO2

Central venous oxygen saturation

O2ER

Oxygen extraction ratio

VCO2

Global carbon dioxide production

VO2

Global oxygen consumption

Notes

Acknowledgements

The authors want to thank David Suarez, PhD for his statistical support.

Author's contributions

All the authors contributed to the elaboration of this manuscript. JM and PS conceived, designed, and coordinated the study. JM, PS, LP, GG, LE, APM, and CE performed data extraction. JM, PS and GG analyzed the data, and drafted the manuscript. All authors read and approved the final version of the manuscript.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interests.

Ethics approval and consent to participate

The local Ethics Committee (Comitè Ètic d’Investigació Clínica, Fundació Parc Taulí) approved the study (protocol reference CEIC-2014/636). Signed informed consent was obtained from each patient’s next of kin.

Supplementary material

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Supplementary material 1 (JPEG 56 kb)
10877_2016_9954_MOESM2_ESM.doc (20 kb)
Supplementary material 2 (DOC 20 kb)

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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Critical Care Department, Hospital de SabadellCorporació Sanitària Universitària Parc Taulí, Universitat Autònoma de BarcelonaSabadellSpain
  2. 2.Serviço de Medicina InternaHospital Prof. Dr. Fernando FonsecaAmadoraPortugal

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