{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,31]],"date-time":"2026-08-31T22:31:02Z","timestamp":1788215462359,"version":"build-2803163510"},"reference-count":102,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2023,7,6]],"date-time":"2023-07-06T00:00:00Z","timestamp":1688601600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Agencia Nacional de Promoci\u00f3n Cient\u00edfica y Tecnol\u00f3gica, Argentina","award":["PICT 2018-03977"],"award-info":[{"award-number":["PICT 2018-03977"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Medicina"],"abstract":"<jats:p>According to Fick\u2019s principle, the total uptake of (or release of) a substance by tissues is the product of blood flow and the difference between the arterial and the venous concentration of the substance. Therefore, the mixed or central venous minus arterial CO2 content difference depends on cardiac output (CO). Assuming a linear relationship between CO2 content and partial pressure, central or mixed venous minus arterial PCO2 differences (Pcv-aCO2 and Pmv-aCO2) are directly related to CO. Nevertheless, this relationship is affected by alterations in the CO2Hb dissociation curve induced by metabolic acidosis, hemodilution, the Haldane effect, and changes in CO2 production (VCO2). In addition, Pcv-aCO2 and Pmv-aCO2 are not interchangeable. Despite these confounders, CO is a main determinant of Pcv-aCO2. Since in a study performed in septic shock patients, Pmv-aCO2 was correlated with changes in sublingual microcirculation but not with those in CO, it has been proposed as a monitor for microcirculation. The respiratory quotient (RQ)\u2014RQ = VCO2\/O2 consumption\u2014sharply increases in anaerobic situations induced by exercise or critical reductions in O2 transport. This results from anaerobic VCO2 secondary to bicarbonate buffering of anaerobically generated protons. The measurement of RQ requires expired gas analysis by a metabolic cart, which is not usually available. Thus, some studies have suggested that the ratio of Pcv-aCO2 to arterial minus central venous O2 content (Pcv-aCO2\/Ca-cvO2) might be a surrogate for RQ and tissue oxygenation. In this review, we analyze the physiologic determinants of Pcv-aCO2 and Pcv-aCO2\/Ca-cvO2 and their potential usefulness and limitations for the monitoring of critically ill patients. We discuss compelling evidence showing that they are misleading surrogates for tissue perfusion and oxygenation, mainly because they are systemic variables that fail to track regional changes. In addition, they are strongly dependent on changes in the CO2Hb dissociation curve, regardless of changes in systemic and microvascular perfusion and oxygenation.<\/jats:p>","DOI":"10.3390\/medicina59071262","type":"journal-article","created":{"date-parts":[[2023,7,7]],"date-time":"2023-07-07T01:41:36Z","timestamp":1688694096000},"page":"1262","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["Venous Minus Arterial Carbon Dioxide Gradients in the Monitoring of Tissue Perfusion and Oxygenation: A Narrative Review"],"prefix":"10.3390","volume":"59","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3349-5447","authenticated-orcid":false,"given":"Arnaldo","family":"Dubin","sequence":"first","affiliation":[{"name":"Facultad de Ciencias M\u00e9dicas, Universidad Nacional de La Plata, C\u00e1tedras de Terapia Intensiva y Farmacolog\u00eda Aplicada, 60 y 120, La Plata B1902AGW, Argentina"},{"name":"Servicio de Terapia Intensiva, Sanatorio Otamendi, Azcu\u00e9naga 870, Ciudad Aut\u00f3noma de Buenos Aires C1115AAB, Argentina"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mario O.","family":"Pozo","sequence":"additional","affiliation":[{"name":"Servicio de Terapia Intensiva, Hospital Brit\u00e1nico, Perdriel 74, Ciudad Aut\u00f3noma de Buenos Aires 1280AEB, Argentina"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,7,6]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1016\/j.jointm.2021.11.002","article-title":"The role of peripheral perfusion markers and lactate in septic shock resuscitation","volume":"2","author":"Kattan","year":"2021","journal-title":"J. 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