The ∆pv-aco2/∆ca-vo2 Ratio as a Predictor of Mortality in Patients With Severe Acute Respiratory Distress Syndrome Related to Covid-19
Jesús Salvador Sánchez Díaz, Karla Gabriela Peniche Moguel, José Manuel Reyes-Ruiz, Orlando Rubén Pérez Nieto, Diego Escarramán Martínez, Eder Iván Zamarrón López, María Verónica Calyeca Sánchez
To evaluate the central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (∆Pv-aCO2/∆Ca-vO2 ratio) as a predictor of mortality in patients with COVID-19-related severe acute respiratory distress syndrome (ARDS).
Most monitoring of critically ill patients maintains an interest in macrohemodynamic variables . On the other hand, the gasometric analysis provides a formal assessment of tissue perfusion  and anaerobic metabolism  through serum lactate, central venous oxygen saturation (ScvO2), venous-to-arterial carbon dioxide pressure difference (∆Pv-aCO2), and central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (∆Pv-aCO2/∆Ca-vO2 ratio). The above is interesting because it has been documented that patients with Coronavirus disease 2019 (COVID-19) have alterations in tissue perfusion  and oxygen metabolism . Serum lactate is the most frequently used marker of tissue perfusion , increasing in the presence of cellular hypoxia or low peripheral perfusion ; a level >2 mmol/L is the most commonly used cut-off point .
Materials and method
A single-center, retrospective cohort study was conducted in the Intensive Care Unit (ICU) of the Unidad Médica de Alta Especialidad, Hospital de Especialidades No. 14, Centro Médico Nacional "Adolfo Ruiz Cortines" of the Instituto Mexicano del Seguro Social (IMSS), Veracruz, Mexico from April 18, 2020, to January 18, 2021. Convenience sampling was performed, which included patients admitted to the ICU with ARDS secondary to SARS-CoV-2. Inclusion criteria were: (1) age >18 years, (2) any gender, (3) confirmed SARS-CoV-2 infection by reverse transcriptase polymerase chain reaction (RT-PCR), and (4) severe ARDS (PaO2/FiO2 ≤100 mmHg) defined according to Berlin criteria  with invasive mechanical ventilation (IVM). (1) Patients with diseases that could affect the hemoglobin or CO2 levels such as hematologic diseases, chronic obstructive pulmonary disease (COPD), known neuromuscular disease or known hyperbaric respiratory failure; (2) patients with an incomplete variable registry; or (3) pregnant were excluded from this study. All patients were intubated in the ICU and some of them received norepinephrine (n = 26, 22.60%) as the only vasopressor.
This study cohort included one hundred and fifteen subjects (Fig 1). Patients were stratified into survivor (n = 54) and non-survivor (n = 61). The median age was 65 years (57.5–73). The predominant gender was male (61.73%), the most frequent comorbidity was SAH (67.82%), and the mean SAPS II was 75.35 points (SD ± 9.26). The medians for lactate, ScvO2, and ∆Pv-aCO2 were 1.6 mEq/L (1.2–2.1), 75% (68.5–81), and 5 mmHg (3–9), respectively. The median anaerobic metabolism index or ∆Pv-aCO2/∆Ca-vO2 ratio was 1.56 mmHg/mL (1.02–2.67).
The priority in patients with ARDS secondary to SARS-CoV-2 will be to avoid dysoxia . Circulatory homeostasis between macrocirculation, microcirculation, and the cell will maintain the flow of oxygen to the different organs avoiding tissue hypoxia, a condition that can cause cell damage and death . Anaerobic metabolism occurs when DO2 decreases to critical levels (< 7 ml/kg/min) concerning VO2 by exhaustion of compensatory mechanisms . Indirect markers such as ScvO2, ∆Pv-aCO2, lactate, and ∆Pv-aCO2/∆Ca-vO2 ratio can help assess VO2/DO2 ratio, tissue perfusion, and anaerobic metabolism [22–24]. We must consider that any parameter has limitations, but it is up to the physician to choose the best marker, contextualizing each patient, which makes multimodal monitoring imperative.
In this study the ∆Pv-aCO2/∆Ca-vO2 ratio >2.14 mmHg/mL was an independent risk factor for mortality (HR 1.17, 95% CI 1.06–1.29, p = 0.001) in patients with severe ARDS secondary to SARS-CoV-2. Hence, the ∆Pv-aCO2/∆Ca-vO2 ratio could help determine the prognosis of these patients.
The authors thank all the health workers, doctors, nurses, and support staff who worked in the UMAE, H. E. No. 14, Centro Médico Nacional "Adolfo Ruiz Cortines", IMSS Veracruz, who were fighting for COVID-19 together.
Citation: Sánchez Díaz JS, Peniche Moguel KG, Reyes-Ruiz JM, Pérez Nieto OR, Escarramán Martínez D, Zamarrón López EI, et al. (2023) The ∆Pv-aCO2/∆Ca-vO2 ratio as a predictor of mortality in patients with severe acute respiratory distress syndrome related to COVID-19. PLoS ONE 18(9): e0290272. https://doi.org/10.1371/journal.pone.0290272
Editor: Samuele Ceruti, Sant Anna Hospital: Clinica Sant’Anna, SWITZERLAND
Received: October 20, 2022; Accepted: August 5, 2023; Published: September 6, 2023
Copyright: © 2023 Sánchez Díaz et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: Data are available from the local Ethics and Research Committee of the Unidad Médica de Alta Especialidad No. 14, IMSS (contact via email@example.com) for researchers who meet the criteria for access to confidential data.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.