Correlation between arterial blood gas and CT volumetry in patients with SARS-CoV-2 in the emergency department

Abstract

•The severity of SARS-CoV-2 patients is difficult to quickly assess in the ED.•The ABG test is a quick and easy tool that can help identify more severe patients.•CT cannot be used on all suspected SARS-CoV-2 infected patients admitted in ED.•The CT volumetry correlates well with the values of severity reported by the ABG test. The extent of pulmonary inflammation caused by SARS-CoV-2 infection seems to correlate well with the patient's prognosis, but not with the severity of clinical manifestations presented at first evaluation in the emergency department (ED) (Colombi et al., 2020Colombi D. Bodini F.C. Petrini M. Maffi G. Morelli N. Milanese G. et al.Well-aerated lung on admitting chest CT to predict adverse outcome in COVID-19 pneumonia.Radiology. 2020; 201433https://doi.org/10.1148/radiol.2020201433Crossref PubMed Scopus (328) Google Scholar, Grasselli et al., 2020Grasselli G. Zangrillo A. Zanella A. Antonelli M. Cabrini L. Castelli A. et al.Baseline characteristics and outcomes of 1591 patients infected with SARS-CoV-2 admitted to ICUs of the Lombardy Region, Italy.JAMA. 2020; 323: 1574-1581https://doi.org/10.1001/jama.2020.5394Crossref PubMed Scopus (3648) Google Scholar). Clinically, a non-negligible percentage of patients with mild symptoms on ED arrival may develop acute respiratory distress syndrome over the next hours (Paules et al., 2020Paules C.I. Marston H.D. Fauci A.S. Coronavirus infections-more than just the common cold.JAMA. 2020; 323: 707-708https://doi.org/10.1001/jama.2020.0757Crossref PubMed Scopus (1303) Google Scholar). Therefore, tools to rapidly identify the extent of the ongoing inflammatory processes are essential. Chest CT appears to be the most effective diagnostic tool for COVID-19 pneumonia, and the morphology of the lung lesions seems to correlate with the severity of the inflammatory process (Colombi et al., 2020Colombi D. Bodini F.C. Petrini M. Maffi G. Morelli N. Milanese G. et al.Well-aerated lung on admitting chest CT to predict adverse outcome in COVID-19 pneumonia.Radiology. 2020; 201433https://doi.org/10.1148/radiol.2020201433Crossref PubMed Scopus (328) Google Scholar, Zhang et al., 2020Zhang N. Xu X. Zhou L.Y. Chen G. Li Y. Yin H. et al.Clinical characteristics and chest CT imaging features of critically Ill COVID-19 Patients.Eur Radiol. 2020; 30: 1-10https://doi.org/10.1007/s00330-020-06955-xCrossref PubMed Scopus (40) Google Scholar, Dai et al., 2020Dai H. Zhang X. Xia J. Zhang T. Shang Y. Huang R. et al.High-resolution chest CT features and clinical characteristics of patients infected with COVID-19 in Jiangsu, China.Int J Infect Dis. 2020; 95: 106-112https://doi.org/10.1016/j.ijid.2020.04.003Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar). However, extensive use of CT on patients leads to an increased risk of radiological exposure and, possibly, a high number of negative scans. Recently, Shang et al. suggested that arterial blood gas (ABG) values may correlate with the presence and morphological characteristics of CT lesions (Shang et al., 2020Shang Y. Xu C. Jiang F. Huang R. Li Y. Zhou Y. et al.Clinical characteristics and changes of chest CT Features in 307 patients with common COVID-19 pneumonia infected SARS-CoV-2: a multicenter study in Jiangsu, China.Int J Infect Dis. 2020; 96: 157-162https://doi.org/10.1016/j.ijid.2020.05.006Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar). If this early evidence were confirmed, ABG, a rapid, inexpensive, and widely used test might become a valuable tool for the preliminary prognostic assessment of patients with SARS-CoV-2 infection in the ED. This preliminary study was designed to investigate whether an ABG performed on patient arrival in the ED correlates with the extent of the pulmonary inflammatory process and with the prognosis in patients with SARS-CoV-2 infection. From March 20, 2020, to April 10, 2020, in the ED of the Merano Hospital (Italy), all patients consecutively evaluated for a suspected SARS-CoV-2 infection were subjected to an ABG test and chest CT. ABG was performed in all suspected patients immediately after arrival in the ED. Retrospectively, only patients who tested positive by polymerase chain reaction for SARS-CoV-2 were included in the present study. ABG values at ED admission were compared both with the volume of lung parenchyma involved in the inflammatory process (calculated as a percentage of the total lung volume) using Pulmo3D® software (Siemens Healthineers, Erlangen, Germany) and with mortality at 28 days. Seventy-nine consecutive SARS-CoV-2 patients underwent CT and ABG during the study period. The median age of the patients was 68 years (range 61–78), and the majority were male (69.6%). The median percent extension of the pulmonary inflammatory process was 14.3% (5.0%–25.2%). Nine patients (11.4%) died within 28 days of ED evaluation. Among the ABG indices, PaO2:FiO2 had an inverse correlation with the percent extension of the pulmonary inflammatory process on CT (r = −0.451, p < 0.001), as did PCO2 (r = −0.294, p = 0.009) and SpO2 (r = −0.444, p < 0.001), while pH had a direct correlation (r = 0.228, p = 0.044). Patients who had died at 28 days presented reduced values of PaO2:FiO2 (215 versus 314, p = 0.005), PCO2 (26.6 versus 31.5, p = 0.049), and SpO2 (82.7 versus 92.3, p = 0.003) on arrival in the ED (Table 1).Table 1Arterial blood gas test values in patients enrolled in the study, divided according to the median percentage of the extension of the pulmonary inflammatory process (14.3%).Parenchymal involvement < 14.2%Parenchymal involvement > 14.2%pPatients, n (%)40 (50.6)39 (49.4)Age, years, median (IQR)64 (57–74)72 (65–82)0.010Male, n (%)24 (60.0)31 (79.5)0.087Onset of symptoms, days (IQR)5 (2–10)5 (3–10)0.715Polycomorbidities15 (37.5)28 (71.8)0.003Arterial blood gas test pH7.44 (7.42–7.49)7.45 (7.43–7.48)0.520 PaO2 (mmHg)71.8 (62.5–80.8)62.9 (53.6–73)0.013 PaCO2 (mmHg)35.9 (32.1–38)32.3 (31–36.8)0.080 HCO324 (23.1–26.4)23.9 (21.5–26.6)0.430 PaO2:FiO2 (mmHg)335 (293–365)250 (198–314)<0.001 SpO295.3 (94.3–97)92.8 (89.1–95.4)0.002Deaths within 28 days2 (5.0)7 (17.9)0.087 Open table in a new tab The regression cubic spline model revealed that reduced PaO2:FiO2 values are associated with a higher percentage of the lung being involved in the inflammatory process, as detected on CT (Figure 1). Preliminary data from this study suggest that values from an ABG test performed upon arrival of a patient with SARS-CoV-2 in the ED may correlate with the extent of the pulmonary inflammatory process and provide indications of the patient's prognosis. The correlation between ABG indices and CT morphological evaluation of patients with COVID-19 pneumonia has recently been reported. Shang et al. demonstrated a moderate correlation between the presence of ground-glass opacities (GGO) and pulmonary fibrosis on the chest CT with the oxygen index and PO2 and a weak correlation with PCO2 (Shang et al., 2020Shang Y. Xu C. Jiang F. Huang R. Li Y. Zhou Y. et al.Clinical characteristics and changes of chest CT Features in 307 patients with common COVID-19 pneumonia infected SARS-CoV-2: a multicenter study in Jiangsu, China.Int J Infect Dis. 2020; 96: 157-162https://doi.org/10.1016/j.ijid.2020.05.006Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar). These results are in line with the correlations observed in the data from this study, in which a higher percentage of the lung being involved in the inflammatory process, as reconstructed on the CT scan, appears to correlate with decreased oxygenation capacity. The presence of diffuse bilateral GGO, causing exclusion of pulmonary parenchyma (consolidations) and air trapping, has been previously identified in clinically severe patients (Dai et al., 2020Dai H. Zhang X. Xia J. Zhang T. Shang Y. Huang R. et al.High-resolution chest CT features and clinical characteristics of patients infected with COVID-19 in Jiangsu, China.Int J Infect Dis. 2020; 95: 106-112https://doi.org/10.1016/j.ijid.2020.04.003Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar). This could explain the difficulty of oxygenating the blood, even with high FiO2 values, and for this reason, an initially low PaO2:FiO2 index appears to underline the severity of the patient. Colombi et al. suggested that software-based reconstruction of the quantity of well-ventilated lung at CT (and thus indirectly the severity of the extension of the pulmonary inflammatory process) can improve the estimation of the patient's severity compared to the morphological evaluation alone (Colombi et al., 2020Colombi D. Bodini F.C. Petrini M. Maffi G. Morelli N. Milanese G. et al.Well-aerated lung on admitting chest CT to predict adverse outcome in COVID-19 pneumonia.Radiology. 2020; 201433https://doi.org/10.1148/radiol.2020201433Crossref PubMed Scopus (328) Google Scholar). Reduced ABG values on ED arrival may suggest a greater underlying extension of the inflammatory process and thus identify a patient who may present an increased prognostic risk even if not clinically compromised. Further confirmatory data are required, but the results of this study suggest that in patients with SARS-CoV-2, the ABG test will be an important tool in the ED due to its rapidity and applicability. This study was approved by the local ethics committee (Protocollo nr. 57-2020). None. None.

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