Comparison of pH and PCO2 between arterial and venous blood gas samples in critically ill patients

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We aimed to determine the utility of venous blood in a medical intensive care unit population. METHODS Seventy-six critically ill patients requiring arterial blood sampling as part of their standard clinical management were prospectively enrolled in this study. A venous blood sample was drawn from the same upper extremity within 5 min of the arterial blood sampling. Venous pH, pCO 2, and pO 2 were measured in venous samples and compared with those in their arterial counterparts. RESULTS The venous pCO 2 was, on average, higher by 5.8 mmHg (standard deviation = 4.6 mmHg) than the arterial pCO 2 with Bland-Altman 95% limits of agreement of −3.4, 15.1 mmHg. CONCLUSIONS Obtaining venous blood from an intact upper extremity in critically ill individuals can provide a reliable estimate of arterial pCO 2 and eliminate the need for invasive arterial blood sampling. blood gas critical care respiratory failure carbon dioxide hypercapnia Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The measurement of pH, partial pressure of oxygen (pO 2 ), and partial pressure of carbon dioxide (pCO 2 ) in arterial blood has been used for decades to assess metabolic disorders and respiratory status 1 . However, arterial blood sampling is invasive, can be painful, and carries the risk of complications 2 . There has been growing interest in using venous blood samples as a surrogate for arterial blood samples. Obtaining venous blood samples is easier, less invasive, and less painful than obtaining arterial blood samples. Venous blood gas (VBG) testing is a valuable tool for assessing acid-base homeostasis and is commonly used in diabetic ketoacidosis 3 . Estimating arterial pCO 2 is challenging, considering the variable contribution of CO 2 by individual organs and perfusion areas. Previous studies demonstrated some utility of VBG testing in heterogeneous populations 4 , 5 . Although a good correlation between arterial and venous pCO 2 has been well established 6 , the reliance on venous blood samples in the clinical management of critically ill patients remains controversial. A meta-analysis 7 of five studies involving patients with chronic obstructive pulmonary disease showed an average difference between arterial and peripheral venous pH and pCO 2 of 0.028 and -5.9 mmHg, respectively. The authors concluded that there was a good agreement on pH; however, the utility of pCO 2 in individual cases was limited. Some researchers have also examined the utility of a central VBG, i.e., a VBG of a mixed central venous sample. A meta-analysis revealed a reasonable correlation regarding pH and pCO 2 in hemodynamically stable patients 8 . However, in shock states, the agreement was too poor to be clinically helpful. Central venous pCO 2 was found to be within 11 mmHg of the arterial pCO 2 in the majority of ventilated trauma patients during initial resuscitation in another study; however, the sample size was small 9 . Some methodological and anatomical considerations are relevant to the challenges in using VBG in clinical practice as well as in designing studies. Depending on the acuity of the situation, the blood gas levels and pH can change within minutes. The mixed venous blood pCO 2 is mostly a function of pulmonary CO 2 clearance (typically the area of clinical interest) but also of CO 2 production 10 . CO 2 production is generally a minor factor affecting arterial blood CO 2 levels in individuals with an intact and unincumbered ventilatory system. Therefore, the pCO 2 is generally determined entirely by alveolar ventilation. The exact venous source is not irrelevant when peripheral venous samples are used. O 2 extraction and CO 2 production in body areas may vary depending on muscle mass (upper vs. lower extremities) or the proximity of a highly metabolic organ (e.g., the brain in the case of the external jugular vein). The available studies are inconsistent with respect to the site of venous access. We postulated that there is a small and predictable difference in the pCO 2 and pH between the arterial and venous sides of a perfusion area characterized by a low metabolic rate, such as the upper extremity, at rest and that the predictability of this difference is of clinical value in the critically ill population. Materials and Methods Subject Population Any patient, 18 years or older, admitted to our medical intensive care unit was eligible for enrollment if ABG testing was expected to be necessary for the patient’s standard of care management. Informed consent was obtained from the participants or appropriate decision-maker surrogates. Pregnant women and prisoners were excluded from this study. The Institutional Review Board of Albany Medical Center approved the study (protocol # 5447, approval date Jan 07, 2020, “Numerical Comparison of pH and pCO2 Values between Arterial Blood Gas and Venous Blood Gas”). Written informed consent was obtained from all participants or their surrogates. All procedures were performed in accordance with the ethical standards of the institutional review board and the 1975 Declaration of Helsinki. Study Procedures The need for ABG testing was based on the clinical needs in the treating physician's opinion. The ABG sample was obtained by a right or left radial arterial puncture after completing an Allen test, as routinely done in clinical practice. Patients were excluded if a different arterial site was used. The extremity had to be fully intact with no ongoing pathology such as local ischemia, soft tissue infections, or compartment syndrome. Once the ABG sample was secured, a venous blood sample for VBG testing was obtained from the ipsilateral superficial forearm vein, typically the median cubital, median basilic, or median cephalic vein. Venous blood samples were obtained within 5 min of arterial puncture. Both samples were processed using a standard blood gas analyzer (Radiometer ABL-90, Danaher Corp, Washington DC, USA) to obtain direct measurements of pO 2 , pCO 2, and pH. Data Collection and Analysis The following baseline data were collected: standard demographics, time elapsed between ABG and VBG tests, site of arterial and venous puncture, use of vasopressors, and Acute Physiology and Chronic Health Evaluation II (APACHE II) score. Descriptive statistics were then obtained. The differences between each pair (arterial-venous) of variables were recorded, along with the arithmetic means and standard deviations. Bland–Altman analysis was performed on the arterial and venous pCO 2 pairs to obtain 95% limits of agreement. All statistical calculations were performed using R-Studio 2022.12.0 (Boston, MA, 2022). The datasets used in this study are available from the corresponding author upon reasonable request. Results Seventy-six subjects were enrolled between 1/2020 and 8/2022. The baseline characteristics of the patients can be seen in Table 1. On average, venous blood pCO 2 exceeded arterial blood pCO 2 by 5.8 mmHg (standard deviation; SD = 4.6 mmHg, Fig. 1). The average pH difference was 0.038 (SD = 0.027 mm Hg, Fig. 2). The average time between obtaining arterial and venous blood samples was 1:30 min. The Bland–Altman 95% limit of agreement between arterial and venous blood samples for pCO 2 was −3.4, 15.1 mmHg (Fig. 3). A mean difference of 49 mmHg (SD = 35.6 mmHg) was observed between arterial and venous blood pO 2 . Additionally, an average saturation drop of 24.0% (SD = 19.75%) was observed. Subjects with higher APACHE II scores did not appear more prone to a widened a-v pCO 2 difference (Fig. 4). Discussion We demonstrated that using a venous blood sample instead of an arterial sample provided a reasonable estimate of arterial pCO 2 and pH in critically ill patients. Our results confirmed previous findings that, on average, changes in pCO 2 and pH from arterial to venous blood are small. Moreover, we did not observe wide variations among the patients regardless of the severity of the critical illness, which has traditionally been a concern. Previous investigations have suggested that this may be the case when central venous blood samples are used, particularly in cases of circulatory compromise 8 . Considering that oxygen extraction in shock states is increased in the setting of limited perfusion to highly metabolically active organs and tissues, the poor correlation between central venous and arterial blood CO 2 levels is not surprising. We found that the average increase in pCO 2 across the vascular bed of an inactive extremity was 5.8 mmHg. Notably, we demonstrated that there were no wide variations between patients, potentially limiting the clinical applicability of venous blood sampling. Our results, thus, provide clinicians reasonable confidence that venous pCO 2 is within 15 mmHg of arterial pCO 2 . The strength of our study lies in the strict protocol used to obtain the blood samples. Arterial and venous blood samples were drawn from the same extremity virtually simultaneously. This approach provides a high degree of certainty that local variations and fluctuations with time are not factors compromising the results and separates our study from previous studies. We specifically focused on the critically ill population, a challenging population with little existing reliable data. To summarize, a peripheral venous blood sample obtained from an intact extremity provides a clinically useful estimate of arterial CO 2 levels in critically ill patients. Declarations Ethical Approval The Institutional Review Board of Albany Medical Center approved the study (protocol # 5447, approval date Jan 07, 2020, “Numerical Comparison of pH and pCO2 Values between Arterial Blood Gas and Venous Blood Gas”). Written informed consent was obtained from all participants or their surrogates. All procedures were performed in accordance with the ethical standards of the institutional review board and the 1975 Declaration of Helsinki. Funding None Availability of data and materials Raw data are available upon a reasonable request from the corresponding author. References Severinghaus JW, Astrup PB. History of blood gas analysis. I. The development of electrochemistry. J Clin Monit. 1985;1(3):180-192. Reichman EF. Chapter 57. Arterial Puncture and Cannulation. In: Emergency Medicine Procedures, 2e. New York, NY: The McGraw-Hill Companies; 2013. Brandenburg MA, Dire DJ. Comparison of arterial and venous blood gas values in the initial emergency department evaluation of patients with diabetic ketoacidosis. Ann Emerg Med. 1998;31(4):459-465. Malatesha G, Singh NK, Bharija A, Rehani B, Goel A. Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial emergency department assessment. Emerg Med J. 2007;24(8):569-571. Koul PA, Khan UH, Wani AA, et al. Comparison and agreement between venous and arterial gas analysis in cardiopulmonary patients in Kashmir valley of the Indian subcontinent. Ann Thorac Med. 2011;6(1):33-37. Rang LC, Murray HE, Wells GA, Macgougan CK. Can peripheral venous blood gases replace arterial blood gases in emergency department patients? CJEM. 2002;4(1):7-15. Lim BL, Kelly AM. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department. Eur J Emerg Med. 2010;17(5):246-248. Chong WH, Saha BK, Medarov BI. Comparing Central Venous Blood Gas to Arterial Blood Gas and Determining Its Utility in Critically Ill Patients: Narrative Review. Anesth Analg. 2021;133(2):374-378. Malinoski DJ, Todd SR, Slone S, Mullins RJ, Schreiber MA. Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients. Arch Surg. 2005;140(11):1122-1125. Patel S, Miao JH, Yetiskul E, Anokhin A, Majmundar SH. Physiology, Carbon Dioxide Retention. In: StatPearls. Treasure Island (FL) .2023. Table Table 1: Baseline characteristics of participants n=76 Gender (n, %) Female 21 (27.6%) Male 55 (72.4%) Age, years (mean, SD) 64.0 (13.2) APACHE II (mean, SD) 12.54 (7.9) Race (n, %) Caucasian 66 African American 4 Asian 3 Hispanic 3 Vasopressor use (n, %) Yes 12 (15.7%) No 64 (84.3%) Mechanical ventilation (including noninvasive) Yes 28 (36.8%) No 48 (63.2%) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4289632","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":296185133,"identity":"48e95780-327a-4be9-abc0-7007cc0cc77d","order_by":0,"name":"Boris 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carbon dioxide pressure in the subject population.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4289632/v1/5d3269ef4f8987df7367af89.jpg"},{"id":55633379,"identity":"222955ae-5996-4564-96a8-05ed2d00495b","added_by":"auto","created_at":"2024-04-30 20:03:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":136531,"visible":true,"origin":"","legend":"\u003cp\u003eA plot depicting the difference between arterial and venous pH.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4289632/v1/73dccf640b88ac3bf0464fb0.jpg"},{"id":55633377,"identity":"265a2aad-e0f6-4fe5-9567-4765592523bf","added_by":"auto","created_at":"2024-04-30 20:03:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":140550,"visible":true,"origin":"","legend":"\u003cp\u003eBland-Altman plot\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4289632/v1/4ffca30aa28346f6ebdbc13e.jpg"},{"id":55633376,"identity":"0e761ecd-040b-4687-a2ca-b486cfa9305b","added_by":"auto","created_at":"2024-04-30 20:03:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":109222,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between arterial-venous pCO\u003csub\u003e2\u003c/sub\u003e and APACHE II score\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4289632/v1/6dca25291b5c1de30075d798.jpg"},{"id":55693048,"identity":"c6a25ecd-336f-4d97-a1b1-e5abc15724d7","added_by":"auto","created_at":"2024-05-02 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status\u003csup\u003e1\u003c/sup\u003e. However, arterial blood sampling is invasive, can be painful, and carries\u0026nbsp;the risk\u0026nbsp;of complications\u003csup\u003e2\u003c/sup\u003e. There has been growing interest in using venous blood samples as a surrogate for arterial blood samples. Obtaining venous blood samples is easier, less invasive, and less painful than obtaining arterial blood samples. Venous blood gas (VBG) testing is a valuable tool for assessing acid-base homeostasis and is commonly used in diabetic ketoacidosis\u003csup\u003e3\u003c/sup\u003e. Estimating arterial pCO\u003csub\u003e2\u003c/sub\u003e is challenging, considering the variable contribution of CO\u003csub\u003e2\u003c/sub\u003e by individual organs and perfusion areas. Previous studies demonstrated some utility of VBG testing in heterogeneous populations\u003csup\u003e4\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e5\u003c/sup\u003e. Although a good correlation between arterial and venous pCO\u003csub\u003e2\u003c/sub\u003e has been well established\u003csup\u003e6\u003c/sup\u003e, the reliance on venous blood samples in the clinical management of critically ill\u0026nbsp;patients remains controversial. A meta-analysis\u003csup\u003e7\u003c/sup\u003e of five studies involving patients\u0026nbsp;with chronic obstructive pulmonary disease showed an average difference between arterial and\u0026nbsp;peripheral venous pH and pCO\u003csub\u003e2\u003c/sub\u003e of 0.028 and -5.9 mmHg, respectively. The authors concluded that there was\u0026nbsp;a good agreement\u0026nbsp;on pH; however, the utility of pCO\u003csub\u003e2\u003c/sub\u003e in individual cases was limited.\u003c/p\u003e\n\u003cp\u003eSome researchers have also examined the utility of\u0026nbsp;a central VBG,\u0026nbsp;i.e., a VBG of a mixed central venous sample. A meta-analysis revealed a reasonable correlation regarding pH and pCO\u003csub\u003e2\u003c/sub\u003e in hemodynamically stable patients\u003csup\u003e8\u003c/sup\u003e. However, in\u0026nbsp;shock states, the agreement was too poor to be clinically helpful. Central venous pCO\u003csub\u003e2\u003c/sub\u003e was found to be within 11 mmHg of\u0026nbsp;the arterial\u0026nbsp;pCO\u003csub\u003e2\u003c/sub\u003e in the majority of ventilated trauma patients during initial resuscitation in another study; however, the sample size was small\u003csup\u003e9\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eSome methodological and anatomical considerations are relevant to the challenges in using VBG in clinical practice as well as\u0026nbsp;in designing\u0026nbsp;studies. Depending on the acuity of the situation,\u0026nbsp;the blood gas levels and pH can change within minutes. The mixed venous blood pCO\u003csub\u003e2\u003c/sub\u003e is mostly a function of pulmonary CO\u003csub\u003e2\u003c/sub\u003e clearance (typically the area of clinical interest) but also of CO\u003csub\u003e2\u003c/sub\u003e production\u003csup\u003e10\u003c/sup\u003e. CO\u003csub\u003e2\u003c/sub\u003e production is generally a minor factor affecting arterial blood CO\u003csub\u003e2\u003c/sub\u003e levels in individuals with an intact and unincumbered ventilatory system. Therefore, the pCO\u003csub\u003e2\u003c/sub\u003e is generally determined\u0026nbsp;entirely by\u0026nbsp;alveolar ventilation. The exact venous source is not irrelevant when peripheral venous samples are used. O\u003csub\u003e2\u003c/sub\u003e extraction and CO\u003csub\u003e2\u003c/sub\u003e production in body areas may vary depending on muscle mass (upper vs. lower extremities) or the proximity of a highly metabolic organ (e.g., the brain in the case of the external jugular vein). The available studies are inconsistent with respect to the site of venous access.\u003c/p\u003e\n\u003cp\u003eWe postulated that there is a small and predictable difference in the pCO\u003csub\u003e2\u003c/sub\u003e and pH between the arterial and venous sides of a perfusion area characterized by a low metabolic rate, such as the upper extremity, at rest and that the predictability of this difference is of clinical value in the critically ill population.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u003cem\u003eSubject Population\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAny patient, 18 years or older, admitted to our medical intensive care unit was eligible for enrollment if ABG testing was expected to be necessary for the patient\u0026rsquo;s standard of care management. Informed consent was obtained from the participants or appropriate decision-maker surrogates. Pregnant\u0026nbsp;women and prisoners were excluded\u0026nbsp;from this study.\u0026nbsp;The Institutional Review Board of Albany Medical Center approved the study (protocol # 5447, approval date Jan 07, 2020, \u0026ldquo;Numerical Comparison of pH and pCO2 Values between Arterial Blood Gas and Venous Blood Gas\u0026rdquo;). Written\u0026nbsp;informed consent was obtained from all\u0026nbsp;participants or their surrogates. All procedures were performed in accordance with the ethical standards of the institutional review board and the 1975 Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eStudy Procedures\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe need for ABG testing was\u0026nbsp;based on the clinical needs\u0026nbsp;in the treating physician\u0026apos;s opinion. The ABG sample was obtained by a right or left radial arterial puncture after completing an Allen test, as routinely done in clinical practice. Patients were excluded if a different arterial site was used. The extremity had to be fully intact with no ongoing pathology\u0026nbsp;such as local ischemia, soft tissue infections, or compartment syndrome. Once the ABG sample was secured, a venous blood sample for VBG testing was obtained from the ipsilateral superficial forearm vein, typically the median cubital, median basilic, or median cephalic vein. Venous blood samples\u0026nbsp;were obtained within 5 min of arterial puncture. Both samples were processed using a standard blood gas analyzer (Radiometer ABL-90, Danaher Corp, Washington DC, USA) to obtain direct measurements of pO\u003csub\u003e2\u003c/sub\u003e, pCO\u003csub\u003e2,\u003c/sub\u003e and pH.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eData Collection and Analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe following baseline data were collected: standard demographics, time elapsed between ABG and VBG tests, site of arterial and venous puncture, use of vasopressors, and Acute Physiology and Chronic Health Evaluation II (APACHE II) score. Descriptive statistics were then obtained. The differences between each pair (arterial-venous) of variables were recorded,\u0026nbsp;along with the arithmetic means and standard deviations.\u0026nbsp;Bland\u0026ndash;Altman analysis was performed on the arterial and venous pCO\u003csub\u003e2\u003c/sub\u003e pairs to obtain 95% limits of agreement. All statistical calculations were performed using R-Studio 2022.12.0 (Boston, MA, 2022). The datasets used in this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eSeventy-six subjects were enrolled between 1/2020 and 8/2022. The baseline characteristics of the patients can be seen in Table 1.\u0026nbsp;On average, venous blood pCO\u003csub\u003e2\u003c/sub\u003e exceeded arterial blood pCO\u003csub\u003e2\u003c/sub\u003e by 5.8 mmHg (standard deviation; SD = 4.6 mmHg, Fig. 1). The average\u0026nbsp;pH difference\u0026nbsp;was 0.038 (SD = 0.027 mm\u0026nbsp;Hg, Fig. 2). The average time between obtaining arterial and venous blood samples was 1:30 min. The Bland\u0026ndash;Altman 95% limit of agreement between arterial and venous blood samples for pCO\u003csub\u003e2\u003c/sub\u003e was \u0026minus;3.4, 15.1 mmHg (Fig. 3).\u003c/p\u003e\n\u003cp\u003eA mean difference of 49 mmHg (SD = 35.6 mmHg) was observed between arterial and venous blood pO\u003csub\u003e2\u003c/sub\u003e. Additionally, an average saturation drop of 24.0% (SD = 19.75%) was observed.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Subjects with higher APACHE II scores did not appear more prone to a widened a-v pCO\u003csub\u003e2\u003c/sub\u003e difference (Fig. 4).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe demonstrated that using a venous blood sample instead of an arterial sample provided a reasonable estimate of arterial pCO\u003csub\u003e2\u003c/sub\u003e and pH in critically ill patients. Our results confirmed previous findings that, on average, changes in pCO\u003csub\u003e2\u003c/sub\u003e and pH from arterial to venous blood are small. Moreover, we did not\u0026nbsp;observe wide variations among the patients\u0026nbsp;regardless of the severity of the critical illness, which has traditionally\u0026nbsp;been a concern. Previous investigations\u0026nbsp;have suggested that this may be the case when central venous blood samples are used, particularly in cases of circulatory compromise\u003csup\u003e8\u003c/sup\u003e. Considering that oxygen extraction in shock states is increased in the setting of limited perfusion to highly metabolically active organs and tissues, the poor correlation between central venous and arterial blood CO\u003csub\u003e2\u003c/sub\u003e levels is not surprising.\u003c/p\u003e\n\u003cp\u003eWe found that the average increase in pCO\u003csub\u003e2\u003c/sub\u003e across the vascular bed of an inactive extremity was 5.8 mmHg. Notably, we demonstrated that there were no wide variations between patients, potentially limiting the clinical applicability of venous blood sampling. Our results, thus, provide clinicians reasonable confidence that venous\u0026nbsp;pCO\u003csub\u003e2\u003c/sub\u003e is within 15 mmHg of arterial pCO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eThe strength of our study lies in the strict protocol used to obtain the blood samples. Arterial and venous blood samples were drawn from the same extremity virtually simultaneously. This approach provides a high degree of certainty that local variations and fluctuations with time are not factors compromising the results and separates our study from previous studies. We specifically\u0026nbsp;focused on the critically ill population, a challenging population with little existing reliable data.\u003c/p\u003e\n\u003cp\u003eTo summarize, a peripheral venous blood sample obtained from an intact extremity provides a clinically useful estimate of arterial CO\u003csub\u003e2\u003c/sub\u003e levels in critically ill patients.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cem\u003eEthical Approval\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe Institutional Review Board of Albany Medical Center approved the study (protocol # 5447, approval date Jan 07, 2020, \u0026ldquo;Numerical Comparison of pH and pCO2 Values between Arterial Blood Gas and Venous Blood Gas\u0026rdquo;). Written\u0026nbsp;informed consent was obtained from all\u0026nbsp;participants or their surrogates. All procedures were performed in accordance with the ethical standards of the institutional review board and the 1975 Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFunding\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003eNone\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAvailability of data and materials\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eRaw data are available upon a reasonable request from the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSeveringhaus JW, Astrup PB. History of blood gas analysis. I. The development of electrochemistry. \u003cem\u003eJ Clin Monit. \u003c/em\u003e1985;1(3):180-192.\u003c/li\u003e\n\u003cli\u003eReichman EF. Chapter 57. Arterial Puncture and Cannulation. In: \u003cem\u003eEmergency Medicine Procedures, 2e.\u003c/em\u003e New York, NY: The McGraw-Hill Companies; 2013.\u003c/li\u003e\n\u003cli\u003eBrandenburg MA, Dire DJ. Comparison of arterial and venous blood gas values in the initial emergency department evaluation of patients with diabetic ketoacidosis. \u003cem\u003eAnn Emerg Med. \u003c/em\u003e1998;31(4):459-465.\u003c/li\u003e\n\u003cli\u003eMalatesha G, Singh NK, Bharija A, Rehani B, Goel A. Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial emergency department assessment. \u003cem\u003eEmerg Med J. \u003c/em\u003e2007;24(8):569-571.\u003c/li\u003e\n\u003cli\u003eKoul PA, Khan UH, Wani AA, et al. Comparison and agreement between venous and arterial gas analysis in cardiopulmonary patients in Kashmir valley of the Indian subcontinent. \u003cem\u003eAnn Thorac Med. \u003c/em\u003e2011;6(1):33-37.\u003c/li\u003e\n\u003cli\u003eRang LC, Murray HE, Wells GA, Macgougan CK. Can peripheral venous blood gases replace arterial blood gases in emergency department patients? \u003cem\u003eCJEM. \u003c/em\u003e2002;4(1):7-15.\u003c/li\u003e\n\u003cli\u003eLim BL, Kelly AM. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department. \u003cem\u003eEur J Emerg Med. \u003c/em\u003e2010;17(5):246-248.\u003c/li\u003e\n\u003cli\u003eChong WH, Saha BK, Medarov BI. Comparing Central Venous Blood Gas to Arterial Blood Gas and Determining Its Utility in Critically Ill Patients: Narrative Review. \u003cem\u003eAnesth Analg. \u003c/em\u003e2021;133(2):374-378.\u003c/li\u003e\n\u003cli\u003eMalinoski DJ, Todd SR, Slone S, Mullins RJ, Schreiber MA. Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients. \u003cem\u003eArch Surg. \u003c/em\u003e2005;140(11):1122-1125.\u003c/li\u003e\n\u003cli\u003ePatel S, Miao JH, Yetiskul E, Anokhin A, Majmundar SH. Physiology, Carbon Dioxide Retention. In: \u003cem\u003eStatPearls.\u003c/em\u003e Treasure Island (FL) .2023.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003e\u003cstrong\u003eTable 1: Baseline characteristics of participants\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"300\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003en=76\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eGender (n, %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;Female\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e21 (27.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;Male\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e55 (72.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eAge, years (mean, SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e64.0 (13.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eAPACHE II (mean, SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e12.54 (7.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eRace (n, %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;Caucasian\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;African American\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;Asian\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eHispanic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eVasopressor use (n, %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e12 (15.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026emsp;No\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e64 (84.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eMechanical ventilation\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(including noninvasive)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e28 (36.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.333333333333336%\" valign=\"top\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"45.666666666666664%\" valign=\"top\"\u003e\n \u003cp\u003e48 (63.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"blood gas, critical care, respiratory failure, carbon dioxide, hypercapnia ","lastPublishedDoi":"10.21203/rs.3.rs-4289632/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4289632/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBACKGROUND\u003c/strong\u003e\u003cem\u003e\u003cbr\u003e\n\u003c/em\u003eThe reliability of peripheral venous blood sampling as a substitute for arterial blood sampling in determining the partial pressure of carbon dioxide (pCO\u003csub\u003e2\u003c/sub\u003e) in critically ill patients remains controversial. We aimed to determine the utility of venous blood in a medical intensive care unit population.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMETHODS\u003c/strong\u003e\u003cbr\u003e\nSeventy-six critically ill patients requiring arterial blood sampling as part of their standard clinical management were prospectively enrolled in this study. A venous blood sample was drawn from the same upper extremity within 5 min of the arterial blood sampling. Venous pH, pCO\u003csub\u003e2,\u003c/sub\u003e and pO\u003csub\u003e2\u003c/sub\u003e were measured in venous samples and compared with those in their arterial counterparts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRESULTS\u003c/strong\u003e\u003cbr\u003e\nThe venous pCO\u003csub\u003e2\u003c/sub\u003e was, on average, higher by 5.8 mmHg (standard deviation = 4.6 mmHg) than the arterial pCO\u003csub\u003e2\u003c/sub\u003e with Bland-Altman 95% limits of agreement of −3.4, 15.1 mmHg.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCONCLUSIONS\u003c/strong\u003e\u003cbr\u003e\nObtaining venous blood from an intact upper extremity in critically ill individuals can provide a reliable estimate of arterial pCO\u003csub\u003e2\u003c/sub\u003e and eliminate the need for invasive arterial blood sampling.\u003c/p\u003e","manuscriptTitle":"Comparison of pH and PCO2 between arterial and venous blood gas samples in critically ill patients","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-30 20:03:51","doi":"10.21203/rs.3.rs-4289632/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0c34cdb5-277c-4afc-bd3c-b556742355c1","owner":[],"postedDate":"April 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-30T20:03:53+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-30 20:03:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4289632","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4289632","identity":"rs-4289632","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}