Mathematical arterialization of venous blood in emergency medicine patients Gitte Tygesen a , Helle Matzen b , Karen Grønkjær b , Lisbeth Uhrenfeldt c , Steen Andreassen d , Ove Gaardboe a and Stephen Edward Rees d Objectives Arterial punctures represent a painful and unpleasant experience. Acid–base and oxygenation status can be assessed from peripheral venous blood, but agreement with arterial values is not always clinically acceptable. This study evaluates a method for mathematically transforming peripheral venous values into arterial values in emergency medicine patients. Methods Paired arterial and peripheral venous samples were analysed in groups A (47 patients) and B (101 patients), corresponding to the clinical need for arterial blood sampling (A) and without (B). Venous values were input into the mathematical arterialization method and the values of arterial pH, PCO 2 and PO 2 were calculated and compared with the measured values. Results The calculated and measured arterial pH and PCO 2 values correlated well with the correlation coefficients (r 2 ) of group A, pH 0.94, PCO 2 0.97; group B, pH 0.87, PCO 2 0.83; and Bland–Altman limits of agreement well within the limits of acceptable laboratory and clinical performance. The calculated values of arterial PO 2 followed a set of predefined rules relating calculated and measured PO 2 levels in all cases. The method represents an improvement on the use of venous blood alone where the correlation coefficients were as follows: group A, pH 0.85, PCO 2 0.88; group B, pH 0.79, PCO 2 0.59; and limits of agreement for PCO 2 at the border of (group A) or beyond (group B) acceptable clinical limits. Conclusion Application of the mathematical arterialization method may reduce the pain associated with assessment of acid–base and oxygenation status, maximize the information obtained from peripheral venous blood and allow venous measurements to be presented as more commonly interpreted arterial values. European Journal of Emergency Medicine 19:363–372 c 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins. European Journal of Emergency Medicine 2012, 19:363–372 Keywords: acid–base, arterialization, peripheral venous blood a Departments of Emergency Medicine, b Clinical Biochemistry, The Hospital Unit Horsens, c The Hospital Research Unit Horsens, Horsens and d Department of Health Science and Technology, Center for Model Based Medical Decision Support Systems, Aalborg University, Aalborg, Denmark Correspondence to Stephen Edward Rees, PhD, Department of Health Science and Technology, Center for Model Based Medical Decision Support, Aalborg University, DK-9220 Aalborg, Denmark Tel: + 45 99 408 793; fax: + 45 98 154 008; e-mail: sr@hst.aau.dk Received 23 May 2011 Accepted 6 October 2011 Introduction Sampling of peripheral venous blood, and analysis of acid– base status, is gaining popularity as a tool for the assessment of acutely ill patients. Arterial samples are commonly obtained through needle punctures, but are more difficult than obtaining venous samples, and asso- ciated with side-effects including haematoma, thrombosis, peripheral emboli or nerve damage [1,2]. Arterial sampling has been shown to be more painful than peripheral venous sampling and represents the most common unpleasant experience for intensive care patients [3,4]. Peripheral venous blood is often sampled for other purposes, meaning that no extra puncture may be required. Despite these advantages, the case for peripheral venous acid–base status is not clear. Rang et al. [5] investigated emergency physicians’ opinion regarding peripheral ve- nous values, reporting clinically acceptable differences between arterial and peripheral venous values to be (mean and 95% confidence interval) 0.05 (0.04–0.06) for pH and 6.6 mmHg (5.6–7.6 mmHg) (0.88 kPa, 0.75–1.01 kPa) for PCO 2 . When comparing the values of arterial and peripheral venous pH and PCO 2 , limits of agreement beyond these ranges have been found, questioning its acceptance in clinical practice [5–8]. Recently, a method has been proposed that enables calculation of the values of arterial acid–base and oxygenation status from measurements performed in peripheral venous blood [9] (see Fig. 1). This ‘mathe- matical arterialization’ has been shown to have reasonable limits of agreement (bias ± 2  SD) when calculating arterial pH (0.002 ± 0.027) or PCO 2 ( – 0.04 ± 0.52 kPa) in patients admitted to the wards of either ICUs or a department of pulmonary medicine [10,11]. In addition, calculated values of PO 2 may be useful. For pulse oximetry readings of SpO 2 96% or less, the limits of agreement of calculated and measured arterial PO 2 were 0.21 ± 1.85 kPa (bias ± 2  SD) [10]. By quantifying the errors in the calculation of PO 2 due to pulse oximetry, Rees et al. [11] proposed a set of clinical rules by which calculated arterial PO 2 values could be interpreted, providing cut-off values for the actual value of PO 2 , given a calculated value. Original article 363 0969-9546 c 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/MEJ.0b013e32834de4c6 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.