Converting venous acid–base and oxygen status to arterial in patients with lung disease

Abstract

The aim of the present study was to evaluate a method for calculating arterial values of pH, carbon dioxide tension (PCO 2 ) and oxygen tension (PO 2 ) from peripheral venous values.In total, 40 patients were studied. Arterial and peripheral venous blood were sampled at a department of respiratory diseases. Arterial values were calculated from venous, and measured and calculated values of arterial pH, PCO 2 and PO 2 were compared.Measured and calculated values of pH and PCO 2 correlated well, with the difference between them having a very small bias and standard deviation (pH -0.001¡0.013, PCO 2 -0.09¡0.28 kPa) within those considered acceptable for laboratory equipment and clinical practice. All but four patients had peripheral oxygen saturation (Sp,O 2 ) f96%, and for these measured and calculated PO 2 correlated well, with a difference such that the bias and standard deviation suggested that calculated PO 2 may be clinically useful (PO 2 0.11¡0.53 kPa).The present study evaluates a method for calculating arterial pH, carbon dioxide tension and oxygen tension from venous blood. It has been shown that arterial pH and carbon dioxide tension can be calculated precisely, and that oxygen tension can be calculated with reasonable precision in the vast majority of patients. This method might be useful in reducing the need for painful arterial punctures.

Comparison of Arterial and Venous Blood Gases and the Effects of Analysis Delay and Air Contamination on Arterial Samples in Patients with Chronic Obstructive Pulmonary Disease and Healthy Controls

“…While there is consensus that such samples are unreliable for assessment of arterial P O 2 or P C O 2 , published studies have suggested that arterial and venous pH values are comparable [13,14,15,16,17]. Other studies have suggested that calculation of arterial acid-base and blood gas status can be made from measurements in the peripheral venous blood [20,21]. International guidelines for instituting non-invasive ventilation for patients with decompensated hypercapnic respiratory failure emphasize the acid-base status of a patient and the level of hypercapnia [22].…”

The Intelligent Ventilator (INVENT) project: The role of mathematical models in translating physiological knowledge into clinical practice

“…the 95% confidence interval. Errors in SpO 2 of ± 4% have been shown to give only small variation in calculated arterial pH and PCO 2 , these errors being fairly constant over the range of SpO 2 values [73].…”

“…However, to understand whether these results reflect in a broader population, it was necessary to consider the sensitivity of calculations to measurement error and to the assumptions contained in the method. This sensitivity analysis was published in [72,73], and a summary follows.…”

“…As discussed previously [73], a pulse oximeter that reads too low, as represented by the bottom dashed line on the figure, potentially results in unecessary supplementary oxygen, fluids or other intervention, i.e. there is no risk of hypoxaemia due to the pulse oximeter reading too low.…”

“…This means that the RQ over the sampling site would be between 0.7 and 1.0 and that the change in BE between arterial and venous blood would approximate zero. The quality of perfusion of a limb can be simply assessed in the clinic, and little difference in arterial-venous BE was seen in studied patients, even when no control was made to ensure normal perfusion [73]. Ethical approval has been obtained to investigate these potential applications.…”