Trending peripheral venous PCO₂in patients with respiratory failure using mathematically arterialised venous blood gas samples

Abstract

BackgroundTrending venous blood gases (VBGs) has been suggested as an alternative to arterial blood gases (ABGs) in patients with respiratory failure, but there are limits to its utility. The aim of this study was to compare the trending of venous carbon dioxide partial pressure (pCO2) (pCO2v) with mathematically arterialised pCO2 (pCO2ca) and to further evaluate whether pCO2ca follows change in arterial pCO2 (pCO2a) more accurately.MethodsWe analysed two data sets. The first was a retrospective study of patients with respiratory failure admitted to the intensive care unit. Venous samples were mathematically arterialised using the vTAC method. The change in pCO2 between two consecutive samples (ΔpCO2) for pCO2v was compared with the change in calculated pCO2ca values. In the second data set taken from previously published work, we analysed 82 trend points (difference between consecutive samples) for change in pCO2. There were pCO2v, pCO2a and pCO2ca values for each trend point. The primary outcome measures were the 95% limits of agreement (LOAs) between different sampling methods for ΔpCO2.ResultsIn the first data set, 46 patients had 203 VBG results giving 157 trend points for ΔpCO2 analysis. The 95% LOAs for ΔpCO2ca and ΔpCO2v were −9.28 to 11.12 mm Hg.In the second data set, 95% LOAs for ΔpCO2 were −9.46 to 9.48 mm Hg for ΔpCO2a and ΔpCO2v, −8.94 to 8.58 mm Hg for ΔpCO2ca and ΔpCO2v, and −4.54 to 4.91 mm Hg for ΔpCO2a and ΔpCO2ca.ConclusionThis study suggests that trending pCO2v is not an accurate way to trend pCO2a in patients with respiratory failure. ΔpCO2ca via vTAC trended differently to ΔpCO2v. Our data suggest pCO2ca more accurately trends pCO2a.

Comparison of mathematically arterialised venous blood gas sampling with arterial, capillary, and venous sampling in adult patients with hypercapnic respiratory failure: a single-centre longitudinal cohort study

“…There is also inherent variability of sampling even when the sample is clearly arterial 15 25. As a pragmatic study, we accepted that patients were unlikely to be physiologically stable from a respiratory perspective at the time of sampling.…”

“…There is also inherent variability of sampling even when the sample is clearly arterial. 15 25 As a pragmatic study, we accepted that patients were unlikely to be physiologically stable from a respiratory perspective at the time of sampling. We did not tend to use local anaesthesia for ABG sampling and recognise this as a weakness against national standards 3 4 though not in comparison to usual practice in the UK.…”

“…Prior studies exploring the agreement between absolute arterial and v-TAC PaCO 2 values indicated a requirement for 41 matched samples at 80% power (β-level 0.20) and 5% significance (α-level 0.05) 8–15. We assumed a proportionate variability for the change in PaCO 2 in the absence of existing data, though aimed to recruit at least 80 patients.…”

Effect of N95 filtering facepiece respirator on venous blood carbon dioxide levels and hemodynamic changes in health care workers

“…Although VBG by peripheral route can be used instead of ABG, it may not reflect the trending changes in PCO 2 accurately. [ 17 ] The difference in CO 2 values between arterial and venous samples can range from 4.4 to 6 mmHg. Although arterial and PvCO 2 show acceptable correlation, this difference can increase and become unpredictable in patients with haemodynamic instability and respiratory failure.…”

Arterial pCO2 prediction using saphenous pCO2 in healthy mechanically ventilated dogs

“…Numerous studies have been conducted in the last few years in human medicine to establish whether there is a relationship between arterial and venous pH and partial pressure of carbon dioxide (pCO 2 ) and how constant and predictable this relationship is, in healthy and ill, conscious and anesthetized patients (Kelly, 2010;Bloom et al, 2014;Byrne et al, 2014). Some authors have even proposed methods to extrapolate arterial values from the VBG analysis (Rees et al, 2006;Lumholdt et al, 2020;Weber and Cave, 2021). Results are different among these studies; however, most of them agree that VBG analysis is a useful tool for the evaluation of pH, since the agreement between arterial and venous values is very good.…”