Time is critical in the diagnosis and treatment of cardiogenic shock, even more so than in septic shock.¹ Early identification enables prompt circulatory support and restoration of tissue oxygenation. Baseline arterial lactate is an early and prognostically relevant biomarker of impaired cellular metabolism and anaerobic glycolysis,² with levels ≥2 mmol/L considered clinically significant.³ However, access to arterial lactate measurements is not always straightforward (eg, during cardiopulmonary resuscitation/ECMO-cannulation, loss of pulsatility, severe vasoconstriction/vasculopathy), and valuable time is often lost in differentiating arterial versus venous samples. This raises the question of the utility of central venous lactate measurements in these critically ill patients for diagnosing cardiac circulatory failure and assessing its severity. Or: what is the correlation between mixed venous and arterial lactate levels in patients with impaired cardiac function?

We performed simultaneous (radial) arterial and (mixed) venous blood gas lactate measurements in 1526 patients at a quaternary cardiac Intensive Care Unit (ICU; both surgical [n=1356, 86%] and nonsurgical [n=170, 14%] cardiac patients), all monitored with a pulmonary artery catheter; From the initial cohort of 1579 patients, 53 patients receiving V-A ECMO support were excluded. Local ethical approval was obtained, with a waiver of consent due to the retrospective, observational nature of the study. Data available on request from the authors. Analysis included 4801 paired samples from the same blood gas analyzer, collected within a median of 8 minutes (interquartile range [IQR], 3–18). Values were compared using simple linear regression, Pearson correlation coefficient (r), and Bland-Altman tests. Data are expressed as median (25th–75th percentile) for non-normally distributed variables.