Association of arterial blood pH at cannulation with 1-year survival among VA-ECMO recipients: the three seven rule

Objective: We aimed to describe the clinical outcomes of patients receiving veno-arterial extracorporeal membrane oxygenation therapy considering clinical context and pH at cannulation. Methods: We reviewed all patients having received veno-arterial extracorporeal membrane oxygenation therapy at a tertiary referral center during the 2005-2020 period with 1-year complete follow up. Our cohort was divided in three groups according to the pH level at cannulation: pH7.2 (group 3). Survival was analyzed using Kaplan–Meier method. Association between pH group and survival was estimated using a Cox model. Results: Among the 951 patients in our database, 572 were included in 3 different groups according to their pH at implantation: 60 patients in group 1, 115 in group 2 and 397 in group 3. Main indications of mechanical support were refractory cardiogenic shock (36%), post cardiotomy (28%), early graft failure (12%), refractory cardiac arrest (11%). One-year survival rate was 13% in group 1, 36% in group 2, 43% in group 3 respectively (p<0.001). Death mainly occurred within the first month. The strong correlation between pH and lactates led to propose a simple “three seven rule”: pH7 was associated with <7% survival. Conclusion: Extracorporeal veno-arterial membrane oxygenation should be considered with caution in patients with pH<7. Lactates and pH level might be important parameters to elaborate a new score to predict survival in this population. The simplicity of the “three seven rule” can be very relevant when facing emergency situations.