Evidence-Based Translational Research Approach May Help to Select the Best Femoral Arterial Cannula for Adolescent/Adult Extracorporeal Life Support Population

I read with great interest, Dr Broman et al.’s recent article entitled ‘Pressure and flow properties of cannulae for extracorporeal membrane oxygenation I: return (arterial) cannulae’. The authors evaluated three different brands (Maquet (15, 17, 21, 23 Fr), Medos (16, 20, 24 Fr) and Medtronic 15, 17, 21, 23 Fr)) of femoral artery cannulae with several different sizes in an adult extra corporeal membrane oxygenation (ECMO) circuitry using human blood (Hematocrit of 27%). The authors concluded that ‘single-lumen return cannulae for peripheral ECMO tested using whole human blood showed different flow rates as compared to those reported by manufacturers using water’, which is an expected outcome because of the higher viscosity of the blood versus water. However, there may be a limitation in their study. Three femoral arterial cannulae (19 Fr Maquet, 18 Fr Medos and 19 Fr Medtronic) for this particular ECMO population were missing from their evaluations.¹ We have already completed the evaluation of these femoral artery cannulae using adult ECMO circuit primed with human packed red cells and lactated ringers solution (hematocrit of 35%). The objective of this translational study is to evaluate eight femoral arterial cannulae (Medtronic and Maquet, 15 Fr, 17 Fr and 19 Fr compared to Medos: 16 Fr and 18 Fr) using an adolescent/adult extracorporeal life support (ECLS) circuitry.

Based on these results for the same patient population in this particular ECLS circuitry, we recommend to use (15 Fr, 17 Fr or 19 Fr) Medtronic or Maquet femoral arterial cannulae instead of 16 Fr or 18 Fr Medos cannula, respectively. Although the Medtronic cannulae in all sizes have the lowest pressure drops, the differences in pressure drops between Medtronic and Maquet cannulae are shallow and may not reach a clinical significance. However, the 16 Fr and 18 Fr Medos cannulae have the highest pressure drops compared to the other two brands and smaller in sizes of cannulae evaluated in our study. Pressure drops of a cannula among different brands at identical experimental conditions are higher than 20 mmHg is considered a clinical significance.

Although the priming of the circuitry with human blood for cannulae evaluations is an important step, it will always be too far from a clinical scenario. Pressure drops of the same cannulae will always be much higher in clinical settings than in-vitro evaluations. In addition to priming the circuitry with human blood for cannulae evaluations, the mean arterial pressures of the pseudo-patients in simulated settings should also be adjusted clinically accepted levels.