Increasing sweep gas flow reduces respiratory drive and dyspnea in non-intubated veno-arterial ECMO patients - a pilot study.

BACKGROUND.:Data on assessment and management of dyspnea in patients on veno-arterial extracorporeal membrane oxygenation (VA-ECMO) for cardiogenic shock are lacking. We hypothesized that increasing sweep gas flow through the VA-ECMO oxygenator may decrease dyspnea in non-intubated VA-ECMO patients exhibiting clinically significant dyspnea, with a parallel reduction in respiratory drive. METHODS.:Non-intubated, spontaneously breathing, supine patients on VA-ECMO for cardiogenic shock who presented with a visual analog dyspnea scale (dyspnea-VAS) ≥ 40/100 mm were included. Sweep gas flow was increased up to +6 L/min by three steps of +2 L/min each. Dyspnea was assessed with dyspnea-VAS and Multidimensional Dyspnea Profile. The respiratory drive was assessed by the electromyographic activity of the alae nasi and parasternal muscles. RESULTS.:We included 21 patients. On inclusion, median dyspnea-VAS was 50 ([interquartile range] 45-60) mm and sweep gas flow was 1.0 L/min (0.5-2.0). An increase in sweep gas flow significantly decreased dyspnea-VAS (50[45-60] at baseline vs 20[10-30] at 6L/min; p<0.001). The decrease in dyspnea was greater for the sensory component of dyspnea (-50%[43-75]) than for the affective and emotional components (-17%[0-25] and -12%[0-17], p<0.001). An increase in sweep gas flow significantly decreased electromyographic activity of the alae nasi and parasternal muscles (-23%[36-10] and -20[41-0], p<0.001). There was a significant correlation between the sweep gas flow and the dyspnea-VAS (r=-0.91 95%CI[-0.94, -0.87]), between the respiratory drive and the sensory component of dyspnea (r=0.29 95%CI[0.13, 0.44]), between the respiratory drive and the affective component of dyspnea (r=0.29 95%CI[0.02, 0.54]) and between the sweep gas flow and the alae nasi and parasternal (r=-0.31 95%CI[-0.44, -0.22] and r=-0.25 95%CI[-0.44, -0.16]). CONCLUSION.:In critically ill patients with VA-ECMO, an increase in sweep gas flow through the oxygenation membrane decreases dyspnea, possibly mediated by a decrease in respiratory drive.