Continuous assessment of neuro-ventilatory drive during 12 hours of pressure support ventilation in critically ill patients

Abstract

Introduction: Pressure support ventilation (PSV) should allow spontaneous breathing with a “normal” neuro-ventilatory drive. Low neuro-ventilatory drive puts the patient at risk of diaphragmatic atrophy while high neuro-ventilatory drive may causes dyspnea and patient self-inflicted lung injury. We continuously assessed for 12 hours the electrical activity of the diaphragm (EAdi), a close surrogate of neuro-ventilatory drive, during PSV. Our aim was to document the EAdi trend and the occurrence of periods of “Low” and/or “High” neuro-ventilatory drive during clinical application of PSV.Method: In 16 critically ill patients ventilated in the PSV mode for clinical reasons, inspiratory peak EAdi peak (EAdiPEAK), pressure time product of the trans-diaphragmatic pressure per breath and per minute (PTPDI/b and PTPDI/min, respectively), breathing pattern and major asynchronies were continuously monitored for 12 hours (from 8 a.m. to 8 p.m.). We identified breaths with “Normal” (EAdiPEAK 5 - 15 mV), “Low” (EAdiPEAK < 5 mV) and “High” (EAdiPEAK >15 mV) neuro-ventilatory drive.Results: Within all the analyzed breaths (177.117), the neuro-ventilatory drive as expressed by the EAdiPEAK, was “low” (<5 mV) in 50.116 breath (28 %), Normal (5-15 mV) in 88.419 breaths (50 %) and High (>15 mV) in 38.582 breaths (22 %). The average times spent in “Low”, “Normal” and “High” class were 1.37 hours, 3.67 hours and 0,55 hours, respectively (p < 0.0001), with wide variations among patients. Eleven patients remained in the “Low” neuro-ventilatory drive class for more than one hour, median 6.1 [3.9 - 8.5] hours and 6 in the “High” neuro-ventilatory drive class, median 3.4 [2.2 – 7.8] hours. The asynchrony index was significantly higher in the “Low” neuro-ventilatory class, mainly because of a higher number of missed efforts.Conclusions: We observed wide variations in EAdi amplitude and unevenly distributed “Low” and “High” neuro ventilatory drive periods during 12 hours of PSV in critically ill patients. Our data suggest that PSV might result in periods of over or under-assistance. Further studies are needed to assess the possible clinical implications of these physiological findings.