Subject-ventilator synchrony during neural versus pneumatically triggered non-invasive helmet ventilation

Abstract

Objective: Patient-ventilator synchrony during non-invasive pressure support ventilation with the helmet device is often compromised when conventional pneumatic triggering and cycling-off were used. A possible solution to this shortcoming is to replace the pneumatic triggering with neural triggering and cycling-off-using the diaphragm electrical activity (EA(di)). This signal is insensitive to leaks and to the compliance of the ventilator circuit.

Design: Randomized, single-blinded, experimental study.

Setting: University Hospital. PARTICIPANTS AND SUBJECTS: Seven healthy human volunteers.

Interventions: Pneumatic triggering and cycling-off were compared to neural triggering and cycling-off during NIV delivered with the helmet.

Measurements and results: Triggering and cycling-off delays, wasted efforts, and breathing comfort were determined during restricted breathing efforts (<20% of voluntary maximum EA(di)) with various combinations of pressure support (PSV) (5, 10, 20 cm H(2)O) and respiratory rates (10, 20, 30 breath/min). During pneumatic triggering and cycling-off, the subject-ventilator synchrony was progressively more impaired with increasing respiratory rate and levels of PSV (p < 0.001). During neural triggering and cycling-off, effect of increasing respiratory rate and levels of PSV on subject-ventilator synchrony was minimal. Breathing comfort was higher during neural triggering than during pneumatic triggering (p < 0.001).

Conclusions: The present study demonstrates in healthy subjects that subject-ventilator synchrony, trigger effort, and breathing comfort with a helmet interface are considerably less impaired during increasing levels of PSV and respiratory rates with neural triggering and cycling-off, compared to conventional pneumatic triggering and cycling-off.

Fig. 1

Example of diaphragm electrical activity (EA_di), and ventilatory assist during pneumatically (left panel) and neurally (right panel) triggered and cycled-off NIV in one healthy subject breathing with the helmet interface. In this example, respiratory rate was 30 bpm, PSV level was 20 cm H₂O. The dashed line shows the start of neural inspiration and the continuous line shows the end of neural inspiration. Note excessive asynchrony during pneumatically triggered and cycled-off NIV

Fig. 2

Differences in inspiratory delays (delay time P_tr − delay time N_tr) during NIV with a pressure support of 5, 10 and 20 cm H₂O and respiratory rates of 10, 20 and 30 bpm were shown. During all combinations of respiratory rates and pressure support levels, there was a significant difference in inspiratory delays being highly increased during pneumatically triggered NIV. Symbols represent group median values and the bars indicate 25th and 75th percentiles. Delay-on inspiratory delay between the onset of the volunteers’ inspiratory effort and the start of the ventilatory support, P _tr pneumatic trigger, N _tr neural trigger, NIV non-invasive ventilation

Fig. 3

Differences in expiratory delays (delay time P_off − delay time N_off) during NIV with PSV of 5, 10 and 20 cm H₂O and respiratory rates of 10, 20 and 30 bpm were shown. During all combinations of respiratory rates and pressure support levels, there was a significant difference in expiratory delays that were highly increased during pneumatically triggered NIV. Symbols represent group median values and the bars indicate 25th and 75th percentiles. Delay-off delay between the onset neural end of inspiration and the end of the ventilatory support, P _off pneumatic cycling-off, N _off neural cycling-off, NIV non-invasive ventilation

Fig. 4

Percentage of asynchrony over the whole breath duration as calculated during N_tr and P_tr NIV: (delay-on + delay-off/neural T _tot × 100). Wasted inspiratory efforts were counted as 100% asynchrony. Percentage of asynchrony during P_tr was markedly higher compared to N_tr. Symbols represent group median values and the bars indicate 25th and 75th percentiles. N _tr neurally triggered, P _tr pneumatically triggered, NIV non-invasive ventilation, PSV pressure support ventilation

Fig. 5

Breathing comfort in mm as assessed by a visual analogue scale during neurally and pneumatically triggered and cycled-off NIV at different levels of assist and respiratory rates (0 very comfortable, 100 unbearable). During all combinations of respiratory rates and PSV levels, comfort of breathing was better during neurally triggered and cycled-off NIV. Symbols represent group median values and the bars indicate 25th and 75th percentiles. NIV non-invasive ventilation, PSV pressure support ventilation, VAS visual analogue scale