Effects of NAVA Compared to SIMV Ventilation on Cardiac Function in Preterm Neonates

Abstract

Background: Neurally Adjusted Ventilatory Assist (NAVA) provides proportional assist ventilation in synchrony with the patient’s respiratory drive and improves patient-ventilator synchronization compared to conventional ventilation (SIMV PC/PS). This improved synchrony on NAVA may also impact the cardiovascular system. Previous studies show systolic blood pressure higher during NAVA compared to conventional ventilation modes. The effect on cardiac function from improved ventilatory synchronization with NAVA is unknown. This study evaluates left ventricular function in preterm neonates on NAVA ventilation when compared to SIMV.

Methods: Randomized, single blinded, crossover trial of preterm neonates, 23 -37 weeks on invasive mechanical ventilation. A coin toss determined the initial mode of ventilation (NAVA vs. SIMV). After a stabilization period (at least 1 hour) initial Doppler echocardiographic measurements were obtained. The patient was then switched to the other mode of ventilation and, after a stabilization period, a repeat Doppler echocardiographic measure of cardiac function was obtained. The patient was then returned back to the original ventilatory mode. Quantitative assessment of LV systolic function was performed using echocardiographic and Doppler measurements. Ejection fraction was measured from parasternal short axis using m-mode, and Simpsons 2 chamber (2c) and 4 chamber (4c) were measured from apical views. Other measurements included Left Ventricular (LV) Velocity Time Integral (VTI) and cross-sectional area (CSA - calculated at the level of aortic valve annulus). The reading cardiologist was blinded to the mode of ventilation. Left ventricular output was calculated as follows: LV output = [VTI (cm/beat) x CSA (cm2) x heart rate /body weight. Paired t-test was used to compare the variables on NAVA vs. SIMV. P <0.05 was considered significant.

Results: Fourteen patients were randomized. Gestational age was 25±3.2 weeks, birth weight was 923±566 grams, age at study was 8.6±5.9 days and weight at study was 776±411 grams. During NAVA, LV output (P < 0.04) and Simpson 2c (P = 0.05) were higher and LV end systolic volume trended lower (P=0.06). There was no difference in heart rate, LV end diastolic volume, Simpson 4c, and ejection fraction.

Conclusions: This pilot study shows that neonates have improved left ventricular output on NAVA ventilation compared to on SIMV. We speculate that higher LV output during NAVA may be the consequence of a better cardio-respiratory synchronization.