Surfactant Treatment Shows Higher Correlation Between Ventilator and EIT Tidal Volumes in an RDS Animal Model

Abstract

Neonatal respiratory distress syndrome (RDS) is a condition of pulmonary surfactant insufficiency in the premature newborn. As such, artificial pulmonary surfactant administration is a key treatment. Despite continued improvement in the clinical outcomes of RDS, there are currently no established bedside tools to monitor whether pulmonary surfactant is effectively instilled throughout the lungs. Electrical impedance tomography (EIT) is an emerging technique in which physiological functions are monitored on the basis of temporal changes in conductivity of different tissues in the body. In this preliminary study, we aimed to assess how EIT tidal volumes correlate with ventilator tidal volumes in an RDS animal model, namely untreated, surfactant-treated, and normal control rabbit pups. Tidal volumes were measured simultaneously on an EIT system and a mechanical ventilator and compared at different peak inspiratory pressures. The linear correlation between tidal volumes measured by EIT and by ventilator had an R ² of 0.71, 0.76 and 0.86 in the untreated, surfactant-treated, and normal control groups, respectively. Bland-Altman analysis showed a good correlation between the measurements obtained with these two modalities. The intraclass correlation coefficients (ICC) between ventilator tidal volume and EIT tidal volume were 0.83, 0.87, and 0.93 (all p < 0.001) in the untreated, surfactant-treated, and normal control groups, respectively, indicating that the higher ICC value, the better inflated status of the lung. In conclusion, we demonstrated that EIT tidal volume correlated with ventilator tidal volume. ICC was higher in the surfactant treated group.

Keywords: alveoli collapse; electronic impedance tomography; homogeneity; mechanical ventilator; neonatal intensive care unit (NICU); premature infant; respiratory distress syndrome.

FIGURE 1

An example of tidal volume measurement and EIT images in a subject from preterm treated group (A) Pressure-volume curves of ventilator tidal volume and EIT tidal volume. (B) The reconstructed chest cross-section EIT according to PIP change. PIP, peak inspiratory pressure.

FIGURE 2

Pressure-volume curves. The graphs were based on the median values of the untreated preterm group (n = 9), surfactant treated group (n = 6), and term group (n = 3). Maximum and minimum values are shown in Table 1. * means statistical significance between the untreated preterm group and surfactant treated preterm group (p = 0.018, 0.026, Mann-Whitney U test). PIP, peak inspiratory pressure; Inf, inflation; Def, deflation.

FIGURE 3

Linear regression analysis and intraclass correlation coefficient (ICC) of tidal volumes determined by the ventilator and EIT V_T in each group.

FIGURE 4

A Bland–Altman plot (A) and violin plot (B) showing differences between the ventilator and EIT with the 95% limits of agreement. PIP, peak inspiratory pressure; Vent V_T, ventilator tidal volume; EIT V_T, EIT tidal volume.