Changes in ventilation distribution during general anesthesia measured with EIT in mechanically ventilated small children

Abstract

Background: Atelectasis during general anesthesia is a risk for perioperative complications. EIT measurements were performed in mechanically ventilated healthy children during elective surgery to demonstrate the changes in ventilation distribution during general anesthesia. The ventilation distribution was quantified by calculating the Global Inhomogeneity index (GI).

Methods: EIT measurements were performed in 23 children (9 weeks-10 years) without lung disease to detect changes in regional ventilation during elective surgery. Three previously defined time points were marked during the measurement: after intubation and start of pressure-controlled ventilation (PCV), change to pressure support ventilation (PSV), and after extubation (spontaneous breathing-SB). Ventilation distribution based on regions of interest (ROI) and changes in end-expiratory volume (∆EELV) were collected at these time points and compared. The Global Inhomogeneity index was calculated at the beginning of pressure-controlled ventilation (PCV).

Results: With increasing spontaneous breathing, dorsal recruitment of atelectasis occurred. The dorsal ventilation fraction increased over the time of general anesthesia with increasing spontaneous breathing, whereas the ventral fraction decreased relatively (Difference ± 5.5 percentage points respectively; 95% CI; 3.5-7.4; p < 0.001). With the onset of spontaneous breathing, there was a significant reduction in end-expiratory volume (Difference: 105 ml; 95% CI, 75-135; p < 0.001). The GI of the lung-healthy ventilated children is 47% (SD ± 4%).

Conclusion: Controlled ventilation of healthy children resulted in increased ventilation of the ventral and collapse of the dorsal lung areas. Restart of spontaneous breathing after cessation of surgery resulted in an increase in ventilation in the dorsal with decrease in the ventral lung areas. By calculating the GI, representing the ratio of more to less ventilated lung areas, revealed the presumed homogeneous distribution of ventilation.

Trial registration: ClinicalTrials.gov Registration ID: NCT04873999. First registration: 05/05/2021.

Keywords: ARDS; EIT; GI; General anesthesia; Pediatrics; Ventilation distribution.

Conflict of interest statement

The authors declare no competing interests.

© 2023. The Author(s).

Figures

Fig. 1

Ventilation distribution based on horizontal layers—ROI 1–4. The middle horizontal marker illustrates the grouping of ROI 1 and 2 as the ventral layer, and ROI 3 and 4 as the dorsal layer. The dorsal layer is 5.5 percentage points more ventilated at the time of spontaneous breathing (SB) than at the time of controlled ventilation (PCV)

Fig. 2

Plot of ventilation at the three intervention time points PCV, PSV and SB. ROIs 1 and 2 were combined into ROI ventrally, ROIs 3 and 4 into ROI dorsally. In the dorsal regions, there is an increase in ventilation by recruitment of dorsal atelectasis by a mean of 5.5 percentage points with increasing spontaneous breathing. In turn, the ventilation fraction of the ventral lung regions decreases

Fig. 3

Plot of EELV changes at the three ventilation mode transitions. Ventral lung areas (left) and dorsal lung areas (right) show how the total ∆EELV change is proportionally distributed between the two regions at the corresponding ventilation mode transitions of ventilation. In addition to the boxplots, the change for each individual patient is plotted. To allow assignment over the course of individual study participants, the values are connected by gray lines. The values of the study population do not show a normal distribution. Due to statistical outliers, the median values are used as measure of location. The dorsal regions show an increase, which can be explained by the recruitment of atelectasis due to the onset of spontaneous breathing. Due to the loss of PEEP after termination of mechanical ventilation, the overdistension in the ventral lung regions decreases and thus the proportion of ∆EELV

Fig. 4

Exemplary representation of the EELV reduction at the different ventilation mode transitions. Orange: reduction in EELV; blue: increase in EELV; black: no change. Changing the mode of ventilation from PCV to PSV (left) shows only a small reduction of EELV which is mostly distributed in the ventral lung areas. After termination of mechanical ventilation (PSV to SB, right), the reduction is much more pronounced and distributed more evenly in both lung regions. The ventral portion decreases in favor of the dorsal by 9.9 percentage points

Fig. 5

Global Inhomogeneity index (GI). The GI suggests that healthy children have a very homogeneous distribution of ventilation