193 - Electrical Impedance Tomography Used to Measure Ventilation-Perfusion Mismatch in Infants

Publication Number: 193.4621

Jessica E. Shui, Harvard Medical School, Lynnfield, MA, United States; Marcus Victor Jr, Harvard Medical School, Boston, MA, United States; Bernard Kinane, MassGeneral Hospital for Children, Boston, MA, United States; Maurizio Cereda, Massachusetts General Hospital, Sherborn, MA, United States; Lorenzo Berra, Massachusetts General Hospital, Boston, MA, United States; Ryan Carroll, MassGeneral Hospital for Children, Boston, MA, United States

Background: Assessing pulmonary ventilation/perfusion (V/Q) match involves transportation, radiation exposure, radioactive tracers, or intravenous contrast injection, all of which are unfavorable or infeasible for critically ill infants.

There is growing interest in pediatric applications of electrical impedance tomography (EIT) as a non-invasive, radiation-free, bedside, real-time lung imaging tool. EIT ventilation assessments can be conducted on children breathing with or without respiratory support. Adult protocols for assessing pulmonary perfusion with EIT, however, require an apnea hold maneuver coupled with an intravenous hypertonic saline injection. Concerns over unwanted effects of medically induced apnea holds and hypertonic saline injections in infants have prompted a search for alternatives. One attractive option is EIT pulsatility measurements, which are electrical impedance changes in the chest, synchronized with heartbeats, primarily related to pulmonary blood content.

Objective: We investigated whether pulsatility measurements can be used in infants to evaluate V/Q mismatch without requiring an induced apnea maneuver or intravenous injection.

Design/Methods: An Enlight 2100 (Timpel, Sao Paulo, Brazil) EIT belt was wrapped around the chest at T4 and changes in electrical impedance was measured in the thorax. Distribution of ventilation between right and left lungs and pulsatility measurements were acquired. Ventilation-pulsatility maps were generated based on ventilation:pulsatility peak ratios. Deadspace (blue) was defined as > 2; shunting (red) was defined as < 0.5; and well-matched areas (green) were defined as 0.5-2. Assessments were conducted for 15 minutes in an infant with congenital lobar emphysema prior to V/Q scan and 1 hour in two infants with unrepaired congenital diaphragmatic hernia.

Results: 1) There is close agreement of 61% perfusion in the right thorax determined by V/Q scan and 63% using EIT pulsatility, in an infant with congenital lobar emphysema. 2) Ventilation-pulsatility maps can be generated in unrepaired CDH, characterizing V/Q mismatch. There is worse mismatch (shunting) in the infant treated with inhaled nitric oxide for poor oxygenation compared to the infant without pulmonary hypertension.

Conclusion(s): EIT generated ventilation-pulsatility maps in infants is feasible, safe, and has the potential of characterizing V/Q mismatch. Studies are underway to further validate EIT pulsatility as a surrogate for pulmonary perfusion measurement in infants and the use ventilation-pulsatility maps to guide management of critically ill infants with pulmonary hypertension.

Figure 1
PAS 2025 Fig 1.pdfOrientation of typical impedance measurements in the thorax using EIT, and graphic of an infant wearing an EIT belt.

Figure 2
PAS 2025 Fig 2.pdfA) Gold-standard lung perfusion scan in a 4-month-old with left congenital lobar emphysema on room air. B) Ventilation, pulsatility, and overlapping ventilation-pulsatility map measured 15 minutes before the lung perfusion scan. There is a close agreement of 61% perfusion in the right thorax determined by perfusion scan (A) and 63% using EIT pulsatility (B, middle). For the composite image (B, far right), the dead space region (blue) is defined as ventilation/pulsatility pixel-amplitude ratios >2; shunting (red) if <0.5; and well-matched (green) if between 0.5 and 2.

Figure 3
PAS 2025 Fig 3.pdfEIT ventilation-pulsatility maps can be generated in unrepaired CDH, characterizing V ̇/Q ̇ mismatch and shunt. A) Ventilation, pulsatility, and overlapping ventilation-pulsatility map of a neonate with unrepaired left-sided CDH with hypoxia supported with FiO2 1.0 and inhaled nitric oxide 20 parts per million; B) Ventilation, pulsatility, and overlapping ventilation-pulsatility map of a well-oxygenated neonate with unrepaired right-sided CDH supported with FiO2 0.48. There is a worse mismatch (shunting) in the neonate with poor oxygenation compared to the well-oxygenated neonate. CDH: congenital diaphragmatic hernia.

Figure 1
PAS 2025 Fig 1.pdfOrientation of typical impedance measurements in the thorax using EIT, and graphic of an infant wearing an EIT belt.

Figure 2
PAS 2025 Fig 2.pdfA) Gold-standard lung perfusion scan in a 4-month-old with left congenital lobar emphysema on room air. B) Ventilation, pulsatility, and overlapping ventilation-pulsatility map measured 15 minutes before the lung perfusion scan. There is a close agreement of 61% perfusion in the right thorax determined by perfusion scan (A) and 63% using EIT pulsatility (B, middle). For the composite image (B, far right), the dead space region (blue) is defined as ventilation/pulsatility pixel-amplitude ratios >2; shunting (red) if <0.5; and well-matched (green) if between 0.5 and 2.

Figure 3
PAS 2025 Fig 3.pdfEIT ventilation-pulsatility maps can be generated in unrepaired CDH, characterizing V ̇/Q ̇ mismatch and shunt. A) Ventilation, pulsatility, and overlapping ventilation-pulsatility map of a neonate with unrepaired left-sided CDH with hypoxia supported with FiO2 1.0 and inhaled nitric oxide 20 parts per million; B) Ventilation, pulsatility, and overlapping ventilation-pulsatility map of a well-oxygenated neonate with unrepaired right-sided CDH supported with FiO2 0.48. There is a worse mismatch (shunting) in the neonate with poor oxygenation compared to the well-oxygenated neonate. CDH: congenital diaphragmatic hernia.