224 - Gradient of arterial and exhaled carbon dioxide predicts elevated pulmonary artery pressure in a preterm ovine model post resuscitation

Publication Number: 224.5210

Mary Divya Kasu, University of Maryland Children's Hospital, Baltimore, MD, United States; Mausma I. Bawa, University At Buffalo, Buffalo, NY, United States; Sylvia Gugino, SUNY at Buffalo, Buffalo, NY, United States; Justin Helman, Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo, Buffalo, NY, United States; Nicole Bradley, Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo, Buffalo, NY, United States; Lori Nielsen, Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo, Clarence Center, NY, United States; Arun Prasath, UT Southwestern Medical Center, Dallas, TX, United States; Clariss Blanco, NYC Health + Hospitals/ Harlem, New York, NY, United States; Hamza Abbasi, John R. Oishei Children’s Hospital, East Amherst, NY, United States; Munmun Rawat, University at Buffalo, Buffalo, NY, United States; Praveen Chandrasekharan, Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo, Buffalo, NY, United States

Background: End-tidal carbon dioxide (ETCO2) is a non-invasive measure of carbon dioxide at the end of expiration. When pulmonary artery pressures (PAP) are higher, it can create a vascular obstructive state, leading to decreased perfusion of ventilated alveoli, and can create a ventilation/perfusion (V/Q) mismatch increasing dead space. As dead space increases, ETCO2 decreases, creating a higher gradient between arterial carbon dioxide (PaCO2) and ETCO2. Could this gradient help identify high PAP? Previously, this relation was evaluated in a term model (PAS2024, Kasu et al.).

Objective: To understand the relationship between the gradient of PaCO2-ETCO2 and PAP.

Design/Methods: Preterm lamb models (126-127d) gestational age were resuscitated after asphyxia. Post resuscitation and surfactant administration (@ 11 - 13 min), preterm lambs were placed on mechanical ventilation for 2 hours. Invasive systemic and pulmonary blood pressure monitoring was done. Preductal blood gases were obtained every 15 minutes. Philips NM3 respiratory monitor was used to monitor tidal volume, peak inspiratory pressure, and ETCO2. PaCO2-ETCO2 gradients were calculated for all the lambs across different time points. The gradient was compared to the mean PAP ratio to mean systemic arterial pressure (MAP). For study purposes, we have divided the data based on the ratio of PAP & MAP. The ratio of < 0.5 - no pulmonary hypertension (PH)/normal, 0.5 to 1.0 to mild PH, 1.0 to 1.5 to moderate PH, and >1.5 to severe PH. Blood gas parameters and PaCO2-ETCO2 gradient were compared during episodes of PH. ANOVA and correlation (R2) were used for analysis.

Results: Post resuscitation and surfactant (N=45), during ventilation, the tidal volume was 7-8ml/kg. PaCO2 levels were not different (Fig Ia). ETCO2 levels were significantly lower when moderate and severe PH were noted (Fig Ib). PaCO2-ETCO2 gradient was significantly higher during severe PH (Fig Ic). PaO2 was significantly lower during all PH episodes (Fig Id). Correlation (R2) for ETCO2 & PaCO2 was 0.97 with normal PAP (Fig Ia). The R2 for ETCO2 & PaCO2 were as follows: during mild PH episodes: 0.54 (good correlation - Fig IIb); during moderate PH episodes: 0.23 (weak correlation - FigIIc), and the severe PH episodes: 0.01 (poor correlation - Fig IId).

Conclusion(s): In preterm lambs post-resuscitation, the gradient between PaCO2-ETCO2 is higher when PAP is greater than MAP. If ventilation parameters and chest inflation are adequate, the ETCO2-PaCO2 gradient can help identify elevated PAP non-invasively, along with other clinical parameters, prompting further management and monitor response to therapy.

Bar graphs showing different blood gas variables (PaCO2, ETCO2, PaCO2-ETCO2 gradient, PaO2) across different groups of PH
bar graphs preterm gradient.jpegFig Ia) Bar graph showing PaCO2 (mm Hg) across the groups. No significant different was noted.
Fig Ib) Bar graph showing ETCO2 (mm Hg) across the groups. ETCO2 was significantly lower in moderate and severe PH groups
Fig Ic) Bar graph showing PaCO2-ETCO2 gradient (mm Hg) across the groups. Gradient was significantly higher in severe PH group
Fig Id) Bar graph showing PaO2 (mm Hg) across the groups. PaO2 was significantly lower in mild, moderate and severe PH groups.
* indicates p<0.05

Correlation analysis. X-axis is PaCO2(mm Hg); Y-axis: ETCO2 (mm Hg) R2 indicates coefficient of variation
Correlation analysis preterm gradient.jpegFig IIa) Correlation graph for no pulmonary hypertension group; R2=0.97 showing strong correlation between PaCO2 and ETCO2
Fig IIb) Correlation graph for mild pulmonary hypertension group; R2=0.54 showing moderate correlation between PaCO2 and ETCO2
Fig IIc) Correlation graph for moderate pulmonary hypertension group; R2=0.23 showing weak correlation between PaCO2 and ETCO2
Fig IId) Correlation graph for severe pulmonary hypertension group; R2=0.01 showing poor correlation between PaCO2 and ETCO2