343 - Is there a “Floor FIO2” during Management of Pulmonary Hypertension?

Publication Number: 343.5953

Payam Vali, University of California, Davis, School of Medicine, sacramento, CA, United States; Amy Lesneski, University of California, Davis, School of Medicine, Davis, CA, United States; Rebecca Valdez, University of California Davis, Davis, CA, United States; Victoria Hammitt, University of California, Davis, School of Medicine, Sacramento, CA, United States; Deepika Sankaran, University of California Davis Children's Hospital, Sacramento, CA, United States; Evan M. Giusto, UC Davis Health, Sacramento, CA, United States; Sylvia Bowditch, University of California Davis Children's Hospital, Sacramento, CA, United States; Satyan Lakshminrusimha, UC Davis, Sacramento, CA, United States

Background: Birth asphyxia and meconium aspiration syndrome (MAS) are associated with hypoxic ischemic encephalopathy (HIE) and pulmonary hypertension (PH). Whole body hypothermia, standard of care for HIE, has been shown to exacerbate PH. The oxygen tension within the alveolus is the primary factor in relaxing the pulmonary vasculature and reducing pulmonary vascular resistance (PVR). Hence, some units avoid weaning FiO2 below a certain level (“Floor FIO2”, usually ~ 0.4) irrespective of SpO2 and PaO2 during the management of PH to avoid exacerbation of hypoxic pulmonary vasoconstriction.

Objective: Determine if weaning FIO2 < 0.4 as long as PaO2 is ≥ 45 mmHg and SpO2 is ≥ 90% in a lamb model of MAS and PH during hypothermia decreases pulmonary blood flow (Qp).

Design/Methods: Nine near-term (139-141d; term is 147d) fetal lambs were instrumented and asphyxiated for ten minutes. The tracheal tube was filled with 20% solution of meconium in amniotic fluid that was aspirated into the lung during fetal gasping. Lambs were delivered and ventilated for 6h. During this period, lambs received hypothermia for 3h. FIO2 was adjusted to maintain goal SpO2 between 90 to 98%. FiO2 wean < 0.4 was allowed as long as preductal PaO2 was ≥ 45 mmHg and SpO2 ≥ 90% could be maintained.

Results: Lamb characteristics, and median (IQR) FIO2, Qp, preductal PaO2, SaO2 and SpO2 are shown in Table 1. We have shown that there is a good positive correlation (r= 0.52) between FIO2 and PaO2 if FIO2 was < 0.7 (Fig 1A). However, the sicker lambs who required an FIO2 > 0.70 had a negative correlation coefficient (r= -0.62) with relatively low PaO2 (Fig 1A). Lambs that required a low FIO2 and with physiological PaO2 (PaO2 45 - 80 mm Hg) had a similar Qp compared to lambs who were given higher FIO2 (Fig 1B). Finally, optimal Qp was demonstrated at a PaO2 range between 45 to 80 mm Hg with a good correlation coefficient of 0.47 between PaO2 and QP, whereas there was no further increase in Qp with PaO2 > 80 mm Hg (Fig 2).

Conclusion(s): In an asphyxiated lamb model of MAS and PH, lower FIO2 below 0.4 does not result in decreased Qp during hypothermia as long as PaO2 is maintained between 45 to 80 mm Hg. We could not demonstrate any exacerbation of hypoxic pulmonary vasoconstriction and low Qp with weaning inspired oxygen below a “Floor FiO2.” Further studies are needed to determine the optimal “minimum” FIO2 for patients with PH.

Lamb Characteristics


Relationship between PaO2 and Pulmonary Blood Flow vs FIO2
There is a good positive correlation between increasing FIO2 and PaO2 until FIO2 increases beyond 0.7 (A). There is no correlation between higher FIO2 and pulmonary blood flow (B).

Pulmonary Blood Flow in Relation to PaO2
Optimal pulmonary blood flow occurs between a PaO2 of 45 to 80 mm Hg