330 - Hypopharyngeal oxygen and carbon dioxide levels in premature infants receiving support via nasal cannula

Publication Number: 330.5446

Waleed Kurtom, University of Miami Leonard M. Miller School of Medicine, Seattle, WA, United States; Jose Tolosa, University of Miami, Miami, FL, United States; Augustin C. Bancalari, Florida International University Herbert Wertheim College of Engineering, Orlando, FL, United States; Deepak Jain, Rutgers, Robert Wood Johnson Medical School, New Brunswick, NJ, United States; Alini Schott, University of Miami Leonard M. Miller School of Medicine, Miami, FL, United States; Ana Cecilia. Aguilar, University of Miami, Miami, FL, United States; Eduardo Bancalari, University of Miami, Miami, FL, United States; Nelson Claure, University of Miami Leonard M. Miller School of Medicine, Miami, FL, United States

Background: Nasal Cannula (NC) is a common method to provide supplemental O2 to extreme premature infants. During NC use, premature infants can entrain ambient air and the actual inspired O2 delivered to the airways at various NC-flow rates is not always known. The tips of the NC can obstruct the nares. This may limit exhalation and result in CO2 rebreathing. The extent to which different NC flow rates result in CO2 rebreathing is unknown.

Objective: To determine the interaction between the concentration of O2 in the gas delivered by NC (NC-O2), NC-flow, infant’s respiratory rate (RR) and body weight with the measured hypopharyngeal O2 and CO2 concentrations in premature infants born between 23-30w gestation.

Design/Methods: This was a prospective crossover study. In each infant, NC-flow rates were set at 0.50, 1.0, 2.0, 4.0 and 6.0 L/min. O2 and CO2 concentrations were measured in continuously sampled gas from the hypopharynx. RR was measured by respiratory inductance plethysmography. After every change in NC-flow, NC-O2 was adjusted in 30-s steps aiming to maintain the hypopharyngeal O2 at near basal level.

Results: Eighteen infants with a mean BW of 702 ± 23 g and 26 ± 1 w gestational age were studied at 35 ± 4 w PMA. Modelling by generalized estimating equations for clustered data showed that hypopharyngeal O2 was associated with NC-flow, NC-O2, body weight and RR (Table 1). Hypopharyngeal CO2 was associated with NC-flow and RR (Table 2). Figures 1 and 2 show representative examples from individual infants.

Conclusion(s): Hypopharyngeal O2 and CO2 can be estimated using a combination of NC-O2, NC-flow, RR, and PMA. These data showed that at lower NC-flow rates hypopharyngeal O2 can be considerably lower than the set NC-O2 and that lower NC-flow rates are associated with increased CO2 rebreathing.

Factors influencing nasopharyngeal O2 and CO2


Hypopharyngeal O2 and CO2 with NC-flow at 1 lpm
Figure shows a representative recording from an individual infant receiving NC-flow at 1 lpm. Note hypopharyngeal O2 is lower than the NC-O2 and hypopharyngeal CO2 is slightly increased.

Hypopharyngeal O2 and CO2 with a reduction in NC-flow from 1 to 0.5 lpm
Figure shows a recording from an individual infant when NC-flow is changed from 1 to 0.5 LPM (arrow). Note the large decrease in hypopharyngeal O2 and the immediate increase in hypopharyngeal CO2.