Neonates with chronic lung disease often require oxygen in the neonatal intensive care unit. The purpose of this study was to determine (1) the actual inspired oxygen concentration (F1O2) delivered to neonates when using a low-flow flowmeter and a nasal cannula, and (2) the accuracy with which F1O2 could be estimated using a formula that we developed. We studied two groups of infants: 18 infants less than 1,500 g and 13 infants greater than 1,500 g. We measured pharyngeal oxygen levels by sampling pharyngeal gas in infants receiving 100% humidified oxygen by nasal cannula from a low range flow flowmeter. The oxygen flow was increased by 25 mL/min increments from 25 to 200 mL/min. The measured F1O2 was compared with the calculated F1O2 using the formula:

F1O2 measured = oxygen flow (mL/min × 0.79) + (0.21 × VE)/VE× 100,

Where minute ventilation (VE) equals the minute ventilation in mL/min (VE = VT × respiratory rate). For both groups of infants, increments of 25 mL/min of flow produced distinctive changes in F1O2 at all levels (P < 0.001). The calculated F1O2 did not significantly differ from the actual F1O2 at any flow. The calculated F1O2 was most predictive when using an assumed tidal volume of 5.5 mL/kg. We conclude that an accurate flowmeter connected to 100% humidified oxygen can produce a wide range of predictable F1O2s for neonates, especially those with birthweights of less than 1,500 g. The proposed formula allows useful estimation of the infant's F1O2 when we assume a tidal volume of 5.5 mL/kg.

Neil N. Finer MD, FRCPC*, Rosanne Bates RRT, Paula Tomat RRT. Low flow oxygen delivery via nasal cannula to neonates. Pediatric Pulmonology, Volume 21, Issue 1, pages 48–51, January 1996