Beverly D Ejiofor1, Ryan W Carroll2,3, William Bortcosh2, Robert M Kacmarek2,3. 1. Massachusetts General Hospital, Boston, Massachusetts. bejiofor@partners.org. 2. Massachusetts General Hospital, Boston, Massachusetts. 3. Harvard Medical School, Boston, Massachusetts.
Abstract
BACKGROUND: High-flow nasal cannulas (HFNC) have been increasingly used in the pediatric critical care patient population. There are different theories about the mechanism by which HFNC reduces work of breathing, including diminishing upper airway dead space by the washout of carbon dioxide. However, one of the likely primary mechanisms by which HFNC reduces work of breathing is by generating PEEP. There are limited data assessing the PEEP delivered by moderate flows (8-50 L/min) of HFNC, which are used most commonly in pediatric patients. METHODS: Pediatric upper-airway models were created with 5 different nares produced by a 3-dimensional printer and connected to a lung simulator. Age-specific flows were delivered via the 5 different setups. Pressure throughout the simulated airway was measured at HFNC flows of 6-60 L/min with 25%, 50%, and 75% air leak to simulate open-mouth breathing. RESULTS: PEEPs of 1.2-36 cm H2O were generated with HFNC flows of 6-60 L/min. In general, for each specific cannula, increasing the flow and decreasing the air leak resulted in higher levels of PEEP delivered (P < .001 and > 10% difference). Changes in lung mechanics as generated by the lung simulator to simulate different patient ages resulted in the establishment of different levels of PEEP. CONCLUSIONS: HFNCs deliver varying amounts of PEEP at the alveolar level with flows of 6-60 L/min. Increasing flow and decreasing leak resulted in the generation of greater PEEP. PEEP levels differed across cannulas and model weights at the same leak level, likely due to differences in the nasal interface between the HFNC device and the model nares.
BACKGROUND: High-flow nasal cannulas (HFNC) have been increasingly used in the pediatric critical care patient population. There are different theories about the mechanism by which HFNC reduces work of breathing, including diminishing upper airway dead space by the washout of carbon dioxide. However, one of the likely primary mechanisms by which HFNC reduces work of breathing is by generating PEEP. There are limited data assessing the PEEP delivered by moderate flows (8-50 L/min) of HFNC, which are used most commonly in pediatric patients. METHODS: Pediatric upper-airway models were created with 5 different nares produced by a 3-dimensional printer and connected to a lung simulator. Age-specific flows were delivered via the 5 different setups. Pressure throughout the simulated airway was measured at HFNC flows of 6-60 L/min with 25%, 50%, and 75% air leak to simulate open-mouth breathing. RESULTS: PEEPs of 1.2-36 cm H2O were generated with HFNC flows of 6-60 L/min. In general, for each specific cannula, increasing the flow and decreasing the air leak resulted in higher levels of PEEP delivered (P < .001 and > 10% difference). Changes in lung mechanics as generated by the lung simulator to simulate different patient ages resulted in the establishment of different levels of PEEP. CONCLUSIONS: HFNCs deliver varying amounts of PEEP at the alveolar level with flows of 6-60 L/min. Increasing flow and decreasing leak resulted in the generation of greater PEEP. PEEP levels differed across cannulas and model weights at the same leak level, likely due to differences in the nasal interface between the HFNC device and the model nares.
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