2007 OPEN FORUM Abstracts
FDO2 OF O2 DELIVERY DEVICES DURING SIMULATED INFANT BREATHING
D. N. Crotwell 1, R. M. DiBlasi 2, J. W. Salyer 1
Introduction: We sought to determine the FDO2 of O2 delivery devices used in pediatric practice.
Methods: A model of an infant face was fabricated from the head of an infant resuscitation manikin intended to mimic a 5 Kg infant. The back of the head was removed and openings for nares and mouth were connected into a single tube using smooth bore plastic tubing to simulate a hypopharynx. The back of the face was stabilized using insulation foam. The model was connected to a breathing simulator (Ingmar ASL 5000), a series of one way valves were fashioned so inspiratory and expiratory flow were isolated. Simulator settings were; CL=8 mL/cmH2O, RAW=30 cmH2O/L/s, f=40/min, and PTP gradient of 3 cmH2O. This produced VT=24 mL (5 mL/Kg). FDO2 was measured in the simulated hypopharynx with a paramagnetic O2 analyzer (GE Healthcare). Devices tested included nasal cannula (NC), simple mask (SM), non-rebreathing mask (NRB), self-inflating resuscitation bag (SIB), and flow inflating resuscitation bag (FIB). O2 flowrates (L/m) tested were; 0.25, 0.50, 1.0, 1.5, 2.0 for NC, 5, 7, 10 for SM, 7 for NRB, and 15 for both SIB and FIB. The SIB was tested with a mask held to the face and the corrugated tubing reservoir held 2” and 4” from the face. The FIB was tested with a mask held on, 2” and 4” from the face. The FIB was tested without a mask as well. FDO2 data were gathered manually for 5 breaths at each of the test conditions. Mean and standard deviation were calculated for each device/condition.
Results: See table. Discussion: This model approximates maximum FDO2 since it does not mix inhaled and exhaled gases. We did this because the lung model would have exhaled higher than normal O2 concentrations since no O2 was consumed. This exhaled gas would have mixed with inhaled gas artificially increasing FDO2. We speculate that in vivo FDO2 is likely to be no higher, but may be lower. Our interest was in describing the effect of entrainment of room air and mixing with O2 that occurs at the interface of pediatric delivery devices and the contour of the infant face. Note that the widespread practice of “blow-by” O2 administration that occurs using both SIB and FIB creates much lower FDO2 than the use of SM or NC at higher flow rates. The swing in airway pressures in this model was 3 cm H2O. At these low pressures, the SIB, when applied to the face with a mask, produced FDO2 equal to FIB, which also dispels the commonly held myth that FIB produce higher FDO2 than SIB.