The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Comparisonof Two Methods to Deliver Subambient Oxygen to Infants with Hypoplastic LeftHearts Via an Oxyhood

DavidM. Dolcini BS RRT, Robert L. Chatburn, RRT, FAARC, Timothy R. Myers BS RRT.Rainbow Babies & Children?s Hospital, Cleveland, OH.

Introduction:Survival of infants with hypoplastic left heart syndrome (HLHS) is dependentupon achieving several therapeutic goals. One goal is to maintain a balancebetween systemic and pulmonary blood flow. This can be achieved using subambientconcentrations of oxygen (15-20%). Subambient oxygen concentrations can be deliveredby adding a measured flow of nitrogen to the inhaled gas (bleed-in technique).Some children with HLHS require mechanical ventilation strictly for the precisedelivery of subambient oxygen to meet the aforementioned goal. Theoretically,mechanical ventilation could be avoided by administering subambient oxygen witha hood setup. Cardiology and Cardiothoracic Surgery at our institution desiresubambient oxygen stability in 5-10 minutes after manipulation. The purposeof this study was to compare the efficacy of delivering subambient oxygen concentrationsvia a high-pressure system previous described (Respir Care.2000; 45(8):1009)vs. a traditional bleed in system.

Methods: FiveTeledyne T-190 (Teledyne Brown Engineering) oxygen analyzers were calibratedper manufacturer?s specifications prior to use (analyzer accuracy for subambientoxygen has been previously documented in Resp Care. 1999;44:1226). We placedan infant resuscitation manikin in a 12?x12?x12? oxygen hood (Nova Health Systems,Blackwood, NJ) for simulation purposes. Oxygen analysis from five sites in thehood would be conducted simultaneously. Analyzer #1 was placed at the humidifier,#2 at the top of the hood, #3 midway between top and bottom, #4 at mouth level,and #5 on the bottom of the hood. Analyzer locations were the same for bothsystems. Blender flow was set at our standard rate of 12 L/m. When assessingthe bleed-in system, flow from the oxygen blender was decrease as the nitrogenflow was bled-in to achieve a similar maximal flow of 12 L/m. Starting witha FiO2 of 21%, the FiO2 was decreased to clinical subambientlevels in increments of 1-4% (e.g. 21% to 17% = 4% change). Time (in seconds)was recorded from stability of analyzer #1 to a steady state on the other analyzersor a maximum time constraint of ten minutes as a test stop point.

Results: Eachanalyzer site (Top, Mid, Mouth & Bottom) had the following number of measurementsfor clinically, relevant changes in FiO2 percentage (6 measurementsat 1% change, 5 measurements at 2% change, 4 measurements at 3% change, and3 measurements at 4% change). The bleed-in system was terminated by time constraint79% (57 out of 72) of all measurements, and in 77% (14 out of 18) of the measurementsmade at mouth level. The high-pressure system was terminated 11% (8 out of 72)of all measurements, and in 0% (0 out of 18) of the measurements made at mouthlevel. When subambient oxygen was analyzed at mouth level, the high-pressuresystem on average was 4:45 faster to stability (18 measurements of 1-4% drop).Data below are average times (min:sec) for all measurements to achieve variousdrops in FiO2 .

 1% Drop2% Drop3% Drop4% Drop
High Pressure4:444:40 6:107:55
Difference3:56 5:04 3:392:05

*denotes termination

Conclusions: Deliveryof subambient oxygen with a high-pressure system results in quicker stabilizationof end-point FiO2 compared to the traditional bleed-in method.



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