The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

UTILIZING 10% NITRIC OXIDE SOURCE GAS TO DELIVER THERAPY WITHOUT REDUCING FIO_{2}

--Lee W. Evey Bs, RRT: Jon K. Moon. PhD: Yuko S. Moon, MD, PhD: Alfred L. Gest. MD: Mary E. Wearden, MD. Texas Children's Hospital - Houston. Texas

INTRODUCTION: Nitric oxide (NO) therapy for the treatment of PPHN is widespread. Most institutions use a source gas of approximately 800ppm to deliver NO concentrations of 1-80ppm. This source gas mixture is composed mostly of nitrogen. Which, when instilled into a ventilator circuit, reduces the delivered FIO_{2} by up to 10%. This reduction in FIO_{2} may adversely affect some patients.

Methods: We designed a low-deadspace system to deliver NO from a 10% (100.000ppm) source directly into the main flow of gas in the ventilator circuit. A 25ml/min mass-flow controller (830 Sierra Instruments, Monterrey, CA) was used to control NO flow. We conducted an acute toxicity trial on 9 rabbits that were mechanically ventilated with 100% O_{2} for 4 hours. Six rabbits received 80ppm NO from a 10% source and 3 control rabbits received O_{2}. NO. nitrogen Dioxide (NO_{2}) and O_{2} concentrations were monitored in the circuit. Concentrations of NO were analyzed by chemiluminescence (42H. Thermoenvironmental Instruments, Franklin, MA) and NO_{2} was analyzed using an electrochemical fuel cell (100. Detcon. The Woodlands, TX). O_{2} concentrations were determined with an electrochemical fuel cell (5590. Hudson/RCI. Temecula, CA). All devices were calibrated according to manufacturers recommendations. Methemoglobin, arterial blood gases, heart rate and blood pressure were recorded q1.

Results: At 80ppm NO an average of 1.1 +/- 0.2 of NO_{2} was detected in the ventilator circuit. Arterial methemoglobin in rabbits who received NO rose by 0.5% from baseline compared to a 0.2% rise for controls (P = 0.001). This difference is not significant. Using a 10% source of NO gas we can deliver 1-80ppm NO while maintaining 99.9% FIO_{2} with no significant increase in NO_{2}. There were no significant differences between the groups in pO_{2}, heart rate and mean arterial pressure.

Conclusions: NO therapy can be safely and accurately delivered from a 10% ppm source of NO. Because our system does not reduce inspired O_{2} it may be appropriate for testing the efficacy of inhaled NO compared to conventional management.

Reference: OF-96-061

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