A SAFE CLINICAL-SYSTEM FOR NITRIC-OXIDE INHALATION-THERAPY FOR PEDIATRIC-PATIENTS

A safe clinical system for nitric oxide (NO) inhalation therapy was de veloped. The system consists of three parts: a NO controller, a NO mon itor, and a patient circuit. NO gas flow and carrier gas flow are cont rolled by a special rust-proof thermal mass flowmeter. Standard gas qu ality NO gas (10,000 ppm, balance nitrogen) is used. The outlet of the NO gas tank is connected to the distal end of a heated humidifer that is very close (12 mt) to the patient, to decrease acidic water precip itation and decrease contact time between NO and oxygen (O-2). Fail-sa fe mechanisms to prevent the delivery of a hypoxic mixture or excessiv e NO concentration are incorporated. inspiratory NO concentration is c ontinuously monitored by a modified electrochemical NO meter. The pati ent circuit consists of a breathing circuit and a ventilator with a sc avenging unit. A modified Mapleson D type circuit is used. Fresh gas, humidified and mixed with NO, is introduced to the patient connection port. A mechanical ventilator, either of conventional or of high-frequ ency oscillation type, is connected to the expiratory limb of the Mapl eson D circuit. A coaxial scavenging unit including activated charcoal is placed in between the expiratory limb and the ventilator. The adju stment of inspiratory NO concentration (y) was-accurate over a wide ra nge (1-80 ppm) of concentrations (x) (y = 0.36 + 0.96x, R(2) = 0.999, n = 45) and showed good agreement with the chemiluminescence method. I nspiratory nitrous oxide (NO2) concentration was less than 0.3 ppm, an d acidic water accumulation as measured by NO2- and NO3- was less than 5 ppm, even at an extremely high NO concentration of 80 ppm with an F 1O2 of 1.0 and 10 L/min of fresh gas flow. Environmental NO and NO2 co ncentrations in the ICU remained below 0.005 and 0.05 ppm, respectivel y. This system was used clinically on 214 pediatric patients and prove d to be accurate, safe, and useful. (C) 1996 Wiley-Liss, Inc.