PREVENTION OF AIR INTRODUCTION IN CATHETER-MANOMETER SYSTEMS FOR ACCURATE NEONATAL BLOOD-PRESSURE MEASUREMENT - AN IN-VITRO STUDY

Objective. Our objective was to find an optimum filling technique to p revent air entrapment in catheter-transducer systems. Ultimately, this may help achieve more accurate neonatal blood pressure measurement. M ethods. We first assembled a catheter-transducer system with a minimum of components fulfilling clinical requirements in neonatology. Then, we tested in vitro different filling techniques: flushing with CO2, fl ushing with alcohol, use of degassed filling liquid, and a combination of all three methods. After the filling procedure, dynamic response w as determined by applying sinusoidal pressures. We calculated natural frequency (fn), damping coefficient (D), and the maximum frequency (fm ax) up to which the amplitude response is uniform (+/-10%). Results. W ith the system filled in the usual clinical way, fmax was 27 Hz (fn = 94 Hz; D = 0.13). With application of the three methods separately, fm ax increased to 34 to 39 Hz. With all methods combined, fmax increased to 51 Hz (fn = 182 Hz; D = 0.14). These techniques were not always su ccessful. Conclusion. A clinical system can be assembled to fulfill th e dynamic requirements for neonatal use. Dynamic response can be impro ved by special filling techniques. We feel that an in vivo quality tes t needs to be developed and evaluated in neonates to ensure accurate b lood pressure measurements.