DYNAMIC-RESPONSE OF A NEONATAL CATHETER-MANOMETER SYSTEM IN-SITU

Objective. The purpose of this study was to develop, validate, and app ly a flush-pulse method to determine the dynamic response of a neonata l catheter-manometer system (CMS) in situ. Methods. In the flush-pulse method, the opened fast-flush valve of the CMS is closed; as a result , the fluid column in the CMS is impacted. This procedure can be done without affecting the net flow of infusion fluid. We validated the met hod in laboratory conditions by comparing 14 paired results obtained w ith this method to the results obtained using a generally accepted ste p-response method. The measurable values are the resonance frequency ( f(r)) and the damping coefficient (delta). The analysis of the flush-p ulse method in situ is complicated by the patient's blood pressure wav e. A remedy for this problem that is based on the first derivative of the pressure signal has been developed. The flush-pulse method is appl ied 14 times in situ. Results. In laboratory settings, the f(r) ranged from 12.5 to 64.0 Hz and delta ranged from 0.14 to 0.32. The correlat ion coefficient was 0.99 for f(r) and 0.91 for delta. We found four ov erdamped systems in situ (delta > 1). In other systems f(r) values bet ween 8.5 and 41.0 Hz and delta values between 0.16 and 0.72 were obser ved. The dynamic response in situ appeared to deteriorate with time du e to routine intensive care procedures. Conclusions. The flush-pulse m ethod proved to be a valid test for determining the dynamic response. The results obtained in situ emphasize the need for a regular evaluati on of the dynamic response of the neonatal CMS in order to assess the shape of the pressure wave.