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 prevent air entrapment in catheter-transducer systems. Ultimately, this may help achieve more accurate neonatal blood pressure measurement.

METHODS

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, flushing with alcohol, use of degassed filling liquid, and a combination of all three methods. After the filling procedure, dynamic response was determined by applying sinusoidal pressures. We calculated natural frequency (fn), damping coefficient (D), and the maximum frequency (fmax) up to which the amplitude response is uniform (+/- 10%).

RESULTS

With 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, fmax 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 successful.

CONCLUSION

A clinical system can be assembled to fulfill the dynamic requirements for neonatal use. Dynamic response can be improved by special filling techniques. We fell that an in vivo quality test needs to be developed and evaluated in neonates to ensure accurate blood pressure measurements.