Methods of experimental and clinical assessment of the relative measurement accuracy of an intracranial pressure transducer - Technical note

The assessment of the actual measurement accuracy of an intracranial pressu re (ICP) transducer is imperative but still very difficult in practice. The authors tested the Codman MicroSensor ICP transducer experimentally. Addit ionally, a bedside test for assessment of measurement accuracy was used bef ore and after clinical monitoring. For laboratory testing, seven new transd ucers were examined for measurement accuracy at increasing pressures rangin g from 0 to 75 mm Hg. Drift was evaluated for 10 days at six different pres sure levels ranging from 0 to 50 mm Hg. Temperature drift was assessed over a temperature range from 20 to 45 degreesC. The percentage absolute differ ence was used in the assessment of measurement accuracy. For clinical testi ng, measurement accuracy was assessed intraoperatively just before the inse rtion of the transducer and in an open water bath after its explantation. a t 10 cm H2O both times. The maximum percentage absolute difference was 9% at a pressure of 10 mm Hg , and declined toward 2.3% at a pressure of 75 mm Hg. The maximum drift ove r 10 days was -4 mm Hg. Within the range of 30 to 40 degreesC, temperature drift was negligible. Over a period of 2 years, between June 1997 and June 1999, 40 ICP transducers were implanted in 35 patients by one surgeon. Of t hese devices, a malfunction was detected in two of them by testing them in a water bath before insertion. Experimental and clinical results indicate t hat this miniature strain-gauge transducer measures accurately; however, co ntrol readings for the probe by means of measurement in an open water bath just before insertion are strongly recommended.