Use of the Median Filter in Haemodynamic Monitoring

摘要

Vigilant observation of the patient forms the basis of intensive care. Automatic monitoring equipment with limit alarms makes a vital contribution to this, but the specificity of these alarms is poor, as about 90% of alarms are false. The authors have studied the properties of hemodynamic data in post-operative open-heart surgery patients. The incidence of outliers and the distribution of the data was analyzed and the duration of deviations of the data outside commonly applied alarm limits was studied. The standard median filter and the vector median filter were applied to the preprocessing of hemodynamic data. Median filtering increased the specificity of alarms and decreased the alarm rate. Multivariate vector median filtering was able to decrease the alarm rate more effectively than one-dimensional median filtering. Vectors derived from the systolic, mean and diastolic values of blood pressure have been used. A novel dual-limit alarm for hemodynamic monitoring employed two standard median filters, followed by alarm limits. Its design ensured an alarm response to major deviations with a very short delay. The proportion of true alarms increased from 12% to 49%, while none were missed in the clinical evaluation.