Aims: To investigate the potential for finding an alternative for the 'pulse check' during CPR, we studied the use of thoracic impedance measured via the defibrillator pads for circulation assessment during CPR.
Materials and methods: Transthoracic impedance, ECG and arterial pressures were recorded on 69 patients with a resulting data set of 434 segments. The circulatory-related impedance waveform was first isolated manually and features characterising its shape were suggested.
Results: The features were correlated with corresponding blood pressure measurements, where a low, but significant, correlation coefficient (0.3) was found. By dividing the data set in groups of sufficient and insufficient circulation and using a neural network, we found that trends in features of the impedance waveform showed a discriminative potential for the two groups. Our classifier achieved a sensitivity of 90% for recognising insufficient circulation with a specificity of 82%.
Conclusions: We have shown that the circulation-related information found in the impedance signal may be used for circulatory assessment, especially the recognition of restoration of spontaneous circulation after cardiac arrest.