Detection of reduced defibrillation pad contact

A method of detecting a loss of electrical contact between at least one electrode of a pair of electrodes that are electrically coupled to a skin of a subject, comprising acts of:

• monitoring transthoracic impedance parameters of a transthoracic impedance signal between the pair of electrodes, wherein the transthoracic impedance signal has a high frequency waveform component that varies with a frequency of CPR chest compressions, and wherein the transthoracic impedance parameters include at least one of a slope of the high frequency waveform component of the transthoracic impedance signal, a shape of the high frequency waveform component of the transthoracic impedance signal, and a relative energy content of the high frequency waveform component of the transthoracic impedance signal at a fundamental frequency of the transthoracic impedance signal and/or at a harmonic of the fundamental frequency of the transthoracic impedance signal;
• establishing baseline levels of the transthoracic impedance parameters;
• detecting whether changes in at least one transthoracic impedance parameter exceeds the a corresponding baseline level by a threshold;
• determining, prior to loss of electrical contact between the at least one electrode of the pair of electrodes and the skin of the subject, that the at least one electrode of the pair of electrodes is losing electrical contact with the skin of the subject in response to the at least one transthoracic impedance parameter exceeding the corresponding baseline level by the threshold;
• and
• issuing an alert in response to a determination that the at least one electrode of the pair of electrodes is losing electrical contact with the skin of the subject.

A life support device, comprising:

• a pair of electrodes configured to be attached to a skin of a subject;
• a therapy interface electrically coupled to the pair of electrodes;
• and
• a transthoracic impedance monitor electrically coupled to the therapy interface, the transthoracic impedance monitor being configured to
• monitor transthoracic impedance parameters of a transthoracic impedance signal between the pair of electrodes, wherein the transthoracic impedance signal has a high frequency waveform component that varies with a frequency of CPR chest compressions, and wherein the transthoracic impedance parameters include at least one of a slope of the high frequency waveform component of the transthoracic impedance signal, a shape of the high frequency waveform component of the transthoracic impedance signal, and a relative energy content of the high frequency waveform component of the transthoracic impedance signal at a fundamental frequency of the transthoracic impedance signal and/or at a harmonic of the fundamental frequency of the transthoracic impedance signal,
• to establish baseline levels of the transthoracic impedance parameters,
• to detect whether changes in at least one transthoracic impedance parameter exceeds a corresponding baseline level by a threshold,
• to determine that at least one electrode of the pair of electrodes is losing electrical contact with the skin of the subject in response to detecting that the changes in the at least one transthoracic impedance parameter exceeds the corresponding baseline level by the threshold, and
• to issue an alert in response to a determination that the at least one electrode of the pair of electrodes is losing electrical contact with the skin of the subject.