A patient monitoring system includes a capacitive electrode connectable to a patient to detect an output signal and a signal generator unit that transmits a carrier signal to the capacitive electrode, the carrier signal having a carrier frequency and a carrier amplitude. The patient monitoring system further includes an amplifier unit that amplifies the output signal detected by the capacitive electrode to generate an amplified output signal. A gain determination module in the patient monitoring system determines an output amplitude of a carrier frequency portion of the amplified output signal, and determines a system gain based on a comparison between the output amplitude and the carrier amplitude. A voltage determination module in the patient monitoring system filters the output signal to isolate a physiological signal detected from the patient, and determines a voltage of the physiological signal based on the system gain.