Methods and systems for determining fluid responsiveness in the presence of noise

A method of determining fluid responsiveness of a subject, the method comprising:

• receiving a physiological signal indicative of light attenuated by the subject;
• determining, using a processor, an instantaneous value indicative of fluid responsiveness of the subject based on the physiological signal;
• determining, using the processor, a difference between the instantaneous value indicative of fluid responsiveness and a previous value indicative of fluid responsiveness of the subject;
• selecting, using the processor, an update characteristic based on whether the difference indicates the fluid responsiveness of the subject is increasing or decreasing, wherein a first update characteristic is selected based on the difference being indicative of increasing fluid responsiveness and a second update characteristic is selected based on the difference being indicative of decreasing fluid responsiveness, and wherein the first update characteristic is different than the second update characteristic;
• and
• determining, using the processor, a parameter indicative of fluid responsiveness of the subject based on the selected update characteristic and a previously reported value indicative of fluid responsiveness.

A physiological monitoring system comprising:

• an input configured to receive a physiological signal, wherein the physiological signal is indicative of light absorbed by a subject;
• a fluid responsiveness calculator coupled to the input configured to determine an instantaneous value indicative of fluid responsiveness of the subject based on the physiological signal;
• and
• a fluid responsiveness differential calculator coupled to the fluid responsiveness calculator configured to determine a difference between the instantaneous value indicative of fluid responsiveness and a previous value indicative of fluid responsiveness of the subject;
• wherein the fluid responsiveness calculator is further configured to:
• select a filter weight for the instantaneous value indicative of fluid responsiveness based on whether the difference indicates the fluid responsiveness of the subject is increasing or decreasing, wherein the selected filter weight is a first filter weight that is smaller when the difference indicates the fluid responsiveness of the subject is increasing than a second filter weight when the difference indicates that the fluid responsiveness of the subject is decreasing, and
• determine a parameter indicative of fluid responsiveness of the subject based on the selected filter weight, the instantaneous value indicative of fluid responsiveness, and one or more previous values indicative of fluid responsiveness.