Up to date, expert answers to frequently asked questions (FAQ) about oxygen supply systems, respiratory care and pulse oximetry written by OCC & collaborators.
How pulse oximeters work
Can pulse oximeters measure volume responsiveness?
Some oximeters, sometimes. Blood pressure fluctuations occur with respiratory (or ventilator) cycles, and changes in the arterial waveform signal due to pulse pressure variation can often be more pronounced in hypovolemic patients. For this reason, pulse pressure variation (PPV) or pulse oximetry plethysmographic signal (POP) are sometimes used to try to assess volume responsiveness in patients.
Similar to a peripheral arterial pressure waveform, many pulse oximeters show a processed representation of the photoplethysmographic waveform. However, visual estimation of variations in the pulse oximeter waveform are unreliable. Some pulse oximeters will populate PPV or POP values that are automatically and continuously calculated based off of the waveform. However, each pulse oximeter manufacturer uses different algorithms to calculate these values and displays, making it very difficult to interpret accurately and clinically.
Some studies have stated that POP appears to be effective for predicting fluid responsiveness in ventilated patients, while others have found that it did not correlate well with arterial pressure waveforms. Overall, using pulse oximeters in isolation to evaluate volume responsiveness is not adequately validated or reliable in the clinical setting at this time. This is due to many limitations of this technique including poor or noisy signal, probe position, motion, vasoconstriction, and highly processed pleth signals which vary among manufacturers.
Keywords: pulse pressure variation, PPV, volume, fluid, POP