Oxygraphy: An Unexplored Perioperative Monitoring Modality

Abstract

Capnography waveforms and capnometry are useful perioperative monitoring tools. The paramagnetic oxygen analyzers incorporated in many clinical monitoring systems estimate oxygen concentration in the breathing circuit during various phases of ventilation. The oxygen concentration is plotted as a real-time waveform and displayed as an oxygraph. However, the clinical utility of oxygraphy is under evaluated. We are reporting four different clinical scenarios in neurosurgical patients, wherein the information yielded by oxygraphy were either not available on the capnograph or were revealed in a more promising way on the oxygraph than on the capnograph. A real-time oxygraphy waveform has four phases similar to a capnograph, although displayed in a reverse manner. Oxygraphy was useful in our patient to determine the adequacy of preoxygenation. Airway complications and unwanted neuromuscular recovery can be detected earlier by oxygraphy compared to capnography. The oxygraphy peak-to-baseline scale difference can be compressed to as low as to 6% of oxygen concentration. When the peak-to-baseline scale difference is 6 mmHg, the oxygraph becomes sensitive to even minute changes in respiratory flow characteristics. Oxygraphy may have a potential role in clinical monitoring.