INVOS™ monitoring does not require establishment of a pre-procedure baseline reference. However, as with intraoperative blood pressure monitoring, obtaining baseline information is sound clinical practice. Moreover, pre-procedure bilateral rSO₂ values can alert the clinician to technical difficulties in need of immediate correction or valid pre-existing symmetrical or asymmetrical subnormal values.³

Fluctuations in cerebral rSO₂ may be observed with the INVOS™ monitor. Variability in rSO₂ values during a momentary hemodynamic fluctuation are not necessarily clinically significant. An example of this could include a change in blood pressure. However, sustained decreases in cerebral rSO₂ should be evaluated.³

Normal cerebral rSO₂ (CrSO₂) values for adults are between 50% and 80%. CrSO₂ values in the upper range of “normal” or exceeding 80% may be the result of administration of supplemental oxygen and/or a decrease in local tissue oxygen demand. Local oxygen demand may be reduced with the use of some anesthetic agents, muscle relaxants, and hypothermia.³

First, assess the signal strength and be confident that the rSO₂ values are accurate. Make sure all connectors are fully engaged, sensors are applied correctly, and equipment is functioning properly and free from moisture. Moisture intrusion may cause inaccurate readings, erratic readings, or no readings at all. Conduct a thorough patient assessment to identify conditions that could affect a change in oxygen supply, oxygen content, or oxygen demand.

Inaccurate readings may be caused by cardio green, indigo carmine, methylene blue, or other intravascular dyes. Inaccurate readings may also be caused by carboxyhemoglobin or other dyshemoglobins, hemoglobinopathies, conjugated hyperbilirubinemia (direct) and myoglobin (Mb) in muscle tissues. It is not recommended to place the sensor on regions with severe tissue edema.

Use of an electrosurgical/electrocautery instrument in the vicinity of the INVOS™ system may interfere with the signal and can result in no readings. Environments with excessive ambient light, such as bright sunlight or strong operating room lighting, may require loosely covering the area of the sensor with an opaque drape. Use only Medtronic recommended or provided accessories. Use of the INVOS™ system with any other sensor will compromise accuracy.³

Normal CrSO₂ values for adults are between 50% and 80%. Some patients may exhibit values <50% and appear normal. However, the INVOS™ system may be detecting a desaturation event prior to other monitoring mechanisms. The patient may re-saturate prior to showing clinical signs, but the INVOS™ monitor alerts the clinician to the desaturation due to its sensitivity.³

The INVOS™ monitor is indicated as an adjunct monitor of regional hemoglobin oxygen saturation of blood in the brain or in other tissues beneath the sensor. Any tissue with a sufficient capillary bed that fits within the INVOS™ system depth of penetration can be monitored.³

To meet the international standard for alarms, software changes were made which established alarm priorities.³

The battery life is 20 minutes of operation capacity when fully charged. It is recommended the monitor be plugged into a power source when the patient arrives at the destination. Recharge from 50% full charge takes approximately 20 hours. Recharge from a drained battery to full charge takes approximately 24 hours.³