Frequently Asked Questions

  • Do I have to set a baseline?
    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.
  • If I don’t set a baseline, how do I know when the patient’s numbers are getting low?
    Fluctuations in cerebral rSO2 may be observed with the INVOS™ monitor. Variability in rSO2 values when seen during a momentary hemodynamic fluctuation, for example a change in blood pressure, are not necessarily clinically significant. However, sustained decreases in cerebral rSO2 should be evaluated. Specific consideration should be given to a large decrease (i.e. >20%) or increase (i.e. >10%) in rSO2 from a pre-procedure or other reference point.
  • When and why do patients have high numbers?
    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.
  • When should I respond to high or low numbers?
    First, determine 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. The following may cause inaccurate readings: “cardio green,” “Indigo Carmine,” “Methylene Blue” or other intravascular dyes, 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 Covidien recommended or provided accessories. Use of the INVOS™ system with any other sensor will compromise accuracy.
  • Why is the number low when the patient appears normal?
    Normal CrSO2 values for adults are between 50% and 80%.8 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.
  • Can I use the INVOS™ system to interrogate tissue during different procedures?
    The INVOS™ monitor is FDA cleared 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.
  • My alarms have changed color, from red to yellow. Why?
    To meet the international standard for alarms, software changes were made which established alarm priorities.
  • Can I transport my monitor?
    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.
  • Why is the number lower in comparison to other cerebral monitors?
    All regional oximeters incorporate certain assumptions in their algorithms. This includes the ratio of venous to arterial blood in the capillary space. The INVOS™ system assumes a ratio of 75% venous blood to 25% arterial blood. Other regional oximeters assume a venous:arterial ratio of 70:30. The +5% difference in the arterial assumption and the -5% venous assumption causes a relative bias. This has inspired competitors to use a different ratio, most commonly 70% venous/30% arterial. This increase in the arterial component in the competitor’s device automatically increases its regional saturation when compared to the INVOS™ system. However, this does not mean that the competitors are more accurate.
  • Is the head the only place I can place the INVOS™ sensor to monitor adults?
    No. The INVOS™ monitor is FDA cleared as an adjunct monitor of regional hemoglobin oxygen saturation of blood in the brain or in other tissues beneath the sensor. Any tissue under the sensor can be monitored on an individual at risk for reduced-flow or no-flow ischemic states. The INVOS™ system is FDA cleared for use on any body site. It is intended for use in monitoring individuals greater than 2.5 kg at risk for reduced-flow or no-flow ischemic states and a trend monitor of regional hemoglobin oxygen saturation of blood in the brain or in other tissue beneath the sensor in any individual. Placements may include (but are not limited to): Posterior flank (T10-L2, right or left of midline), forearm, calf, upper arm, top of foot and upper leg.