Seeing Red: An Introduction to the Nellcor™ SpO2 Pulse Oximeter

by Brie Eteson, Digital Surgery
Measuring blood oxygen saturation levels

Digital Surgery is excited to announce its first simulation with audio content. Specifically, we include sound clips to demonstrate various alarm states on a pulse oximetry monitor. In our new simulation, we feature the Nellcor™ SpO2 Pulse Oximeter. This device from Medtronic provides a safe, simple, and noninvasive method of assessing oxygen saturation levels in the blood.1 Percutaneous oxygen saturation (SpO2), calculated through pulse oximetry, is an indirect measure of arterial oxygen saturation (SaO2), or estimate of oxygen saturation. This simulation introduces all the latest features the Nellcor™ SpO2 Pulse Oximetry has to offer, including Cardiac Gated Averaging, SatSeconds™, and OxiMax™ sensor technology.

But what is it used for?

Arterial blood oxygenation may need to be monitored to understand if there is enough oxygen in the blood. This can be valuable information when there are concerns about low oxygen levels at home or in the hospital. One example is monitoring for critical congenital heart defects in neonatal intensive care units (NICU).2,3

This device measures the percentage of hemoglobin (Hb) saturated with oxygen in the blood, providing accurate results even during forms of signal interference, like motion or low perfusion.

Pulse oximetry in brief

Oxygenation is an essential process of respiration. It refers to the transport of oxygenated blood from the lungs into the tissues of the body. Nellcor™ is able to measure the level of saturation of hemoglobin in arterial blood (SpO2) by measuring the amount of oxygen bound to each hemoglobin molecule. The amount of oxygen in the blood is measured by the partial pressure of oxygen, PaO2.

The color of blood varies according to the level of oxygen it contains. The pulse oximeter sensor measures the amount of light (red and infrared beams) that are absorbed into an arteriolar bed. Oxyhemoglobin absorbs more infrared light, allowing more red light to pass through, and deoxyhemoglobin absorbs more red light, allowing more infrared light to pass through.4 This is then translated into a graphical representation for each pulse, in the form of a plethysmographic (pleth) waveform. This pleth waveform corresponds to blood flow.5

Common issues encountered by clinicians in pulse oximetry monitoring include the management of patient motion, signal interference, low perfusion, and low saturation. Nellcor™ pulse oximetry technology introduces a range of features to tackle these issues.

Pulse oximeter sensor passes red and infrared beams of light into an arteriolar bed to measure the light absorbed

Switch between several patient and response modes to modify alarm limits optimally for each patient

Device features

Cardiac Gated Averaging helps to reduce random patient motion signal interference. It identifies any inconsistencies in the average pulse by looking for changes in the pulse waveform, amplitude, and frequency. Those that are consistent are processed as normal. Inconsistent segments are given low priority in the averaging to reduce the influence of random interference.

In any monitoring device, it is important to provide an Alarm Management system to alert the clinician if anything unusual occurs and to ensure patient safety. 

When the monitor detects conditions that require attention, it enters an alarm state. Alarms can be categorized into different priorities, low, medium, or high. Audible alarms include pitched tones, beeps, and a buzzing tone.

Patient modes can be adjusted individually. These modes modify the alarm limits. For example, the alarm limits for adult and pediatric patients are 100% and 90%, with the upper pulse rate alarm limit at 170 bpm, and the lower limit at 50 bpm. In neonatal patients, the limits are changed to 95% and 85%, with the pulse rate alarm limits at 200 bpm and 100 bpm.

Available patient modes include:

  • Adult
  • Pediatric
  • Neonatal
  • Response mode (normal/fast/slow)
  • Homecare mode
  • Sleep study mode
  • Standard mode

Furthermore, Nellcor SatSeconds alarm management technology allows the clinician to differentiate between serious hypoxemia and minor transient events by generating alarms based on depth and desaturation. An alarm only sounds if desaturation is clinically significant, thus minimizing nuisance alarms. The default settings can be modified via the Alarm Limits menu. You can learn more about how the limits are calculated and how they relate to SatSeconds™ in the full simulation. 

The NellcorSatSecondsSafety Net is built-in for cases when a patient’s saturation levels frequently drop below the limit, but quickly rise again before an alarm is triggered. The safety net triggers an alarm to sound when three or more limit violations occur within 60 seconds.

Sensors are developed and validated for specific patient sizes, sensor sites, and clinical challenges

Flexibility in sensor design

Pulse oximetry sensors are used to analyze SpO2 from a physiological signal. Nellcor™ OxiMax™ sensors rely on the pulse, a true cardiac signal, to measure SpO2, which enables the pulse oximeter to operate reliably even during challenging conditions. There are a wide variety of Nellcor™ OxiMax™ sensors for specific patient requirements, including size, sensor placement site, and clinical challenges. Some considerations when selecting a sensor are patient weight and activity level. Additional considerations should be made based on the adequacy of perfusion, available sensor sites, infection control concerns, and the anticipated duration of monitoring. Each sensor type is explained in detail, including appropriate selection criteria and maintenance of single-use and reusable sensors.

There’s the whistlestop tour of Nellcor™ SpO2 Pulse Oximetry. To experience a realistic simulation of the device with interactive animations and audible sound clips, head over to the Touch Surgery™ app today.†

†The Nellcor pulse oximetry monitoring system should not be used as the sole basis for diagnosis or therapy and is intended only as an adjunct in patient assessment.

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How to cite this simulation: Medtronic. Nellcor SpO2 Pulse Oximetry. Touch Surgery Simulations. Published Sep. 17, 2021.


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