Oximetry

Overview:

Oxygen saturation is a relative measure of the quantity of dissolved or carried oxygen in the blood. In medicine, oxygen saturation (SO₂) is measured as percentage of hemoglobin binding sites occupied by oxygen in the bloodstream. At low partial pressures of oxygen, most hemoglobin is deoxygenated.

The oxygen saturation level may be measured from different areas of the body and include:

• Arterial oxygen saturation (SaO₂) to measure the amount of oxygen bound to hemoglobin in the arterial system; commonly referred to as Saturation of Peripheral Oxygen (SpO₂) when measured using oximetry
• Venous oxygen saturation (SvO₂) to measure how much oxygen the body consumes
• Tissue oxygen saturation (StO₂) can be measured by near infrared spectroscopy to estimate tissue oxygenation in various conditions

Method:

Arterial oxygen saturation can be measured using non-invasive oximetry techniques and avoids technical and ethical concerns associated with arterial sampling for blood oxygen (O₂) level determination.

Pulse oximetry or oximetry is a non-invasive method, which relies on the light absorption characteristics of saturated hemoglobin and thus allows monitoring of the oxygenation of a subject's hemoglobin. Oximetry involves placing a sensor on a thin part of the subject’s anatomy such as a fingertip or earlobe, and light containing both red and infrared wavelengths is passed from one side to the other. These light waveforms are transmitted by a semiconductor light emitting diode and detected by a photodetector.

Oximetry determines SpO₂ by analyzing two wavelengths of light (660 nm and 910 nm) that are differentially absorbed by specific hemoglobin structures in the blood. Oxygenated hemoglobin (HbO₂) absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin (Hb) absorbs more red light and allows more infrared light to pass through. The relative absorption of these wavelengths reflects the ratio of oxygenated to total haemoglobin, and this ratio is expressed as a percentage. As oximetry does not detect the presence of carboxyhemoglobin and methemoglobin, SaO₂ must strictly be referred to as SpO₂. For a healthy human adult, a SpO₂ of 97% to 99% is considered normal.

The ADInstruments Oximeter Pod is used for measuring blood oxygen saturation in humans. The unit connects directly to a PowerLab Pod Port and is supplied with either a Finger Clip or Ear Clip sensor to monitor SpO₂. The Oximeter Pod takes approximately 10 seconds to determine an accurate output from the time it is plugged in and the transducer is attached to the subject. It provides readings in an oxygen saturation range of 70 to 100% and performs one reading per second with a resolution of 1%. The option of an alarm to sound if the value of the SpO₂ drops below 70% is also available.

Blood oxygen saturation measurements in animals can also be performed using the Animal Oximeter Pod and a Tail Wrap, Animal Clip or Base Sensor.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

• ADInstruments Oximeter Pods are pre-calibrated to read in %SpO₂
• If acquiring the pulse signal from the Oximeter Pod, then Cyclic Measurements can be used to calculate heart rate online
• LabChart data files can be marked with events using the Comments feature
• Maximum, minimum and average signal amplitudes can be calculated using the Data Pad
• The display of the signal can be compressed for long term trend observations
• Data can be easily transferred into popular spreadsheet and graphing programs for further analysis and reporting
• Threshold alerts may be configured within LabChart to notify users of low %SpO₂ values

LabChart

LabChart software (for Windows and Macintosh) together with a PowerLab data acquisition system offers up to 32 channels of real-time data acquisition, data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Additional acquisition and analysis functionality is provided with the use of specialized LabChart Extensions and LabChart Modules. Modules are available as part of LabChart Pro while Extensions are free for download from the website for existing LabChart users.

GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

• PL3504 PowerLab 4/35 - 4 Channels
• PL3508 PowerLab 8/35 – 8 Channels
• PL3516 PowerLab 16/35 – 16 Channels

Signal Conditioners 

• ML320/F Oximeter Pod (Finger clip) that is supplied with a Finger SpO₂ Sensor
• ML320/E Oximeter Pod (Ear clip) that is supplied with an Ear Clip SpO₂ Sensor

• ML325/AC Animal Oximeter Pod (Animal Clip) that is supplied with an Animal Clip SpO₂ Sensor
• ML325/AW Animal Oximeter Pod (Tail Wrap) that is supplied with a Tail Wrap SpO₂ Sensor
• ML325/BS Animal Oximeter Pod (Base Sensor) that is supplied with a Base Sensor

• Nonin Medical Inc.
• Nellcor
• Datex-Ohmeda

Transducers and Accessories

• MLT321 SpO2 Finger Clip
• MLT322 SpO2 Ear Clip
• MLT323 SpO2 Animal Clip
• MLT324 SpO2 Tail Wrap
• MLT325 Base Sensor Transducer

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