Pulse OximetryBy sabry amin

Pulse Oximetry– A portable device for the rapid noninvasivemeasurement of arterial O2 saturation– Assists in the diagnosis of hypoxia (lack ofoxygen)

Pulse Oximetry

There are many different makes, models, and styles of pulse oximeters

• Some pulse oximeters have a screen which shows a wave form, some also have an additional attachment to monitor carbon dioxide levels in the blood

• The pulse oximeter will also give you a heart ratereading as well

Oxygen saturation is an indicator of the percentage ofhemoglobin saturated with oxygen at the time of themeasurement. The reading, obtained through pulse

oximetry, uses a light sensor containing two sources oflight (red and infrared) that are absorbed by

hemoglobin and transmitted through tissues to aphotodetector. The amount of light transmitted through

the tissue is then converted to a digital valuerepresenting the percentage of hemoglobin saturated

with oxygen

Pulse Oximetry

• Uses spectrophotometry based on the Beer-Lambert law

• Differentiates oxy from deoxy Hb by the differences in absorption of light at 660 nm and 940 nm

• Minimizes tissue interference by separating out the pulsatile signal

• Estimates HR by measuring cyclic changes in light transmission

• Estimates functional Hb by comparing amounts of oxy and deoxy Hb

The accuracy of SpO2 measurements requires consideration of a number of physiologic variables. Such patient variables include the following:

• Hemoglobin level• Arterial blood flow to the vascular bed• Temperature of the digit or the area where• the oximetrysensor is located• Patient's oxygenation ability• Percentage of inspired oxygen• Evidence of ventilation-perfusion mismatch• Amount of ambient light seen by the sensor• Venous return at the probe location

Indications:• Patients in respiratory distress• All critically ill patients• Patients requiring O2 concentrations of 40% orgreater• Stable patients at risk from sudden deterioration• Monitoring during procedures such as suctioning

indications

• hypoxemia• During bronchoscopy• 2.monitoring during anaesthesia• 3.exercise testing• 4.sleep studies – detect hypoxemia

indications

Intensive care units Emergency rooms Operating rooms

How to Apply the PulseOximeter

Step 1– Body Substance Isolation• Step 2– Remove fingernail polish if it applies• Step 3 – Apply pulse oximet

Step 4– Leave finger probe on for 15-30 (can take up

to 60) seconds to obtain an accurate reading• Step 5– Record time and reading

Contraindications:

Contraindications:• Severe peripheral vascular disease• Severe anemia (decreased Hemoglobin)• Hypothermia A quality signal may be unobtainable in

10% of patients with a temperature less than 35.0 degrees Celsius A signal failure will occur at temperatures less than 28.5 degrees Celsius

• Hypotension (Low b/p)• Placement distal to a tourniquet, or blood pressurecuff

limitations

• 1.loss of pulsation• Hypothermia , hypotension• 2.inadequate hemoglobin – anaemia• 3.dysfunctional hemoglobin –carboxy-Hb• Methhemoglobinemia• 4.fetal hemoglobin• 5.factors affecting oxygen dissociation curve

( alkalosis )

• DEVICE LIMITATIONS/VALIDATION OF RESULTS:1 Factors, agents, or situations that may affect readings, limit precision, or

limit the performance or application of a pulse oximeter include 7.1.1 motion artifact7.1.2 abnormal hemoglobins (primarily carboxyhemoglobin [COHb] and met-

hemoglobin [metHb]) 7.1.3 intravascular dyes 7.1.4 exposure of measuring probe to ambient light during measurement 7.1.5 low perfusion states 7.1.6 skin pigmentation 7.1.7 nail polish or nail coverings with finger probe 7.1.8 inability to detect saturations below 83% with the same degree of

accuracy and precision seen at higher saturations(

DEVICE LIMITATIONS/VALIDATION OF RESULTS

7.1.9 inability to quantitate the degree of hyperoxemia present(

7.1.10 Hyperbilirubinemia has been shown not to affect the accuracy of SpO2 readings.

HAZARDS/COMPLICATIONS:Pulse oximetry is considered a safe procedure, but

because of device limitations, false-negative results for hypoxemia and/or false-positive results for normoxemia or hyperoxemia may lead to inappropriate treatment of the patient.

In addition, tissue injury may occur at the measuring site as a result of probe misuse (eg, pressure sores from prolonged application or electrical shock and burns from the substitution of incompatible probes be-tween instruments).

INFECTION CONTROL:No special precautions are necessary, but Universal

Precautions are recommended..1 If the device probe is intended for multiple patient use,

the probe should be cleaned between patient applications according to manufacturer recommendations.

.2 The external portion of the monitor should be cleaned according to manufacturer's recommendations whenever the device remains in a patient's room for prolonged periods, when soiled, or when it has come in contact with potentially transmissible organisms.

Advantages

• 1.noninvasive• 2.continuous real time information• 3.no calibration• 4.rapid response time (5-7 sec)• 5.minimal saturation error (1-2%) over range

of 60-90 %

SOURCES OF ERROR

• Sensitive to motion• Sats below 85% have increased error• Calibration is performed by company on

normal patients breathing various gas mixtures, so cal is accurate only down to 80%

• Low perfusion state increases error• Ambient light interferes with reading• Delay in reading of about 12 seconds

SOURCES OF ERROR

• Skin pigmentation– Darker color may make the reading more variable

due to optical shunting– Dark nail polish has the same effect, especially

black, blue, and green…red is OK– Hyperbilirubinemia has no effect

• Methylene blue and indigo carmine (dyes) cause underestimation of the saturation

SOURCES OF ERROR

• Dysfunctional hemoglobin– Carboxyhemoglobin leads to overestimation of

sats because it absorbs at 660 nm like oxyHb does– MetHb can mask the true saturation because it

absorbs at both wavelengths used…sats are overestimated

• Thank you