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Pulse-Oximetry

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Najwa subuh- MSN in Pediatric * * Najwa subuh- MSN in Pediatric * A pulse-oximeter is a device that measures the amount of saturated hemoglobin in blood. – PowerPoint PPT presentation

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Title: Pulse-Oximetry


1
Pulse-Oximetry
2
  • A pulse-oximeter is a device that measures the
    amount of saturated hemoglobin in blood.
  • An oximeter uses blood that has been removed from
    a patient and placed into a measuring cell where
    its oxygen content is accurately measured.

3
O2 Saturation
  • - Oxygen capacity, maximum amount of collective
    oxygen that can be attached to hemoglobin
    dissolved in plasma. - Oxygen content, actual
    amount of oxygen that is carried in blood can
    be different from oxygen capacity.

4
Oxygen capacity
  • One gram of hemoglobin can carry a maximum 1.34ml
    of oxygen
  • In a liter of blood there are 150gm of hemoglobin
  • Approximately 10ml of oxygen dissolved in plasma

5
  • In 1 Liter of blood oxygen capacity will be
  • 150 X 1.34X 10 211ml
  • If a person is carrying 211ml of oxygen per
    liter of blood his oxygen saturation will be 100

6
Oxygen saturation (SO2)
  • Oxygen saturation (SO2)
  • oxygen content X100
  • oxygen capacity

7
SpO2 and SaO2
  • There is different pulse-oximeter the terms SaO2
    SpO2 and often these are used interchangeably.
  • SaO2 refers to the oxygen saturation of arterial
    blood as measured by a CO-oximeter and SpO2
    refers to the oxygen saturation of arterial blood
    as measured by a pulse oximeter.

8
What can be learned by monitoring blood oxygen
saturation?
9
  • Oxygen saturation is an indicator of oxygen
    transport in the body, and indicates if
    sufficient oxygen is being supplied to the body,
    especially to the lungs.
  • The pulse oximeter can also measure pulse rate.
    The volume of blood being pumped by the heart per
    minute is called the cardiac output.

10
What is the purpose of the pulse oximeter?
  1. Determining the severity of a disease
  2. Blood gas analysis
  3. Deciding on hospitalization of patients with
    chronic diseases when in acute phase
  4. Home oxygen therapy, prescribing oxygen, and
    educating patients receiving home oxygen therapy
  5. Assessment and risk management of respiratory
    rehabilitation exercise therapy
  6. Screening for sleep apnea syndrome

11
Why the difference?
  • There is more than one form of hemoglobin.
    Typically we all have oxyhemoglobin,
    methemoglobin, carboxyhemoglobin, sulfhemoglobin
    carboxysulf hemoglobin. Admittedly
    oxyhemoglobin predominates but the others, the
    so-called dysfunctional hemoglobin's are always
    there.

12
Does the ratio of PaO2 to SpO2 always remain the
same?
  • The amount of oxygen dissolved in the blood is
    proportional to the partial pressure of oxygen.
    The amount of oxygen bound to hemoglobin will
    increase as the partial pressure of oxygen
    increases.
  • In contrast, the amount of oxygen bound to
    hemoglobin does not increase in proportion to the
    partial pressure of oxygen.

13
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14
  • If the body temperature decreases and pH
    increases, the curve will shift to the left. If
    the temperature increases and pH decreases, the
    curve will shift to the right.
  • In the following graph, the low pH curve shows
    that when PaO2 is 80mmHg (Torr), oxygen
    saturation is 80.

15
How Does Pulse Oximetry Work?
  • Pulse oximeter is medical devices that measure
    the pulse rate and the amount of oxygen
    saturation of the blood. More specifically, they
    measure the arterial oxygen saturation of the
    hemoglobin
  • This process emits light from an oximeter and
    measures the transmission and absorption of the
    light by the hemoglobin in the blood.
  • A microprocessor in the device uses this
    information to calculate your pulse and oxygen
    saturation. In order for the light to reach the
    blood, the oximeter is attached to a relatively
    translucent part of your body with good blood
    flow, such as your finger. This procedure is
    instantaneous, painless and noninvasive.

16
Oxygen Saturation
  • The goal of breathing and blood circulation is to
    deliver oxygen to all areas of the body. Oxygen
    is carried in the blood by the protein
    hemoglobin, which chemically binds oxygen
    molecules to itself. Each molecule of hemoglobin
    is capable of carrying four molecules of oxygen.
  • Oxygen saturation is the quantity of hemoglobin
    that is carrying oxygen versus the total amount
    of hemoglobin in the blood. Normal levels of
    oxygen saturation are 95- 100 depending on age.

17
  • This means that 95-100 of all available
    hemoglobin in the blood should be carrying
    oxygen. Any reading lt90 can lead to
    life-threatening complications.
  • Certain factors can cause a decrease in oxygen
    saturation such as disease, aging, carbon
    monoxide poisoning and a traumatic injury.
  • Low levels of oxygen saturation indicate that
    hypoxic (oxygen starved) and require medical
    treatment and supplemental oxygen.

18
  • The percentage of oxygenated hemoglobin and
    deoxygenated hemoglobin is determined by
    measuring the ratio of infrared red light
    detected by the pulse oximeter.
  • The pulse oximeter emits red (R) and infrared
    (IR) LED light that passes through the body,
    receives data from a photo detector, and
    calculates the oxygen saturation by determining
    the ratio of the two waveforms.

19
What does a pulse oximeter measure?
  • The oxygen saturation of hemoglobin in arterial
    blood - which is a measure of the average amount
    of oxygen bound to each hemoglobin molecule.
  • The percentage saturation is given as a digital
    readout together with an audible signal varying
    in pitch depending on the oxygen saturation.

20
Principles of modern pulse oximetry
  • Oxygen is carried in the bloodstream mainly bound
    to hemoglobin. One molecule of hemoglobin can
    carry up to four molecules of oxygen, which is
    then 100 saturated with oxygen.
  • In addition, a very small quantity of oxygen is
    carried dissolved in the blood, which can become
    important if the hemoglobin levels are extremely
    low. The latter, however, isn't measured by pulse
    oximetry.

21
  • The relationship between the arterial partial
    pressure of oxygen (PaO2) and the oxygen
    saturation is described by the hemoglobin-oxygen
    dissociation curve.
  • The sigmoid shape of this curve facilitates
    unloading of oxygen in the peripheral tissues
    where the PaO2 is low and oxygen is required for
    respiration. The curve may be shifted to the left
    or right by various patient characteristics e.g.
    recent blood transfusion, pyrexia

22
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23
What factors cause errors in the pulse oximeter?
  • 1. Abnormal hemoglobin
  • 2. Medical dyes
  • 3. Manicure and pedicure
  • 4. Major body motion
  • 5. Blood flow blocked due to pressure on arms or
    fingers
  • 6. Peripheral circulatory failures
  • 7. Excessive ambient light (panel lamp,
    fluorescent lamp, infrared heating lamp, direct
    sunlight, etc.)
  • 8. Ambient electromagnetic waves
  • 9. Probe attached incorrectly

24
Alarms
  • If the Low Oxygen Saturation alarm sounds, check
    that the patient is conscious if that is
    appropriate. Check the airway and make sure the
    patient is breathing adequately. Lift the chin or
    apply other airway maneuvers as appropriate. Give
    oxygen if necessary. Call for help.
  • If the Pulse Not Detected alarm sounds, look for
    the displayed waveform on the pulse oximeter.
    Feel for a central pulse. If there is no pulse,
    call for help, start the procedures for Basic and
    Advanced Life Support. If there is a pulse, try
    repositioning the probe, or put the probe on a
    different digit.
  • On most pulse oximeter, the alarm limits for
    oxygen saturation and pulse rate can be altered
    according to your needs. However, do not alter an
    alarm just to stop it sounding - it could be
    telling you something important! 

25
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