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Patient Monitoring. Stuart Nurre, MS, R.R.T. Oxygenation. Goal of respiratory therapy is return the patient to a normal oxygenation status, while minimizing risks. Normal oxygen saturations are > 90% Normal PaO 2 is 80-100 mmHg. Factors that interfere with oxygenation are many.

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Patient monitoring

Patient Monitoring

Stuart Nurre, MS, R.R.T.


Oxygenation
Oxygenation

  • Goal of respiratory therapy is return the patient to a normal oxygenation status, while minimizing risks.

  • Normal oxygen saturations are > 90%

  • Normal PaO2 is 80-100 mmHg.

  • Factors that interfere with oxygenation are many.

  • Hypoxia is when delivery falls below the level of cellular needs.


  • Causes of hypoxia

    • Hypoxemia

      •  PIO2

      • Hypoventilation

      • Low V/Q

      • Shunt

      • Diffusion defect

    • Hemoglobin Deficiency

    • Low Blood Flow

    • Dysoxia


Oxygen Content

[Hgb x SaO2 x 1.34] +

[PaO2 x 0.003]

Normal value is 20 vol%

Oxygen Delivery

CaO2 x Cardiac output

(C.O. = SV x HR)


Ventilation perfusion
Ventilation/Perfusion

  • The lung and perfusion system are not perfect. Due to gravity and lung structure the two systems do not meet equally

  • The apex of the lung receives more ventilation then does the base.

  • The apex of the lung receives less perfusion than the base.

  • These differences occur in healthy lungs.

  • This difference is more pronounced in the diseased lung.


  • Ventilation/Perfusion is , there is usually a  CO2 and a  O2.

  • Ventilation/Perfusion is , there is usually a  CO2 and a O2 .

  • Areas of  V/Q are referred to as DEADSPACE.

  • Areas of  V/Q are referred to as LOW or SHUNT.


Oximetry
Oximetry

  • The machine is an oximeter and the test performed is an oximetry.

  • Oximetry is used to asses the oxygenation of a patient. It can be invasive or non-invasive.

  • Visual recognition of hypoxia is difficult.

    • Cyanosis, tachycardia, tachypnea, SOB,  WOB, altered LOC.


  • The theory of oximetry is based on two principles, spectrophotometry and photoplethysmography.

  • Spectrophotometry uses the Beer-Lambert law. Which states that the concentration of a species is directly related to the amount of light it absorbs. Oxyhemoglobin (O2Hb) absorbs light at a different wavelength that deoxyhemoglobin (HHb).

    • O2Hb > 940 nm

    • HHB > 640 nm


  • Photoplethysmography spectrophotometry and photoplethysmography. measures the change in blood volume by the change in the amount of light absorbed.

  • Veins and tissues have a constant amount of light absorbed. But as systole occurs, more blood arrives and more light is absorbed. This allows the machine to subtract the constant amount from the dynamic amount.

  • All of this information is calculated in the computer and a SaO2 is displayed.


Oxyhemoglobin Dissociation Curve spectrophotometry and photoplethysmography.

  • Left shift

  • Decreases

  • H+

  • Temperature

  • 2,3 - DPG

Right Shift

Increases

1.H+

2. Temperature

3. 2,3 - DPG



Capnography
Capnography spectrophotometry and photoplethysmography.

  • Capnometry is a number produced to estimate the arterial PaCO2.

  • Capnography is a graphical representation of the level of PaCO2.

  • Most capnograms work by using infra-red spectroscopy. The amount of light absorbed is related to the amount of CO2 present.


  • There are two main types of capnograms used in most ICUs. spectrophotometry and photoplethysmography.

    • Mainstream

    • Sidestream

  • The number displayed is referred to as the ETCO2. (PETCO2) This number should be 4-6 mmHg below the PaCO2. This is referred to the the gradient.

  • When the gradient increases it is due to increased in dead space ventilation.


  • Deadspace ventilation is caused by spectrophotometry and photoplethysmography.

    • Lung disease

    • Pulmonary embolic events

    • Changes in cardiac output

  • The uses of capnography are:

    • Alveolar ventilation measurements

      • A potentially misleading monitor is worse than no monitor at all.

    • Deadspace ventilation trending

    • Cardiopulmonary resuscitation.


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