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Patient Monitoring

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

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  1. Patient Monitoring Stuart Nurre, MS, R.R.T.

  2. 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.

  3. Causes of hypoxia • Hypoxemia •  PIO2 • Hypoventilation • Low V/Q • Shunt • Diffusion defect • Hemoglobin Deficiency • Low Blood Flow • Dysoxia

  4. 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)

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. Oxyhemoglobin Dissociation Curve • Left shift • Decreases • H+ • Temperature • 2,3 - DPG Right Shift Increases 1.H+ 2. Temperature 3. 2,3 - DPG

  11. Physiologic and technical Considerations of oximetry. • NOT VENTILATION • Low flow states • Dyshemoglobinemia • Dyes • Nail polish/acrylic nails • Skin pigmentation • Ambient light • SaO2 levels • Oximetry vs CO-Oximetry

  12. Capnography • 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.

  13. There are two main types of capnograms used in most ICUs. • 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.

  14. Deadspace ventilation is caused by • 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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