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Waveforms

Waveforms. RC 270. Pressure Volume Curves. Graphic display of changes in compliance and resistance Used for TREND analysis! One set of waveforms must be compared to another set Pressure is on the x-axis; volume on the y-axis Separate curves for static and dynamic. Static Curve.

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Waveforms

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  1. Waveforms RC 270

  2. Pressure Volume Curves • Graphic display of changes in compliance and resistance • Used for TREND analysis! • One set of waveforms must be compared to another set • Pressure is on the x-axis; volume on the y-axis • Separate curves for static and dynamic

  3. Static Curve • If static curve shifts, than static compliance and elastic resistance have changed • Plateau pressure also will change • A change in the static curve causes the dynamic curve to shift also • Just as a plateau pressure change also affects peak pressure • Rightward shift: decreased static compliance and increased elastic resistance • Leftward shift: increased static compliance and decreased elastic resistance

  4. Dynamic Curve • Is affected by both elastic and airway resistance • If the dynamic curve shifts, but the static curve doesn’t, than only airway resistance has changed • Rightward means increased airway resistance • Leftward means decreased airway resistance

  5. When to plot P-V Curves • Initiation of CMV • Q 8-12 • PRN • Change in patient status • After any therapeutic intervention

  6. P-V Loop: Overdistension(Hyperinflation)

  7. Flow-Time Curve: Air Trapping(AutoPeep)

  8. Continuous Positive Pressure Breathing Breathing at a baseline airway pressure that is greater than ambient

  9. Positive End Expiratory Pressure (PEEP) When patient is on CMV Continuous Positive Airway Pressure When patient is breathing without CMV Types of CPPB

  10. Indication for PEEP/CPAP: Refractory Hypoxemia PaO2 < 60mmhg on an FIO2 of 60% or >

  11. Refractory Hypoxemia Usually Indicates Alveolar Instability • Decreased surfactant • Increased interstitial pressure • Nitrogen washout • Oxygen toxicity

  12. Alveolar Instability • Atelectasis • Decreased FRC • Increased shunting • Decreased static compliance (increased elastic resistance) • Increased W.O.B.

  13. PEEP/CPAP • Airway pressure does not drop to ambient • Helps stabilize alveoli and small airways

  14. Without PEEP/CPAP

  15. With PEEP/CPAP PEEP/CPAP acts like a “splint” to stabilize alveoli/airways

  16. PEEP/CPAP EFFECTS • Increases FRC back towards normal • Decreases shunt • Increases static compliance (decreases elastic resistance) • Decreases W.O.B. • Acceptable PaO2 at lowest possible FIO2

  17. PEEP/CPAP Precautions

  18. Potential Side Effects • Increased mean intrathoracic pressure (ITP) • Hemodynamic compromise • Decreased venous return • Decreased cardiac output • Decreased blood pressure • Increased intracranial pressure (ICP) • Pulmonary baro/volutrauma • Fluid retention • If PEEP/CPAP is indicated and applied appropriately, these effects should be minimized

  19. PEEP/CPAP Precautions • Unilateral lung disease • Neuro patients • COPD

  20. PEEP/CPAP Controversy • Classical indication: increased elastic resistance • Controversy: Increased airway resistance too?

  21. Can we please take a break!

  22. PEEP/CPAP Systems: Flow Resistor

  23. PEEP/CPAP Systems: Threshold Resistor

  24. Selecting a PEEP/CPAP Level • Random • Start at 5 cmH2O and watch PaO2 • Optimal/Best -Set PEEP/CPAP 2 cmH2O greater than lower inflection point (LIP or Pflex) on P-V curve • Best/Optimal PEEP alternative • Peep only—use PEEP level that gives best static compliance

  25. LIP or Pflex LIP

  26. Best PEEP always occurs at the lowest /\ P Remember /\P is gauge plateau pressure minus the peep

  27. What if more than one PEEP level gives the same highest Cstat? • Look at blood pressure • Look at PvO2 • Look at C.O. • Look at %shunt • Look at mixed venous saturation • Look at P/F ratio • PaO2 divided by FIO2 (expressed in decimal form)

  28. Recruitment Maneuver • Also known as Open Lung Tool • A Sustained Maximal Inspiration (SMI) performed after optimal/best PEEP/CPAP has been determined and set Example: 40 cmh2o of CPAP applied for 40 seconds (the 40/40 technique)

  29. PEEP/CPAP works best for diseases that cause increased elastic resistance May be of help in diseases with increased airway resistance

  30. Lets see what we can dig up

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