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  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

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

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

P-V Loop: Overdistension (Hyperinflation)

Flow-Time Curve: Air Trapping (AutoPeep)

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

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

Indication for PEEP/CPAP: Refractory Hypoxemia PaO2

Refractory Hypoxemia Usually Indicates Alveolar Instability  Decreased surfactant  Increased interstitial pressure  Nitrogen washout  Oxygen toxicity

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

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

Without PEEP/CPAP

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

PEEP/CPAP EFFECTS II ncreases FRC back towards normal DD ecreases shunt II ncreases static compliance (decreases elastic resistance) DD ecreases W.O.B. AA cceptable PaO2 at lowest possible FIO2

PEEP/CPAP Precautions

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

PEEP/CPAP Precautions  Unilateral lung disease  Neuro patients  COPD

PEEP/CPAP Controversy  Classical indication: increased elastic resistance  Controversy: Increased airway resistance too?

Can we please take a break!

PEEP/CPAP Systems: Flow Resistor

PEEP/CPAP Systems: Threshold Resistor

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

LIP or Pflex LIP

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

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)

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)

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

Lets see what we can dig up