Review 1.5

• Waveforms


  Graphical representation of ventilator parameters over time
• Interpretation of waveforms has improved

  Recognition rate of asynchrony and its clinical outcomes
• Ventilator graphics


  Allow assessment and evaluation of the adequacy of inspiratory flow during Volume ventilation
• Ventilator graphics


  Displayed in scalar and loop forms
• Scalar waveforms


  • Flow-time
  • Volume-time
  • Pressure-time
• Loop waveforms


  • Flow-volume
  • Pressure-volume
• Scalar


  Single variable displayed against time, main components are pressure, flow, volume
• Time axis


  X axis
• Flow, Volume, Pressure axis

  Y axis
• Flow-time scalar


  • Inspiration above and expiration below baseline
• Square waveform in VC mode

  Helps reduce severe air trapping, and for recruitment maneuvers
• Decelerating waveform in VC mode

  Patients tend to tolerate better as it mimics natural breathing
• Flow-time waveform in PCV mode

  Decelerating flow
• Flow-time waveform in PSV mode

  Sine wave flow
• Airway obstruction


  Prolonged expiratory flow and decrease in Peak Expiratory Flow Rate (PEFR)
• Positive response to bronchodilator therapy

  Return to baseline in a shorter period and increase in PEFR
• Air trapping


  Expiratory flow does not return to baseline, new breath starts below baseline
• Air trapping


  Also known as Autopeep
• Causes of air trapping

  Short expiratory time, long inspiratory time, high respiratory rate
• Volume-Time Scalar


  Visual representation of inspiratory and expiratory tidal volume
• Volume waveform


  Should begin and end at baseline
• Air leaks


  Assessed by looking at Volume-Time Scalar
• Causes of air leaks

  Volume loss through circuit, chest tubes, bronco-pulmonary fistula, decrease in cuff pressure
• Pressure-Time Scalar


  Shows visual representation of PIP and PEEP
• Baseline pressure


  Also known as PEEP level
• Rise time


  Rate at which flow increases from baseline to peak during pressure-support or pressure-controlled breaths
• Rapid rise time


  • Bump in the pressure-time waveform at beginning of inspiration
• Slow rise time


  • Pressure-time waveform is more curved and less square
• Pressure-Volume Loop direction


  Counter-clockwise for mechanical breath, clockwise for spontaneous breath
• Pressure-Volume Loop shift to the right

  Compliance decreases
• Pressure-Volume Loop shift to the left

  Compliance increases
• Lung overdistention on Pressure-Volume Loop

  • Bird Beak, excessive stretching or inflation of the lung
• Air leaks on Pressure-Volume Loop


  Expiratory waveform does not return to zero volume/set PEEP
• Flow-Volume Loop


  Displays peak inspiratory flow rate, peak expiratory flow rate, tidal volume
• Flow-Volume Loop


  • Can assess air leaks, increased airway resistance, and airway secretions/condensation accumulation
• Air leak on Flow-Volume Loop

  • Loop never closes, gap indicates magnitude of leak
• Increased airway resistance


  Scoop in expiratory tracing of flow-volume loop, decrease in PEFR
• Increased airway resistance on Flow-Volume Loop


  • Scooped out pattern, universal sign for obstructive lung disease
• Airway secretions or condensate on Flow-Volume Loop


  • Sawtooth pattern on inspiration or expiration
• Know the PFT Flow Volume Loops of Respiratory Diseases