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Ventilator waveforms
- 2. Summary of the basic modes of ventilation
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- 6. Figure 4 Copyright © 2022 Wolters Kluwer Health, Inc. and/or its subsidiaries. All rights reserved. 7
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- 8. Figure 6 10
- 9. Figure 7 11
- 11. Figure 9 Flow-volume loop of pressure ventilation with a descending ramp flow patternInspiration is represented by the curve above the baseline and expiration by the curve below the baseline. Expiration 13
- 12. Identification of Patient Ventilator Desynchrony 14
- 13. Types of Waveform Abnormalities Auto PEEP Flow Desynchrony Trigger Desynchrony Cycle Desynchrony Air Leak 15
- 14. Figure 10 Auto-PEEP on a flow-time curveWhen the expiratory curve doesn't return to baseline before the next inspiration, the patient has auto-PEEP. 16
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Editor's Notes
- A ventilator-initiated mandatory breath (A) is characterized by positive pressure rising immediately at the beginning of inspiration. In contrast, a patient-initiated mandatory breath (B) has a negative deflection at the beginning. PEEPe is set at 5 cm H2O in this example
- The square waveforms are characteristic of pressure-control ventilation. In this example, PEEPe is set at 5 cm H2O. Pressure rising directly from the baseline (A) indicates a ventilator-initiated breath. A small negative deflection before the second positive-pressure rise (B) suggests a patientinitiated breath.
- Compare a spontaneous breath without pressure support or PEEPe (A) to one with pressure support of 10 cm H2O (B). Note the rapid rise of pressure to the predetermined level of pressure support, which gives the inspiratory portion of waveform B a square shape.
- A normal volume-time curve is shown in (A); in (B), the expiratory curve hasn’t returned to baseline, indicating an air leak from the ventilator’s expiratory limb or auto-PEEP. In (C), the expiratory curve drops below the baseline because of active exhalation or inaccurate calibration of the flow transducer.
- The square flow pattern (A) leading to a higher PIP and shorter inspiratory time may be seen in volume-control ventilation. Curves (B) and (C) show decelerating and descending ramps, respectively, which are associated with lower PIP and longer inspiratory time. They occur in pressure-control and pressure-support ventilation. The sine waveform (D) may increase PIP and may be used in volume-control ventilation.
- The loop starts at the zero point and is plotted clockwise
- The loop starts at the set PEEPe of 5 cm H2O and travels counterclockwise.
- The patient’s effort produces a small “trigger-tail” waveform on the left side of the PV loop at the beginning of inspiration. PEEPe is set to 5 cm H2O.
- Inspiration is represented by the curve above the baseline and expiration by the curve below the baseline.
- When the expiratory curve doesn’t return to baseline before the next inspiration, the patient has auto-PEEP.
- A flow-volume loop that doesn’t close on the inspiratory curve indicates auto-PEEP.
- Compare the convex inspiratory curve representing normal, adequate flow (A) to the concave inspiratory curve with a drop in airway pressure (B) indicating flow dyssynchrony (also called flow starvation).
- The concavity in the inspiratory curve suggests that airflow isn’t adequate to meet patient demand.
- In this example, the figure-eight appearance of the loop suggests flow dyssynchrony.
- Note the negative deflection (the patient’s breathing effort), which isn’t followed by a rise in positive pressure above the baseline because of an insensitive sensitivity setting.
- Because of auto-PEEP, the patient’s effort can’t trigger the ventilator.
- The pressure spike (A) at the end of inspiration on a pressure-time curve indicates that the patient started exhaling before the ventilator cycled to expiration. Shortening the inspiratory time by adjusting the cycling criteria (B) eliminated the pressure spike.
- Compare the negative deflections indicating patient effort: Minor patient effort is needed to trigger a mandatory breath (A), an ineffective effort elicits no ventilator response (B), and increased patient effort is needed to trigger a mandatory breath because of an insensitive sensitivity setting (C).
- An increase in the size of the “trigger tail” means that the patient must make a greater effort to trigger the ventilator because of an insensitive setting.
- In this waveform, A and C are spontaneous breaths; B is the ventilator being triggered without patient effort. The mode is pressure-support ventilation at 10 cm H2O.
- A decrease in PEFR on a flow-time curve suggests an air leak from the ventilator circuit’s expiratory limb, or increasing airway resistance.
- In this waveform, the decrease in PIP suggests an air leak from the ventilator’s inspiratory limb, or a decrease in airway resistance.
- Delivered tidal volume less than set tidal volume indicates an air leak from the ventilator’s inspiratory limb.
- The expiratory curve on this loop doesn’t return to the starting point, suggesting an air leak of 100 mL.
- The same 100-mL expiratory air leak on an FV loop, again indicated by the expiratory portion of the loop not closing at the zero point.
- Auto-PEEP that causes active patient exhalation is shown as a negative deflection on the volume-time curve because the exhaled volume exceeds the inspired volume.
- Before-and-after waveforms showing how effective bronchodilator therapy reduces airway resistance. In the pressure-time curve (top), PIP falls. In the flow-time curve (middle), PEFR rises and auto-PEEP is decreased. Expiratory time is reduced in the flow-time and volumetime curves (bottom).
- The dashed line shows decreased PEFR on an FV loop, indicating increased airway resistance. Effective bronchodilator therapy increases PEFR and restores the expiratory curve to a more linear shape (solid line).
- A patient-initiated breath (breakthrough breathing) at the 4-second mark on this waveform indicates that neuromuscular blockage is inadequate or is tapering off. The mode is volume-control ventilation.
- The normal PV loop, shown as a solid line, widens or bows (dashed line) when the patient’s airway resistance increases.
- Decreasing lung compliance reduces the slope of a PV loop (dashed line); improving compliance increases the slope (solid line).