Basic Ventilator Waveforms

Ventilator Waveforms and Scalars

• There are three scalars: pressure versus time, volume versus time, and flow versus time.
• These scalars provide information about airway compliance, lung recruitment, and patient-ventilator asynchrony.

Pressure Versus Time Scalar

• The pressure scalar represents the pressure in the airway as a function of time.
• It is useful for identifying the plateau pressure (Pplat), which is the pressure in the airway under static conditions.
• The Pplat is calculated by adding the pressure created by airway resistance, the pressure related to the lung's compliance, and the total PEEP.
• The pressure scalar can also show other pressure measurements, such as PIP and PEEP.

Volume Versus Time Scalar

• The volume scalar represents the amount of gas delivered into the lungs by the ventilator over time.
• It is calculated from the measurement of flow.
• The upslope of the curve represents the inspiratory volume, and the downslope represents the expiratory volume.
• Differences in inspiratory and expiratory volumes can indicate air leaks or intrinsic positive end-expiratory pressure (auto-PEEP).

Flow Versus Time Scalar

• The flow scalar represents the gas flow in and out of the lungs.
• Inspiratory flow is a positive value on the graph, and expiratory flow is a negative value.
• The area under the curve represents the volume moved during inspiration and expiration.
• The shape of the flow curve can indicate changes in resistance to air flow or compliance of the lung.

Patient-Ventilator Asynchrony

• Patient-ventilator asynchrony (PVA) occurs when the patient is not interacting well with the ventilator.
• PVA can be associated with negative side effects, including increased sedation needs, increased work of breathing, and worse outcomes.
• PVA can be detected using ventilator graphic interpretation.
• There are several types of asynchrony, including:
  • Asynchronies related to cycling: premature cycling, delayed cycling, and auto-triggering.
  • Asynchronies related to breath initiation: auto-triggering.
  • Asynchronies related to flow: flow starvation.

Loops

• Loops are graphical representations of the relationship between pressure or flow and volume during a breath.
• There are two types of loops: pressure-volume loops and flow-volume loops.
• The pressure-volume loop shows the pressure plotted against the volume during a breath.
• The flow-volume loop shows the flow plotted against the volume during a breath.
• Loops can provide information about respiratory mechanics, such as airway resistance and lung compliance.

Pressure-Volume Curve

• The pressure-volume curve is a graphical representation of the relationship between pressure and volume during a breath.
• The curve has an inspiratory and expiratory limb.
• The inspiratory limb takes on a sigmoidal shape, with an initial flat part, a middle steep part, and a flattening of the curve again.
• The curve can be used to identify changes in lung compliance and recruitment.

Flow-Volume Curve

• The flow-volume curve is a graphical representation of the relationship between flow and volume during a breath.

• The curve has an inspiratory and expiratory limb.

• The curve can be used to identify changes in airway resistance and obstruction.

• The curve can also be used to identify air trapping or auto-PEEP.### Ventilator Graphics and Respiratory Mechanics

• The article "Essentials of ventilator graphics" by Restrepo and Khusid provides a comprehensive review of ventilator graphics in pediatric patients.

• Ventilator waveforms are essential in assessing respiratory system mechanical function, as discussed in "Assessing Respiratory system mechanical function" by Restrepo et al.

• A review of ventilator graphics and its use in assessing respiratory mechanics is provided by Dexter and Clark in "Ventilator graphics: scalars, loops, & secondary measures".

• Lower tidal volumes are recommended for acute lung injury and acute respiratory distress syndrome, as demonstrated by the study "Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome" by Acute Respiratory Distress Syndrome Network.

Respiratory Mechanics in Mechanically Ventilated Patients

• Respiratory mechanics in mechanically ventilated patients are discussed in "Respiratory mechanics in mechanically ventilated patients" by Hess.
• Fifty years of research in ARDS have led to significant advancements in understanding respiratory mechanics in acute respiratory distress syndrome, as discussed by Henderson et al. in "Fifty years of research in ARDS: Respiratory mechanics in acute respiratory distress syndrome".

Learn about the volume versus time scalar in ventilation, which represents the gas delivery into the lungs over time. Explore how to interpret inspiratory and expiratory volumes from this scalar.