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Quick guide

Understanding the Value of Patient Spirometry

Patient spirometry measures airway pressures, flow, volumes, compliance and airway resistance breath-by-breath at the patient’s airway. The dynamic interrelationships of pressure and volume or flow and volume are displayed as graphical loops. In addition, the inspired and expired gas concentrations (CO₂, O₂ and anesthetic agents) are measured.

All parameters are measured through a single, lightweight flow sensor and gas sampler placed at the patient’s airway. The close-to-the-patient measurement is a sensitive and continuous reflector of patient’s ventilatory status, obtained independently of the ventilator used.

This guide explains how the D-lite™ pressure and flow sensor is used to calculate essential parameters including total positive end expiratory pressure, compliance and airway resistance. By showing sample of graphical loops, the guide shows how spirometry can help clinicians:
• Detect leaks and obstructions in the airway
• Monitoring changes during laparoscopy.
• Detect initiation of spontaneous breathing

Patient Spirometry is an excellent tool for managing the patient’s ventilation during anesthesia and critical care. Measurement at the airway delivers real patient values not influenced by hoses or other breathing system components. Saved reference loops allow fast visual detection of changes, help in adjusting optimal ventilator settings, and help in comparing actual and previous ventilatory status.

The system’s modular flexibility enables its use with a variety of ventilators and enables flexible change of modules between patients. Ventilatory and hemodynamic information display on a single screen to give a complete picture of patient status. Graphical and numerical trends are provided to help evaluate patients’ histories.

What is Patient Spirometry?

Patient Spirometry measures airway pressures, flow, volumes, compliance and airway resistance breath-by-breath at the patient’s airway. The dynamic interrelationships of pressure and volume or flow and volume are displayed as graphical loops.

In addition the inspired and expired gas concentrations are measured (CO₂, O2 and anesthetic agents).

Pressure / Volume Loop — Pressure/Volume Loop

All parameters are measured through a single, lightweight flow sensor and gas sampler, placed at the patient’s airway. The “close to the patient” measurement is a sensitive and continuous reflector of patient’s ventilatory status, obtained independently of the ventilator used.

Spirometry split screen of spirometry loops and numerical values. — Spirometry split screen enables real-time monitoring of spirometry loops and numerical values, combined with hemodynamic information or real-time waveforms of airway pressure, flow and gases.

How is Patient Spirometry measured?

D-lite™ is an innovative, patented pressure and flow sensor.

Its two pitot tubes measure the pressure difference created by the gas flow. This pressure difference is used together with gas concentration information to calculate the flow. From the flow, both inspiratory and expiratory volumes are calculated.

Total positive end expiratory pressure (PEEPtot) is the sum of externally applied PEEP (extrinsic PEEP, PEEPe) and intrinsic PEEP (PEEPi).

PEEPtot= PEEPi + PEEPe

Dynamic PEEPi is detected when the expiratory flow has not stopped before the next inspiration starts. Presence of PEEPi indicates the air trapping situation in the lung, which may lead
both in respiratory and hemodynamic side effects.

Compliance reflects the distensibility of the respiratory system. It is defined as a pressure difference required to expand the lung by a certain volume.

Compl = TVexp/(Pplat-PEEPtot)

As a continuous dynamic value it provides an easy tool for the clinician to follow respiratory changes and to adjust ventilator settings accordingly.

Airway resistance (Raw) is calculated by using an equation, which gives an average system resistance between the lungs and the D-lite sensor over the total breathing cycle.

Paw(t) = Raw x V(t) + V(t)/Compl + PEEPtot

Clinical examples of Patient Spirometry

Leak in the airway

Leak in the airway is indicated by a loop remaining open at the end of expiration.

Leak in breathing system, in endotracheal tube or laryngeal mask, or even in the patient’s lung may remain unnoticed without loop monitoring.

Flow/Volume loop showing leak in the airway

Obstruction in the airway

A loop moving towards the horizontal axis indicates airway obstruction that increases airway pressure without corresponding increase in tidal volume.

An obstruction caused by a kinked tube, airway secretion or malposition of endotracheal tube can be immediately detected.

Pressure/Volume loop showing obstruction in the airway

In Anesthesia

Monitoring of changes during laparoscopy

This figure illustrates the patient’s ventilatory pattern before (1) and during CO2 insuflation (2) in the laparoscopic operation.

A decrease in compliance and increase in airway pressure are clearly visible.

Pressure/Volume loop monitoring of changes during laparoscopy

Spontaneous breathing efforts

This loop illustrates an initiation of a spontaneous breath during anesthesia.

Pressure/Volume loop showing best possible PEEP

In Critical Care

Intrinsic PEEP (autoPEEP)

Presence of intrinsic PEEP can be seen as a loop, where the flow is not reaching zero line and also as an increased PEEPi value in the number field.

Intrinsic PEEP demonstrates air trapping situation which may lead to hyperinflation of the lung and increase the risk of the ventilation-induced lung injury.

Best possible PEEP

This figure demonstrates effects of different PEEP settings on patient compliance. The saved loop (1) illustrates decreased compliance.

The situation is altered by increasing PEEP setting to 8 cmH2O which clearly improves the lung
compliance (2).

Additional resources

For white papers, guides and other instructive materials about our clinical measurements, technologies and applications, please visit http://clinicalview.gehealthcare.com/