Mainstream Vs Sidestream Capnography – What’s the Difference?

If you’ve got or are thinking about buying a patient monitor, it’s also a good time to consider if you need a capnograph.

Plus, right now, if you buy any Bionet BM Elite Series Monitor and choose a capnography accessory to go with it, you’ll get 5% discount on the monitor. Bionet are also giving away a FREE Oxy9Wave Vet monitor with the purchase of any Bionet BM Elite Series patient monitor – all until July 31st.

It’s been acknowledged that the development of capnography saw fascinating scientific investigation, no small amount of genius and the ability to overcome resistance to change. John Scott Haldane first described a CO2 analyser in the early 20th century, while Karl Luft introduced the first infrared CO2 measuring and recording device in 1943, making capnography essential to the effective monitoring of anaesthetised and critical care patients.

Capnography enables you to measure, in real time, the CO2 concentration in the respiratory gases during breathing. The end-tidal CO2 (ETCO2) is usually measured in mmHg and the procedure can be non-invasive. In practice, it’s now considered the most effective method of diagnosing early respiratory depression and reducing further complications.

Mainstream Capnography Vs Sidestream Capnography

Mainstream or sidestream capnometry simply describes the location of the measurement chamber or airway sampling site. We would agree that neither is clearly superior over the other and the choice between them is mostly down to the Vet’s personal preference.

Mainstream Capnographs

Characterised as invasive and non-diverting, Mainstream Capnometers position the measurement chamber within the airways, enabling almost instantaneous C02 measurement.

So, for example, in Mainstream Capnography, CO2 is measured directly in the breathing system by an optical chamber inserted between the endotracheal tube and the breathing circuit.

If Mainstream Capnometry has drawbacks, they include that it can be easily damaged; presence increases dead space, it’s difficult to use in spontaneously breathing patients and water condensation often occurs on the sensor.

Sidestream Capnographs

Non-invasive and diverting, Sidestream capnometers sample air aspirated out of the airway through fine bore tubing to a measurement chamber outside the device.

In a Sidestream system, a sampling port and tubing are attached to the breathing circuit.

One of the advantages of Sidestream analysis is that is the units often measure other gases including oxygen and anaesthetics. However, slight delays may occur because of movement of the sample through the tubing and secretions from the airway can obstruct the tubing.

Both types of Capnography are still today the most compact, least expensive and most popular methods of ETCO2 measurement. And while pulse oximetry is an effective method of monitoring a patient, changes in the percentage of haemoglobin saturated with oxygen will be delayed. Capnography can more promptly identify apnoea and airway issues by instantly identifying the changes that occur with ETCO2 when the next breath fails detection. An abrupt decrease in ETCO2 can be an early and reliable indictor of an impending cardiovascular collapse or cardiac arrest.

In practice, Capnography is most commonly used in anaesthetised patients, but many Vets also find it to be a useful modality in conscious patients for non-invasive PCO2 monitoring. The waveforms can also give a lot of information about a patient’s condition and give an early warning of serious airway and perfusion issues.

We carry a range of ETCO2 Capnography accessories for our BM Vet Pro Series Monitors. Get in touch to ask us about our Capnostat 5 Mainstream CO2 sensor or our LOFLO Sidestream CO2 sensor and which would be best for your patients and your practice.