Mainstream and Sidestream end-tidal carbon dioxide (EtCO2) monitoring are two methods used in capnography to measure the concentration of carbon dioxide (CO2) at the end of expiration. They differ mainly in how they sample the exhaled gas:

Mainstream Capnography in Veterinary Medicine:

Mainstream capnography is characterised as invasive and non-diverting, meaning that the measurement of the ETCO2 is done at the airway, or the sample site, thus providing a real-time measurement of the carbon dioxide pressure.

The Process of Mainstream Capnography:

An airway adapter is inserted directly between the breathing circuit and the endotracheal tube. An infrared source and EtCO2 sensor are attached to the airway adapter. The EtCO2 sensor is then attached to the main monitor via an electrical wire.

• Mainstream capnography is commonly used in veterinary anaesthesia, especially in larger animals such as dogs and horses.

 

• It involves placing the CO2 sensor directly in the animal's airway, typically between the endotracheal tube and the anaesthesia circuit.

 

• Mainstream capnography provides real-time measurements of end-tidal CO2 levels, enabling close monitoring of ventilation and respiratory function during anaesthesia.

Sidestream Capnography in Veterinary Medicine:

Sidestream, on the other hand, is non-invasive and diverting. This means that the sample respiratory gas is transported from the sample site through a plastic tube and analysed in a sample cell. This results in a couple seconds delay of the analysis and a possible distortion of the analysis, which can be consequential in an emergency situation.

The process of Sidestream Capnography:

In Sidestream capnography, the EtCO2 Sensor is in the main unit itself (away from the airway) and a very small pump aspirates gas samples (usually 50-150 mL/min, depending on whether the machine measures other gases) from the patient's airway through a small tube that is connected to a T type away adapter that is inserted in an endotracheal tube or anaesthesia mask connector. The gas that is withdrawn from the patient often contains anaesthetic gas; the exhausted gas from the capnograph must be routed to a gas scavenger or returned to the patient's breathing system. 

• Sidestream capnography is also used in veterinary anaesthesia, particularly in smaller animals like cats and rabbits, where the use of mainstream capnography may be more challenging.

 

• It involves aspirating a sample of exhaled gas from the animal's airway using a thin tube connected to the CO2 sensor, which is located away from the patient.

 

• Sidestream capnography may introduce a slight delay in measurement due to the sampling process, but it still provides valuable information about end-tidal CO2 levels and respiratory status.

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The key differences between Mainstream & Sidestream:

• Patient Size and Accessibility: Mainstream capnography may be more straightforward to implement in larger animals with easier access to the airway, while sidestream capnography may be preferred for smaller animals or situations where direct measurement is impractical.

• Equipment Adaptation: Veterinary anaesthesia machines and monitoring equipment may need specific adaptations or attachments to accommodate mainstream or sidestream capnography for different animal sizes and species.

• Both mainstream and sidestream capnography are essential tools in veterinary anaesthesia, enabling veterinarians to monitor respiratory function and ensure the safety of animals undergoing anaesthesia or sedation procedures. The choice between the two methods depends on factors such as the size of the animal, equipment availability, and clinical preference of the veterinary team.

• Location of Sensor: Mainstream capnography sensors are placed directly in the airway, while sidestream sensors are placed away from the airway, with a sampling tube connecting the patient to the sensor.

• Real-time Measurement vs. Delay: Mainstream capnography provides real-time measurement since it directly samples the exhaled gas, while sidestream capnography introduces a slight delay due to the time it takes to aspirate the gas sample to the sensor.

See how Mainstream and Sidestream capnography measuring techniques effect the operating capabilities of Biolight Multi parameter monitors in the handy comparison table below. Both Mainstream and Sidestream capnography are essential tools in veterinary anaesthesia, enabling veterinarians to monitor respiratory function and ensure the safety of the animals undergoing anaesthesia or sedation procedures. The choice between the two methods depends on factors such as the size of the animal, equipment availability, and the clinical preference of veterinary teams.