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Understanding Sidestream vs. Mainstream Capnography

Tracy Timmerman, Director of Marketing, Midmark Medical

By: Mandi Gerigk
Clinical Specialist, Monitoring and Critical Care

September 3, 2025

 

When adding capnography to your anesthesia monitoring protocol, one of the most common questions is: sidestream or mainstream? Both are trusted methods used in veterinary settings, and both can deliver reliable CO₂ readings. Understanding those differences can help your team select the best option for your patients and procedures. 

When evaluating capnography options, some monitors will have a choice of sidestream or mainstream sensor styles. Both methods are clinically valid and used effectively in veterinary anesthesia, but understanding how each functions can help your team select the best fit for patients and workflow.

  • Sidestream capnography uses a sampling line at the airway that continuously aspirates a small sample of patient breath to the sensor. The sampling line is slightly lighter and smaller, creating less endotracheal tube traction and less bulk when working in the patient’s mouth. Sampling lines may also offer an option for connection to a large animal ET tube, making this style the appropriate choice for equine practices and research programs using species larger than dogs and cats. Because moisture can accumulate in the sampling line, regular replacement is needed to protect the internal components of the CO2 sensor or monitor. For this reason, systems with externally housed sensors may offer additional protection and ease of maintenance.
  • Mainstream capnography positions the sensor directly at the airway, between the endotracheal tube and the breathing circuit, allowing for instantaneous readings. While both styles have consumable parts, it is possible that the mainstream tube adapters could remain useful longer than the sampling lines of the sidestream. However, added weight at the airway may require consideration for smaller or exotic species, or when working in the mouth.

 

 

The Critical Role of Capnography

Mandi Gerigk CVT, BAS, shares practical insights on using capnography to enhance patient safety during anesthesia.

Learn more

 

 

Choosing with Confidence

Both options provide accurate CO₂ measurements when maintained properly. The choice ultimately depends on patient size, procedural needs and clinical preference.

While each style has its strengths, most practices will be well served by either option. Advances in sensor design have minimized many of the traditional trade-offs, making the decision less about technical limitations and more about how the equipment fits into your workflow. In general, sidestream is the preferred choice for use in equine cases, large-breed animals, or around CT equipment. For most small animal procedures, either option will perform effectively and reliably.

 

 

 

 

Looking for flexibility in your practice?

Midmark Multiparameter Monitors are compatible with both sidestream and mainstream capnography, allowing your team to choose the sensor style that best fits the patient or procedure. You can switch between sensor types as needed, depending on the case—giving you the versatility to support a wide range of caseloads and clinical settings.

 

 

 

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Sources

1. Tinker JH, Dull DL, Caplan RA, Ward RJ, Cheney FW. Role of monitoring devices in prevention of anesthetic mishaps: a closed claims analysis. Anesthesiology. 1989;71(4):541-546.