Specializing in Canine and Feline Neurology and Neurosurgery for Over 30 Years

capnograph

Purpose:  Instrument used to measure the carbon dioxide (CO2) concentration in exhaled breath and rate of breathing.  It is a real time objective assessment of the effectiveness of breathing by directly reflecting the elimination of CO2 by the lungs to an anesthesia device. Indirectly, it reflects the production of CO2 by tissues and the circulatory transport of CO2 to the lungs.

How Works:  Measures the absorption of infrared light, which is absorbed particularly well by gases of molecules that contain at least two dissimlar atoms, such as carbon dioxide. The amount of infrared radiation absorbed is proportional to the number of CO2 molecules present in a chamber. Carbon dioxide concentration is measured continuously throughout the respiratory cycle to give a graph of expiratory CO2 plotted against time. When expired CO2 is related to expired volume rather than time, the area beneath the curve represents the volume of CO2 in the breath, and thus over the course of a minute, this method can yield the CO2 minute elimination, an important measure of metabolism. If breathing stops, the CO2 monitor will immediately flat line, whereas the pulse oximeter will appear normal for several minutes.

Example of Uses: 

  • detemine adequacy of ventilation
  • confirm esophageal intubation and endotracheal tube placement
  • indicate disconnection from ventilator
  • confirm elimination of CO2 from anesthesia circuit and ventilator
  • determine respiratory patterns, pulomonary perfusion, alveolar ventilation
  • CO2 is also a vasodilator and high levels could further increase intracranial pressure in neurologic patients who already have high intracranial pressure (due to tumor, inflammation, etc.).