The significance of exhaled CO 2 monitoring extends well beyond the very basic utilization of monitoring the adequacy of ventilation. The technological advancement of exhaled CO 2 monitoring has coincided with the progression of use and importance in clinical practice. 5 Miniature CO 2 monitors that can fit into the palm of the hand and are capable of displaying an exhaled CO 2 capnogram are currently available.

4 With the introduction of the smaller infrared sensor, portable exhaled CO 2 monitors came to the bedside in the 1980s. 3, 4 Periodic measurements of the partial pressure of end-tidal CO 2 (P ETCO 2) occurred on a timed schedule or in a sequential loop as the sampling cycle rotated between a number of monitored beds. By the 1970s, exhaled CO 2 was monitored in ICUs using mass spectrometry systems that aspirated exhaled gas through long lengths of capillary tubing to a central monitoring location.

The collected CO 2 in each bag was then analyzed multiple times to yield the average CO 2, which was plotted over time, thus resulting in the first exhaled capnogram. 2 This process entailed capturing exhaled gas using a system the size of a telephone booth consisting of a series of electro-mechanically controlled valves, which directed sequential portions of expired air into 6 small rubber bags. A decade later, a technique was developed to analyze exhaled CO 2 from a single breath during vigorous exercise. The volume of absorbed CO 2 was then compared with the total gas volume, which yielded the fraction or percentage of CO 2 present. 1 This process of analysis was painstakingly tedious, using an intricate apparatus that involved measuring quantities of CO 2 and other gases that were chemically absorbed from a known gas volume. The measurement of CO 2 in air was first developed around 1918 and performed to analyze gas concentrations in mines.

Physiologic dead space equation