![]() Despite this heightened level of awareness and the regulatory and organizational guidance, exhaled CO 2 monitoring is often underutilized. The recognition and importance of monitoring exhaled CO 2 in many areas of patient care has led to the expanding recommendation for its use by regulatory agencies and inclusion in the standards and practice guidelines of many professional organizations, such as the American Society for Anesthesia (ASA), the American Heart Association, the American Association for Respiratory Care, the Joint Commission, and the Centers for Medicare and Medicaid Services. The volume of exhaled CO 2 per minute (V̇ CO 2) can also be used to estimate the metabolic rate and nutritional requirements of the critically ill patient. 8 Exhaled CO 2 can also be described as the vital sign for ventilation and perfusion because the volume of CO 2 excreted by the cardiorespiratory system is a sensitive indicator not only of ventilation efficiency but also of pulmonary perfusion and cardiac output. Of critical significance is the use of P ETCO 2 to gauge the effectiveness of cardiopulmonary resuscitation (CPR), to predict outcome, and to guide the continuation of resuscitation efforts. The patient protection enhancements provided by CO 2 monitoring also include: the detection of invasive airway disconnection, dislodgement, or obstruction and monitoring for respiratory depression postoperatively, during procedural sedation, and during patient-controlled analgesia. Detection of exhaled CO 2 has proven to be an invaluable mechanism for confirming tracheal intubation, recognizing accidental esophageal intubations, and other critical patient safety benefits. 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.
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