Chapter 16

Introduction

Keywords

• instrumentation

• gas concentrations

• infrared absorption

• mass spectrometry

• Raman scatter analysis

• monitoring methods

• gas concentrations

• oxygen

• nitrogen

• carbon dioxide

• anesthetic gases and vapors

How comfortable would you be not having end-tidal carbon dioxide monitoring after intubating a patient? Although we might be called on to intubate a patient in the intensive care unit (ICU) or emergency department (ED) without the benefit of capnography, we certainly rely on it in the operating room (OR). It is a standard of care for our specialty. Not only do we rely on capnography to ensure tracheal intubation, but we also are able to use the values and even the waveforms derived from capnography to diagnose and treat the patient.

Along with pulse oximetry, capnography was introduced into wide usage in anesthesia in the mid 1980s. Then clinicians had two monitors that aided in the detection of two of the most dreaded and serious events that could happen during a case: unseen hypoxemia and undetected esophageal intubation. Before capnography, undetected esophageal intubation was a main cause of anesthesia morbidity and mortality. There are old stories of the surgeon saying the blood looked darker than normal being the first symptom of esophageal intubation. What panic that would cause!

Although anesthetic agent respiratory monitoring is not as vital to good outcomes as end-tidal carbon dioxide is, it is a standard of care. We rely on it in a myriad of ways during an anesthetic case. This chapter discusses the history, types, and physics (ouch!) involved with capnography and anesthetic respiratory gas monitoring.

We will not go into the physiology and interpretation of capnography waveforms. Although it is a fascinating subject and is of importance for you to know, this topic is covered in other texts in a more detailed way than we could do here. We encourage you to learn as much as you can about capnography waveform interpretation because not only is it vital for you to know in order to provide good care to the patient, it is also often of value when you need to troubleshoot problems with your machine or monitor.

A Brief History

You can go into as much detail regarding the history of capnography as you want, much in the same way that you can go into as much detail regarding the physics of capnography and anesthetic gas monitoring as you want. Again, we stand on giants’ shoulders; contributions from chemists, physicists, electrical engineers, and physiologists all connect into capnography. It should not be a surprise to you that much of the driving force to develop capnography in fact came from the study of respiratory physiology. The first regular clinical use of capnography was not in the OR, but in the ICU during care of ventilated patients. As mentioned, capnography became common in the OR in the mid 1980s and became an American Society ...

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