EMS World

AUG 2011

EMS World Magazine is the most authoritative source in the world for clinical and educational material designed to improve the delivery of prehospital emergency medical care.

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| Cover report by David Wampler, PhD, LP The capnography waveform is a key vital sign when determining treatment for patients in the field Carbon dioxide (CO2 ) is a waste gas, so why do we care about it as long as we and our patients can get it out of the body? Just like an automobile’s perfor- mance can be monitored by a probe put in the exhaust pipe, an evolving technology allows emergency providers to precisely monitor the performance of a number of critical human processes in an ill or injured patient. This article describes the use of technology to monitor metabolism, circulation and ventilation in the emergency patient. The Relevance of CO2 Long ago, Greek philosophers believed we had tiny internal combustion engines inside our bodies that produced “smoke,” or capnos. It turns out, the Greeks were correct. Our internal combustion engines are really mitochondria that are fueled by hydrocarbons (sugars, fats and proteins) essential in the human diet. After eating and movement through the digestive processes, sugars enter the mitochon- dria, where they are “combusted” and carbon dioxide is “exhausted.” Once CO2 is transported to the lungs via the circula- tory system, it is exhaled with alveolar air. The gases we breathe in are measured in partial pressure. So, a person standing at sea level under normal weather condi- tions would have 1 atmosphere of pressure being exerted by the gases in the air he breathes. An atmosphere of pressure is equivalent to 760 millimeters of mercury (mmHg). If the atmosphere contains approximately 79% nitrogen and 20% oxygen, the partial pressure of each is 600 mmHg nitrogen and 150 mmHg oxygen. The approximately 10 mmHg of air pres- sure remaining is composed of all of the other gases and vapors—mostly water vapor. Inhaled air contains essentially no carbon dioxide, while exhaled air is rich with CO2 . The portion of pressure being exerted by carbon dioxide is called partial pressure and is typically 35–45 mmHg in the healthy person at rest. Partial pressure can be monitored on either the intubated or non-intubated patient. The monitoring process can be either discrete (one time or quick look) or continuous. Capnography works by capturing exhaled air and redirecting it into the capnography device. The air then passes between a light and a detector that EMSWORLD.com | AUGUST 2011 37 Photo copyright Oridion Medical 1987 Ltd.

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