Transition Series: Topics for the EMT—Ventilation

Brady is pleased to share with you a preview of our forthcoming EMS Transition Series. Our first offering is for the EMT level. Transition Series: Topics for the EMT by Joseph Mistovich and Daniel Limmer provides both an overview of new information contained within the Education Standards at the EMT level and a source of continuing education for practicing EMTs. Intended for a new generation of EMTs, the text integrates new “topics” that were not contained in the U.S. DOT 1994 EMT-Basic National Standard Curriculum and existing “topics” at a much greater depth and breadth than what was contained in the typical EMT-Basic education program. This text covers what new EMTs need such as medical terminology, expanded pathophysiology and critical thinking. Educating and training EMTs using the new Education Standards, this text provides a solid foundation of knowledge to practice prehospital care. Visit www.bradybooks.com for more information.

Introduction

The pathophysiology included in this topic is among the most formative and challenging changes to the new education standards. Previously, EMTs had to know only about the air moving in and out of the body—and, quite frankly, in very simple terms and concepts. It was the belief, in creating the standards that include this information, that EMTs would understand the internal processes of perfusion and gas transport that would make assessment and care performed more intuitive and effective.

Regulation of Ventilation

Although breathing can be altered voluntarily, it is primarily controlled involuntarily by the autonomic nervous system. A large part of the regulation is related to maintaining normal gas exchange and normal blood gas levels. Receptors within the body constantly measure the amount of oxygen (O₂), carbon dioxide (CO₂), and hydrogen ions (pH) and signal the brain to adjust the rate and depth of respiration (Figure 1). Centers responsible for ventilatory control are the chemoreceptors, lung receptors, and specialized centers in the brainstem.

Chemoreceptors

Chemoreceptors are specialized receptors that monitor the number of hydrogen ions (pH) and the carbon dioxide and oxygen levels in the arterial blood. There are two different types of chemoreceptors: central and peripheral.

The central chemoreceptors are located near the respiratory center in the medulla. These receptors are most sensitive to changes in the amount of carbon dioxide in arterial blood and the pH of cerebrospinal fluid (CSF). The pH of CSF is directly related to the amount of carbon dioxide in the arterial blood. Carbon dioxide readily crosses the blood–brain barrier and moves into the CSF. In the CSF, the CO₂ combines with water (H₂O) to form carbonic acid (H₂CO₃). Thus there is an association between CO₂ and the level of acid in the body as follows:

• An increase in the amount of CO₂ in the blood will increase the amount of acid in the blood.
• A decrease in the amount of CO₂ in the blood will decrease the amount of acid in the blood.

The central chemoreceptors are highly sensitive to the amount of hydrogen in the CSF. After the CO₂ and H₂O molecules combine to form H₂CO₃, the hydrogen ions (H⁺) disassociate from the H₂CO₃, enter the CSF, and stimulate the central chemoreceptors. Small changes in the H⁺ level in the CSF will stimulate a change in respirations. Because CO₂ is needed to produce H₂CO₃, the changes in the breathing rate and depth are geared toward increasing or decreasing the CO₂ level in the arterial blood. The response of ventilation can be summarized as follows:

• An increase in arterial CO₂ will increase the number of hydrogen ions in the CSF, stimulating an increase in the rate and depth of respiration to blow off more CO₂.
• A decrease in arterial CO₂ will decrease the number of hydrogen ions in the CSF, causing a decrease in the rate and depth of respiration to blow off less CO₂.