Page 39 - Critical Care Nursing Demystified

24 CRITICAL CARE NURSING DeMYSTIFIED

process of diffusion. Internal respiration can only happen through the process of
diffusion, which requires an adequate number of red blood cells to transport and
release oxygen to the body cells and tissues and to absorb carbon dioxide.
Ventilation is regulated by components of complex brain activity and
depends on the rhythmic operation of brainstem centers and intact pathways
to the respiratory muscles. Such components are identified as follows:

1. Control of ventilation – Several areas that work together to provide coordi-
nated ventilation are located within the central nervous system. The medulla
and pons of the brainstem regulate and stimulate automatic breathing. The
cerebral cortex promotes voluntary ventilation and overrides automatic ven-
tilation. Spinal cord neurons process information from the brain, and periph-
eral receptors send information to the muscles of ventilation. Efferent nerve
fibers carry impulses from the controller to the effectors, while afferent nerve
fibers carry impulses from sensors back to the controller.
2. Effectors – These are muscles of ventilation working in a coordinated and
symmetrical manner. Scalene and sternocleidomastoid are the muscles of
inspiration. The diaphragm, abdominal accessory, and intercostals are the
muscles of expiration.
3. Sensors – These are chemoreceptors that respond to chemical changes in Downloaded by [ Faculty of Nursing, Chiangmai University 5.62.158.117] at [07/18/16]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.
blood composition and hydrogen ion concentration. Known as central
chemoreceptor sensors, they are located near the ventral surface of the
medulla and are in close contact with cerebral spinal fluid. These sensors
are sensitive to changes in CO content and will increase respirations to
2
blow off CO .
2
Peripheral chemoreceptors – These are located above and below the aor-
tic arch and at the bifurcation of the common carotid arteries. They are
sensitive to changes in oxygen content in arterial blood and are thought
to be the only receptors that increase ventilation in response to PaO arte-
2
rial hypoxemia of less than 60 mm Hg.
Irritant sensors – These lie between airway epithelial cells and stimulate
bronchoconstriction and hyperpnea in response to inhaled irritants.
Stretch receptors in the airway are stimulated by changes in lung volume
and will prevent inhalation of irritants and protect the lungs from overin-
flation, known as the Hering-Breuer reflex.
Juxta capillary receptors or J receptors – These are found in the alveolar
walls near the capillaries. Rapid, shallow breathing results from stimula-
tion of engorged pulmonary capillaries and an increase in interstitial fluid
volume of the alveolar wall.