CHAPTER FIFTEEN Respiratory System The respiratory unit focuses on pathophysiologic condi- c. The alveolar ducts are located at the end of the tions, which interfere with gas exchange. When problems respiratory bronchioles. of gas exchange occur, regardless of the precipitating d. Alveoli: area of gas exchange; diffusion of oxygen cause, a hypoxic state is frequently the result. A thorough (O2) and carbon dioxide (CO2) between the blood understanding of hypoxia and the appropriate nursing and the lungs occurs across the alveolar membrane. interventions for the client in a hypoxic state are a high e. Surfactant is produced in the alveoli; its primary priority. function is to reduce surface tension, which facili- tates alveolar expansion and decreases the ten- dency of alveoli to collapse. PHYSIOLOGY OF THE RESPIRATORY 4. Premature infants frequently have inadequate pro- SYSTEM duction of surfactant. 5. Blood supply to the lungs. Organs of the Respiratory System a. Pulmonary arteries to pulmonary capillaries to A. Bronchial tree. alveoli, where exchange of gas occurs. 1. Trachea divides below the carina into the right and b. Bronchial arteries supply the nutrients to the lung left main stem bronchi, which extend into the lungs. tissue and do not participate in gas exchange. 2. The right main stem bronchus is shorter, wider, and straighter than the left; therefore foreign objects are Physiology of Respiration more likely to enter the right side. External respiration is a process by which gas is exchanged 3. Lobar bronchi: three in the right lung and two in the between the circulating blood and the inhaled air. left lung; lobar bronchi subdivide several more times A. Atmospheric pressure: pressure exerted on all body parts to form segmental and subsegmental bronchi. by surrounding air. 4. Bronchioles: branching from the subsegmental B. Intrathoracic pressure: pressure within the thoracic cage. bronchi; no cartilage in the walls. Bronchioles branch C. Gases flow from an area of high pressure to an area of into the terminal bronchioles; no mucus glands or cilia. low pressure; pressure below atmospheric pressure is B. Lungs (organs of respiration). designated as negative pressure. 1. Lungs are located within the thoracic cavity (Figure D. Inspiration. 15-1) 1. Stimulus to the diaphragm and the intercostal muscles 2. Pleura: transparent serous membrane around the lung. by way of the central nervous system. a. Each lung is sealed within its own compartment 2. Diaphragm moves down, and intercostal muscles by the pleura. move outward, thereby increasing the capacity of the b. Visceral pleura: adheres to the surface of the lung. thoracic cavity and decreasing intrathoracic pressure c. Parietal pleura: covers the inner wall of the chest. to below atmospheric pressure. d. Pleural space: potential space between the visceral 3. Through the airways, the lungs are open to atmo- and parietal pleura membrane; area between spheric pressure; air will flow into the lungs to equal- pleural layers contains a small amount of fluid to ize intrathoracic pressure with atmospheric pressure. lubricate and allow for smooth motion of lung E. Expiration. tissue during respirations. 1. Diaphragm and intercostal muscles relax and return 3. Lungs. to a resting position; therefore lungs recoil and capac- a. Divided into lobes. ity is decreased. (1) Right lung: three lobes. 2. Air will flow out until intrathoracic pressure is again (2) Left lung: two lobes. equal to atmospheric pressure. b. Each terminal bronchiole branches into respira- F. Negative pressure is greater during inspiration; therefore tory bronchioles. air flows easily into the lungs. L 269 270 CHAPTER 15 Respiratory System H b. Activity of the respiratory center is regulated H Pharynx by chemoreceptors. These receptors respond to Nasal cavity H Epiglottis changes in the chemical composition of the cere- H Larynx brospinal fluid (CSF) and the blood (specifically, Trachea H5 Right main- the Pao2, Paco2, and pH). Carina H stem bronchus 2. The medulla contains the central chemoreceptors H responsive to changes in CO2 blood levels. Segmental bronchi H a. CO2 diffuses into cerebrospinal fluid (CSF), H increasing the hydrogen ion concentration of H10 CSF. This has a direct stimulating effect on the H chemoreceptors in the medulla. H b. CO2 saturation of the blood regulates ventilation H through its effect on the pH of the CSF and the H effects of the CSF on the respiratory center in the H15 medulla. Terminal Mucus H v bronchiole Cilia H NURSING PRIORITY The primary respiratory stimulus is H Respiratory CO2; when the Paco2 is increased, ventilation is initiated. H bronchiole H20 3. Carotid and aortic bodies contain the peripheral H Alveolar chemoreceptors for arterial O2 levels. duct H a. Primary function is to monitor arterial O2 levels H Goblet cell and stimulate the respiratory center when a H decrease in Pao2 occurs. H25 b. When arterial O2 decreases to below 60 mm Hg, H stimulation to breathe is initiated by the H Alveoli chemoreceptors. H Septa Pores of Kohn c. In a person whose primary stimulus to breathe is H hypoxia, this becomes the mechanism of ventila- H30 FIGURE 15-1 Respiratory system. (From Lewis SL et al: Medical- tory control. surgical nursing: assessment and management of clinical problems, H J. The process of gas exchange. ed 7, St. Louis, 2007, Mosby.) H 1. Ventilation: the process of moving air between the H atmosphere and alveoli. H 2. Diffusion. H35 G. Compliance describes how elastic the lungs are or how a. The process of moving O2 and CO2 across the H easily the lungs can be inflated; when compliance is alveolar capillary membrane. H decreased, the lungs are more difficult to inflate. b. Links the processes of ventilation and perfusion. H H. Respiratory volumes. c. Gas diffuses across the alveolar capillary mem- H 1. Tidal volume (VT or TV): amount of air moving in brane from an area of high concentration to an H40 and out of the lungs in one normal breath. Normal = area of low concentration. H 500 mL (5-10 mL/kg). d. Factors affecting diffusion: surface area of the H 2. Vital capacity (VC): amount of air forcibly exhaled in lung, thickness of the alveolar capillary membrane, H one breath after a maximum inhalation. Normal = characteristics of the gases. H 4500 mL. H45 3. Residual volume (RV): air remaining in the lungs at NURSING PRIORITY When mucus is retained and pools in the lungs, gas diffusion is decreased; provides a medium for H the end of a forced (maximum) expiration. bacteria growth. H I. Control of respiration. H 1. Movement of the diaphragm and accessory muscles 3. Perfusion. H of respiration is controlled by the respiratory center a. The process of linking the venous blood flow to H50 located in the brainstem (medulla oblongata and the alveoli. H pons). b. Dependent on the volume of blood flowing from H a. The respiratory center will control respirations by the right ventricle into and through the pulmonary H way of the spinal cord and phrenic nerve. The circulation. H diaphragm is innervated by the phrenic nerve H55 coming from the spinal cord between C-3 and Oxygen and Carbon Dioxide Transport H56 C-5; the intercostal muscles are innervated by Internal respiration is the exchange of gases between the H57 nerves from the spinal cord between T-2 and blood and interstitial fluid. The gases are measured by an H58 L T-11. analysis of arterial blood (Table 15-1). CHAPTER 15 Respiratory System 271 C. Effects of altitude on O transport. Table 15-1 NORMAL ARTERIAL BLOOD 2 GAS VALUES 1. At high levels (above 10,000 feet), there is reduced O2 in the atmosphere, resulting in a lower inspired Acidity index pH 7.35-7.45 O2 pressure and a lower Pao2. Commercial planes are Partial pressure of Pao2 80 to 100 mm Hg pressurized to an altitude of 8000 feet. dissolved oxygen Percentage of hemoglobin Sao2 95% or above saturated with oxygen NURSING PRIORITY Clients who are on oxygen or who Partial pressure of Paco2 35 to 45 mm Hg have a Pao of less that 72 mm Hg on room air should consult dissolved carbon dioxide 2 − with their physician before planning air travel. Bicarbonate HCO3 22 to 28 mEq/L NURSING PRIORITY An SaO2 below 95% indicates respiratory difficulty. 2. Body compensatory mechanisms. a. Increase in the number of red blood cells or hema- tocrit from body storage areas, thereby increasing the total hemoglobin-carrying and O2-carrying A. O2. capacity of the blood. 1. Transported as a dissolved gas; Pao2 refers to the b. Hyperventilation. partial pressure of O2 in arterial blood. c. Renal erythropoietic factor (erythropoietin) is 2. O2 is primarily transported chemically bound to released, thereby enhancing the production of red hemoglobin; when hemoglobin leaves the pulmonary blood cells (secondary polycythemia). It takes capillary bed, it is usually 95% to 100% saturated with approximately 4 to 5 days to actually increase red O2. It may be referred to as the arterial oxygen satura- blood cell production. tion (Sao2). O2 can also be carried (physically dis- solved) in the plasma. ALERT Apply knowledge of pathophysiology to monitoring for 3. Oxygenated hemoglobin moves through the arterial complications; identify client status based on pathophysiology. system into the cellular capillary bed, where O2 is released from the hemoglobin and made available for cellular metabolism. 3. Extended exposure to high altitudes will result in an 4. Venous blood contains about 75% O2 as it returns to increased vascularization of the lungs, thus increasing the right side of the heart. the capacity of the blood to carry O2. 5. O2 delivered to the tissue is dependent on cardiac 4. Problem with oxygenation at high altitudes. output.