Which interpretation by the nurse is accurate if the anteroposterior chest diameter equals the transverse chest diameter in an infant?

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PULMONARY SYSTEM

Elizabeth Flasch, Nicole Brueck, Justin Lynn, and Jennifer Henningfeld

DEVELOPMENTAL ANATOMY OF THE PULMONARY SYSTEM

A.    Embryology of the Lung

In humans, there are five well-recognized stages of lung development: embryonic, pseudoglandular, canalicular, saccular, and alveolar (Figure 2.1).

B.    Postnatal Lung Development

Normal lung growth is a continuous process that begins early in gestation and extends through infancy and childhood. Estimates of alveolar number at birth vary greatly but the general accepted number is 50 million. Eventually 300 million alveolar will form after birth. Lung volume will increase 23-fold, alveolar number will increase sixfold, alveolar surface area will increase 21-fold, and lung weight will increase 20-fold. Alveolar development is thought to continue through early childhood with implications for recovery of lung function after certain childhood insults (Schnapf & Kirley, 2010).

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FIGURE 2.1    Embryonic development of the lungs.

C.    Upper Airway Development

The upper airway is responsible for warming, humidifying, and filtering air before it reaches the trachea. There are notable differences between pediatric and adult airways (Table 2.1).

TABLE 2.1    Anatomic Differences Between Pediatric and Adult Airways

D.    Lower Airway Development (Figures 2.2 and 2.3)

FIGURE 2.2    Epithelial and endothelial development.

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FIGURE 2.3    Upper and lower airway anatomy.

E.    Thoracic Cavity

F.    Pulmonary Circulation

The development of pulmonary circulation closely follows the development of the airways and alveoli.

DEVELOPMENTAL PHYSIOLOGY OF THE PULMONARY SYSTEM

A.    Physiologic Function

The primary function of the lung is gas exchange. Its prime function is to allow oxygen to move from the air into the venous blood and for carbon dioxide to move out. Other functions include metabolizing certain compounds, filtering the blood, and acting as a reservoir for blood. During inspiration, the diaphragm contracts, the chest wall expands, and the volume of the lungs increases. Gas flows from the atmosphere into the lungs and oxygen diffuses into the blood at the alveolar–capillary interface. During expiration, the diaphragm and the chest wall relax, thoracic volume decreases, intrathoracic pressure increases, and gas flows out of the lungs. This process is affected by pulmonary compliance and resistance and by pulmonary vascular pressures and resistance (West, 2012).

FIGURE 2.4    Compliance curve. Compliance reflects the amount of pressure required to deliver a given volume of air into an enclosed space such as the lung. Increased compliance of a lung unit indicates that less pressure is needed to distend the lung with a given volume. Decreased compliance indicates that more pressure is required to deliver the same volume of air.

FIGURE 2.5    Ventilation–perfusion relationships.

R = ΔP/Q

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FIGURE 2.6    Chemical control of breathing.

PCO2, partial pressure of carbon dioxide; PO2, partial pressure of oxygen.

B.    Gas Exchange and Transport

Respiratory gas exchange involves the movement of gas from the atmosphere to the alveoli to the pulmonary capillary blood. The alveolar capillary membrane permits the transfer of oxygen and carbon dioxide while restricting the movement of fluid from the pulmonary vasculature to the alveoli.

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FIGURE 2.7    Lung volumes.

(Hgb × 1.34 × SaO2) + (0.003 × PaO2)

43TABLE 2.2    Normal Oxygenation Profile Values

a-vDO2, arteriovenous oxygen difference; CaO2, arterial oxygen content; CI, cardiac index; CvO2, venous oxygen content; DO2, oxygen delivery; Hgb, hemoglobin; O2ER, oxygen extraction ratio; PaO2, arterial oxygen partial pressure; PvO2, venous partial pressure of oxygen; SaO2, arterial oxygen saturation; SvO2, venous oxygen saturation; VO2, oxygen consumption.

FIGURE 2.8    Oxyhemoglobin dissociation curve.

PaO2, arterial oxygen partial pressure.

CLINICAL ASSESSMENT OF PULMONARY FUNCTION

A.    History

B.    Physical Examination

FIGURE 2.9    Anatomic landmarks of the thorax. The lower lobes of both lungs have only small projections on the anterior plane on the x-ray film and can be better visualized on a lateral or posterior x-ray film. The midaxillary line, midclavicular line, vertebral line, and intercostal spaces are frequently used landmarks in describing the location of pulmonary findings. (A) Anterior view: Left lung is divided into two lobes by the left oblique fissure. The right lung is divided into three lobes by the horizontal fissure with landmarks between the fourth rib medially and the fifth rib laterally. The right oblique fissure is found from the inferior margin (midclavicular line) to the fifth lateral rib. (B) Posterior view: Fissures dividing upper and lower lobes begin at T3, medially, extending in a line inferiorly below the inferior tips of the scapula.

FIGURE 2.10    Thoracic contours by age. Illustrates the comparison of the anteroposterior diameter and contour of the chest wall according to age.

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FIGURE 2.11    Variations in respiratory patterns. Breathing patterns as associated with anatomic regions of the brain. Lesions causing global injury tend to cause an orderly progression of respiratory patterns down to the brain stem. Focal lesions may cause a lower CNS pattern; higher function is otherwise noted on examination.

CNS, central nervous system; HTN, hypertension; VT, tidal volume.

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FIGURE 2.12    Percussion of the thorax. Differences in densities are noted to detect the presence of abnormal air, fluid, bones, or mass.

C.    Abnormal Physical Examination Findings

FIGURE 2.13    Etiology of cyanosis.

AV, arteriovenous; CNS, central nervous system; CV, cardiovascular; NB, newborn.

TABLE 2.4    Common Causes of Cough by Age Groups

CF, cystic fibrosis; TEF, tracheoesophageal fistula.

INVASIVE AND NONINVASIVE DIAGNOSTIC STUDIES

A.    Diagnostic Approach

B.    Baseline Respiratory Monitoring

C.    Laboratory Studies (Table 2.5)

D.    Blood Gas Analysis

52TABLE 2.5    Summary of Diagnostic Laboratory Evaluation of Pulmonary Function

CF, cystic fibrosis; CSF, cerebrospinal fluid; IgA, immunoglobulin A; IgD, immunoglobulin D; IgE, immunoglobulin E, IgG, immunoglobulin G; IgM, immunoglobulin M; PMNs, polymorphonuclear neutrophils; WBC, white blood cell.

E.    Radiologic Procedures for Pulmonary Evaluation

A variety of imaging techniques allow visualization of anatomy, motion dynamics, and identification of abnormalities. Frequently, a patient may require more than one imaging procedure to detail a specific anatomic site.

RESPIRATORY MONITORING

A.    Oxygen Monitoring

B.    Carbon Dioxide Monitoring

C.    Diagnostic PFTS

Critically ill children require continuous surveillance of pulmonary function. For those who are not in frank respiratory failure, clinical assessment, including respiratory rate, observation of chest expansion, and use of accessory muscles, provides an estimation of adequacy of minute ventilation (VE). For those in distress, further measurements may be warranted. With children, standard measurements of pulmonary function may not be possible because of lack of patient cooperation.

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FIGURE 2.14    Comparison of pulmonary function measurements in the person with obstructive and restrictive pulmonary disease. The ratio of FEV1/FVC is greater than 80%. Note that in restrictive disease the ratio is normal, but the separate measurements of FEV1 and FVC are abnormally low.

FEV1, forced expiratory volume in the first second of exhalation; FRC, functional residual capacity; FVC, forced vital capacity.

PULMONARY PHARMACOLOGY

A.    General Principles

B.    Routes of Drug Delivery

C.    Neuromuscular Blocking Agents

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D.    Sedatives and Analgesics

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E.    Dexmedetomidine

F.    Remedial Agents

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G.    Agents That Affect Ventilation–Perfusion Matching

H.    Bronchodilators and Anti-Inflammatory Agents

AIRWAY-CLEARANCE THERAPIES

Airway clearance may be impaired in patients with disorders that are associated with abnormal cough mechanics (muscle weakness), altered mucus rheology (CF), altered mucociliary clearance (primary ciliary dyskinesia), or structural defects (bronchiectasis). A variety of interventions is used to enhance airway clearance with the goal of improving lung mechanics and gas exchange, and preventing atelectasis and infection. Airway-clearance therapies (ACTs) are indicated for individuals whose function of the mucociliary escalator and/or cough mechanics are altered and whose ability to mobilize and expectorate airways secretions is compromised. Early diagnosis and implementation of ACT, coupled with medical management of infections and airway inflammation, can reduce morbidity and mortality associated with chronic pulmonary and neurorespiratory disease (Table 2.10; Lester & Flume, 2009; McCool & Rosen, 2006; Strickland, 2015; Strickland et al., 2013).

TABLE 2.10    Types of Airway-Clearance Therapies

CF, cystic fibrosis; FET, forced expiratory technique; IPV, intrapulmonary percussive ventilator; PEP, positive expiratory pressure.

CONGENITAL ANOMALIES OF THE PULMONARY SYSTEM

Congenital Diaphragmatic Hernia

A.    Definition

Congenital diaphragmatic hernia (CDH) occurs in anywhere from one in 2,000 to one in 5,000 live births. It is characterized by the incomplete formation of the fetal diaphragm and usually occurs on the left side. Anomalies associated with this condition include neural tube defects, cardiac defects, and midline anomalies (Abel, Bush, Chitty, Harcourt, & Nicholson, 2012; Grover et al., 2015).

B.    Pathophysiology

C.    Clinical Presentation

D.    Patient Care Management

E.    Outcomes

Tracheoesophageal Fistula

A.    Definition

Esophageal atresia is a congenital anomaly in which the esophagus is segmented with a blind pouch separating the upper and lower portion. In most instances, there is also a fistula connecting the distal esophagus and trachea. There are several types of tracheoesophageal deformities. The three main types include esophageal atresia with distal tracheoesophageal fistula (TEF), isolated esophageal atresia, and TEF without esophageal atresia (H-type). The most common type is esophageal atresia with distal TEF (Abel et al., 2012; Keckler & Schropp, 2010).

B.    Pathophysiology

The esophagus and trachea develop embryologically at the same time. The development of the esophagus and trachea is believed to occur by the proliferation of endodermal cells on the lateral walls of the diverticulum. 71These cell masses become ridges of tissue that divide the foregut into two separate channels forming the esophagus and trachea. This process is completed by 36 days after fertilization. During the fourth week of fetal life, interruptions in development may result in abnormalities of the esophagus with and without fistula formation between the two structures (Abel et al., 2012; Keckler & Schropp, 2010).

C.    Clinical Presentation

D.    Patient Care Management

E.    Outcomes

Choanal Atresia

A.    Definition

Choanal atresia is the most common cause of true nasal obstruction. It occurs in approximately one in 10,000 live births. It can be unilateral or bilateral, isolated or associated with other congenital abnormalities. Unilateral choanal atresia is twice as common as bilateral choanal atresia (Greenough, Murthy, & Milner, 2012; Keckler & Schropp, 2010).

B.    Pathophysiology

The exact embryologic malformation causing choanal atresia is unknown; however, certain theories now point to a failure of mesodermal flow to reach preordained positions in the facial process. Any abnormalities in this flow would affect the normal penetration of the nasal pits and the thinning that allows breakthrough at the anterior choana (Greenough et al., 2012; Keckler & Schropp, 2010).

C.    Clinical Presentation

72D.    Patient Care Management

E.    Outcomes

Tracheomalacia

A.    Definition

B.    Clinical Presentation

C.    Patient Care Management

D.    Outcomes

Generally, children outgrow the condition by 1 to 2 years of age (Greenough et al., 2012; Keckler & Schropp, 2010).

Tracheal Stenosis

A.    Definition

A rare but potentially life-threatening disorder that often leads to severe respiratory insufficiency. In most cases, stenotic lesions are composed of complete tracheal rings of cartilage. The severity of symptoms correlates with 73the length of affected trachea, the presence of concomitant respiratory conditions, degree of luminal narrowing, and any bronchial involvement.

B.    Pathophysiology

C.    Clinical Presentation

D.    Patient Care Management