PATHO UNIT 8

Croup

Acute laryngotracheobronchitis and almost always occurs in children between 6 months and 5 years with a peak incidence at 2 years. In 85% of cases, croup is caused by a virus, most commonly parainfluenza and in other instances by influenza A, rhinovirus, or RSV. Incidence is higher in males and is most common during winter months. Approximately 15% of affected children have a strong fan history of it. Spasmodic croup usually occurs in older children, The etiology is unknown although association w/ viruses, allergies, asthma, and gastreoesophageal reflux disease (GERD) is being investigated. Bacterial laryngotracheitis is the most common potentially life-threatening upper airway infection in children. It is most often caused by S. aureus (including MRSA), H. influenza, or group A beta-hemolytic Streptococcus.

Genetic & Immunologic Advancements in Lung Cancer Treatment

Although new chemotherapeutic agents have improved outcomes slightly in the management of lung cancer, overall survival rates remain poor and the toxicities of these regimes limit their use. New understanding of the genetic and immunologic features of lung cancer cells have led to new treatment options. Gene therapy is emerging as a way of restoring normal tumor-suppressor gene function and increasing tumor responsiveness to chemoradiation through gene transfer, restoring normal DNA methylation patterns, and altering microRNA function. Immunologic therapies include antibodies to epidermoid growth factor receptors (erlotinib, gefitinib, and cetuximab) and antiangiogenesis drugs. The effectiveness of these strategies is still being evaluated, but new knowledge is leading to opportunities for innovative treatment.

Hyperventilation

Alveolar ventilation exceeding metabolic demands. The lungs remove CO2 faster than it is produced by cellular metabolism, resulting in decreased PaCO2, or hypocapnia.

Alveolar Surface Tension

Alveolar ventilation, or distension, is made possible by surfactant, which lowers surface tension by coating the air-liquid interface in the alveoli. Surfactant, a lipoprotein produced by type II alveolar cells, includes 2 groups of surfactant proteins. One group consists of small hydrophobic molecules that have a detergent-like effect that separates the liquid molecules, thereby decreasing alveolar surface tension. As the radius of a surfactant-lined sphere (alveolus) shrinks the surface tension decreases, and as a radius expands the surface tension increases. This occurs b/c the smaller radius causes surfactant molecules to crowd together and then repel one another strongly. A larger radius spreads them apart, decreasing their mutual repellence. Normal alveoli are much easier to inflate at low lung volumes (after expiration) than at high volumes (after inspiration). The decrease in surface tension caused by surfactant also is responsible for keeping the alveoli free of fluid. If surfactant isn't produced in adequate quantities, alveolar surface tension increases, causing alveolar collapse, decreased lung expansion, increased work of breathing, and severe gas exchange abnormalities. The second group of surfactant proteins consist of larger hydrophilic molecules (collectins) that are capable of inhibiting foreign pathogens.

Oxygen Transport

Approximately 1000ml of oxygen is transported to the cells of the body each minute. Oxygen is transported in the blood in two forms: a small amount dissolves in plasma, and the remainder binds to Hb molecules. W/o Hb, oxygen would not reach the cells in amount sufficient to maintain normal metabolic function.

Aspiration of Foreign Bodies

Aspiration of foreign bodies into the airways usually occurs in children 1-3 years. More than 100,000 cases a year. Most objects are expelled by the cough reflex, but some objects may lodge in the larynx, trachea, or bronchi. Large objects may occlude the airway and become life-threatening. Items of particular concern would be batteries or magnets. The aspiration event commonly is not witnessed or is not recognized when it happens b/c the coughing, chocking, or gagging symptoms may resolve quickly. FBs lodged in the larynx or upper trachea cause cough, stridor, hoarseness or inability to speak, respiratory distress, and agitation or panic; the presentation is often dramatic or frightening. If the child is acutely hypoxic and unable to move air, immediate action such as sweeping the oral airway or performing abdominal thrusts may be required to prevent tragedy. Otherwise, bronchoscopic removal should be performed urgently. If an aspirated FB is small enough, it will be transferred to a bronchus before becoming lodged. If the FB is lodged in the airway for a notable period of time, local irritation, granulation, obstruction, and infection will ensue. Thus children may present w/ cough or wheezing, atelectasis, pneumonia, lung abscess, or blood-streaked sputum. These children are treated by prompt bronchoscopic removal of the object and administration of antibiotics as necessary.

Cyanosis

Bluish discoloration of the skin and mucous membranes caused by increasing amounts of desaturated or reduced Hg (which is bluish) in the blood.

Neurochemical Control of Ventilation

Breathing is usually involuntary, b/c homeostatic changes in ventilatory rate and volume are adjusted automatically by the nervous system to maintain normal gas exchange. Voluntary breathing is necessary for talking, singing, laughing, and deliberately holding one's breath. The mechanisms that control respiration are complex.

Lung Cancer

Bronchogenic carcinomas arise from the epithelium of the respiratory tract. Lung cancer excludes other pulmonary tumors, including sarcomas, lymphomas, blastomas, hematomas, and mesotheliomas. Most common cause of cancer death in the US; responsible for 31% of all cancer deaths in men and 26% in women. 5-year survival rate is 20%. The most common cause is tobacco smoking, Smokers with obstructive lung disease are at even greater risk. Other risk factors include secondhand smoke, occupational exposures to certain workplace toxins, radiation, and air pollution. Genetic risks include polymorphisms of the genes responsible for growth factor receptors, DNA repair, and detoxification of inhaled smoke.

Disorders of the Upper Airways

Can came significant obstruction to airflow. Common causes in children are infections, foreign body aspiration, and obstructive sleep apnea.

Acute Respiratory Distress Syndrome (ARDS)

Characterized by acute lung inflammation and diffuse alveolocapillary injury.

Obstructive Lung Diseases

Characterized by airway obstruction that is worse with expiration. More force is required to expire a given volume of air and emptying of the lungs is slowed. Asthma, chronic bronchitis and emphysema. Chronic bronchitis & emphysema together are called chronic obstructive pulmonary disease (COPD). The unifying symptoms are dyspnea, and the unifying sign is wheezing.

Restrictive Lung Disease

Characterized by decreased compliance of the lung tissue. Aspiration, atelectasis, bronchiectasis, bronchiolitis, pulmonary fibrosis, inhalational disorders, pneumoconiosis, allergic alveolitis, pulmonary edema, and acute respiratory distress syndrome.

Asthma

Chronic inflammatory disorder of the bronchial mucosa that causes hyper responsiveness and constriction of the airways, Occurs at all ages, w/ approximately half of all cases developing during childhood and another third before age 40. Has been diagnosed in more than 34 million persons. Death rates have declined since 1995 but the incidence of asthma has increases, especially in urban areas. Familial disorder and more than 100 genes have been identified that may play a role in the susceptibility and pathogenesis of asthma, including those that influence the production of interleukin-4 (IL-4) and interleukin-5 (IL-5), IgE, eosinophils, mast cells, and B-adrenergic receptors as well as those that increase bronchial hyper responsiveness. The expression of these genetic factors is influenced by other risk factors (age at the onset of disease,levels of allergen exposure; urban residence, exposure to air pollution, tobacco smoke, environmental tobacco smoke, recurrent respiratory tract viral infections, gastroesophageal reflux disease, obesity). There is evidence that exposure to high levels of certain allergens during childhood increases the risk for asthma. Decreased exposure to certain infectious organisms appears to create an immunologic imbalance that factors the development of allergy and asthma. This complex relationship has been called hygiene hypothesis. Urban exposure to pollution and cockroaches, decreased exercise, and increased obesity play a role in the increasing prevalence of asthma, particularly in children.

Large Cell Carcinomas

Constitute 10-15% of bronchogenic carcinomas.

Chronic Cough

Cough that has persisted for more than 3 weeks, although 7 or 8 weeks may be a more appropriate timeframe b/c acute cough and bronchial hyper reactivity can be prolonged in some cases of viral infection.

Acute Cough

Cough that resolves within 2 to 3 weeks of the onset of illness or resolves with treatment of the underlying condition.

TNM Classification

Current accepted system for the staging of non-small cell cancer. T denotes the extent of the primary tumor, N indicates the nodal involvement, M describes the extent of metastasis.

Acute Respiratory Failure

Defined as inadequate gas exchange such that PaO2 < 50mm Hg or PaCO2 >50mm Hg with pH <7.25. Can result from direct injury to the lungs, airways, or chest wall or indirectly b/c of injury to another body system (brain or spinal cord). It can occur in individuals who have an otherwise normal respiratory system or in those with underlying chronic pulmonary disease. Most pulmonary diseases can cause episodes of ARF. If the failure is primarily hypercapnic, it is the result of inadequate alveolar ventilation and the individual must receive ventilatory support (bag-valve mask or mechanical). If the failure is primarily hyperemic, it is the result of inadequate exchange of oxygen between the alveoli & the capillaries and the individual must receive supplemental oxygen therapy. Many people w/ combined will receive both kinds of support. Important potential complication of any major surgical procedure, especially those that involve the CNS, thorax, or upper abdomen. The most common postoperative pulmonary problems are atelectasis, pneumonia, pulmonary edema, and pulmonary emboli. People who smoke are at risk, particularly if they have preexisting lung disease. Limited cardiac reserve, chronic renal failure, chronic hepatic disease, and infection also increase the tendency to develop postoperative failure. Prevention of postoperative failure includes frequent position changes, deep breathing exercises, and early ambulation to prevent atelectasis and accumulation of secretions. Humidification of inspired air can help loosen secretions. Incentive spirometry gives individuals immediate feedback about tidal volumes, which encourages them to breath deeply. Supplemental oxygen is given for hypoxemia, and antibiotics are given as appropriate to treat infection. If failure develops, the individual may require mechanical ventilation for a time.

Obstructive Sleep Apnea

Defined by partial or intermittent complete upper airway obstruction during sleep with disruption of normal ventilation and sleep patterns. Childhood OSAS is common, with an estimated prevalence of 2-3% of children 12-14 years and up to 13% of children between 3-6 years. Prevalence is estimated to be 2-4 times higher in vulnerable populations (blacks, hispanics, preterm infants). In children, OSAS occurs equally among girls and boys. Possible influences early in life may include passive smoke inhalation, socioeconomic status, and snoring together w/ genetic modifiers that promote airway inflammation. OSAS also is more likely to occur in children who have a history of clinically significant episode of RSV bronchiolitis in infancy; this is believed to change the neuroimmunimodulatory pathways in the upper airway.

Work of Breathing

Determined by the muscular effort (and therefore oxygen and energy) required for ventilation.

Tuberculosis Evaluation & Treatment

Diagnosed by a + tuberculin skin test (TST; purified protein derivative [PPD])., sputum culture, immunoassays, and chest radiographs. A + skin test indicates the need for yearly chest radiographs to detect active disease. When active pulmonary disease is present, the tubercle bacillus can be cultured from the sputum and may be seen with an acid fast stain. However, sputum culture can take up to 6 weeks to become +. Treatment consists of antibiotic therapy to control active disease or prevent reactivation of LTBI. Recommended treatment includes a combination of as many as 4 different drugs to which the organisms is susceptible. Side effects are common and new drugs are being explored. Two worrisome treatment categories have become more prevalent in recent years. Multi-drug resistant TB now accounts for approximately 5% of cases worldwide. Even more concerning is the emergence of extensively drug resistant TB, for which finding effective treatment is even more difficult.

Orthopnea

Dyspnea that occurs when an individual lies flat and is common in individuals with heart failure. The recumbent position redistributes body water, causes the abdominal contents to exert pressure on the diaphragm, and decreases the efficiency of the respiratory muscles.

Pulmonary Fibrosis

Excessive amount of fibrous or connective tissue in the lung.

Hemoptysis

Expectoration of blood or bloody secretions.

Tuberculosis Pathophysiology

HIghly contagious and transmitted from person to person in airborne droplets. In immunocompetent individuals, the microorganism is usually contained by the inflammatory and immune response systems. This results in latent TB infection (LTBI) and is associated with no clinical evidence of disease. Microorganisms lodge in the lung periphery, usually in the upper lobe. Some bacilli migrate through the lymphatics and become ledger in the lymph nodes, where they encounter lymphocytes and initiate the immune response. Once the bacilli are inspired into the lungs, they multiply and cause localized nonspecific lung inflammation. Inflammation in the lung causes activation of alveolar macrophages and neutrophils. These phagocytes engulf the bacilli and begin the process by which the body's defense mechanisms isolate the bacilli, printing them from spreading. The neutrophils and macrophages seal off the colonies of bacilli, forming a granilomatous lesion called a tubercle. Infected tissues within the tubercle die, forming cheese like material called caseation necrosis. Collagenous scar tissue then grows around the tubercle, completing isolation of the bacilli. The immune response is complete after about 10 days, preventing further multiplication of the bacilli. Once the bacilli are isolated in tubercles and immunity develops, TB may remain dormant for life. If the immune system is impaired, reactivation with progressive disease occurs and may spread through the blood and lymphatics to other organs. Infection w/ HIV is the single greatest risk factor for reactivation of TB infection, Cancer, immunosuppresive medications, poor nutrition, and renal failure can also reactivate disease.

Acute Epiglottitis

Historically caused by H. influenzae type B. Since the advent of H. influenzae vaccine, the overall incidence has been reduced by 80-90%; however, up to 25% are still caused by nontypeable strains of H. influenzae. Current cases in children are usually related to vaccine failure or are cause by other pathogens, such as GABHS, S. pneumonia, Candida species, S. aureus, MRSA, or viral pathogens.

Asthma Clinical Manifestations

If bronchospasm is not reversed by usual measures, the individuals considered to have severe bronchospasm or status asthmaticus. If status asthmatics continues, hypoxemia worsens, expiratory flows and volumes decrease further, and effective ventilation decreases. Acidosis develops as PaCO2 level begins to rise. Asthma becomes life-threatening at this point if treatment does not reverse this process quickly. A silent chest (no audible air movement) and a PaCO2 > 70mm Hg are ominous signs of impending death.

OSAS Evaluation & Treatment

If obstructive sleep apnea is documented or strongly suspected clinically, children are most often referred for tonsillectomy and adenoidectomy (T&A) on the basis of described symptoms and physical finding, such as enlarged tonsils, adenoidal facies, and mouth breathing.

Hypoventilation

Inadequate alveolar ventilation in relation to metabolic demands. Occurs when minute volume is reduced and caused by alterations in pulmonary mechanics or in the neurologic control of breathing.

Hypercapnia

Increased CO2 concentration in the arterial blood, is caused by the hypoventilation of the alveoli.

Tuberculosis

Infection caused by Mycobacterium tuberculosis, an acid-fast bacillus that usually affects the lungs but may invade other body systems. Leading cause of death from a curable infectious disease in the world. TB cases increased greatly during mid 1990s are a result of AIDS. Emigration of infected individuals from high-prevelence countries, transmission in crowded institutional settings, homelessness, substance absurd, and lack of access to medical care also have contributed to the spread.

Pneumonia

Infection os the lower respiratory tract caused by bacteria, virus, fungi, protozoa, or parasites. It is the 6th leading cause of death in US; highest in elderly. Risk factors include advanced age, compromised immunity, underlying lung disease, alcoholism, altered consciousness, impaired swallowing, smoking, endotracheal intubation, malnutrition, immobilization, underlying cardiac or liver disease, and residence in a nursing home, and poverty. The causative microorganism influences how the individual presents clinically, how the pneumonia should be treated and the prognosis. Community-acquired tends to be caused by different microorganisms as compared with those acquired in the hospital. The characteristics of the individual are important in determining in which etiologic microorganism is likely (immunocompromised individuals tend to be susceptible to opportunistic infections that are uncommon in normal adults). Nosocomial infections and those affecting immunocompromised individuals have a higher mortality are than CAP. Most common community-acquired is caused by S. pneumonia, which results in hospitalization in more than half of affected individuals and an overall hospital mortality of 10%. Mycoplasm pneumonia is a cause in young people, especially those living in dorms or barracks. MRSA is becoming more common. Influenza and respiratory syncytial virus are the most common causes of viral community in adults. Nosocomial is a frequent complication in the ICU, most often in persons on mechanical ventilation. Pseudomonas aeruginosa (gram -) & S. aureus are the most common etiologic agents in nosocomial. Immunocompromised individuals (HIV, organ transplant) are especially susceptible to Pneumocytis jiroveci, mycobacteria infections, and fungal infections of the respiratory tract. These can be difficult to treat and have a high mortality.

Pharmacogenetics and Beta Agonists in the Treatment if Asthma

Long-acting beta agonists (salmeterol and formoterol) are recommended by the NEPP to be used in conjunction w/ inhaled corticosteroids as step 3 therapy for asthma. LABAs have been found to improve symptoms and exert both a bronchodilatory and anti-inflammatory effect on the airways. The safety has been questioned b/c of increased mortality. Recent evidence suggests that the reason for this is that those individuals who exhibited worsening symptoms whole taking LABAs used their medications alone, instead of in conjunction with inhaled steroids, thus making ongoing inflammation and airway damage. Evidence also suggest that persons who have a polymorphism of the beta-adrenergic receptor gene (ADRB2) are at risk for complications. The polymorphism is known as Arg16Arg genotype and is associated w/ increased risk for worsening bronchospasm, hospitalizations and mortality when using LABA. The genotype occurs more frequently in black and may explain some of the differences in asthma mortality amoung these individuals.

Ventilation

Mechanical movement of gas or air into and out of the lungs. It is often misnamed respiration, which is actually the exchange of oxygen and CO2 during cellular metabolism.

Small Call Carcinomas

Most common type of neuroendocrine lung tumors.

Pulmonary Embolism Clinical Manifestations

Nonspecific, so evaluation of risk factors and predisposing factors is an important aspect of diagnosis. Although most emboli originate from clots in the lower extremities, DVT is often asymptomatic, and clinical examination has low sensitivity for the presence of a clot, especially in the thigh. An individual with PE usually presents with the sudden onset of pleuritic chest pain, dyspnea, tachypnea, tachycardia, and unexplained anxiety. Occasionally syncope (fainting) or hemoptysis occurs. W/ large emboli, a pleural friction rub, pleural effusion, fever, and leukocytosis may be noted. Recurrent small emboli may not be detected until progressive incapacitation, precordial pain, anxiety, dyspnea, and R ventricular enlargement are exhibited. Massive occlusion causes severe pulmonary hypertension and shock.

Pulmonary Embolism

PE is occlusion of a portion of the pulmonary vascular bed by an embolus. Most commonly results from embolization of a clot from deep venous thrombosis involving the lower leg. Other less common emboli include tissue fragments, lipids, a foreign body, or an air bubble. Risk factors include conditions and disorders that promote blood clotting as a result of venous stasis (immobilization, heart failure), hyper coagulation (inherited coagulative disorders, malignancy, hormone replacement therapy, oral contraceptives), and injury to the endothelial cells that line the vessels (trauma, causative IV infusions). Genetic risks include factor V Leiden, antithrombin II, protein S, protein C, and prothrombin gene mutations. No matter its source, a blood clot becomes an embolus when all of part of it detaches from the site of formation and begins to travel in the bloodstream.

PaO2

Partial pressure of oxygen in arterial blood.

Aspiration

Passage of fluid and solid particles into the lungs. It tends to occur in individuals whose normal swallowing mechanism and cough reflex are impaired by central or peripheral nervous system abnormalities. Predisposing factors include an altered level of consciousness caused by substance abuse, sedation, or anesthesia; seizure disorder; stroke; and neuromuscular disorders that cause dysphagia. Elderly at increased risk. The right lung (right lower lobe) is more susceptible to aspiration than the left lung b/c the branching angle of the right is straighter than the branching angle of the left. Aspiration of acidic gastric fluid (pH <2.5) may cause severe pneumonitis (lung inflammation).

PaCO2

Patrial pressure of carbon dioxide in arterial blood.

Pleural Effusion

Presence of fluid in the pleural space.

Empyema (infected pleural effusion)

Presence of microorganisms and cellular debris (pus) in the pleural space.

Respiratory Distress Syndrome of the Newborn

Previously called hyaline membrane disease (HMD) is a significant cause of neonatal morbidity and mortality. It occurs almost exclusively in premature infants and the incidence has increased in the US over the past 2 decades. RDS occurs in 50-60% of infants born at 29 weeks' gestation and decreases significantly by 36 weeks. Infants of diabetic mothers and those with C sections also are more likely to develop RDS. It is more common in boys than girls and more common in whites. Death rates have declined significantly since the introduction of antenatal steroid therapy and postnatal surfactant therapy.

Types of Lung Cancer

Primary lung cancers arise from cells that line the bronchi within the lungs and are called bronchogenic carcinomas. It is now believed that most of these cancers arise from mutated epithelial steel cells. Although there are many types of ling cancer, they can be divided into 2 main categories (non-small cell lung carcinoma and neuroendocrine tumors). Neuroendocrine tumors of the lung arise from the bronchial mucosa and include small cell, large cell neuroendocrine, typical carcinoid and atypical carcinoid. Small cell is the most common of these neuroendocrine tumors, accounting for 15-20% of all lung cancers. many cancers that arise in other organs of the body metastasize to the lungs; however, these are not considered lung cancers and are categorized by their primary site or origin.

Cough

Protective reflex that helps clear the airways by an explosive expiration.

Signs & Symptoms of Pulmonary Disease

Pulmonary disease is associated with many signs and symptoms, the most common of which as dyspnea and cough. Other include abnormal sputum, hemoptysis, altered breathing patterns, hypoventilation and hyperventilation, cyanosis, clubbing, and chest pain.

V/Q*

Ratio of ventilation to perfusion.

Hypoxemia

Reduced oxygenation of arterial blood is caused by respiratory alterations.

Hypoxia

Reduced oxygenation of cells in tissues, may be caused by alterations of other systems as well.

Pneumoconiosis

Represents any change in the lung caused by inhalation of inorganic dust particles, usually in the workplace.

Laryngeal Cancer

Represents approximately 2-3% of all cancers in the US. Primary risk factors include tobacco smoking; risk is further heightened with the combination of smoking and alcohol consumption HPV has also been linked to both benign or malignant diseases. The highest incidence is in men between 50 & 75 years.

Pulmonary Embolism Evaluation & Treatment

Routine chest radiographs and pulmonary function tests are not definitive for PE. Arterial blood gas analyses usually demonstrate hypoxemia and hyperventilation (respiratory alkalosis). The diagnosis is made by measuring elevated levels of D-dimer in the blood in combination with scanning using spiral computed tomography. Serum brain natriuretic peptide levels are increased in PE and levels are correlated with severity of associated hemodynamic complications. Prevention of PE depends on elimination of predisposing factors for individuals at risk. Venous stasis in hospitalized persons is minimized by leg elevation, bed exercises, position changes, early postoperative ambulate, and pneumatic calf compression. Clot formation is also prevented by prophylactic low-dose anticoagulant therapy usually with low-molecular-weight heparin or warfarin. Newer medications such as antithrombotics fondaparinux, idraparinux, and ximelagatran are superior to standard prevention in high-risk individuals undergoing orthopedic surgery. Anticoagulant therapy is the primary treatment for pulmonary embolism. Initial anticoagulant therapy usually includes low-molecular-weight heparins (enoxaparin), fondaparinux, or unfractionated heparin. If a massive life-threatening embolism occurs, a fibrinolytic agent such as streptokinase, is sometimes used, and some individuals will require surgical thrombectomy. After stabilization, coumadin or low-molecular-weight heparin is continued for several months.

Clubbing

Selective bulbous enlargement of the end of a digit. Its severity can be graded from 1 to 5 based on the extend of nail bed hypertrophy and the amount of changes in the nailed themselves or as early, moderate, or severe.

Paroxysmal Nocturnal Dyspnea (PND)

Some individuals with pulmonary or cardiac disease awake at night gasping for air and have to sit or stand to relieve the dyspnea.

Non-Small Cell Lung Cancer

Squamous cell carcinoma accounts for about 30% of bronchogenic carcinomas. Accounts for 75-85% of al lung cancers and can be divided into 3 types (squamous cells, adenocarcinoma, large cell undifferentiated).

Dyspnea

Subjective experience of breathing discomfort that is comprised of qualitatively distinct sensations that vary in intensity. The experience derives from interactions amount multiple physiological, psychological, social, and environmental factors, and it may induce secondary physiological and behavioral responses. Breathlessness, air hunger, shortness of breath, labored breathing, and preoccupation with breathing.

Croup Clinical Manifestations

The child experiences rhinorrhea, sore throat, and low-grade fever for a few days, and then develops a harsh (seal-like) barking cough, inspiratory stridor, and hoarse voice. The quality of voice, cough, and stridor may suggest the location of the obstruction. Most cases resolve spontaneously within 24-48 hrs and do not warrant hospital admission. A child with severe croup usually displays deep retractions, stridor, agitation, tachycardia, and sometimes pallor of cyanosis.

Asthma Evaluation & Treatment

The diagnosis is supported by a history of allergies and recurrent episodes of wheezing, dyspnea, and cough or exercise intolerance. Further evaluation includes spirometry, which may document reversible decreases in FEV1 during an induced attack. The evaluation of acute asthma attack requires the rapid assessment of arterial blood gases and expiratory flow rates & a search for underlying triggers (infection). Hypoxemia & respiratory alkalosis are expected early in the course of an acute attack, The development of hypercapnia w/ respiratory acidosis signals the need for mechanical ventilation. Management of the acute asthma attack requires immediate administration of O and inhaled beta-agonist bronchodilators. In addition, oral corticosteroids should be administered early in the course of management. Careful monitoring of gas exchange and airway obstruction in response to therapy provides info necessary to determine whether hospitalization is necessary. Antibiotics are not indicated for acute asthma unless there is a documented bacterial infection. Management of asthma begins w/ avoidance of allergens and irritants. Individuals with asthma tend to underestimate the severity and extensive education is important, including use of a peak flow meter and adherence to an action plan should symptoms worsen. In the mildest form (intermittent), short-acting-beta-agonist inhalers are prescribed. For all categories of persistent asthma, anti-inflammatory medications are essential and inhaled corticosteroids are the mainstay of therapy. In individuals who are not adequately controlled with inhaled corticosteroids, leukotriene antagonists can be considered. In more severe asthma, long-acting-beta-agnoists can be used to control persistent bronchospasm; however, these agonists can actually worsen asthma in some individuals w/ certain genetic polymorphisms. Immunotherapy has been shown to be an important tool in reducing asthma exacerbations and can now be given sublingually. Monoclonal antibodies to IgE (omalizumab) have been found to be helpful in selected individuals.

Acute Epiglottitis Pathophysiology

The epiglottis arises from the posterior tongue base and covers the laryngeal inlet during swallowing. Bacterial invasion of the mucosa with associated inflammation leads to the rapid development of edema causing severs, life-threatening obstruction of the upper airway.

Major & Accessory Muscles of Breathing

The major muscles of inspiration are the diaphragm and the external intercostal muscles (muscles between the ribs). When the diaphragm contracts and flattens downward, it increases the volume of the thoracic cavity, creating a negative pressure that draws gas into the lungs through the upper airways and trachea. The external intercostals may contract during quiet breathing, inspiration at rest is usually assisted by the diaphragm only. The accessory muscles of inspiration are the sternocleidomastoid and scalene muscles. There are no major muscles of expiration b/c normal, relaxed expiration is passive and requires no muscular effort. The accessory muscles of expiration, the abdominal and internal intercostal muscles, assist expiration when minute volume is high (coughing or obstructed airway).

Chest Wall & Pleura

The membrane covering the lungs is the visceral pleura; that lining the thoracic cavity is the parietal pleura. The area between the two pleurae is called the pleural space or pleural cavity. Normally, only a thin layer of fluid is secreted by the pleura (pleural fluid) fills the pleural space, lubricating the pleural surfaces and allowing the two layers to slide over each other w/o separating.

Pulmonary Edema

The most common cause of is left-sided heart disease. When the left ventricle fails, filling pressures on the left side of the heart increase. Vascular volume redistributes into the lungs, causing an increase in pulmonary capillary hydrostatic pressure. When the hydrostatic pressure exceeds oncotic pressure (which holds fluid in the capillary), fluid moves out into the interstitial space (the space between alveolus and capillary). When the flow of fluid out of the capillaries exceeds the lymphatic system's ability to remove it, pulmonary edema develops.

OSAS Pathophysiology

The most common predisposing factor in children is adenotonsillar hypertrophy, which causes physical impingement on the nasopharyngeal airway. Also may occur in children who are overweight or obese, and in those with craniofacial anomalies (w/ structurally small nasopharyngeal airways) or reduced motor tone of the upper airways (as may be seen in neurologic disorders, cerebral palsy, and Down syndrome). Allergy and asthma also may contribute.

Oxyhemoglobin Association & Dissociation

The oxyhemoglobin dissociation curve is shifted to the right by acidosis (low pH) and hypercapnia (increased PaCO2). In the tissues, the increased levels of carbon dioxide and hydrogen ions produced by metabolic activity decrease the affinity of Hb for oxygen.

Pneumothorax

The presence of air or gas in the pleural space caused by a rupture in the visceral pleura (which surrounds the lungs) or the parietal pleura and chest wall. As air separates the visceral and parietal pleurae, it destroys the negative pressure of the pleural space and disrupts the equilibrium between elastic recoil forces of the lungs and chest wall. The lung then tends to recoil by collapsing toward the helium. Primary (spontaneous) pneumothorax, which occurs unexpectedly in healthy individuals (usually men) between 20 and 40 years of age, is caused by the spontaneous rupture of blebs (blister-like formations) on the visceral pleura.