Definition

The term acute respiratory failure is often used synonymously with acute (formerly adult) respiratory distress syndrome (ARDS). Although ARDS may be caused by or associated with a variety of clinical conditions, most patients with this disease demonstrate similar clinical and pathologic features regardless of the cause of lung injury. Common features include: (1) a history of a preceding noxious event that served as a trigger for the subsequent development of ARDS; (2) an interval from hours to days of relatively normal lung function after the insult; and (3) the rapid onset and progression over several hours of dyspnea, severe hypoxia, diffuse bilateral pulmonary infiltration, and stiffening and noncompliance of the lungs.

Incidence and prevalence

Risk factors for the development of ARDS appear to be additive. The incidence of occurrence is 25% with the presence of one risk factor, 42% with the presence of two, and 85% with the presence of three. The mortality rate for ARDS remains high, ranging from 50% to 70% and often exceeds 90% when gram-negative septic shock precedes ARDS development. Events and risk factors associated with the development of ARDS include: (1) shock (septic, cardiogenic, or hypovolemic), (2) trauma, (3) pulmonary infection (e.g., with Pneumocystis carinii [jiroveci] or Escherichia coli), (4) disease states that result in the release of inflammatory mediators (e.g., extrapulmonary infections, disseminated intravascular coagulation, anaphylaxis, coronary bypass grafting, and transfusion reactions), (5) exposure to various agents (e.g., narcotics, barbiturates, and O₂), (6) diseases of the central nervous system (CNS), (7) aspiration (e.g., of gastric contents or as in drowning), and (8) metabolic events (e.g., pancreatitis and uremia).

Pathophysiology

The pathophysiology of ARDS is centered around severe damage and inflammation to the alveolocapillary membrane. Irrespective of the cause of acute respiratory failure, the lung’s structural response to injury and subsequent repair occurs in a similar fashion. Although the exact mechanisms of this response and repair remain unclear, research has focused on the release of cytokines and membrane-bound phospholipids from the capillary endothelium and the activation of leukocytes and macrophages (via the complement system) within the lungs.

Clinical manifestations

The clinical presentation includes patients who are dyspneic, hypoxic, and hypovolemic and require intubation and mechanical ventilation. Recovery of lung function is unpredictable. Milder cases resolve quickly, but others progress to fibrosis and death.

Treatment

Because lung infections (e.g., P. carinii [jiroveci] pneumonia) mimic ARDS, antibiotic therapy often is initiated before the cause of respiratory failure is known. Maintenance of tissue oxygenation and replacement of lost intravascular fluids are the main goals of therapy. Preservation of end-organ perfusion is of utmost importance. Treatment is supportive and includes correction of hypoxia, preload and afterload reduction, and inotropic support as indicated.

Anesthetic considerations

Anesthetic preparation includes evaluation of the patient’s respiratory, cardiac, and renal status. Ventilator settings should be noted and special attention devoted to peak inspiratory pressures and positive end-expiratory pressure (PEEP) levels. If the anesthesia ventilator cannot accommodate these settings, then arrangements must be made to bring the patient’s ventilator into the operating room. The nature of lung sounds and amount of secretions should be noted. The presence of excess secretions should alert the anesthesia provider to the potential risk of airway obstruction. The degree of barotrauma from prolonged mechanical ventilation with high levels of PEEP can be assessed by the presence of chest tubes and subcutaneous emphysema secondary to pneumothorax. The effectiveness of therapy with bronchodilators should be assessed because the use of these drugs may be initiated preoperatively and continued intraoperatively if effective. An arterial line should be placed preoperatively and arterial blood gas (ABG) analysis performed. If possible, lactic acid values should be determined.

Volume status should be evaluated closely because patients with ARDS often are hypovolemic. Invasive monitoring via central venous lines and pulmonary artery catheters often is available, and cardiac filling pressures along with CO values should be assessed. Patients requiring inotropic support may arrive for surgery with infusions of dopamine or dobutamine. For all procedures, renal function should be monitored with a bladder catheter. Antibiotic therapy should be continued intraoperatively, and continuation of steroid preparations should be considered if patients were receiving these medications preoperatively.

Because patients with ARDS often are hemodynamically unstable, careful titration of anesthetic agents and adjunct agents is necessary. Owing to the multisystemic involvement characteristic of ARDS, drug metabolism and elimination should be carefully considered.

Transport should be carefully planned so that complications are minimized and safe arrival in the intensive care unit is ensured. Patients should undergo pulse oximetry, electrocardiography (ECG), and blood pressure transport monitoring (by arterial line or noninvasively) before departure from the operating room.

Breath sounds should be continually assessed with a precordial stethoscope. A full tank of O₂ and PEEP adapter valves should be available for transport. The potential need for emergency medications and a defibrillator should be considered. If the patient’s ventilator needs to be returned to the intensive care unit, plans should be made so that it arrives there before the patient does. Finally, if possible, another member of the anesthesia team should accompany the patient during transport. Pulmonary dysfunction is the most common cause of postoperative complications after the administration of general anesthesia. To minimize pulmonary derangement, the anesthesia provider must identify patients who are at risk for the development of pulmonary impairment and must have a thorough understanding of the preexisting lung dysfunction.

Definition

Two entirely separate clinical aspiration disorders exist. One occurs after the aspiration of solid food and produces a picture of laryngeal or bronchial obstruction, an the other results from direct acid injury to the lung and produces an “asthma-like” syndrome. Pulmonary aspiration occurs when the gastric contents escape from the stomach into the pharynx and then enter the lungs. This results from preexisting disease, airway manipulation, and the inevitable compromise in protective reflexes accompanying the anesthetized state. Aspirates are commonly categorized as contaminated, acidic, alkaline, particulate, and nonparticulate. Fewer than half of all aspirations lead to pneumonia. Pneumonia occurs most often in patients with aspiration of infected material or who are immunocompromised.

Incidence and prevalence

Although the incidence of regurgitation is estimated to be frequent (as high as 15%), pulmonary aspiration complicates only about one in 3000 anesthetics. This incidence is roughly doubled for cesarean section surgery and emergency surgery. Fortunately, the majority of aspiration incidents require little or no treatment.

Pathophysiology

Although vomiting and gastroesophageal reflux are common clinical events, aspiration usually occurs only when normal protective reflexes (swallowing, coughing, gagging) fail. Three broad categories of failure are (1) depression of reflex protection, (2) alteration in anatomic structures, and (3) iatrogenic disorder. Reflex responses to aspiration are automatically blunted with depression of consciousness. The most common setting for depression of reflex protection occurs during anesthesia induction and emergence.

Three aspiration syndromes have been identified: (1) chemical pneumonitis (Mendelson syndrome), (2) mechanical obstruction, and (3) bacterial infection. Because acute chemical pneumonitis poses the greatest difficulty to anesthesia providers, the pathophysiology, presentation, and anesthetic implications of Mendelson syndrome are discussed. The triphasic sequence of (1) immediate respiratory distress combined with bronchospasm, cyanosis, tachycardia, and dyspnea followed by (2) partial recovery and (3) a final phase of gradual return of function is characteristic of Mendelson syndrome. This acute chemical pneumonitis is caused by the irritative action of hydrochloric acid, alkaline aspirates, or particulate materials, which are damaging to the lungs.

The pathophysiology of aspiration pneumonitis is typically characterized by four stages: (1) The aspirated substance causes immediate damage to the lung parenchyma, resulting in tissue necrosis. (2) Atelectasis results within minutes caused by a parasympathetic response that leads to airway closure and a decrease in lung compliance. (3) One to two hours after the injury, there is an intense inflammatory reaction characterized by pulmonary edema and hemorrhage. Inflammatory cytokines play a central role in this, including interleukin-8 and tumor necrosis factor alpha (TNF-α) released by alveolar macrophages. Neutrophils also play a key role in this phase by releasing oxygen radicals and proteases. Fluid fills the alveolar capillary membrane, causing hypoxia and hypercarbia. (4) Later, secondary injuries result from fibrin deposits and necrosis of alveolar cells by 24 hours after the insult.

Clinical manifestations and diagnosis

Arterial hypoxemia, the hallmark sign of aspiration pneumonitis, is frequently the first sign of aspiration. Because the majority of aspiration incidents are asymptomatic or mildly symptomatic, unexplained hypoxemia occurring in otherwise healthy patients postoperatively may frequently be a vague sign of silent aspiration. Other signs to alert the anesthetist to the possibility of aspiration include tachypnea, dyspnea, tachycardia, hypertension, and cyanosis.

Anesthetic considerations

Treatment of aspiration pneumonitis

Definition

Asthma is a chronic inflammatory disorder of the airways characterized by increased responsiveness of the tracheobronchial tree to a variety of stimuli. Many cells and cellular elements play a role, particularly mast cells, eosinophils, T lymphocytes, neutrophils, and epithelial cells. In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness, and cough, particularly at night and in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment.

Various subtypes of asthma exist. The most important consideration is the identification of exacerbating factors whenever possible. A well-known system classifies asthmas as either extrinsic or intrinsic. Although this system is conceptually helpful, its two groups are not mutually exclusive. Whereas extrinsic asthma (or allergic asthma) most commonly affects children and young adults and involves infectious, environmental, psychological, or physical factors, intrinsic asthma (or idiosyncratic asthma) usually develops in middle age without specifically identifiable attack-provoking stimuli. The term atopy, which refers to a hereditary, immunoglobulin E (IgE)–mediated, clinical hypersensitive state, is often used when extrinsic asthma is described.

Incidence and prevalence

Up to 15 million persons in the United States have asthma. It is the most common chronic disease of childhood, affecting an estimated 4.8 million children. People with asthma collectively have more than 100 million days of restricted activity and 470,000 hospitalizations annually. More than 5000 people die of asthma each year.

Pathophysiology

Asthma is a heterogeneous clinical syndrome characterized by episodes in which airways are hyperresponsive, interspersed with symptom-free periods. Bronchoconstriction is a factor long associated with the asthmatic symptom complex, but asthma is much more than bronchoconstriction. Airway inflammation and a nonspecific hyperirritability of the tracheobronchial tree are now recognized as being central to the pathogenesis of even mild cases of asthma. Permanent changes in airway anatomy, referred to as airway remodeling, magnify the inflammatory response.

Allergic asthma (atopic or immunologic disease) is triggered by antigens that provoke a T-lymphocyte–generated, IgE-mediated immune response. It is often associated with a personal or familial history of allergic disease. Potent biochemical mediators released from proinflammatory and airway epithelial cells promote vasoconstriction, increased smooth muscle tone, enhanced mucous secretion, submucosal edema, increased vascular permeability, and inflammatory cell chemotaxis. Leukotrienes have been identified as especially potent spasmogenic and proinflammatory substances. Released molecules that are toxic to the airway epithelium cause patchy desquamation, which exposes cholinergic nerve endings and compounds the bronchoconstrictive and hyperresponsive response.

The asthmatic diathesis creates airways that are inflamed, edematous, and hypersensitive to irritant stimuli, and the degree of airway hyperresponsiveness and bronchoconstriction appears to parallel the extent of inflammation. When airway reactivity is high, asthmatic symptoms are generally more severe and unrelenting, and the amount of therapy required to control the episode is greater.

The mechanisms underlying idiosyncratic asthma (nonimmunologic disease) are less clearly defined. Nonimmunologic asthma occurs in patients with no history of allergy and normal serum IgE. These patients typically develop asthmatic symptoms in response to some provocative or noxious stimulus such as cold air, airway instrumentation or irritation, climate changes, or an upper respiratory illness. Recent upper respiratory infection may precipitate bronchospasm in any patient, but the risk is higher in patients with a history of asthma.

The mechanism of exercise-induced asthma is unknown. Regardless of the mechanism, most symptoms last less than 1 hour and are usually quickly reversed with administration of β₂-adrenergic receptor agonists. Occupational asthma develops when irritants directly stimulate vagal nerve endings in the airway epithelium. Infection-induced asthma with acute inflammation of the bronchi may be caused by viral, bacterial, or mycoplasmal infections. Aspirin-induced asthma occurs when, in some predisposed persons, cyclooxygenase promotes an increase in leukotriene levels via the arachidonic acid pathway, thereby triggering the asthma attack. This peculiar response can occur with the use of other nonsteroidal anti-inflammatory agents. The aspirin-induced asthma variant is not IgE mediated or allergic in nature; furthermore, it is clinically associated with nasal polyps. Patients with aspirin-induced asthma may be at increased risk of bronchospasm after ketorolac (Toradol) administration.

Clinical manifestations

Key hallmarks of asthma in the awake patient include the following:

Typically, attacks are short lived, lasting minutes to hours. Between attacks, the patient with asthma may be entirely symptom free; however, underlying airway remodeling is still evident. Severe obstruction persisting for days or weeks is known as status asthmaticus. Use of accessory muscles of respiration and the increased work of breathing associated with a protracted asthmatic episode can result in respiratory muscle fatigue and respiratory failure. During exacerbations, pulmonary function tests may reflect acute expiratory airflow obstruction (decreased forced expiratory flow [FEF]_25%–75% and decreased ratio of forced expiratory volume in one second to forced vital capacity [FEV₁/FVC]). Viscid mucous secretion may compound the airway narrowing and produce airway collapse.

The asthmatic episode produces not only airflow obstruction but also gas exchange abnormalities. The resulting low ventilation/perfusion (V/Q) state produces arterial O₂ desaturation. Hypoxemia is common, but in most patients with acute bronchospasm, CO₂ elimination is relatively well preserved until V/Q abnormalities are severe. An increased arterial CO₂ tension may indicate impending respiratory failure in an acutely ill patient with asthma. Chronic asthma may eventually lead to irreversible lung destruction, loss of lung elasticity, pulmonary hypertension (PH), and lung hyperinflation.

Anesthetic considerations

Several important anesthetic considerations and risk reduction strategies have been reported (see the following box).

Definition

Chronic obstructive pulmonary disease (COPD) is a “disorder characterized by abnormal tests of expiratory flow that does not change markedly over periods of several months of observation.” Asthma, chronic bronchitis, and emphysema are all common obstructive diseases characterized by decreased air flow through the tracheobronchial tree and small airways.

The terms chronic obstructive pulmonary disease and chronic obstructive lung disease are widely used as synonyms for the combination of chronic bronchitis and emphysema. Because of the prevalence of cigarette smoking, the combination of these two entities is encountered much more commonly than either of the two in its “pure” form. As a rule, the combination of chronic bronchitis and emphysema is seen in those who smoke heavily, and the disease process takes 30 years or longer to manifest. Differential diagnosis of COPD compared with other common lung disorders is described in the following table.

Incidence and prevalence

COPD affects an estimated 15 to 20 million Americans and is the fifth leading cause of death in the United States, accounting for approximately 60,000 deaths each year. Chronic bronchitis and emphysema are the most common causes of COPD.

Pathophysiology

The dominant feature of the natural history of COPD is progressive air flow obstruction, as reflected by a decrease in FEV₁. Three causes of decreases in FEV₁ are as follows:

Clinical manifestations

The clinical presentation of COPD varies markedly, and crippling changes for one person may be a minor incapacity for another. Chronic productive cough and progressive exercise limitation are the hallmarks of COPD. The clinical and functional changes are noted in the following tables.

Anesthetic considerations

Definition

The term cor pulmonale or pulmonary heart disease refers to patients exhibiting pulmonary arterial hypertension (PAH) resulting in progressive right ventricular hypertrophy, dilation, and eventual cardiac decompensation. This arises from disorders that affect ventilatory drive or musculoskeletal respiratory mechanics; pulmonary airway, infiltrative, fibrotic, or vascular diseases; and diseases that are primarily cardiac but affect the pulmonary circulation and the lungs.

Incidence and prevalence

In individuals older than 50 years of age, cor pulmonale is the third most common cardiac disorder (after ischemic heart disease and hypertensive cardiac disease). The male-to-female ratio of incidence of the disease is 5:1; 10% to 30% of patients admitted to the hospital with coronary heart failure exhibit cor pulmonale.

The prognosis is determined by the pulmonary disease responsible for the increased pulmonary vascular resistance (PVR). In patients with COPD in whom Pao₂ can be maintained at near-normal levels, the prognosis is favorable. However, cor pulmonale associated with hypoxic lung disease is associated with a 70% rate of mortality within 5 years after onset of associated peripheral edema. The prognosis is poor for patients in whom cor pulmonale is the result of gradual obstruction of pulmonary vessels by intrinsic pulmonary vascular disease or pulmonary fibrosis. These anatomic changes cause irreversible alterations in the pulmonary vasculature, resulting in fixed elevations of PVR.

Pathophysiology

COPD is associated with the functional loss of pulmonary capillaries and the subsequent arterial hypoxemia; these events initiate pulmonary vasoconstriction, which is the leading cause of chronic cor pulmonale. Sustained pulmonary vasoconstriction produces hypertrophy of the smooth muscle in the tunica media and an irreversible increase in the PVR. In the presence of chronically elevated pulmonary capillary pressure, the lungs are increasingly resistant to pulmonary edema because lymph vessels expand and their ability to carry fluid away from the interstitial spaces increases. The lymphatic pumping action creates a suction effect, which results in a negative pleural pressure. The rate at which right ventricular dysfunction develops depends on the magnitude of pressure increase in the pulmonary circulation and on the rapidity with which this increase occurs. For example, PE may result in right ventricular failure in the presence of a mean PAP as low as 30 mmHg. By contrast, when PAH occurs gradually, as it does in COPD, right ventricular compensation occurs; congestive heart failure rarely occurs before mean PAP exceeds 50 mmHg.

Clinical manifestations and diagnosis

Clinical manifestations of cor pulmonale often are nonspecific and obscured by coexisting COPD. Right-sided heart catheterization usually is required for diagnosis. Cardiac catheterization combined with pulmonary angiography provides the most definitive information on the degree of PAH, cardiac reserve, and the effects of pulmonary vasodilator treatment. Symptoms of cor pulmonale are retrosternal pain, cough, dyspnea on exertion, weakness, fatigue, early exhaustion, and hemoptysis. Occasionally, hoarseness secondary to left recurrent laryngeal nerve compression by the enlarged pulmonary artery is present. Syncope on effort may occur, reflecting the inability of the right ventricular stroke volume to increase in the presence of a fixed elevation of PVR.

Physical signs of cor pulmonale include the following:

Treatment

The three major drug classes for treatment of PAH are prostanoids, endothelin receptor antagonists, and phosphodiesterase inhibitors. The goals of treatment are decreasing the workload of the right ventricle, reducing PVR, preventing increases in PAP, and avoiding major hemodynamic changes. Improvement of gas exchange is the primary focus of treatment in COPD patients with cor pulmonale. Treatment includes supplemental administration of O₂ in order to maintain a Pao₂ of greater than 60 mmHg or an arterial O₂ saturation of greater than 90%. O₂ is the only vasodilator with a selective effect on pulmonary vessels that is not associated with a risk of worsening hypoxemia.

Anesthetic considerations

Regional anesthesia technique may be appropriate as long as a high sensory level of anesthesia is not required because any decrease in systemic vascular resistance in the presence of a fixed PVR may produce undesirable degrees of systemic hypotension.

Definition

Cystic fibrosis is the most common life-shortening autosomal recessive disorder.

Incidence and prevalence

Cystic fibrosis affects an estimated 30,000 persons in the United States, with 1000 new cases per year. Most are diagnosed between the ages of 3 months and 6 years, but 8% are not diagnosed until after 18 years. One in 31 Americans is an asymptomatic carrier of the defective gene. More than 80% of those born with cystic fibrosis are born to parents with no history of the disease.

Pathophysiology

Cystic fibrosis is caused by a mutation of a gene on chromosome 7. The result is defective chloride ion transport in epithelial cells in the lungs, pancreas, liver, gastrointestinal tract, and reproductive organs. This decrease in chloride transport results in a decrease of sodium and water transport. This results in dehydrated, viscous secretions that can cause obstruction, destruction, and scarring of exocrine glands.

Laboratory results

Because cystic fibrosis is an expiratory airflow obstructive disease, most pulmonary function test results will be abnormal. The white blood cell count may be elevated because of frequent pulmonary infections.

Clinical manifestations

Pancreatic insufficiency, meconium ileus at birth, diabetes mellitus, azoospermia, and obstructive hepatobiliary tract disease (cirrhosis and portal hypertension) are often present. The primary causes of morbidity and mortality are bronchiectasis and COPD. Typically, a cough, chronic purulent sputum production, and exertional dyspnea will be seen.

Treatment

Treatment is similar to that for bronchiectasis and focuses on alleviation of symptoms (mobilization and clearance of lower airway secretions and treatment of pulmonary infections) and correcting organ dysfunction (pancreatic enzyme replacement). Treatment of secretions is usually done by chest physical therapy with postural drainage. Bronchodilator therapy may also be instituted. Antibiotics are often given to relieve the increased secretions from pulmonary infections. If no pathogens are seen, bronchoscopy to remove lower airway secretions may be indicated if there is no response to common antibiotics.

Anesthetic considerations

Management is based on the same principles as in patients with COPD and bronchiectasis. Elective procedures are delayed until optimal pulmonary function is ensured by controlling infections and removing secretions from the airways. Vitamin K may be given if liver function is poor or if absorption of fat-soluble vitamins is poor in the gastrointestinal tract. Preoperative sedation is probably unnecessary because of possible respiratory depression. Maintenance of anesthesia with a volatile agent and oxygen can decrease airway resistance by decreasing the bronchial smooth muscle tone. Volatile agents are also helpful in decreasing the responsiveness of hyperreactive airways. Humidified gases are also important to decrease the viscosity of secretions. Frequent suctioning is also necessary.

Definition

Pneumothorax is the presence of air or gas in the pleural space. Hemothorax is the presence of blood in the pleural space.

Incidence and prevalence

Spontaneous pneumothorax occurs unexpectedly in healthy persons, most often in men 20 to 40 years of age. Secondary pneumothorax and hemopneumothorax are generally the result of trauma.

Pathophysiology and treatment

Pathogenesis

Different presentations may be distinguished, according to the mechanism of injury, as described in the following sections.

Laboratory results

The chest radiograph frequently shows subcutaneous emphysema, pneumomediastinum, and pneumopericardium. Free fluid, as with hemothorax, may be best seen on a cross-table lateral radiograph.

Anesthetic considerations

Pneumothorax or hemothorax can significantly interfere with oxygenation and ventilation. Decreased cardiac output, as with tension pneumothorax, can exacerbate intrapulmonary shunting. Cyanosis indicates both cardiac and pulmonary involvement. Nitrous oxide can quickly expand the size of a pneumothorax if a chest tube is not in place. Nitrous oxide is acceptable for use if the chest tube is patent and functioning. A closed pneumothorax is a contraindication to the administration of nitrous oxide. Decreased pulmonary compliance (increased pulmonary inspiratory pressure) during administration of anesthesia to patients with a history of chest trauma may reflect the expansion of an unrecognized pneumothorax.

In the case of ventilator-related pneumothorax, the mortality rate is significantly reduced if a chest tube is placed in less than 30 minutes. Development of tension pneumothorax during general anesthesia is manifested by sudden hypotension, loss of pulmonary compliance, or decreased ventilating volume. Patients with significant trauma may require fluid resuscitation and cardiovascular support. Agents chosen should have minimal cardiac depressant effects.

Definition

Pulmonary arterial hypertension usually represents an advanced stage of a large number of cardiovascular diseases. The mortality rate associated with PAH is high. PAH exists if the mean level of PAP increases by 5 to 10 mmHg or if pulmonary artery systolic pressure exceeds 30 mmHg and mean PAP exceeds 20 mmHg.

Incidence

Pulmonary arterial hypertension may be (1) primary or idiopathic (unexplained) or (2) secondary to an associated condition. In young adults, the female-to-male incidence of primary pulmonary arterial hypertension (PPAH) is 4:1; this incidence is similar to that in older groups of men and women.

Pathophysiology

Pulmonary arterial hypertension may be caused by many associated conditions, including pulmonary venous hypertension caused by left atrial outflow obstruction or pulmonary venous occlusive disease and PAH caused by hyperdynamic circulation (e.g., secondary to burns or sepsis), vasoconstriction, viscosity, obstruction, and reactive vascular disease.

Pulmonary arterial hypertension is characterized by a rapidly progressive course with a 79% mortality rate within 5 years of clinical diagnosis. The degree of increase in pressure in the pulmonary circulation has an important influence on the patient’s life expectancy. Resistant PAH has long been identified as a major cause of early death. The prognosis is largely determined by right ventricular integrity.

Pulmonary arterial hypertension is characterized by an increase in vascular tone and the growth and proliferation of pulmonary vascular smooth muscle. Initial reversible vasoconstriction may progress to muscle hypertrophy and irreversible degeneration.

Clinical manifestations and diagnosis

Pulmonary arterial hypertension may be either acute or chronic. In almost all patients with PAH, dyspnea and exercise intolerance usually are the first complaints. Patients also may have angina. Right atrial hypertrophy or right ventricular hypertrophy (or both) may be evident on ECG. Chest radiography may demonstrate an enlarged pulmonary artery. Cardiac catheterization combined with pulmonary angiography is most informative in assessment of PAH, cardiac reserve, and the effects of pulmonary vasodilator therapy. Vasodilator therapy is attempted when a vasoconstrictor component is identified. Vasodilator challenge may be performed with cardiac catheterization using a rapid and effective pulmonary vasodilator such as nitroglycerin, isoproterenol, nifedipine, prostaglandin E₁, prostacyclin, prostaglandin E₂, hydralazine, nitroprusside, or adenosine for evaluation of the reversibility of PAH. Frequently, open-lung biopsy is performed for assessment of the histopathologic composition of small pulmonary arteries. Noninvasive evaluation includes Doppler echocardiography for measurement of the velocity of tricuspid regurgitation (which correlates well with invasive PAP measurements) and pulmonic peak flow velocity.

Anesthetic considerations

Attempts to alleviate PH disease states have had varied success. Vasodilator agents are used most commonly and may be helpful in patients with reversible vasoconstriction. A list of vasodilators used in PAH is provided in the table below. Possible beneficial effects of pulmonary arterial dilation are preservation of lung function; prevention of right ventricle deterioration; and, it is hoped, improved survival. The principal objectives during anesthesia in patients with PAH are prevention of increases in PAH and avoidance of major hemodynamic changes. Considerations that apply to the care of patients with cor pulmonale also apply to those with PAH. Information regarding PAH and intravenous induction agents is lacking; however, most agents either have little effect on PVR or decrease it. Ketamine, which causes an increase in PVR, may be the exception.

Definition

Pulmonary edema is the accumulation of excess fluid in the interstitial and air-filled spaces of the lung. The mechanisms responsible for its development include an increase in hydrostatic pressure within the pulmonary capillary system, an increase in the permeability of the alveolocapillary membrane, and a decrease in intravascular colloid oncotic pressure.

Pulmonary edema is classified as being either cardiogenic (high pressure, hydrostatic) or noncardiogenic (increased permeability).

Clinical manifestations

Physical examination reveals an increased work of breathing. As water accumulates, the lungs become heavy and noncompliant, and a decrease in FRC occurs. This increase in the volume of extravascular lung fluid provides a potent stimulus for surrounding interstitial stretch receptors (j-receptors) whose activation results in tachypnea. Tachypnea is not relieved by the administration of oxygen and the return of arterial oxygen tension (Pao₂) to normal. Intercostal retractions and use of accessory muscles are apparent on physical examination. Signs of sympathetic stress stimulation such as hypertension, diaphoresis, and tachycardia often are noted. The expectoration of pink, frothy sputum signals that alveoli have been flooded.

The detection of basilar crackles on auscultation is the traditional hallmark of early pulmonary edema. In reality, by the time these crackles become audible, excess water has already flooded the alveoli and has overflowed into the terminal bronchioles. It is in the bronchioles, not in the alveoli, that the crackles of pulmonary edema are generated. The earliest and most often disregarded clinical sign is rapid, shallow breathing.

In cardiogenic pulmonary edema, heart size may be increased. High central venous pressures (CVPs), an S₃ or S₄ gallop, and jugular venous distention often are observed. Chest radiography is still the most reliable and expedient tool for early detection of pulmonary edema. In cardiogenic pulmonary edema, the cardiac silhouette may appear abnormal or enlarged; in noncardiogenic pulmonary edema, it can be enlarged or remain normal. Interstitial edema can be observed before the alveoli flood and the onset of clinical signs occurs. Pleural effusions are common, and a “whited-out” or “butterfly” appearance may be noted.

Arterial blood gas analysis reveals hypoxemia secondary to V/Q abnormalities. When right-to-left shunting is great, the Pao₂ can be affected by any change in the central venous oxygen content. Increases in oxygen consumption or decreases in cardiac output further reduce the Pao₂. The arterial carbon dioxide tension (Paco₂) may be low, normal, or elevated. The initial hypocarbia is related to tachypnea and high minute volumes; at later stages, hypercarbia is frequently secondary to muscle fatigue and exhaustion. Changes in pH usually reflect changes in Paco₂, but metabolic and V/Q or lactic acidosis may occur from tissue oxygen deficiency, low cardiac output, or sepsis.

Treatment and anesthetic considerations

Treatment includes prompt recognition of the condition, securing a patent airway, supportive therapy with oxygenation, and the administration of diuretics. Although the onset of pulmonary edema after laryngospasm usually is immediate, cases have been reported of the occurrence of pulmonary edema several hours after laryngospasm. Therefore, it is recommended that patients who develop laryngospasm be observed postoperatively longer than the typical 60 to 90 minutes. The diagnosis of pulmonary edema and its differentiation into cardiac and noncardiac categories require the taking of a detailed medical history, physical examination, chest radiography, and ABG analysis.

Pulmonary edema is considered a medical emergency, and immediate intervention is required for treating the underlying disease, supporting other failing organ systems, and optimizing oxygen delivery. Oxygen should be administered by nasal cannula, face mask, or ETT. If oxygenation does not improve with the administration of high fractions of inspired oxygen, positive-pressure ventilation with either PEEP or continuous PAP must be initiated. Institution of positive-pressure mechanical ventilation in patients with acute pulmonary edema usually results in a prompt increase in oxygenation and, in some cases, in cardiac output. Improvement occurs because of superior inflation and V./Q. matching.

Pharmacologic therapy includes the use of vasodilators, inotropes, steroids, and diuretics. Morphine sulfate has been used in the treatment of cardiogenic pulmonary edema because of its venodilatory properties. Nitroprusside is very effective at decreasing preload, afterload and left ventricular afterload. This may result in better cardiac function, with a subsequent lowering of left atrial pressures. Inotropic agents such as dopamine or dobutamine improve myocardial contractility and lower cardiac filling pressures. In patients with chronic congestive heart failure and pulmonary congestion, digitalis augments contractility and promotes decreases in left atrial and ventricular filling pressures.

Fluid balance is managed with both fluid restriction and diuresis. This therapy helps achieve a “negative” fluid balance in hydrostatic pulmonary edema. Potent diuretics such as furosemide not only lower left atrial filling pressure by decreasing systemic venous tone but also induce diuresis of the expanded extravascular volume. The type of fluid, whether crystalloid or colloid, that should be used in the presence of pulmonary edema remains controversial. Regardless of type used, it is generally agreed that fluid administration proceeds slowly.

Definition

Pulmonary embolism (PE) is considered by some to be a clinical manifestation of deep venous thrombosis (DVT) rather than a separate entity. Most emboli (90%) arise in the proximal deep veins of the lower extremities, with the remainder originating from pelvic veins. DVT at proximal sites is more likely to cause symptoms. Three major factors promote the formation of venous thrombi: stasis of blood flow, venous injury, and hypercoagulation states. Other less common causes of PE include air, tumor, bone, fat, catheter fragments, and amniotic fluid. Fillers used in illicit drug preparations by intravenous drug abusers also may cause PE. Of particular concern to anesthesia providers are air emboli caused by the opening of venous structures during surgery or by disconnected intravenous lines.

Most pulmonary emboli resolve within 8 to 21 days of the initial presentation. Chronically unresolved emboli that lodge in major pulmonary arteries may become incorporated into the vascular walls and obstruct blood flow. Patients with such emboli are surgical candidates, representing approximately 1000 cases in the United States each year.

Pathophysiology

When a thrombus has formed, it rarely remains static. It can be dissolved through fibrinolysis, become “organized” into a vessel wall, or be released into the circulation. Because thrombi are most friable early in their development, it is then that the greatest risk for embolism exists. Emboli are most often seen in the lower lung lobes, which receive the greatest amount of blood flow. Fortunately, these lower lung lobes also tend to receive the least ventilation, so much of the V./Q. ratio is preserved in patients with small- to moderate-sized emboli. The three components of the Virchow triad—stasis, hypercoagulability, and vessel wall injury—lead to venous thrombosis.

Clinical manifestations and diagnosis

The patient’s clinical presentation depends largely on the size of the embolus. Signs and symptoms of PE vary, and the differential diagnosis according to size of emboli may be difficult. Dyspnea of sudden onset appears to be the only common historical complaint. Hypoxia is a constant feature of PE, possibly owing to intrapulmonary shunting.

Massive emboli can produce sudden cardiac collapse. Preceding symptoms range from pallor, shock, and central chest pain to sudden loss of consciousness. In patients with cardiac collapse, the pulse becomes rapid and weak, blood pressure decreases, neck veins become engorged, and cardiogenic shock may be present or impending. Also, a decrease in Petco₂ and an increase in Paco₂ occur, with the difference between the values for these two indexes increasing as conditions worsen. If a pulmonary artery catheter is in place, PAPs are observed to increase rapidly; also, the ECG may begin to show right ventricular strain. The prognosis for these patients is very poor.

Diagnostic testing

Few of the common preoperative tests indicate the presence of PE. A number of imaging and laboratory tests are now available for diagnosis as listed below. In patients with PE, ABG analysis generally reveals hypoxemia and increased differences between Paco₂ and Paco₂, which result from ventilation of unperfused alveoli.

Massive PE is associated with severe hypoxemia and hypocapnia. An initial difference between Paco₂ and Petco₂ is common early during the embolic event. Some common conditions associated with an increased risk for DVT are listed as follows.

Treatment

Aggressive efforts at prevention have been successful in reducing the incidence of DVT in surgical patients. Treatment is mainly aimed at prevention of further embolism and at provision of ventilatory support as shown in the table below. Use of graded compression stockings, intermittent pneumatic compression, administration of various anticoagulants and thrombolytics, and ambulation are typical measures for preventing embolus formation. It must be remembered that PE is a mechanical disease caused by acute pulmonary obstruction in a previously healthy patient.

Treatment requires rapid intervention before vital signs are affected by hypoxia and mechanical failure of the heart. Guidelines for treatment of PE are summarized in the following box.

Anesthetic considerations

Anesthesia for patients at risk for PE is aimed at supporting vital organ function and minimizing anesthetic-induced myocardial depression. The use of a high Fio₂ aids in prevention of pulmonary vasoconstriction, and the monitoring of PAP helps the anesthesia provider optimize right-sided heart function and assess the effects of anesthetic management on PVR. Many anesthesia providers choose not to place pulmonary artery catheters because of concerns about the possibility that these catheters will dislodge clots in the right side of the heart.

Intravenous fluid infusion must be adjusted so that right ventricular stroke volume is optimized in the presence of marked increase in afterload. A continuous catecholamine infusion may be needed to enhance cardiac contractility. Induction is often performed with etomidate or ketamine (for maintenance of hemodynamic stability), but ketamine must be titrated judiciously because it may increase PVR.

The use of N₂O is generally believed to be acceptable. However, this may not be possible with the use of a high Fio₂. Use of N₂O should be discontinued if PVR increases. Obviously the use of N₂O is contraindicated in patients with venous air embolism. Patients with moderate to severe PE often are experiencing acute right-sided heart failure. Cardiac function can be optimized by the use of minimally depressing cardiac agents such as narcotics.

Persistent severe hypotension, such as that accompanying a massive PE, may necessitate the use of a cardiotonic agent. The goal is preservation of perfusion to the brain and heart until cardiopulmonary bypass is started and surgical removal of the clot attempted. As always, heparin should be readily available, and when needed, it should be administered into a central line while blood aspiration is verified before and after injection. Reports of operative mortality during pulmonary embolectomy range from 11% to 55%, with much higher rates among patients experiencing cardiac arrest.

Definition

Restrictive pulmonary disease is defined as any condition that interferes with normal lung expansion during inspiration. Typically, it includes disorders that increase the inward elastic recoil of the lungs or chest wall. Consequently, the alteration in pulmonary dynamics results in decreases in lung volumes and capacities and in lung or chest wall compliance. Some restrictive diseases produce ventilation abnormalities and V/Q mismatching, and others lead to impairment of diffusion. FEV₁ and FVC are both decreased owing to a reduction in TLC or a decrease in chest wall compliance or muscle strength. However, the FEV₁/FVC ratio is normal or elevated.

Incidence and prevalence

Statistics vary according to the acute intrinsic, chronic intrinsic, or chronic extrinsic nature of the restrictive disease.

Pathophysiology

Impairment-producing restrictive pulmonary diseases can be classified as (1) acute intrinsic, (2) chronic intrinsic, or (3) chronic extrinsic. Acute intrinsic disorders are primarily caused by the abnormal movement of intravascular fluid into the interstitium of the lung and alveoli secondary to the increase in pulmonary vascular pressures occurring with left ventricular failure, fluid overload, or an increase in pulmonary capillary permeability. Examples of acute intrinsic disorders include pulmonary edema, aspiration pneumonia, and ARDS. Chronic intrinsic diseases are characterized by pulmonary fibrosis. Conditions that produce fibrosis of the lung include idiopathic pulmonary fibrosis, radiation injury, cytotoxic and noncytotoxic drug exposure, O₂ toxicity, autoimmune diseases, and sarcoidosis. Chronic extrinsic diseases can be defined as disorders that inhibit the normal lung excursion. They include flail chest, pneumothorax, atelectasis, and pleural effusions. They also include conditions that interfere with chest wall expansion, such as ascites, obesity, pregnancy, and skeletal and neuromuscular disorders.

Clinical manifestations

Clinical manifestations depend on the disorder but may include tachypnea, dyspnea, cough, bronchospasm, pulmonary vascular vasoconstriction, PH, cor pulmonale, and arterial hypoxemia. The pulmonary function tests reveal decreased vital capacity with normal expiratory flow rates.

Treatment

Treatment also depends on the specific restrictive disorder and may include oxygen therapy, bronchodilators, corticosteroids, and mechanical ventilation with PEEP.

Anesthetic considerations

Definition

Tuberculosis is a chronic granulomatous disease that is spread primarily by aerosol transmission.

Incidence and prevalence

In the past and before specific antimicrobial therapy, tuberculosis was a significant cause of death and disability in North America. It currently affects approximately 28,000 persons in North America. Elderly, debilitated, and malnourished individuals, and people who are immunosuppressed and living in crowded conditions are most often affected.

Pathophysiology

Tuberculosis is caused by the acid-fast bacillus Mycobacterium tuberculosis. After being inspired, the bacilli multiply, causing nonspecific pneumonitis.

Some bacilli migrate to the lymph nodes, encounter lymphocytes, and precipitate the immune response. Phagocytes engulf colonies of bacilli in the lung, isolate them, and form granulomatous tubercles. Infected tissues inside the tubercles create caseation necrosis (a cheeselike material). Isolation of the bacilli is completed by formation of scar tissue around the tubercle. After approximately 10 days, the immune response is complete, and further bacilli multiplication is prevented. After isolation of bacilli and development of immunity, tuberculosis can remain dormant for life. Reactivation may occur if live bacilli escape into bronchi or in states of decreased immunity. Patients with laryngeal tuberculosis or lung cavitation have the highest infectivity rate.

Laboratory results

Diagnosis is made by positive tuberculin skin (purified protein derivative) testing, chest radiography, and positive sputum culture. A positive skin test result alone for tuberculosis may indicate only exposure to the tuberculin bacteria and is not by itself evidence of active disease. Chest radiography findings consistent with tuberculosis in the presence of acquired immune deficiency (AIDS) may be atypical.

Clinical manifestations

Many patients are asymptomatic. Common manifestations include a low-grade fever, fatigue, weight loss, anorexia, lethargy, and a worsening cough (i.e., purulent sputum). Some patients occasionally develop pleural effusions, meningitis, bone or joint disease, genitourinary abscesses, or peritonitis. Chest pain, dyspnea, and hemoptysis are not common.

Treatment

Drugs of choice for treatment include isoniazid, rifampin, streptomycin, and ethambutol.

Anesthetic considerations

Patients are placed in respiratory isolation until such time or therapy that they are no longer transmitters of the disease. Whenever possible, disposable equipment (i.e., filters and anesthesia circuits) should be used. Nondisposable equipment must be thoroughly sterilized. Elective surgery should be postponed in actively infected patients until adequate chemotherapy has been administered (usually 3 weeks of treatment) and verified by a negative sputum sample result. The implications of organ dysfunction that may be secondary to the disease or its treatment must be considered. Although the disease most commonly affects the pulmonary system, chemotherapeutic agents used for treatment may lead to organ toxicity (i.e., liver, kidneys, or peripheral nervous system).