Restrictive respiratory diseases and lung transplantation

Pulmonary edema

The leakage of intravascular fluid into the interstitium and the alveolar space leads to pulmonary edema. Acute pulmonary edema can be caused by increased capillary pressure (hydrostatic or cardiogenic pulmonary edema) or by increased capillary permeability. Both of these lead to a condition called capillary stress failure. Pulmonary edema typically appears as bilateral, symmetric perihilar opacities on chest radiography. This so-called butterfly fluid pattern is more commonly seen with increased capillary pressure than with increased capillary permeability. The presence of air bronchograms suggests increased-permeability pulmonary edema. Pulmonary edema caused by increased capillary permeability is characterized by a high concentration of protein and secretory products in the edema fluid. Diffuse alveolar damage is typically present with the increased-permeability pulmonary edema associated with acute respiratory distress syndrome (ARDS). Recently bedside lung ultrasound has emerged as a new modality to help diagnose pulmonary edema ( Fig. 3.3 ).

Cardiogenic pulmonary edema

Cardiogenic pulmonary edema is characterized by marked dyspnea, tachypnea, and signs of sympathetic nervous system activation (hypertension, tachycardia, diaphoresis) that is often more pronounced than that seen in patients with increased-permeability pulmonary edema. This form of pulmonary edema is seen in acute decompensated heart failure and is characterized as dyspnea with elevated cardiac pressures. Cardiogenic pulmonary edema should be high in the differential if a patient has decrease in cardiac function either systolic or diastolic. One of the most underappreciated causes of cardiogenic pulmonary edema is diastolic dysfunction and should be actively sought after. Conditions that acutely increase preload such as acute aortic regurgitation and acute mitral regurgitation will also predispose to cardiogenic pulmonary edema; conditions increasing afterload and systemic vascular resistance such as left ventricular outflow tract (LVOT) obstruction, mitral stenosis, and renovascular hypertension could also cause cardiogenic pulmonary edema.

Negative pressure pulmonary edema

Negative pressure pulmonary edema follows the relief of acute upper airway obstruction. It is also called postobstructive pulmonary edema. It is caused by postextubation laryngospasm, epiglottitis, tumors, obesity, hiccups, or obstructive sleep apnea in spontaneously breathing patients. Spontaneous ventilation is necessary to create the marked negative pressure that causes this problem. The time to onset of pulmonary edema after relief of airway obstruction ranges from a few minutes to as long as 2 to 3 hours. Tachypnea, cough, and failure to maintain oxygen saturation above 95% are common presenting signs and may be confused with pulmonary aspiration or pulmonary embolism. Many cases of postoperative oxygen desaturation may be due to some degree of unrecognized negative pressure pulmonary edema.

The pathogenesis of negative pressure pulmonary edema is related to the development of high negative intrapleural pressure by vigorous inspiratory efforts against an obstructed upper airway (Mueller or reverse Valsalva maneuver). This high negative intrapleural pressure decreases the interstitial hydrostatic pressure, increases venous return, and increases left ventricular afterload. In addition, such negative pressure leads to intense sympathetic nervous system activation, hypertension, and central displacement of blood volume. Together these factors produce acute pulmonary edema by increasing the transcapillary pressure gradient.

Maintenance of a patent upper airway and administration of supplemental oxygen is usually sufficient treatment since this form of pulmonary edema is typically self-limited. Mechanical ventilation may occasionally be needed for a brief period. Hemodynamic monitoring reveals normal right and left ventricular function. Central venous pressure and pulmonary artery occlusion pressure are also normal. Radiographic evidence of this form of pulmonary edema resolves within 12 to 24 hours.

Neurogenic pulmonary edema

Neurogenic pulmonary edema develops in a small proportion of patients experiencing acute brain injury. Typically this form of pulmonary edema occurs minutes to hours after central nervous system (CNS) injury and may manifest during the perioperative period. There is a massive outpouring of sympathetic impulses from the injured CNS that results in generalized vasoconstriction and a shift of blood volume into the pulmonary circulation. Presumably the increased pulmonary capillary pressure from this acute translocation of blood volume leads to transudation of fluid into the interstitium and alveoli. Pulmonary hypertension and hypervolemia can also injure blood vessels in the lungs.

The association of pulmonary edema with a recent CNS injury should suggest the diagnosis of neurogenic pulmonary edema. The principal entity in the differential diagnosis is aspiration pneumonitis. Unlike neurogenic pulmonary edema, chemical pneumonitis resulting from aspiration frequently persists longer and is often complicated by a bacterial infection.

Reexpansion pulmonary edema

The rapid expansion of a collapsed lung may lead to pulmonary edema in that lung. The risk of reexpansion pulmonary edema after relief of pneumothorax or pleural effusion is related to the amount of air or liquid that was present in the pleural space (>1 L increases the risk), the duration of collapse (>24 hours increases the risk), and the rapidity of reexpansion. The finding of high protein content in the pulmonary edema fluid suggests a role of enhanced capillary membrane permeability as a mechanism for the development of pulmonary edema. Treatment of reexpansion pulmonary edema is supportive.

Drug-induced pulmonary edema

Acute noncardiogenic pulmonary edema can occur after the administration of several drugs, but especially opioids (heroin) and cocaine. The high protein concentration in the pulmonary edema fluid would suggest high-permeability pulmonary edema. Cocaine can also cause pulmonary vasoconstriction, acute myocardial ischemia, and myocardial infarction. There is no evidence that the administration of naloxone speeds the resolution of opioid-induced pulmonary edema. Another condition that needs to be in the differential is diffuse alveolar hemorrhage (DAH). If pulmonary edema on chest x-ray does not respond to diuretics, then this should be considered DAH. Treatment of patients who develop drug-induced pulmonary edema is supportive and may include tracheal intubation for airway protection and mechanical ventilation.

High-altitude pulmonary edema (HAPE)

HAPE may occur at heights ranging from 2500 to 5000 m and is influenced by the rate of ascent to that altitude. The onset of symptoms is often gradual but typically occurs within 48 to 72 hours at high altitude. Fulminant pulmonary edema may be preceded by the less severe symptoms of acute mountain sickness. The cause of this high-permeability pulmonary edema is presumed to be hypoxic pulmonary vasoconstriction, which increases pulmonary vascular pressure. Treatment includes administration of oxygen and quick descent from the high altitude. Inhalation of nitric oxide may improve oxygenation.

Management of anesthesia in patients with pulmonary edema

Elective surgery should be delayed in patients with pulmonary edema, and every effort must be made to optimize cardiorespiratory function before surgery. Large pleural effusions may need to be drained. Persistent hypoxemia may require mechanical ventilation and positive end-expiratory pressure (PEEP). Hemodynamic monitoring may be useful in both the assessment and treatment of pulmonary edema. Patients with pulmonary edema are critically ill. Intraoperative management should be a continuation of critical care management and include a plan for intraoperative ventilator management. Current evidence shows that it might be beneficial to ventilate with low tidal volumes (e.g., 6–8 mL/kg) with a ventilatory rate of 14 to 18 breaths per minute while attempting to keep the end-inspiratory plateau pressure at less than 30 cm H ₂ O. Careful titration of PEEP in conjunction with inspiratory pause is recommended to optimize lung compliance. Patients with restrictive lung disease typically have rapid, shallow breathing. Tachypnea is likely during the weaning process and should not be used as the sole criterion for delaying extubation if gas exchange and results of other assessments are satisfactory.

Chemical pneumonitis

Patients with decreased airway reflexes either due to their disease process or medications are at risk for aspiration. Intubation and extubation are high-risk periods for aspiration. Some authors recommend keeping the head of the bed elevated for intubations to decrease the chance of aspiration. Chemical pneumonitis could manifest with abrupt onset of dyspnea, tachycardia, and decreased oxygen saturations. When gastric fluid is aspirated, it is rapidly distributed throughout the lungs and produces the destruction of surfactant-producing cells and damage to the pulmonary capillary endothelium. As a result, there is atelectasis and leakage of intravascular fluid into the lungs, producing capillary-permeability pulmonary edema. This acute lung injury (ALI) might present with tachypnea, bronchospasm, and acute pulmonary hypertension. Arterial hypoxemia is commonly present. Chest radiography may not demonstrate evidence of aspiration pneumonitis for 6 to 12 hours after the event. Evidence of aspiration, when it does appear, is most likely to be in the superior segment of the right lower lobe if the patient aspirated while in the supine position. If an aspiration event is noted, the oropharynx should be suctioned and the patient turned to the side. Trendelenburg position or head-down position will not stop gastric reflux. Trendelenburg position can prevent aspiration once gastric contents are in the pharynx. After an episode, patients may need to be monitored for 24 to 48 hours for development of symptoms.

Measurement of gastric fluid pH is useful, since it reflects the pH of the aspirated fluid. Measurement of tracheal aspirate pH is of no value because airway secretions rapidly dilute the aspirated gastric fluid. The aspirated gastric fluid is also rapidly redistributed to peripheral lung regions, so lung lavage is not useful unless there has been an aspiration of particulate material.

Aspiration pneumonitis is best treated by the delivery of supplemental oxygen and PEEP. Bronchodilation may be needed to relieve bronchospasm. There is no evidence that prophylactic antibiotics decrease the incidence of pulmonary infection or alter the outcome. Antibiotics may be considered if a patient remains symptomatic after 48 hours and narrowed to specific therapy based on culture results. Corticosteroid treatment of aspiration pneumonitis remains controversial.

E-cigarette (or vaping) product use–associated lung injury (EVALI)

It is a well-known fact that interstitial lung disease (ILD) can be caused by several factors, including inhalation of dusts, gases or fumes, and drugs. This may present as desquamative interstitial pneumonia, respiratory bronchiolitis–associated ILD, pulmonary Langerhans cell histiocytosis (PLCH), and idiopathic pulmonary fibrosis. A relatively newer entity, EVALI is now seen in patients using e-cigarettes and vaping (Cherian et al, 2020). EVALI is a form of ALI and is commonly associated with pneumonia, diffuse alveolar damage, acute fibrinous pneumonitis, and bronchiolitis. There may be varied presentation, including DAH. Additives such as tetrahydrocannabinol (THC), vitamin E acetate, nicotine, cannabinoids (CBD), and (rarely) other oils have been associated with EVALI. Most commonly one can see dyspnea, cough, nausea, vomiting, diarrhea, abdominal pain, and pleuritic or nonpleuritic chest pain. Patients may be febrile with tachycardia and tachypnea. Hypoxia and hemoptysis may also be noted. Radiologic findings are similar to diffuse alveolar damage seen in ARDS. Empiric antibiotics, systemic steroids, and supportive care are mainstays of therapy.

COVID-19 induced restrictive lung disease

Survivors of severe acute SARS-CoV-2 infection have been noted to have persistent inflammatory interstitial lung disease. The spectrum of pulmonary manifestations ranges from dyspnea to failure to wean form ventilator and pulmonary fibrosis. In one study the median 6min walking distance was lower than the normal range for approximately 25% of patients at 6months very similar to that seen with SARS and MERS survivors (Huang et al, 2021). A drop in diffusion capacity is the most commonly reported finding and directly co-relates to the severity of initial disease process. Patients who needed invasive or noninvasive form of mechanical ventilation were at the highest risk for long term pulmonary complications (Nalbandian et al, 2021). Along with the above-mentioned findings the survivors have decreased exercise capacity, hypoxia requiring supplemental oxygen, ground glass opacities on Computed Tomography (CT) scan. There is a lot of ongoing research on survivors of COVID 19.

Some recommended assessment strategies for recovery include pulse oximetry, 6minute walk test, Pulmonary function testing, high-resolution computed tomography of the chest and computed tomography pulmonary angiogram as clinically appropriate. Without a data from large systematic trials, it would be difficult to predict how patients with SARS-CoV-2 related persistent lung disease will do in the perioperative period.

Overview

Respiratory failure is the inability to provide adequate arterial oxygenation and/or elimination of carbon dioxide. It has a myriad of causes. Acute respiratory failure is considered to be present when the Pao ₂ is below 60 mm Hg despite oxygen supplementation and in the absence of a right-to-left intracardiac shunt. In the presence of acute respiratory failure, Paco ₂ can be increased, unchanged, or decreased depending on the relationship of alveolar ventilation to the metabolic production of carbon dioxide. A Paco ₂ above 50 mm Hg in the absence of respiratory compensation for metabolic alkalosis is consistent with the diagnosis of acute respiratory failure.

Acute respiratory failure is distinguished from chronic respiratory failure based on the relationship of Paco ₂ to arterial pH (pHa). Acute respiratory failure is typically accompanied by abrupt increases in Paco ₂ and corresponding decreases in pHa. With chronic respiratory failure, the pHa is usually between 7.35 and 7.45 despite an increased Paco ₂ . This normal pHa reflects renal compensation for chronic respiratory acidosis via renal tubular reabsorption of bicarbonate.

Respiratory failure is often accompanied by a decrease in functional residual capacity (FRC) and lung compliance. Increased pulmonary vascular resistance and pulmonary hypertension are likely to develop if the respiratory failure persists. ARDS is a condition that falls within the spectrum of acute respiratory failure.

Treatment of acute respiratory failure is directed at initiating specific therapies that support oxygenation and ventilation. The three principal goals in the management of acute respiratory failure are (1) a patent upper airway, (2) correction of hypoxemia, and (3) removal of excess carbon dioxide.

Mechanical support for ventilation

Supplemental oxygen can be provided to spontaneously breathing patients via nasal cannula, Venturi mask, nonrebreathing mask, or T-piece. These devices seldom provide inspired oxygen concentrations higher than 50% and therefore are of value only in correcting hypoxemia resulting from mild to moderate ventilation/perfusion mismatching. When these methods of oxygen delivery fail to maintain the Pao ₂ above 60 mm Hg, continuous positive airway pressure (CPAP) by face mask can be initiated. CPAP may increase lung volumes by opening collapsed alveoli and decreasing right-to-left intrapulmonary shunting. A disadvantage of CPAP by face mask is that the tight mask fit required may increase the risk of pulmonary aspiration should the patient vomit. Maintenance of the Pao ₂ above 60 mm Hg is adequate because hemoglobin saturation with oxygen is over 90% at this level. In some patients, it may be necessary to perform tracheal intubation and institute mechanical ventilation to maintain acceptable oxygenation and ventilation. Typical devices that provide positive pressure ventilation include volume-cycled and pressure-cycled ventilators ( ).

Volume-cycled ventilation

Volume-cycled ventilation provides a fixed tidal volume with inflation pressure as the dependent variable. A pressure limit can be set; when inflation pressure exceeds this value, a pressure relief valve prevents further gas flow. This valve prevents the development of dangerously high peak airway and alveolar pressures and warns that a change in pulmonary compliance has occurred. Significant increases in peak airway pressure may reflect worsening pulmonary edema, development of a pneumothorax, kinking of the tracheal tube, or the presence of mucous plugs in the tracheal tube or large airways. Tidal volume is maintained despite small changes in peak airway pressure. A disadvantage of volume-cycled ventilation is the inability to compensate for leaks in the delivery system. The primary modalities of ventilation using volume-cycled ventilation are assisted/controlled (A/C) ventilation and synchronized intermittent mandatory ventilation (SIMV) ( Fig. 3.4 ).

A/C ventilation.

In the assist control mode, a preset respiratory rate ensures that a patient receives a predetermined number of mechanically delivered breaths even if there are no inspiratory efforts. In the assist mode, however, if the patient can create some negative airway pressure, a breath at the preset tidal volume will be delivered.

SIMV.

The SIMV technique allows patients to breathe spontaneously at any rate and tidal volume, while the ventilator provides predefined minute ventilation. The gas delivery circuit is modified to provide sufficient gas flow for spontaneous breathing and permit periodic mandatory breaths that are synchronous with the patient’s inspiratory efforts. Theoretical advantages of SIMV compared with A/C ventilation include continued use of respiratory muscles, lower mean airway and mean intrathoracic pressure, prevention of respiratory alkalosis, and improved patient–ventilator coordination.