Restrictive Lung Diseases: General and Ventilatory Management
A A restrictive lung disease is any disease in which the ability to inhale is affected.
B Restrictive diseases of pulmonary origin are frequently associated with an increase in pulmonary fibrous tissue. The result is an overall increase in pulmonary elastance and a decrease in pulmonary compliance.
C Characteristic pulmonary function findings (Table 22-1)
TABLE 22-1
Changes in Pulmonary Function Associated With Obstructive and Restrictive Lung Disease
| Pulmonary Function Study | Obstructive Disease | Restrictive Disease |
| TLC | Normal or increased | Decreased |
| VC | Normal or decreased | Decreased |
| FRC | Increased | Normal or decreased |
| RV | Increased | Normal or decreased |
| RV/TLC ratio | Increased | Normal |
| FEV1% | Decreased | Normal |
| MMEFR25%-75% | Decreased | Normal or decreased |
1. Decreased or normal tidal volume (Vt).
2. Decreased or normal residual volume (RV).
3. Decreased or normal expiratory reserve volume (ERV).
4. Decreased or normal inspiratory reserve volume (IRV).
5. Decreased total lung capacity (TLC).
6. Decreased vital capacity (VC).
7. Decreased inspiratory capacity (IC).
8. Decreased or normal functional residual capacity (FRC).
9. Flow rate studies usually are normal in pure restrictive lung diseases; however, flow rates may be decreased when an obstructive component is also present.
10. Pulmonary and/or thoracic compliance and total compliance are usually severely decreased.
11. There is a progressive increase in the work of breathing as the severity of the disease increases.
a. Initially alveolar minute ventilation is normal or increased, but as the disease progresses alveolar minute ventilation progressively decreases.
b. Arterial blood gases may follow the same pattern as that seen in obstructive lung disease. The initial presenting symptom may be chronic respiratory alkalosis with hypoxemia, but as the disease progresses chronic respiratory acidosis with hypoxemia may develop.
II Pulmonary Restrictive Lung Diseases
A Interstitial pulmonary fibrosis: A disease characterized by the excessive formation of connective tissue in the process of repairing chronic or acute tissue injury.
1. Etiology: Any permanent injury to the lung (e.g., infection, inflammation, and allergy).
a. Causes of localized fibrosis
(1) Long-term exposure to various inhalants. Specific pneumoconioses are listed in Table 22-2.
TABLE 22-2
| Disease | Causative Agent |
| Silicosis | Silica dust |
| Farmer’s lung | Moldy hay |
| Stannosis | Tin dust |
| Silo-filler’s disease | Nitrogen dioxide |
| Coal worker’s pneumoconiosis | Coal dust |
| Asbestosis | Asbestos |
| Berylliosis | Beryllium |
| Siderosis | Iron dust |
(2) Short-term exposure to toxic inhalants may also cause diffuse fibrosis (e.g., chlorine gas, ammonia, polyvinyl chloride, smoke inhalation, and radiation therapy).
(3) Diseases of unknown etiology that often show diffuse fibrosis:
a. Inflammatory reaction in response to organic or inorganic foreign agents.
b. Inflammation is followed by cellular infiltration and acute vasculitis with local hemorrhage and thrombus formation, resulting in scar tissue.
a. Primary symptom: Progressive dyspnea on exertion and ultimately at rest.
c. As disease continues, progressive respiratory impairment and often cor pulmonale.
d. Physical examination findings:
(3) Restricted chest wall and diaphragmatic movement
(4) Diffuse, dry, crackling rales
(5) Increased work of breathing
(1) Small lung with large heart and elevated diaphragm
(2) Fine reticular or nodular pattern involving entire lung but predominantly the lower lobes
f. Arterial blood gases and pulmonary function studies as outlined in Section I, General Comments.
a. Removal of patient from environment causing the fibrotic changes if possible
b. Therapy for underlying disease entity
e. Oxygen therapy: As disease progresses, increased dyspnea is reported. Many patients are relatively refractory to oxygen therapy. Continuous positive airway pressure (CPAP) is often helpful. Care must be taken when disconnecting patient from CPAP because severe acute hypoxemia may ensue.
f. Penicillamine therapy has improved subjective assessment of patients.
g. Cyclosporine is used in late stages.
h. Plasmapheresis is effective in a few patients with high titers of immune complexes in later stages.
i. Total heart-lung transplant has been successful in some patients.
j. Mechanical ventilation: If these patients progress to mechanical ventilation, Vt delivery is limited because of decreased compliance. This results in increased inspiratory pressure that is not associated with overdistention of the lung.
B Pleural effusion: Accumulation of fluid in pleural space.
1. Normally the capillary network of the visceral pleural surface produces the fluid lining of the pleura, and any excess is removed by the lymphatic system.
2. Any disturbance in production of this fluid or in its removal can lead to the development of pleural effusion.
3. Primary causes: Inflammation and circulatory disorders.
4. The effusion compresses the lung on the affected side.
5. The effusion is gravity dependent and may shift with positional change.
a. Hydrothorax: A thin clear transudate caused by CHF, chronic nephritis, or pulmonary neoplasm.
b. Empyema (pyothorax): An effusion consisting entirely of pus caused by a bacterial infection.
c. Hemothorax: Frank blood caused by a malignancy, pulmonary infarction, or ruptured blood vessel.
d. Chylothorax: Accumulation of chyle resulting from the obstruction or trauma of the thoracic duct.
e. Fibrothorax: An accumulation of fibrous tissue normally secondary to a prolonged effusion.
C Pneumothorax: Accumulation of air within the pleural space.
1. If air enters the pleural space, the pressure within the space changes from subatmospheric to atmospheric or supraatmospheric pressure.
a. The increased pressure compresses lung tissue and results in atelectasis.
b. Ventilation of the lung on the affected side is decreased as a result of elimination of the subatmospheric intrapleural pressure.
a. Diagnosis is suggested by history and clinical presentation.
b. Definitive diagnosis is confirmed by chest radiography (Figure 22-2).
3. Types: Open and under tension.
a. In an open pneumothorax, there is no buildup of pressure because the gas is allowed to move freely in and out of the pleural space.
b. A tension pneumothorax results from the presence of a one-way valve, which allows gas only to enter the pleural space and not to leave it. This results in significant increases in pressure within the pleural space. If untreated it may quickly result in cardiac arrest.
(a) Increased difficulty in ventilation: If patient is mechanically ventilated, airway pressure increases with each breath.
(b) Patient’s vital signs begin to deteriorate as mean intrathoracic pressure increases.
(c) Breath sounds are absent on the affected side.
(d) The affected side is hyperresonant to percussion.
(e) Trachea and mediastinum may be shifted toward the unaffected side as the extent of tension pneumothorax increases.
(h) These clinical signs are more predominant if the patient is using a mechanical ventilator than if he or she is ventilating spontaneously. This is because of the greater pressure gradients developed, forcing more gas into the pleural space.
(2) Treatment: Decompression of the thorax by chest tube insertion.
D Cardiogenic pulmonary edema: Active movement of fluid across alveolar capillary membrane into alveoli as a result of increased capillary hydrostatic pressures.
1. Normally a fine balance exists among capillary colloid osmotic (oncotic) pressure, capillary hydrostatic pressure, interstitial hydrostatic pressure, and interstitial colloid osmotic (oncotic) pressure across the pulmonary capillary bed (see Chapter 14).
2. Usually a small net pressure forces fluid into the interstitial space. This interstitial fluid is drained by the lymphatics.
3. If capillary hydrostatic pressure increases significantly, the net pressure forcing fluid into the interstitial space increases, and eventually fluid moves directly into the alveoli.
4. Primary cause: Acute left ventricular failure (CHF)
a. The hydrostatic pressure of the pulmonary vascular bed is increased because of the inability of the left side of the heart to accept the blood presented to it.
b. This increased pressure offsets the normal pressure dynamics at the alveolar capillary membrane.
5. Secondary cause: Increased vascular volume causing an increase in pulmonary capillary hydrostatic pressure.
6. Acute right ventricular failure (CHF)
a. Systemic edema develops as a result of right ventricular failure.
b. The inability of the right side of the heart to accept the blood presented to it results in blood pooling in the periphery.
c. Dependent edema (pedal edema), neck vein distention, and hepatomegaly are common clinical findings.
d. It is not unlikely for patients with right-sided heart failure to eventually develop left-sided heart failure and those with left-sided heart failure to develop right-sided heart failure.
b. Intraaortic balloon counterpulsation
c. Oxygen therapy: Frequently high FIO2 is required.
d. CPAP, by mask, at 8 to 12 cm H2O has been helpful in some patients and may avoid intubation if pulmonary edema can be stabilized quickly.
e. Noninvasive positive pressure ventilation (NPPV) has also been shown to improve oxygenation. It offers the added benefit of improving ventilation in patients who begin to develop respiratory muscle fatigue.
(1) Mechanical ventilation with PEEP can improve or further worsen cardiac function.
(2) The increased mean airway pressure (as with CPAP) decreases venous return in left-sided heart failure.
(3) Marked increases in mean airway pressure can markedly reduce pulmonary perfusion and increase deadspace ventilation.
(4) When mechanical ventilator settings are titrated, markedly increasing minute ventilation should be avoided because PCO2 increases with hemodynamic instability.
(5) Stabilization of cardiac function improves the deadspace volume/tidal volume (Vd/Vt) ratio and thus returns PCO2 to normal.
(6) If increases in minute ventilation result in no change or an increase in PCO2, lack of pulmonary perfusion is most likely the cause of the PCO2 increase.
(7) Ventilator settings generally are similar to those for all patients without lung disease. Efforts should be made to improve ventilation and oxygenation without causing a secondary, ventilator-induced lung injury (see Chapters 39, 40, and 41).
(8) These patients generally require pharmacologic control during ventilation.
E Noncardiogenic pulmonary edema
1. The development of interstitial or true pulmonary edema from noncardiogenic origins.
2. Pathophysiologic etiologies
a. Altered permeability of capillary endothelial cells, allowing an increased quantity of fluid into the interstitial space.
b. Decreased capillary colloid osmotic pressure, which increases the pressure gradient, allowing more fluid to enter the interstitial space.
c. Altered lymphatic function, preventing normal drainage of the pulmonary interstitium, thereby allowing fluid to accumulate.
d. Alveolar epithelial damage, allowing fluid to enter the alveoli.
(1) Neurogenic origin is primarily a result of an acute insult to the central nervous system.
(2) It causes an increased sympathetic discharge, leading to a sudden intravascular fluid shift into the pulmonary circulation.
(3) The imbalance in hydrostatic and osmotic pressures created causes fluid to enter the interstitial space.
