Page 698 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 58: Restrictive Disease of the Respiratory System 517

narrowing or torsion and eligibility for placement of an endobronchial patient is stable. A broad spectrum of abnormalities, including central
stent. Theophylline titrated to a serum level of 10 μg/mL may be con- and obstructive sleep apnea, has been identified that may contrib-
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sidered to increase respiratory muscle strength, help clear secretions, ute to chronic hypoxemia, cor pulmonale, and early death. Chronic
and decrease airway resistance; however, its narrow therapeutic window ventilatory failure is an indication for noninvasive nocturnal ventila-
requires close attention to drug-drug and drug-patient interactions. tory support, which can improve daytime blood gases, sleep pattern,
Although there are no controlled trials to help guide ventilator and respiratory muscle strength. Other options include mechanical
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management in patients with thoracic deformity, we suggest small insufflation- exsufflation, daytime IPPV, negative-pressure ventilation,
tidal volumes (6-7 mL/kg) and high respiratory rates (20-30/min) to and mechanical ventilation via tracheostomy. In patients receiving long-
minimize the hemodynamic effects of positive-pressure ventilation and term mechanical ventilation, patient-healthcare team communication
the risk of barotrauma, and effect diaphragm unloading. We generally is crucial for optimal treatment, including early home treatment of
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maintain plateau pressures (Pplat) <30 cm H O to decrease the risk of infection-related episodes of respiratory failure. Physical rehabilita-
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2
over-distention beyond physiologic TLC and hyperinflation-induced tion programs are recommended and appear to improve spirometric
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lung injury. However, Pplat is affected by properties of the chest wall measures of lung function and 6-minute walk distance. The role of
65
and abdomen and will be higher in a patient chest wall deformity orthopedic surgery in adolescents is debated and beyond the scope of
or abdominal distension for the same degree of lung hyperinflation, this chapter.
perhaps allowing less concern when Pplat exceeds 30 cm H O. We recommend serial assessments of right ventricular function
2
One consequence of small tidal volume ventilation is reduced alveolar and pulmonary artery pressure by echocardiography. The presence of
ventilation and hypercapnia. Fortunately, hypercapnia is generally well pulmonary hypertension gives added importance to oxygen therapy
does not exceed 90 mm Hg and acute increases and mandates exclusion of other treatable causes such as pulmonary
tolerated as long as Pa CO 2
are avoided. However, hypercapnia does cause cerebral vaso- embolism. Prostacyclin analogues, endothelin receptor antagonists, and
in Pa CO 2
dilation, cerebral edema, decreased myocardial contractility, systemic phosphodiesterase inhibitors have not been studied adequately in this
vasodilation, and pulmonary vasoconstriction and accordingly should setting but may be options in select patients.
be avoided in patients with raised intracranial pressure (as might occur
in the setting of anoxic brain injury after arrest) and severely depressed PATIENTS WITH PULMONARY FIBROSIS
myocardial function. The use of small tidal volumes demands added
attention to lung volume recruitment and prevention of atelectasis. To When normal air spaces and blood vessels are replaced by fibrotic tissue,
this end, we initially apply 5 cm H O of PEEP to prevent alveolar closure the lungs become small and noncompliant. In some of the disease pro-
2
at end-expiration, and gradually increase tidal volume when atelectasis cesses that result in fibrosis there may be adjacent areas of inflammation
is suspected, keeping plateau pressure <30 cm H O. amenable to immunomodulatory therapy. However, it is generally well
2
In refractory hypoxemia, a trial of increasing PEEP (in an attempt to accepted that fibrosis without significant inflammation is unresponsive
≤0.6) helps clar- to current pharmacologic treatment. 66,67
achieve 90% saturation of the arterial blood with an Fi O 2
ify the pathophysiology. To avoid overdistention at end-inspiration, tidal A number of acute and chronic disorders of known and unknown
volume may need to be decreased during PEEP titration. Since the chest etiology are associated with pulmonary fibrosis. Among these are the
wall is often poorly compliant in these patients, high alveolar pressures idiopathic interstitial pneumonias (IIPs). One of the most common and
increase pleural pressure more than in diseases characterized by non- refractory of the IIPs, idiopathic pulmonary fibrosis (IPF) is the focus
compliant lungs, thereby further decreasing venous return to the right of this section.
atrium and reducing cardiac output. PEEP may also increase pulmonary As the name implies, IPF is a disease of unknown etiology, character-
vascular resistance and worsen right-to-left intracardiac shunt. ized by the histologic appearance of usual interstitial pneumonia. 67-69
The approach to weaning and extubation from mechanical ven- It most often presents insidiously in patients >50 years old and is progres-
tilation is similar to that described elsewhere in this text. We favor sive regardless of therapy. The hallmarks of IPF are dyspnea and cough.
early determination of respiratory muscle strength as assessed by the Dyspnea occurs initially with activity and can result in a sedentary lifestyle
maximum negative inspiratory force (NIF), and of respiratory system that further adds to functional disability. As the disease progresses, patients
load as determined by the resistive and static pressures generated develop worsening dyspnea and a rapid and shallow breathing pattern,
during positive pressure ventilation. Inadequate strength for a given often maintaining higher-than-normal levels of minute ventilation.
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load manifests as a rapid shallow breathing pattern, which generates Constitutional symptoms include fatigue, malaise, and weight loss; symp-
a high frequency to tidal volume ratio. A slower and deeper pattern is toms of sleep-disordered breathing may be present. The median survival
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achieved when strength increases and/or load decreases. Respiratory of patients with IPF is two to three years, although there is significant
muscle strength is improved by correction of shock, anemia, acidosis, heterogeneity in survival and rate of progression. Disease progression
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electrolyte abnormalities, institution of nutrition, and a nonfatiguing eventually leads to respiratory failure and death.
graded program of respiratory muscle exercise. Treating pulmonary Auscultation of the chest frequently reveals dry, “Velcro-like” crackles
edema, atelectasis, pneumonia, and airflow obstruction decrease load. heard loudest at the bases of the lungs; in the late stages of the disease,
When time of extubation is near, ventilation with tidal volumes that cardiac examination may reveal signs of pulmonary hypertension.
mimic the patient's spontaneous tidal volume may allow for a smoother Clubbing of the fingers and toes commonly occurs in IPF and asbestosis
transition to spontaneous breathing. In borderline cases, NIV can be but is less common in other interstitial lung diseases.
used to facilitate return to spontaneous breathing and reduce ICU length
of stay. Tracheostomy may be required in refractory cases, but may ■ LABORATORY ABNORMALITIES
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be technically difficult in patients with cervical spine curvature and a Hypoxemia that worsens with exercise or sleep 71,73 and respiratory alka-
distorted airway. losis are common in IPF. The development of hypercapnia is an ominous
■ LONG-TERM MANAGEMENT sign of imminent death. Despite hypoxemia, polycythemia is rare.
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Elevations of sedimentation rate, serum immunoglobulins, antinuclear
Primary considerations for long-term management include the use of antibodies, and rheumatoid factor can occur. Increased angiotensin-
home oxygen therapy, nocturnal NIV, and a bronchial hygiene regimen. converting enzyme or antineutrophil cytoplasmic antibodies suggests
Patients with moderate to severe KS may demonstrate significant hypox- alternate diagnoses. 68
emia on exercise that is prevented by ambulatory oxygen therapy. Radiographic features that suggest IPF include peripheral reticular
62
Derangements in breathing pattern and oxyhemoglobin desatura- opacities most prominent at the bases with subpleural honeycombing
tion during sleep should be excluded with polysomnography once the and low lung volumes. Traction bronchiectasis occurs when fibrotic

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