Acute Respiratory Failure, Acute Lung Injury/Acute Respiratory Distress Syndrome, and Acute Chest Syndrome

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Chapter 24 Acute Respiratory Failure, Acute Lung Injury/Acute Respiratory Distress Syndrome, and Acute Chest Syndrome

Prema R. Menon, MD , Gilman B. Allen, MD

1 What is acute respiratory failure (ARF)?

ARF is a syndrome in which the respiratory system fails in gas exchange, in either oxygenation, carbon dioxide elimination, or both. ARF can occur within minutes or over hours.

2 What are the types of ARF?

ARF can be either hypoxemic, hypercapnic, or a combination of both. Arterial blood gas analysis is the gold standard for diagnosis of respiratory failure. An arterial PO₂ of less than 50 mm Hg while breathing ambient air is considered hypoxemic, and hypercapnia is defined as a PCO₂ of greater than 50 mm Hg.

5 What are the most important immediate goals of therapy for ARF?

Hypoxia is the major immediate threat to organ function, and therefore initial goals should be directed toward oxygen supplementation and reversal or prevention of tissue hypoxia. Hypercapnia is generally better tolerated if not sudden or associated with severe acidosis. Supplemental oxygen should be delivered to achieve a PaO₂ > 55 mm Hg. This can be achieved with nasal prongs or face mask, but in many cases mechanical ventilation is required to reverse hypoxemia. Mechanical ventilation can maximize both inspired O₂ and alveolar ventilation (decrease PaCO₂).

6 What are the main indications for endotracheal intubation and mechanical ventilation?

Bradypnea, apnea, or respiratory arrest; acute respiratory distress syndrome; respiratory muscle fatigue; obtundation or coma; PaO₂ less than 55 mm Hg despite supplemental oxygen; PCO₂ greater than 50 mm Hg with arterial pH < 7.2.

7 What are acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)?

The American-European Consensus Conference recommended the following criteria for definition of ARDS:

Bilateral infiltrates on chest radiograph

Pulmonary artery wedge pressure ≤ 18 mm Hg or the absence of clinical evidence of left atrial hypertension

PaO₂/FiO₂ ratio ≤ 200 * for ARDS

Acute lung injury is defined by all of the above except a PaO₂/FiO₂ ratio ≤ 300 *

8 What is the pathogenesis of ARDS?

The early phase of ALI or ARDS is characterized by injury and increased permeability of the endothelial and epithelial barriers of the lung leading to the accumulation of protein-rich edema fluid in the interstitium and alveolar airspace. This fluid contains plasma proteins, inflammatory cells (mostly neutrophils), and necrotic debris that can pack down into dense eosin-staining hyaline membranes, the latter of which are pathognomonic for the pathology of ARDS, termed diffuse alveolar damage. Leukocytes, fibroblasts, and epithelial cells release cytokines that enhance the inflammatory response. Because of up-regulation of procoagulant pathways diffuse intravascular thrombi formation and fibrin deposition occur. Patients usually begin to recover in the first 5 to 14 days of disease. During the later phase of injury, type II pneumocyte hyperplasia and collagen deposition occur and can serve to repopulate the epithelium during the healing process but can also progress to fibrosis. This latter fibroproliferative phase can lead to prolonged time using the ventilator and increased mortality but can also be self-limited and resolve entirely.

9 What are risk factors for the development of ARDS?

Several conditions can predispose one to the development of ARDS, such as aspiration of gastric contents, pneumonia, sepsis (most common cause), trauma, transfusion of blood products (particularly plasma-rich products), pancreatitis, fat emboli, and near-drowning. Comorbid conditions can be predictive of outcomes as well. Patients with a history of active malignancy, chronic alcoholism, liver disease, and right ventricular dysfunction have a higher likelihood of death from ALI and ARDS.

10 What is multiple-organ dysfunction syndrome (MODS)?

MODS is a process characterized by incremental degrees of physiologic derangement in individual organs, such as the liver, gut, kidney, brain, or cardiovascular and hematologic systems. Alterations in organ function can vary widely from a mild degree of organ dysfunction to irreversible organ failure. MODS is the single most important predictor of death in ALI and ARDS and a much more common cause of death in ALI or ARDS than is refractory hypoxemia.

11 What is the mortality associated with ARDS?

When ARDS was first described in 1967, the mortality rate was approximately 58%. The overall mortality rate of patients with ARDS over the past several decades is approximately 43%. The mortality rate of ARDS has progressively declined over the last decade to approximately 30% but is still 41% to 45% in those between 65 and 84 years of age and approximately 60% in patients over the age of 85 years.

12 How do patients with ARDS die?

Sepsis syndrome with multiorgan failure remains the leading cause of death in patients with ARDS. Unsupportable respiratory failure is a much less common cause of death.

13 What medical therapy is available for the treatment of ARDS?

Despite many promising results from experimental animal studies, currently no specific therapies are proven to be effective in reducing ARDS mortality. Surfactant replacement therapy, N-acetylcysteine, ketoconazole, nitric oxide, steroids, lisofylline, activated protein C, β-agonists, and inhaled prostacyclins have all been studied in phase III randomized trials. Although some interventions such as recombinant surfactant protein C and prone positioning have been effective in improving oxygenation, but none of these therapies has demonstrated a reduction in mortality. The only interventions thus far shown to reduce ARDS mortality are the use of low tidal volumes and neuromuscular blockade (NMB). Although low tidal volumes have since been adopted as best practice, the data on NMB are limited, and controversy remains over whether paralysis should be uniformly applied to all patients with ARDS.

14 How should the lungs of patients with ARDS be ventilated?

In the 1980s, animal studies revealed that ventilation with large tidal volumes and high inspiratory pressures led to the development of inflammatory infiltrates, alveolar flooding, and hyaline membranes. Since then several clinical studies have shown a benefit from using low tidal volumes in patients with ARDS. The most influential of these studies, conducted by the ARDS Network, showed a nearly 9% absolute reduction in the risk of death in patients with ARDS receiving ventilation with low tidal volumes (6 mL/kg predicted body weight) and targeted plateau pressures of ≤ 30 cm H₂O.

Other modes of ventilation in ARDS have been and remain to be studied, such as higher positive end-expiratory pressure (PEEP), alveolar recruitment maneuvers, prone positioning, and high-frequency oscillatory ventilation (HFOV). None has demonstrated a reduction in mortality, but studies evaluating pressure-targeted PEEP and HFOV are ongoing.

15 What is the role of alternate modes of ventilation?

Prone positioning has been shown to improve oxygenation but does not lead to a reduction in mortality. Although inverse ratio ventilation, airway pressure release ventilation, and HFOV may be considered as rescue modes in patients with life-threatening refractory hypoxemia receiving conventional low tidal volume ventilation, randomized controlled trials demonstrating their efficacy are lacking, and therefore these modes cannot be recommended for first-line management.

16 What are the sequelae in survivors of ARDS?

The spectrum of impairments in survivors of ARDS is broad. Surprisingly, limitations are minimal based on mean values of pulmonary function after 5 years. However, the range of values for forced vital capacity and diffusing capacity among survivors suggest a wide spectrum from moderate to no impairment at all. The majority of the physical impairment is related to decreased exercise capacity and musculoskeletal weakness. Quality of life among survivors is also negatively impacted by a large prevalence of cognitive deficits, depression, and anxiety as far as 2 years out from discharge, as well as musculoskeletal weakness, orthopedic injuries (heterotropic ossification, frozen shoulder), vocal cord dysfunction, and cosmesis (procedural scars from tracheostomy, chest tube insertions, and central and arterial lines).

17 What is acute chest syndrome (ACS)?

ACS is a frequent complication of sickle cell disease. It is defined as a combination of acute onset fever, chest pain, new pulmonary infiltrates, and signs and symptoms of pulmonary disease (i.e., tachypnea, dyspnea, and cough). ACS resembles bacterial pneumonia clinically but is entirely different in its pathology. It can be brought on by various physiologic insults or stressors, including infection, vasoocclusive crisis, embolization of marrow fat from infarcted bone, and lung infarction, but uniformly involves an acute occlusion of the pulmonary vascular bed by sickle erythrocytes.

18 What are the treatment options for ACS?

Blood transfusion, hydration, pain control, and antibiotics are the current mainstays of therapy. Red cell transfusion has no proven benefit over standard supportive care, but it can improve oxygenation and thus is still recommended. The role of corticosteroids is unclear. Studies examining the use of glucocorticoids have generated variable results. Some experts recommend the use of dexamethasone, primarily in patients with asthma and ACS. However, the risk for increased pain and subsequent readmission remains a limitation. A randomized controlled trial of dexamethasone in the treatment of ACS is currently underway.

19 Is there a role for exchange transfusion in sickle cell disease?

Simple or exchange transfusion successfully and rapidly increases oxygenation in patients with ACS. In patients requiring mechanical ventilation with multilobar processes who have already received simple transfusions, the current expert recommendation is to proceed with red cell exchange transfusions, but no randomized control studies have been done to date that demonstrate proven benefit from exchange transfusion in ACS.

20 Is pulse oximetry reliable in patients with sickle cell disease?

Pulse oximetry measurements may overestimate the oxygen saturation by including methemoglobin and carboxyhemoglobin, which are both slightly increased in hemoglobin (Hb) S disorders. Automated blood gas analyzers may also overestimate the saturation because they calculate O₂ saturation on the basis of standard HbA. Cooximetry is the most accurate method to analyze oxygen saturation in HbS disorders.

21 What is the mortality for ACS?

The overall mortality for ACS is 3%. However, adult patients have a higher overall mortality rate of 9%. The leading causes of death are respiratory failure and bronchopneumonia, but sepsis, pulmonary hemorrhage, hypovolemic shock, and intracranial hemorrhage are additional common causes of death in ACS.

1 The Acute Respiratory Distress Syndrome Network: Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342:1301–1308.

2 Bernard G.R., Artigas A., Brigham K.L., et al. The American-European Consensus Conference on ARDS. Definitions, mechanisms, relevant outcomes, and clinical trial coordination. Am J Respir Crit Care Med. 1994;149:818–824.

3 Esteban A., Fernandez-Segoviano P., Frutos-Vivar F., et al. Comparison of clinical criteria for the acute respiratory distress syndrome with autopsy findings. Ann Intern Med. 2004;141:440–445.

4 Graham L.M.Jr. The effect of sickle cell disease on the lung. Clin Pulm Med. 2004;11:369.

5 Herridge M., Tansey C., Cheung A., et al. Functional disability 5 years after acute respiratory distress syndrome. N Engl J Med. 2011;364:1293–1304.

6 Hudson L.D., Milberg J.A., Anardi D., et al. Clinical risks for development of the acute respiratory distress syndrome. Am J Respir Crit Care Med. 1995;151:293–301.

7 Papazian L., Forel J.M., Gacouin A., et al. Neuromuscular blockers in early acute respiratory distress syndrome. N Engl J Med. 2010;363:1107–1116.

8 Rubenfeld G.D., Caldwell E., Peabody E., et al. Incidence and outcomes of acute lung injury. N Engl J Med. 2005;353:1685–1693.

9 Slutsky A.S. Mechanical ventilation. American College of Chest Physicians’ Consensus Conference. Chest. 1993;104:1833–1859.

10 Stapleton R.D., Wang B.M., Hudson L.D., et al. Causes and timing of death in patients with ARDS. Chest. 2005;128:525–532.

11 Suchyta M.R., Orme J.F., Morris A.H. The changing face of organ failure in ARDS. Chest. 2003;124:1871–1879.

12 Tomashefski J.F.Jr. Pulmonary pathology of acute respiratory distress syndrome. Clin Chest Med. 2000;21:435–466.

13 Turner J.M., Kaplan J.B., Cohen H.W., et al. Exchange versus simple transfusion for acute chest syndrome in sickle cell anemia adults. Transfusion. 2009;49:863–868.

14 Vichinsky E.P., Neumayr L.D., Earles A.N., et al. Causes and outcomes of the acute chest syndrome in sickle cell disease. National Acute Chest Syndrome Study Group. N Engl J Med. 2000;342:1855–1865.

15 Ware L.B., Matthay M.A. The acute respiratory distress syndrome. N Engl J Med. 2000;342:1334–1349.

^* Relevance of oxygenation index is questionable because it has not been shown to be prognostic and does not account for positive end-expiratory pressure, body position, inspiratory time, or other factors that might influence overall oxygenation.

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