Acute Respiratory Distress Syndrome (ARDS)

Dr. Belal Hijji, RN, PhD

October 26, 2011

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Learning Outcomes

At the end of this lecture, students will be able to:

• Define ARDS, describe its pathophysiology and clinical manifestations.

• Discuss the process of assessment and diagnostic findings of ARDS.

• Discuss the medical and nursing management of ARDS.

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Introduction

• Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by a sudden and progressive pulmonary edema, increasing bilateral infiltrates on chest x-ray, and hypoxemia. These signs occur in the absence of left-sided heart failure.

• Patients with ARDS usually require mechanical ventilation with a higher-than normal airway pressure.

• A wide range of factors are associated with the development of ARDS including direct injury to the lungs (eg, smoke inhalation) or indirect insult to the lungs (eg, shock).

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Anteroposterior (AP) portable chest radiograph in a patient with acute respiratory distress syndrome. This image shows bilateral patchy opacities in mostly the middle and lower lung zones.

Normal Posterior to Anterior (PA) Chest X-ray.

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Pathophysiology

• ARDS occurs as a result of an inflammatory trigger that initiates the release of cellular and chemical substances, causing injury to the alveolar capillary membrane. This results in leakage of fluid into the alveolar interstitial spaces.

• Alveoli collapse because of the inflammatory infiltrate, blood, and fluid. Small airways are narrowed because of interstitial fluid and bronchial obstruction. The lung compliance becomes markedly decreased (stiff lungs), and the result is severe hypoxemia.

• The blood returning to the lung for gas exchange is pumped through the nonventilated, nonfunctioning areas of the lung. This means that blood is interfacing with nonfunctioning alveoli and gas exchange is markedly impaired, resulting in severe hypoxemia.

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Clinical Manifestations

• The acute phase of ARDS is marked by a rapid onset of severe dyspnea.

• A characteristic feature is arterial hypoxemia that does not respond to supplemental oxygen.

• On chest x-ray, the findings are bilateral infiltrates that quickly worsen.

• The patient has decreased pulmonary compliance (“stiff lungs,” which are difficult to ventilate).

• In the recovery phase, hypoxemia gradually resolves, chest x-ray improves, and the lungs become more compliant

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Assessment and Diagnostic Findings

• Through auscultation, crackles are heard as the fluid begins to leak into the alveolar interstitial space, acute onset of respiratory distress, bilateral pulmonary infiltrates, and clinical absence of left-sided heart failure.

• The ratio of partial pressure of oxygen of arterial blood to fraction of inspired oxygen [concentration of oxygen delivered (1.0 = 100% oxygen)] (PaO2/FiO2) is < 200 mm Hg (severe hypoxemia) [Normal range ≥ 400].

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Medical Management

• The primary focus of ARDS management includes identification and treatment of the underlying condition.

• Adequate fluid volume and supplemental oxygen for hypoxemia.

• Intubation and mechanical ventilation for progressive hypoxemia.

• Positive end-expiratory pressure (PEEP) is required to improve oxygenation. PEEP is an elevation of transpulmonary pressures at the end of expiration. PEEP is often employed when alveolar inflammation and edema, coupled with dysfunctional surfactant, produce poorly ventilated regions as well as regions that actually collapse during all or part of the ventilatory cycle.

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Medical Management (Continued…)

• Systemic hypotension may occur as a result of hypovolemia (due to leakage of fluid into the interstitial spaces and ↓ cardiac output from high levels of PEEP therapy. Intravenous crystalloid solutions are administered, with careful monitoring of pulmonary status. Inotropic agents may be required.

• Pulmonary artery pressure catheters are used to monitor the patient’s fluid status and the severe and progressive pulmonary hypertension sometimes observed in ARDS.

Adequate nutritional support (35 to 45 kcal/kg per day) is vital in the treatment of ARDS. Enteral feeding is the first consideration; however, parenteral nutrition also may be required.

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Nursing Management

• The patient with ARDS is critically ill and requires close monitoring because the condition could quickly change to a lifethreatening situation.

• Most of the treatment options (Oxygen administration, nebulizer therapy, chest physiotherapy, endotracheal intubation or tracheostomy, mechanical ventilation, suctioning, and bronchoscopy) are used in this situation.

• Frequent assessment of the patient’s status is necessary to evaluate the effectiveness of treatment.