A 51-year-old man develops acute respiratory distress syndrome while hospitalized for acute pancreatitis. On his third day in the intensive care unit, the patient is sedated, intubated, and ventilated with a positive end-expiratory pressure of 15 cm water and fraction of inspired oxygen of 0.6 (60%). His pulse acutely increases from 100 to 140/min, systolic blood pressure drops from 120 to 90 mm Hg, and central venous pressure increases from 10 to 15 cm water. On chest auscultation, breath sounds are absent on the left side. Which of the following is the most likely explanation for the sudden deterioration of this patient?

Question

A 51-year-old man develops acute respiratory distress syndrome while hospitalized for acute pancreatitis.  On his third day in the intensive care unit, the patient is sedated, intubated, and ventilated with a positive end-expiratory pressure of 15 cm water and fraction of inspired oxygen of 0.6 (60%).  His pulse acutely increases from 100 to 140/min, systolic blood pressure drops from 120 to 90 mm Hg, and central venous pressure increases from 10 to 15 cm water.  On chest auscultation, breath sounds are absent on the left side.  Which of the following is the most likely explanation for the sudden deterioration of this patient?

Quizplus · Accepted Answer

11ec25c8_d4c3_c7ce_bc81_435b17c13359_MD0003_00 Despite the potential benefits, positive pressure mechanical ventilation can cause numerous complications including alveolar damage, pneumothorax, and hypotension. Patients with underlying lung disease such as acute respiratory distress syndrome (ARDS), pneumonia, or obstructive airway disease are especially predisposed to barotrauma due to the already compromised lung tissue. In ARDS, lung injury causes inflammation and edema, leading to alveolar collapse and poor oxygenation. Positive end-expiratory pressure (PEEP) maintains airway pressures above atmospheric pressure at the end of expiration, preventing alveolar collapse, increasing the functional residual capacity, and decreasing the work of breathing. Unfortunately, delivery of positive pressure ventilation to such patients can rupture the fragile lung parenchyma, resulting in air leakage into the pleural space. Pneumothorax may result, which can cause absent breath sounds on the affected side (eg, left in this patient, right in the image) and lead to compression of structures in the mediastinum and impaired right ventricular filling, resulting in hypotension and tachycardia. As the intrapleural space fills with air, intrathoracic pressure increases and results in decreased venous compliance. When the central veins lose their ability to stretch and expand (ie, increased venous stiffness), the central venous pressure also rises. (Choice A) Cardiac tamponade can lead to hypotension and an elevated central venous pressure (as in this patient), but unilateral absence of breath sounds is far more suggestive of tension pneumothorax. (Choices B and C) If the endotracheal tube shifts into the right main-stem bronchus, atelectasis of the left lung can result. Mucous plugging can also cause atelectasis. Patients with atelectasis present with cough, dyspnea, and decreased oxygen saturation. However, atelectasis does not lead to compression of the mediastinum, so hypotension or other serious vital sign derangements would not be expected. (Choice E) Like pneumothorax, pulmonary embolism can present with sudden-onset shortness of breath, tachypnea, hypoxia, and (if massive) hypotension. However, absence of breath sounds would not be expected. Educational objective: Know the complications of positive pressure ventilation: Alveolar damage, pneumothorax, and hypotension. Pneumothorax presents with sudden-onset shortness of breath, hypotension, tachycardia, tracheal deviation, and unilateral absence of breath sounds. References: Clinical presentation of patients with tension pneumothorax: a systematic review. (http://www.ncbi.nlm.nih.gov/pubmed/25563887) Iatrogenic pneumothorax related to mechanical ventilation. (http://www.ncbi.nlm.nih.gov/pubmed/24834397)

A 51-Year-Old Man Develops Acute Respiratory Distress Syndrome While Hospitalized