A 65-year-old man is evaluated for hypotension and increasing shortness of breath shortly after placement of a right-sided subclavian central venous catheter. The patient was recently diagnosed with colon cancer without metastasis and is scheduled for surgical resection. Blood pressure is 80/50 mm Hg, pulse is 110/min, and respirations are 24/min. Examination shows jugular venous distension. Breath sounds are decreased on the right and the trachea is deviated to the left. Which of the following is the most likely cause of this patient's hypotension?
Pneumothorax | |
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Diagnosis | Chest x-ray:
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*If tension pathophysiology is present. COPD = chronic obstructive pulmonary disease. | |
This patient with shortness of breath, hypotension, unilaterally decreased breath sounds, and tracheal deviation shortly after subclavian catheter placement likely has a tension pneumothorax. Because of the close proximity of the subclavian vein to the apex of the lung, there is risk of lung puncture during the procedure.
Lung puncture allows air to pass into the pleural space. If the puncture is small, the patient may remain asymptomatic. With a large puncture, air rushes into the pleural space, leading to pressure equalization and loss of intrapleural negative pressure, which causes shortness of breath due to inability to expand the affected lung. Intrapleural and lung pressures usually remain nearly equivalent (ie, simple pneumothorax), and symptoms are limited to chest pain and respiratory difficulty.
Sometimes lung puncture results in formation of a one-way tissue valve that opens during inspiration to allow air into the pleural space and closes during expiration to trap that air, causing intrapleural pressure to progressively increase with each breath (ie, tension pathophysiology). The increasing pressure leads to contralateral mediastinal shifting (eg, tracheal deviation) and vena cava collapse, resulting in decreased venous return to the heart. Cardiac output is reduced, leading to hypotension and tachycardia (ie, obstructive shock). Treatment requires emergency decompression of the pleural space with needle insertion or chest-tube placement to prevent cardiac arrest.
(Choices A and B) Decreased intravascular volume is the cause of hypovolemic shock (eg, due to massive hemorrhage), and decreased systemic vascular resistance is the primary disturbance in distributive shock (eg, due to sepsis). The jugular veins are flat with these conditions, and unilaterally decreased breath sounds and tracheal deviation are not expected.
(Choice D) An impaired baroreceptor reflex can cause or worsen hypotension due to failure of reflex-mediated vasoconstriction and increased heart rate. This patient's tachycardia suggests that the baroreceptor reflex is intact.
(Choice E) Increased intrapericardial pressure occurs in cardiac tamponade. The increased pressure impairs diastolic filling of the right ventricle, leading to obstructive shock. Although jugular venous distension is expected, cardiac tamponade does not explain this patient's unilaterally decreased breath sounds and tracheal deviation.
Educational objective:
Tension pneumothorax involves progressively increasing intrapleural pressure that leads to contralateral mediastinal shifting (eg, tracheal deviation) and vena cava collapse. Hypotension, tachycardia, and obstructive shock develop due to decreased venous return to the heart.