Question:

A 60-year-old man undergoes a right lung biopsy for diagnosis of restrictive lung disease. Two hours after the procedure, he develops severe shortness of breath and chest pain. His other medical problems include hypertension, hyperlipidemia, pernicious anemia, and an inguinal hernia repair 10 years ago. The patient does not smoke and drinks alcohol only occasionally. Blood pressure is 70/40 mm Hg, pulse is 118/min, and respirations are 30/min. He is diaphoretic, and the skin is cold and clammy. Pupils are equal and reactive to light bilaterally. Intraarterial blood pressure monitoring is established, and pulmonary artery catheterization is performed. Initial measurements are as follows:

Cardiac index	2.3 L/min/m² (normal, 2.8-4.2)
Pulmonary capillary wedge pressure	26 mm Hg (normal, 6-12)

Which of the following is the most likely diagnosis in this patient?

Anaphylaxis

Myocardial infarction

Noncardiogenic pulmonary edema

Pulmonary artery embolism

Pulmonary parenchymal hemorrhage

Septic shock

Tension pneumothorax

Volume depletion

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Explanation:

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Hemodynamic measurements in shock
Parameter	Hypovolemic shock	Cardiogenic shock	Obstructive shock	Distributive shock
CVP (right-sided preload)	↓	↑	↑	↓
PCWP (left-sided preload)	↓	↑	↓*	↓
Cardiac index (LV output)	↓	↓	↓	↑**
SVR (afterload)	↑	↑	↑	↓
SvO₂	↓	↓	↓	↑**
In tamponade, left-sided preload is decreased, but measured PCWP is paradoxically increased due to external compression by pericardial fluid. Cardiac index & SvO₂ are usually decreased in neurogenic shock due to impaired sympathetic reflexes. CVP* = central venous pressure; LV = left ventricular; PCWP = pulmonary capillary wedge pressure; SvO₂ = mixed venous oxygen saturation; SVR = systemic vascular resistance.

Respiratory distress and shock could be due to a number of causes (eg, septic, cardiogenic, obstructive); hemodynamic monitoring (eg, via pulmonary artery catheterization) can elucidate the etiology. In this patient with chest pain, hypotension, and severe dyspnea, the hemodynamic parameters suggest likely cardiogenic shock due to an acute myocardial infarction.

Disruption of blood flow to the myocardium results in myocardial death, which can lead to impaired contractility and acute left ventricular systolic failure.

Decreased myocardial contractility leads to a low cardiac index (CI) and resulting hypotension and reflexive tachycardia. Failure of forward flow causes blood to back up into the lungs, resulting in pulmonary edema (eg, dyspnea, tachypnea, hypoxemia).
Pulmonary capillary wedge pressure (PCWP), which provides an estimate of left atrial pressure, is elevated. In an effort to maintain organ perfusion, systemic vascular resistance (SVR) is increased via vasoconstriction, resulting in cool extremities.

This patient's advanced age, hypertension, and hyperlipidemia all increased his risk of myocardial infarction, particularly after a procedure (eg, lung biopsy).

(Choices A and F) The primary disturbance in anaphylaxis and septic shock is peripheral vasodilation resulting in decreased SVR. CI is initially increased due to the decrease in SVR. PCWP is usually low in both sepsis and anaphylaxis due to displacement of intravascular volume.

(Choice C) Noncardiogenic pulmonary edema (eg, acute respiratory distress syndrome) occurs due to leakage of fluid from the pulmonary capillaries. PCWP and CI are typically normal, indicative of normal left ventricular function.

(Choices D and G) Pulmonary artery embolism causes decreased blood delivery through the pulmonary circulation to the left atrium. Right-sided tension pneumothorax causes pinching of the vena cava with decreased venous return to the right atrium. Although both of these conditions can develop following a lung biopsy, they generally lead to obstructive shock, typically with low PCWP and CI.

(Choice E) Pulmonary parenchymal hemorrhage describes diffuse alveolar hemorrhage, which results in hypoxemia but would cause a responsive elevation (rather than depression) in CI.

(Choice H) Volume depletion (eg, massive hemorrhage) causes decreased venous return to the right atrium and can lead to hypovolemic shock. PCWP and CI are both low.

Educational objective:
Myocardial infarction can lead to cardiogenic shock (eg, hypotension, poor organ perfusion) due to impaired left ventricular contractility. Cardiac index is reduced, and pulmonary capillary wedge pressure (estimate of left atrial pressure) is elevated due to failure of forward blood flow.