Which of the following conditions could be responsible for causing obstructive shock?

Obstructive shock occurs when there is a physical obstruction in the circulatory system that impedes blood flow, resulting in decreased cardiac output and inadequate perfusion of tissues. In this context, pulmonary embolism stands out as a significant cause. A pulmonary embolism involves a blockage in one of the pulmonary arteries in the lungs, usually due to a blood clot that has traveled from another part of the body, such as the deep veins of the legs. This blockage reduces blood flow to the lungs, leading to impaired gas exchange, increased pressure in the right ventricle of the heart, and ultimately resulting in decreased cardiac output, manifesting as obstructive shock.

The other conditions listed can impact the body's circulatory system and may lead to shock, but they do not primarily cause obstructive shock. For example, pneumonia is an infection that causes inflammation and can lead to septic shock, but it does not obstruct blood flow in the same way. Anaphylactic reaction results in an extreme allergic response, leading to distributive shock due to widespread vasodilation and increased capillary permeability. Cardiac arrest is a cessation of heart activity, and while it leads to shock, it does not fit the definition of obstructive shock as it does not involve a blockage