## Core Concept
The patient in this scenario has suffered a severe burn injury, with 45% total body surface area (TBSA) burned, of which half is third-degree. Third-degree burns extend through all layers of the skin and into the subcutaneous tissue, leading to significant tissue damage and potential for systemic complications. One of the complications of severe burns is the development of stress ulcers or **Curling's ulcers**, which can lead to gastrointestinal bleeding.

## Why the Correct Answer is Right
The presence of bloody drainage from a nasogastric tube and a decrease in hematocrit on the third post-burn day suggests that the patient is experiencing stress-induced gastric ulcer bleeding, likely **Curling's ulcer**. This condition is a well-known complication in burn patients, resulting from mucosal ischemia and acid hypersecretion in the setting of severe stress. The management of such a condition involves stabilizing the patient and controlling the bleeding. **Endoscopy** is crucial in diagnosing the source of bleeding and can also be therapeutic, allowing for cauterization or application of clips to stop the bleeding. This makes option the most appropriate next step.

## Why Each Wrong Option is Incorrect
- **Option A:** While fluid resuscitation and monitoring are critical in burn patients, the presence of active bleeding from a stress ulcer requires more direct intervention than just supportive care.
- **Option B:** Although blood transfusion might be necessary to stabilize the patient if there's significant blood loss, it does not address the underlying cause of the bleeding.
- **Option C:** H2 receptor antagonists or proton pump inhibitors might be used to reduce acid production in the stomach and can be part of the management of stress ulcers, but they do not directly address acute bleeding and are not as immediately effective as endoscopy in controlling hemorrhage.

## Clinical Pearl / High-Yield Fact
A key point to remember is that severe burns increase the risk of **Curling's ulcers**, which can present with gastrointestinal bleeding. Early recognition and intervention, including **endoscopy**, are critical in managing such complications.

## Correct Answer Line
**Correct Answer: .**