**Core Concept**
The Sengstaken-Blakemore (SB) tube is a specialized balloon tamponade used to control bleeding from esophageal varices. The pressure required to achieve hemostasis is crucial, as excessive pressure can lead to complications.

**Why the Correct Answer is Right**
The optimal pressure for the SB tube is between 40-60 mmHg. This range is sufficient to compress the varices and control bleeding without causing undue pressure on the esophagus or stomach. The goal is to achieve a pressure that is just enough to stop the bleeding, but not so high that it compromises the integrity of the esophageal or gastric mucosa. The use of a pressure gauge allows for real-time monitoring and adjustment of the balloon pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Pressure of 80 mmHg or higher is generally not recommended, as it can lead to esophageal or gastric mucosal necrosis and perforation.
**Option B:** A pressure of 20 mmHg is too low to effectively control bleeding from esophageal varices.
**Option C:** There is no evidence to suggest that a pressure of 100 mmHg is beneficial in controlling variceal bleeding.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the SB tube should be used as a temporary measure to control bleeding, and definitive treatment, such as endoscopic variceal ligation or sclerotherapy, should be initiated as soon as possible.

**Correct Answer:** D. 60 mmHg