The patient’s presentation of hematemesis, hypotension (BP 90/60), and tachycardia indicates active upper gastrointestinal bleeding with hemodynamic instability, most likely from varices due to alcoholism. The priority is to stabilize circulation with blood transfusion to restore volume and improve oxygen delivery. Simultaneously, urgent endoscopy is needed to identify and treat the bleeding source, such as variceal band ligation, to prevent exsanguination. Delaying intervention increases the risk of mortality. Other measures like IV PPI or vitamin K are supportive but not immediately lifesaving. Nasogastric lavage may help diagnosis but does not replace urgent resuscitation and therapeutic endoscopy.

Reference: Sleisenger and Fordtran's Gastrointestinal Disease, Feldman et al., 11th Edition.