ATP is considered the universal currency of energy in cells because it directly provides the energy required for most cellular functions. Its high-energy phosphate bonds release energy upon hydrolysis, fueling processes such as muscle contraction, active transport, and biochemical synthesis. Unlike glucose or NADH, ATP is immediately usable without further metabolic conversion. This rapid energy transfer is critical in surgical contexts, where cellular metabolism and tissue repair depend on efficient ATP availability. Understanding ATP's role aids in managing conditions involving energy deficits or ischemia during surgery.

Reference: Principles of Physiology, Guyton and Hall, 14th Edition.