Final answer:
Desflurane is the anesthesia agent known for causing an increase in sympathetic outflow and tachycardia when rapidly increased to high levels.
Step-by-step explanation:
The inhalation anesthesia agent that is known for causing an increase in sympathetic outflow, leading to tachycardia, when its level is suddenly increased to high levels is desflurane (C). Desflurane has a property that can trigger an increase in heart rate and contractility as it activates the sympathetic nervous system. While other agents like isoflurane, sevoflurane, and halothane are also widely used, desflurane is distinctive in its ability to produce these specific cardiovascular effects.