Final answer:
Halothane is the anesthetic agent most likely to precipitate worsening mitral regurgitation due to its negative impact on cardiac function, including its effects on myocardial depression and vasodilation which can increase regurgitant flow.
Step-by-step explanation:
The anesthetic agent most likely to precipitate worsening mitral regurgitation in the scenario of a 73-year-old man with diabetes, GERD, and grade 2+ mitral regurgitation undergoing hernia repair is halothane. Halothane is known for its negative effects on cardiac function, including the potential to worsen mitral regurgitation due to its depressant effects on the myocardium and its propensity to cause vasodilation, which can lead to increased regurgitant flow across the mitral valve. This risk is not as prevalent with other anesthetic agents such as desflurane, isoflurane, and sevoflurane which are generally considered to have less negative impact on cardiac function. Nitrous oxide, while it could increase pulmonary vascular resistance and potentially affect cardiac function, is less likely than halothane to exacerbate mitral regurgitation in this patient.