The new chief executive of Boston-based New England Baptist Hospital has launched a strategic review that could result in unspecified cutbacks, according to an e-mail sent to employees. Patricia L. Hannon, who began running the hospital in November, told workers that its financial surplus for fiscal 2009 was inadequate. "This is not enough to reinvest in our institution to ensure our mission," Hannon said, "so we must improve the surplus to at least 4% or better through growth opportunities and more efficient ways of obtaining the same result."