Barbara Bush, wife of former President George H.W. Bush, was hospitalized Monday for a respiratory-related issue at Methodist Hospital.
While there was no timetable for her release, family spokesman Jim McGrath said, "we're hopeful that will take place sooner than later."
McGrath said doctors may exercising extra caution by keeping her at the hospital.
"She is 88," he said. "She is a national treasure."
The mother of former President George W. Bush is 88 years old. She had heart surgery in March 2009 for a severe narrowing of the main heart valve. She also was hospitalized in November 2008 for a perforated ulcer. In 2010, she was admitted to the hospital after having a mild relapse of Graves disease, a thyroid condition for which she was treated in 1989.
The Associated Press contributed to this report.