George HW Bush and his wife Barbara both remain in hospital in Houston, with the former US president in intensive care as he is treated for pneumonia.
His wife is being watched after complaining of fatigue and coughing.
Mr Bush (92) went into the intensive care unit on Wednesday and underwent a procedure "to protect and clear his airway that required sedation", said family spokesman Jim McGrath.
Mr Bush was stable and resting comfortably at Houston Methodist Hospital, Mr McGrath said.
The 41st president was placed in the unit to address "an acute respiratory problem stemming from pneumonia".