What Causes Coughing Up Of Sputum With Blood After Being On Anesthesia?

Is it ok that on day 5 after a general anaesthetic lasting 2 hrs, I coughed up some sputum that was blood, not bright red, but a brownish red. about a rounded teaspoonful , and then just a few more tiny amounts. now it is day 7 and i have not coughed up any more of the same. What caused that, and should I still see my GP?