Yep, just lost a lot of blood.. not enough of it is getting to his brain for oxygen. Low hemoglobin is anemia. With a blood transfusion it's all fixable! Blood transfusions do miracles, they really do.
I also suggest you ask the doctor. Haemoglobin is a protein in red blood cells that provides tissues with oxygen. If your father lost a lot of blood due to the surgery, he may have a low Hgb count as a result. But like Ironwand said, there may be other reasons for that. Best of luck to your father!
There are many causes for low haemoglobin count, some serious, some not. It could be as you suggest, but it may depend on what the surgery was for. Best to ask a doctor rather than us bunch of armchair medics on here.
i think it is a mix of the red and white cells in the blood. low red or low white.