What are reasons why there are more complications with anesthesia in the obese?

Obesity, causes difficulty breathing, higher stomach acid that causes aspiration pneumonia, sleep apnea, diabetes, heart disease, hypertension, difficult intubation . . . Surgery much less risk if not obese.
Obesity. Anaesthesia doesn't cause the complication. It is the physiology of obesity that leads to complications. In the hands of a trained anaesthesiologist, these potential complications are well managed.