It could be that marijuana is still in your system. The best advice is to avoid smoking it long enough to get it all out of your system before the surgery, typically this is around 30 days either side of the surgery.
This is caused by the by product in the weed that will affect the blood and the lungs, both used to help with this procedure.
There could be a number of serious, possibly life-threatening side effects that may occur when anaesthetics are given to people who use street drugs. Anyone who uses or takes marijuana or other street drugs should make sure their doctor or dentist knows what they have taken.
Other risks to taking marijuana before general anaesthesia may cause things like acute uvular oedema and post-operative airway obstruction. Furthermore during general anaesthesia, additive effects of marijuana and potent inhaled anaesthetics can result in pronounced myocardial depression and even septic shock.
Marijuana has also been shown to increase the activity of liver enzymes; anaesthesia is broken down by the liver, so you might not get the right dose which could result in being awake for the operation or waking up during the procedure.