"I began experimenting with THC to help with my chronic back pain. I started with it in September 2017 and stopped in early Feb 2018."
More research needs to be done in this area, as there simply isn’t much information out there on this topic. A recent literature review conducted by Huson, Granados and Rasko (2018) found that “marijuana increased cardiac workload, myocardial infarctions and strokes in young, chronic users.” The literature review also found that those who smoked marijuana were more likely to require increased anesthetic doses to place laryngeal airways (just like smoking, marijuana causes airway obstruction). “Use within 72 hours of general anesthesia was advised against” (Hunson, Granados and Rasko, 2018).
Based on the above literature review, it looks like you should be fine because you will have abstained from using cannabis for over a month by the time you receive general anaesthesia. I do however recommend that you let your health care providers (including your surgeon) know that you have been experimenting with THC oil recently.
Huson, H.B., Granados, T.M., and Rasko, Y. (2018). Surgical considerations of marijuana use in elective procedures. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6139487/ on March 2nd, 2019.
When talking about surgery anesthesia and marijuana, all types of marijuana should be avoided. That means smoking marijuana, edibles, and synthetic marijuana. The use of marijuana, especially immediately prior to surgery, can change the doses needed for sedation. It has been found that cannabis users requires substantially higher doses of anesthesia. There are other reasons why use of cannabis can compromize operative and post operative period, such as airway obstruction , respiratory cardiovascular distress, increrased depression of central nervous system (when barbiturates given after surgery), inhibition of other medication action going the same liver metabolic pathway (Huson , Granados, Rasko, 2018).
Therefore, abstaining from marijuana in the weeks before surgery can decrease the likelihood of complications during and after surgery.
Huson, H. B., Granados, T. M., & Rasko, Y. (2018). Surgical considerations of marijuana use in elective procedures. Heliyon, 4(9), e00779. doi:10.1016/j.heliyon.2018.e00779