So there are two MAC terms you might hear. One is a billing term, and another is in reference to the depth of anesthesia. Confusing…I know. So let’s break it down. 

The billing term/type of anesthesia “MAC” – means “monitored anesthesia care”. You might hear this in reference to what type of anesthesia the patient is getting – “Is this patient getting a general anesthetic or a MAC?” At a high level, this means the patient is going under sedation (not general anesthesia).  It involves varying levels of sedation and analgesia tailored to the patient’s needs, ensuring comfort and safety while allowing the patient to maintain spontaneous ventilation and responsiveness. The patient typically maintains their own airway (no LMA or ETT) and the depth is lighter than a general anesthetic which means faster recovery. 

The depth of anesthesia “MAC” – this stands for Mean Alveolar Concentration. In this context, MAC is the concentration of an inhaled anesthetic in the alveoli of the lungs that prevents movement (immobility) in response to a surgical stimulus (like an incision) in 50% of patients. It’s a standard measure of anesthetic potency. On the anesthetic machine, you’ll see the CRNA adjust the anesthetic gas up and down, sometimes as high as 1.0 or 1.2 MAC (or more) when we want them “deeper”, and then down to 0 when we want them to wake up (the reality is patients start to move/stir before we get them to 0 MAC, you’ll see!) 

So at a MAC of 1.0 – 50% of patients will move/respond to surgical stimulus – that’s the definition. But remember, by the time the surgeon makes incision, they’ve got way more than just anesthetic gas on board – they’ve got Fentanyl, Versed, maybe some Precedex or Ketamine. That means they might need less gas (than a MAC of 1.0) in order to not move in response to surgical stimulus. Plus, many times they’re relaxed (aka paralyzed).