The mechanics of anesthesia, a post by request.

This post is inspired by the following comment:

I have a question for you, and can’t seem to find your contact info, so I’m choosing this completely inappropriate forum to ask it. Hope you don’t mind! Would you consider doing a post or something of that ilk on what to expect when one goes in for surgery? Not the actual surgery part…doctors always talk about that. What I mean are the mechanics of the anesthesia. Things like, if I’m going under general, will it likely be given by IV or mask? What’s more common? Do you guys tend to give a sedative first so patients aren’t freaked out? I know not all surgeries are the same, but I’m assuming (from my completely layman’s perspective) that there are some common threads…

As you know, I have surgery coming up, and my orthopod is too busy giggling to himself over all the bones he gets to crack and screws he gets to drive to talk to me about what’s going to happen before the screwing/cracking/crunching. Sigh. Orthopods. They’re just shop jocks with scalpels, you know?

I have a few friends who are orthopods and they are very smart people – at least from a visuospatial sense.  Admittedly, none of the orthopods I know would be at all offended by the description of shop jocks with scalpels…in fact, I am thinking of one in particular that would be quite tickled.  But they haven’t spent much (if any) time behind the “blood brain barrier” as we call the drape the separates the surgeon from the anesthesiologist and our machine that goes “ping.”

In fact, what we do remains a mystery to many of our colleagues, as well as our patients.

I’m going to attempt to answer this question about “what happens when you go for an anesthetic,” baring in mind that there may be some subtle differences in practice between centers.  Generally, the hospital performing your surgery will have education materials (either on-line or in pamphlet form) that you can access.

Every anesthetic starts with a patient assessment.  If you are young-ish and healthy-ish this will probably occur on the day of your operation in the preoperative area.  If you are old-ish and non-healthy-ish or have experienced an adverse event under anesthesia in the past or significant side effects from anesthesia, you are probably a patient that we would like to see in assessment….i.e. several days to weeks before the day of your operation so that we can figure out if you need any preoperative testing or optimization.

The assessment begins with a medical history and includes a physical examination.  One of the most important components is an airway examination.  You will be asked to move your neck all around and open your mouth as wide as you can as we try to predict whether or not it will be difficult to ventilate and oxygenate you after you are under general anesthesia.  We need to figure this out even if we are planning to do the procedure under local anesthetic or a nerve block.

The assessment concludes with a discussion about anesthetic options which may include local anesthetic, peripheral nerve blocks, neuraxial techniques (spinal or epidural anesthetics), general anesthesia or a combination depending on the surgical procedure, and the needs and speed of the surgeon.  Sedation may be combined with any technique other than general anesthesia.  For example, if you are having a knee replacement under a spinal anesthetic, you could be awake or sedated so that you snooze during the procedure.  Another example, would be an epidural for post-operative pain (say after an operation on the lungs or upper abdomen) placed first followed by general anesthesia for the actual operation.  You should expect to have a discussion about the anesthetic options and their risks and benefits as well as the risks posed by any medical conditions you may have.  The two of you will agree on a plan although for most operations the anesthetic options are fairly limited.  Sometimes, extra monitoring will be required based on the procedure or medical conditions you may have and this will be explained to you also.

There may be some medications offered to you prior to going into the OR.  For example, preoperative doses of simple analgesics (like acetaminophen and/or an NSAID) are pretty common.  There is good evidence that pre-emptive analgesia is more effective than “rescue” analgesia.  Some patients benefit from antacids.  A dose of antibiotics given prior to, but within 60 minutes of, surgical incision has been shown to reduce surgical site infections for some, but not all, surgical incisions/ operations.  If a certain operation is short and the incision is one that is have a very low infection rate, antibiotics will probably not be given.  If you have body hair at the site of the incision and you feel like you want to help out by shaving the day of your surgery – don’t.  Freshly shaved skin at the operative site is a risk factor for infection.  We will use single-use clippers after you are under anesthesia.

For operations where there is a significant reduction in mobility, or if the patient has risk factors for deep vein thrombosis (generally blood clots in the large veins of the legs and/or pelvis), an injection of heparin or low molecular weight heparin, will be given under the skin either in the preop area or in the OR.

Usually an IV is started in the preop area by nursing staff but it might be done in the OR by the anesthesiologist or their assistant.  If you are very anxious, usually you can request some medication in the preoperative area to take the edge off of things.

We will take away your clothes and make you wear a very unflattering gown and some ridiculous OR socks as well as a gauze shower cap.  It’s not a very appealing outfit.  You’ll have to remove all of your jewelry (it’s best to leave it at home) because metal on the body may cause burns when cautery is used.  We’ll also have you remove any dentures or removable bridges because they may be damaged or cause damage to the inside of your mouth during the anesthetic.  Bridges and dentures will travel with you to the recovery room.  If you have eyeglasses, we’ll leave them on until you get to the OR, remove them just before the start of the anesthetic and return them to you in the recovery room.  Please don’t wear contact lenses – we’ll ask you to remove them.

The surgeon will be required to mark the operative site before you are moved into the OR.  Generally, you are offered a chance to use the washroom prior to being taken to the OR.  If the operation is long enough, a urinary catheter will be inserted after you are under anesthetic.  Please don’t be worried about urinating on or soiling yourself while on the operating table.  It’s rare, but if it does happen we take it in stride.

Once you arrive in the OR, you’ll probably be asked to identify yourself by name and state what you are having done and to what side.  In fact, you’ll probably have to do that three or four times between arriving at the hospital and undergoing anesthesia.  The anesthetic monitors will be applied.  At a minimum these are a pulse oximeter, a blood pressure cuff and some EKG leads.  If you are going to have a peripheral nerve block or spinal or epidural (for anything other than obstetrics), a little bit of sedation is usually given before the procedure and the anesthesiologist and OR nurses will talk through what is happening with you.  We understand that almost everyone is nervous and we are very good at distraction techniques.  If you need something (like a moment to collect yourself or an explanation or a distraction) just ask.

General anesthesia is induced through an IV about 99% of the time in adults – and yes, I just made that number up out of personal experience.  If you have a true needle phobia there are certainly things we can do to make the IV start more comfortable for you.  These would range from oral medication for sedation and anxiolysis to breathing in laughing gas during the IV start.  Very occasionally, an inhalational induction is offered for the needle-phobic.  Inhalational induction is a good tool for patients that can’t comply (young children, adult patients with developmental delay or other challenges) and in those rare cases where we need an unconscious patient but it’s unsafe to interrupt their respirations.

Before the anesthetic induction drugs are given, you will be asked to breath 100% oxygen via a tight-fitting facemask.  This step confuses many patients who think that they are receiving an inhalational induction.  It’s actual purpose is to wash out all of the nitrogen in your lungs and replace it with oxygen to provide a reserve that your body can draw on.  The induction of anesthesia causes apnea (cessation of breathing effort) and this extra oxygen will allow a normal sized individual a safety buffer of about 6 minutes before desaturation occurs.

I get asked by many patients how I know how much anesthetic to give them.  Some of them think that all of the anesthetic is given up front and they are worried it will wear off either too quickly or too slowly.  The drugs that induce anesthesia are given by weight-based dosing.  Their effect will diminish in a few minutes as they become distributed and metabolized by your body.  After induction, anesthesia is maintained either through inhalational agents (given via the endotracheal tube or airway) or IV agents given by infusion or a combination.  These agents are short acting so we give them continuously until the operation is over and then turn them off and await return of consciousness.

While you are under anesthetic, the anesthesiologist remains with you monitoring your vital signs and the depth of the anesthesia.  We manage your heart rate, blood pressure, ventilation and oxygenation.  We make sure you don’t get too cold.  We make sure fluid deficits from fasting and blood loss is appropriately replaced with fluids.  We give medication for pain.  Towards the end of the operation we give medication to prevent nausea and vomiting as well.

When you are asleep, in conjunction with the surgeon, we are responsible for your body.  In addition to keeping you physiologically stable (as above) we also ensure that you are treated with dignity while you are unaware.  We make sure that the position of your body and padding is arranged to decrease the risk of pressure injury to vulnerable body parts (eyes, peripheral nerves, breasts, fingers, etc).

At the end of the operation, we take you to the recovery room or post-anesthesia care unit (PACU) so that your vital signs can be watched closely while you recover from the anesthetic.  There are always a few surgical complications that, if they are going to occur, are going to occur in the first few hours after the operation and we watch for those in the PACU also.  In order to get out of the PACU to go either to the ward or home (if it’s day surgery), you have to have stable vitals, controlled pain and not be actively vomiting.  Of course, patients that will have complicated recoveries or who prove themselves to be very hard to stabilize during in the OR go directly to an intensive care unit rather than the PACU.

General anesthesia and sedation can cause confusion and difficulties with memory.  The surgeon will see you in the PACU and tell you how things went, but you might not remember.  That’s why day surgery patients get sent home with written instructions and have everything explained to their responsible adult escort.  You must not drive for 24 hours after an anesthetic…for that matter, don’t sign any legal documents either.  General anesthesia can leave you feeling like you have a bad flu.  Some of this is the drugs, some of it is an inflammatory response from surgical stress.  This generally lasts for a few days but some patients have reported longer symptoms.



  1. Machine that goes ping. Giggle. I love Monty Python!! 😀

  2. This is wonderfully informative. Thank you!

  3. Anj · · Reply

    You forgot the antihistamine-like drug to “dry up your secretions”. I had a GA surgery only once and it resulted in horrible dry mouth for about twelve hours after. After my third glass of water I asked why my mouth was so DRY and that’s what they told me.

    When my son was put under for dental work, I asked the ana what drugs he used and he told me. A total of four, IIRC. The initial knockout drug (propofol), an antihistamine-type and two other drugs. He explained things very accurately. Yes, the initial drug created a disturbing glassy eyed (eyes open, fixed gaze) appearance. Then he administered the GA and I had to leave,

    1. What does IIRC mean?

      You probably had an anti-cholinergic like glycopyrrolate or atropine. It is given with neostigmine to reverse the muscle relaxant drug. Not all surgeries require muscle relaxation so not all patients will get atropine or glyco. It’s pretty old school to give it to “dry up secretions” unless you’re having a bronchoscopy or something like that.

      And I agree, the dry mouth really is horrible.

      1. Stacey Jw · · Reply

        IIRC- If I recall correctly.

        Thanks for the post!

        Let me add one thing for other readers: if they offer to use Ketamine, just say NO! I had it when they had an issue taking my cerclage out and fentanyl wasn’t helping at all. I have done Ketamine recreationally (insane, I know), and told them this, and asked if it would be similar. I was told it was different, but it was just the same and super scary! Yikes. Easily the worst part of the entire LnD stay. Hopefully it works better on other 🙂 I wasn’t in the mood for a psychedelic trip that day.

  4. Saw this and thought of you…

    1. Courtney · · Reply

      My family has a go-to orthopedic surgeon. Apparently, good bones don’t run in the family. He’s done great work for us all -caring for injuries and chronic conditions with and without surgery. However, his mannerisms are certainly an acquired taste!

  5. […] The mechanics of anesthesia, &#1072 post by request. […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: