Extremely rare but potentially catastrophic complications
Before reading this and getting frightened, I have performed thousands of anaesthetics and I have not seen any of the following complications except for severe allergy (twice when I was a registrar – both patients recovered well although their surgeries were postponed) and severe aspiration (once when I was a registrar – the patient died of septic shock but not because of the aspiraton).
The most severe form of allergy is known as “anaphylaxis”
As an anaesthetist, we administer lots of different medications to you – sometimes more different medications than you have had before in the rest of your life so far. There is a small chance that you could have a severe allergic reaction to one of them.
“Muscle relaxants” aren’t required for all surgery, but sometimes they are. I try to use muscle relaxants with a lower rate of anaphylaxis wherever possible, but some muscle relaxants have a rate of anaphylaxis of around 1 in 5000.
Antibiotics also have a rate of anaphylaxis of around 1 in 5000, but prophylactic antibiotics when indicated do a lot more good than harm in reducing surgical site infection.
If you do have a severe allergic reaction under anaesthesia, the good news is that you are in the best place to have it managed. Usually people recover from it, although the surgery may be postponed. There is always a chance if the allergic reaction is extremely aggressive that it could lead to death.
When we put people off to sleep, there is a chance that stomach contents could regurgitate into their mouth, and then they could breath those stomach contents into their lungs. This can be very bad for the lungs.
This chance is close to zero if there is nothing in the stomach, and this is why we ask people to not eat any food (including most fluid and chewing gum) for at least 6 hours before their surgery. However, some people still have some stomach acid in their stomach even though they are appropriately fasted.
Largely due to all of the precautions that we take, severe aspiration is very rare. Even if severe aspiration does occur, it rarely leads to death, but it can lead to an admission to the intensive care unit and people can get other lung complications afterwards.
Failure to establish an airway
On rare occasions, it may be difficult for your anaesthetist to supply air (including oxygen) to your lungs once we have put you off to sleep.
This is a great fear of all anaesthetists, and we attend training courses and refresher courses so that we are drilled to manage this situation if it ever does occur before severe injury due to lack of oxygen occurs to our patient. I also routinely look for any previous anaesthetic notes to see if anybody else has had trouble managing my pateint’s airway in the past.
It is possible but improbable that at some point during my career, a patient of mine planning to have routine surgery could wake up with an emergency tracheostomy tube in their neck. If they do, then this will have saved their life, but I hope that I never have to do this.
Severe, permanent spinal cord damage may occur in association with a spinal anaesthetic, and it may also occur in association with a general anaesthetic with similar frequency. It is exceedingly rare – occuring on average once every few years in the whole of Australia.
Transient peripheral nerve damage is more common, occuring a few times each year in Australia. This may occur in association with a local anaesthetic nerve block, or it may occur due to pressure or stretch of the nerve due to the positioning of our patient, which is one reason that we always take meticulous care with you when you are anaesthetised and can’t take care of yourself. It even occurs when there has been no obvious cause.
The rate of this type of nerve damage is about 1 in 5000. The ulnar nerve, which supplies part of the forearm and hand, is the most common nerve for this to happen to, and it can happen spontaneously (we always check that the ulnar nerve is not under pressure). In most cases the nerve will recover, but it can take 3-6 months to recover.
The rate of nerve damage from nerve blocks used to be around 1 in 250 before we used ultrasounds, but it seems to be much less since ultrasounds have become widespread and used for nerve blocks. We don’t have exact numbers because it is difficult to collect good data for very rare events, but it looks to be less than 1 in 1000.
It is possible to suffer a stroke while under anaesthetic. This is very rare, but it can be devastating if it does occur.
Sometimes after the complication, investigators can look through the anaesthetic records and suggest that maybe the blood pressure was too low, or maybe something else was wrong.
Sometimes though there is no obvious cause.
Strokes are common in society, and it is quite possible that sometimes the stroke that was about to occur anyway just happened to occur while the operation was taking place.
Post-operative cognitive decline (POCD)
This condition describes when somebody’s mental ability declines after the operation, and never completely recovers.
It was first noted to occur after cardiac surgery, and was initially put down to microscopic gas bubbles in the blood from the “heart-lung” machine causing damage to the microcirculation of the brain. It was initially referred to as “bubble brain”.
However, heart surgery developed techniques so that they could perform coronary artery bypass grafting without using the heart-lung machine, and patients still experienced POCD with similar frequency. So something other than gas bubbles is at least part of the cause.
After closer investigation, it was noticed that POCD occured after other operations too.
We do not know what causes POCD, but it appears that the more extensive the surgery is, the more often it appears to occur. Also, it is very rare in people who are completely mentally intact before the operation. Studies have tested people with complicated and sensitive cognitive (ie, intellectual function) tests before and after their surgery, and most people who experienced POCD had some degree of early cognitive decline before the surgery, even if nobody noticed and they functioned normally in society.
It also appears that, although people with POCD by definition never fully recover their intellectual capacity, a year later their intellectual function is at a level close to where it would have been anyway, even without the operation, as other people’s cognitive function has declined over that year to “catch up” with them.
We are very careful with people’s eyes while they are under anaesthesia. We keep them closed and covered so that they do not dry out, we pad them if they are going to be at risk of being inadvertently poked by the surgeons, and we make sure that there is no pressure on them during the operation. We look after the blood pressure so that the eyes, along with everything else, gets good blood flow.
Very rarely though, for no apparent reason, someone can wake up from anaesthesia and be blind in one eye. Specialist examination after this occurs generally shows that it is something to do with the blood supply of the retina, but (like with strokes), sometimes everything is perfect during the operation but it still happens.
Lots of people snore. Lots of people who snore have sleep apnoea (during which their airway obstructs during their sleep and no air moves for a few attempted breaths, before their airway obstruction resolves and they manage to take a deep breath). Some people with sleep apnoea have a severe form of sleep apnoea (if measured, their blood oxygen levels would drop quite low during their sleep due to their airway obstruction), and some people even die in their sleep at home, never 100% proven, but probably from their sleep apnoea.
The problem with sleep apnoea and surgery is that opioid analgesia (such as morphine) causes the sleep apnoea to become a little bit worse. That little bit of difference might be the difference between successfully relieving the airway obstruction and taking that deep breath before the blood oxygen levels get too low, or failing to take that breath until after the blood oxygen levels become critically low.
Every year or two there is a case report of somebody in Australia who appears to have died in hospital from sleep apnoea exacerbated by surgery and opioid analgesia.
It is probably a very low risk though, because there are so many people with sleep apnoea who don’t even know that they have it, who have surgery without any extra precautions, and there is still only a tiny number of deaths.
If we know that somebody has significant sleep apnoea and is about to undergo an operation that it likely to exacerbate their sleep apnoea, then we will arrange for them to have continuous monitoring and nursing staff supervision for the first night or two after their surgery (such as high dependency unit care). These patients will be safe.
The problem potentially occurs when there is somebody with severe sleep apnoea that nobody including themselves knows about.
Awareness under anaesthesia is the most feared complication of many patients, and rightly so.
Thankfully, these days it is extremely rare.
Any awareness under anaesthesia seems to occur at a rate of 1-2 in 1000. Most often this is only for a small period of time before the surgery begins, in high-risk patients who we cannot safely give too large a dose of anaesthetic to at the start of the operation. This is still not a good thing, but it is not as severe as the classic horror scenario that people fear.
The classic horror story of “I was completely awake for the whole surgery but unable to move” is exceedingly rare these days.
Firstly, for most surgeries, your muscles still work. (For some surgeries we need to administer “muscle relaxant” drugs to stop your muscles tightening and obstructing the surgeon). Therefore, if your muscles work and you are aware, then you will move your arms or legs when your brain tells them to move. Unless muscle relaxants are in your system, there is no “locked-in” syndrome.
Secondly, about 20 years ago, the “gas analyser” became part of our anaesthetic monitoring equipment. This measures the amount of anaesthetic vapour that you breathe out (which is very close to the concentration in your brain) every breath. Imagine being able to do 10 blood tests per minute to instantly monitor the concentration of any other chemical!
Since “gas analysers” came into use, the incidence of awareness dropped from being a significant risk to being almost zero.
In some occasions it is not appropriate to use anaesthetic vapour, and we need to use an infusion of intraveinous anaesthetic medication. This was once associated with a higher risk of awareness, until about 8-10 years ago when “depth of anaesthesia” monitors became available. (I refer to these as “brain-wave” monitors). These monitors monitor your brain activity to make sure your brain stays asleep.
Arguably there is not a lot of benefit in using a depth of anaesthesia monitor when you are being kept asleep with anaesthetic vapour, as the gas analyser appears to be better at minimising the risk of awareness than the depth of anaesthesia monitor. Having the gas analyser for some people and the depth of anaesthesia monitor for other people (with some people being monitored with both) has reduced the incidence of awareness under anaesthesia to very close to zero.