“But how much anaesthetics knowledge do I need to pass medical school?”
Every med student ever.
It’s a good question, because there’s a whole lot of anaesthetics, and relatively little exposure to it during your medical school years, so it’s hard to judge just how big a role it plays when it comes to your revision and the dreaded final exams in medical school.
I certainly had very little idea when I was studying for finals myself, and ended up playing guessing games as to which aspects to focus on, to try and optimise as many marks as possible.
Focus on principles, rather than details
I am a third year anaesthetics trainee, with an extra year of intensive care under my belt, and I’m struggling to get my head around the finer details of anaesthesia for my fellowship exams, so there’s absolutely no way they’re going to expect you to know the ins and outs of each drug, procedure or piece of equipment at a medical school level.
It is a very useful goal, however, to try and understand the fundamental principles of anaesthesia and what we as anaesthetists are trying to achieve, because you can use that as a framework that can often allow you to work out the answers to questions on exam day.
The Components of Anaesthesia
Anaesthesia literally means ‘without sensation’, so it seems logical that our main job is to ensure our patient is unaware of what’s going on, and much of the time it is.
However there are often situations where our role is a little more nuanced than just knocking people unconscious and then doing our best to ensure that process is temporary.
There is a well-known triad of anaesthesia
- A lack of awareness of what is happening
- Keeping still, largely for the surgeon’s benefit
- Adequate pain relief
If these three conditions are satisfactorily met, then you have a successful anaesthetic on your hands, however how you go about achieving these parameters is entirely up to you as the anaesthetist. For example, most total knee replacements are now done under regional anaesthesia, such as a spinal anaesthetic.
In this case, a few millilitres of a local anaesthetic such as levobupivacaine are injected into the cerebrospinal fluid around the base of the spinal cord, causing numbness and temporary paralysis of the lower limbs for a few hours. The patient can then remain wide awake, or be given a little sedation if they’d rather not hear the orthopaedic surgeon’s hammers and drills. The benefit of doing this is that it avoids the risks of general anaesthesia, allows patients to go home sooner and reduces the amount of postoperative pain, nausea, vomiting and confusion.
On the other hand, a major abdominal operation usually requires a general anaesthetic because having major abdominal surgery while awake is unpleasant to say the least.
The anaesthetist also needs more control of the patient’s breathing to prevent the diaphragm interfering with the surgical field, and it is essential that the patient stays completely still. Both of these are achieved by giving a muscle relaxant, which stops the patient being able to move their muscles for an hour or two, allowing the anaesthetist to control the patient’s breathing with a ventilator. Muscle relaxants are only given to patients once they are deeply asleep, for obvious reasons.
In each of these scenarios, every anaesthetist will have their own ways of achieving the same outcome – a comfortable, safe and happy patient. This is one of the joys of the anaesthetics as a specialty, you get to learn and perfect your own craft, picking up tips and tricks from your colleagues and mentors, to truly build your own anaesthetic.
If there’s one thing the stereotypical anaesthetist likes doing other than drinking coffee and cycling, it’s intubating people. But we don’t just going around tubing people for the sheer fun of it, because in reality there are two and only two reasons to put an endotracheal tube into a patient’s trachea
- They are not protecting their own airway from aspiration
- They are exhausted or temporarily need help with work of breathing
If you understand this, you can then work out whether intubation is necessary for a patient. I’ll give you some examples.
A young man comes in having drunk multiple litres of alcohol, and is now unconscious and vomiting. His lungs and breathing are fine, but he is so profoundly unconscious that his cough reflex isn’t going to protect his lungs from the vomit. He needs a tube with a cuff to physically prevent anything tracking down into the delicate respiratory tree. This is the definition of a definitive airway – a cuffed endotracheal tube that completely protects the respiratory tract from contamination.
So just how unconscious do you have to be to need a tube?
The generally accepted number is a GCS or glasgow coma score of 8 or lower.
If you’ve not heard of it, GCS is a widely used way of measuring conscious level that uses three parameters:
The exact details of the GCS score is beyond the scope of this page, but in essence
Less than eight - intubate
A middle-aged woman needing a hernia repair who has been given a general anaesthetic. She’s now unconscious, not protecting her airway, and has been given a muscle relaxant, meaning she won’t breathe for herself. She needs to be intubated for both reasons – to protect her airway, and to allow the ventilator to breathe for her until the operation is over and the muscle relaxant has worn off.
The third example is a patient with severe pneumonia, who’s lungs are so full of infection, pus and debris that the poor patient is working unbelievably hard just to breathe enough to get sufficient oxygen into their blood.
This is tiring in itself, and not only that, the harder they work, the more oxygen their respiratory muscles are going to use in order to breathe, making the whole situation worse.
In this case the patient temporarily needs help with their work of breathing while the antibiotics get to work and help them fight off the infection. Now there are several ways of doing this, including fancy things like:
- High flow nasal oxygen which fires warmed, humidified oxygen down the back of a patient’s nasopharynx into their lungs
- A tight fitting mask that supplies pressure to help keep the lungs inflated (as in the case of CPAP)
- The same mask can assist with the effort of breathing by driving oxygen down into the lungs (as in BIPAP or non-invasive ventilation)
Often patients will be started on one of these first, to try and avoid needing intubation, because we know patients that end up on a ventilator have worse outcomes than those who manage to avoid it, and this is something we’ve particularly seen with COVID.
The key thing to note here, is that it is the work of breathing that matters, not necessarily oxgenation. A ventilator cannot provide an intubated patient with more oxygen than a tight-fitting CPAP mask, as both can only give 100% pure oxygen.
An endotracheal tube doesn’t magically mean you can supply a patient with more oxygen, it just does allows the ventilator to do the breathing for them to give them a rest.
The reason I hammered the point of it being temporary support, is there has to be a reversible problem that the patient can overcome.
Because ventilators are bad for your lungs. Your lungs are meant to breathe by gently drawing in low pressures of 21% oxygen, not to have 100% oxygen blasted under huge amounts of positive pressure into them by a ventilator. If you take a healthy fit person and give them 100% oxygen on a ventilator for three days, they’ll hardly be able to walk up the stairs for a good few weeks, it’s that damaging.
This means that if a patient has a chronic irreversible lung disease that is so bad that they can’t even keep their oxygen levels up high enough using something like a tight fitting mask, then it wouldn’t be appropriate to put them into a medically induced coma and onto a ventilator, because their condition is not reversible, and they will therefore not improve to a condition where they can be weaned off the ventilator.
So the problem has to be temporary, like a nasty infection in otherwise healthy lungs, otherwise intubating the poor patient isn’t going to fix anything. This is why ICU doesn't just take absolutely everyone and put them on a ventilator when they get severely unwell.
Local anaesthesia and pain
Another key component of an anaesthetist’s job is helping manage both acute and chronic pain, in the form of medications and interventional procedures. An example of this would be injecting local anaesthetic around the nerves that supply the ribs for a patient with rib fractures. This is usually done in theatre as a mini surgical procedure under sterile conditions using ultrasound, and is performed by the anaesthetist. The local anaesthetic drug, such as bupivacaine or ropivacaine, can be infiltrated around the target nerves, or a thin plastic catheter can be left in, allowing further top-up doses to be administered at regular intervals on the ward.
Hopefully this gives a bit of guidance as to the scope of anaesthetic knowledge required for medical school, please let us know if you feel anything is missing or unclear!
Useful blog articles
As we continue to build anaestheasier.com, we’ll be writing blog posts about a variety of subjects, many of which we hope you’ll find useful, which you can find here.
Check out our podcast!
We’ve started a podcast in which we discuss everything we love about anaesthetics, provide tips and tricks for revision, as well as revision episodes aimed at the dreaded FRCA exam. Find it on Spotify here, or search for Anaestheasier on your podcast platform.