wellingtongoose (wellingtongoose) wrote,

How Sherlock Survived a Cardiac Arrest

The Most Miraculous Thing

The medical explanation I am about to give for Sherlock’s survival is nowhere near as uplifting or exhilaration as watching Sherlock struggling out the steps of his mind palace with the sheer determination to live for John. If you want to keep thinking about Sherlock’s “revival” as a miracle of love and a testimony to our inner strength, please free to do so.

The reason I am writing this article is to explain the medicine behind the poignant scene for people who are interested to know how things work in real life.

Do you think it is realistic that Sherlock came back from the dead?

I have been asked this many times in the past week whether I thought it was realistic that Sherlock spontaneously came back from the dead. I don’t think it is realistic for Sherlock to come back from being dead – but he wasn’t dead at any point in the episode. In fact he was very much alive despite “flatlining”.

In the pivotal scene we see that Sherlock is in asystole i.e. his ECG is a flat line, there is no electrical activity. Asystole alone isn’t enough to officially pronounce someone dead because you need to confirm brain death. Given that Sherlock managed to recover from his cardiac arrest without any neurological problems – I would say that his brain was very much alive throughout the entire ordeal.

I would like to take this opportunity to say that survival of cardiac arrests is very low. In medical dramas just about everyone has a cardiac arrest, is successfully shocked out it and then makes a full recovery. This rarely happens in real life. Only 20% of patients who have a cardiac arrest leave hospital alive. Less than 10% recover without any significant long term problems. The most common problem post-arrest is brain hypoxia leading to permanent neurological defects.

The miraculous thing in this episode is not that Sherlock died and was resurrected; it was that Sherlock survived with his brain intact.

Why would the doctors stop trying to save Sherlock if he was still alive?

The reason that Sherlock managed to survive with his brain intact was because the doctors had been doing CPR on him up until the moment we see them turn away. Doctors hate giving up on patients, particularly healthy young men like Sherlock. They didn’t just see Sherlock flatline on the table and decide to start packing up their tools. They would have given their last ounce of strength to try and revive him. However after a long time, CPR becomes futile and you have to stop somewhere. Usually the decision to stop CPR is made by the entire team. If just one doctor feels that it should be continued the entire team carries on.

I believe those surgeons and anaesthetists would have been performing CPR for hours before they decided to give up. I can personally attest to how exhausting CRP is, no one can perform CPR effectively for more than 4 minutes (two cycles) before become tired.

When CPR ceases you are in effect letting the patient die because the CPR was the only thing keeping them alive.

The reason why they would have decided to stop in Sherlock’s case is because he remained in asystole regardless of their best efforts. Cardiac arrest means that there isn’t detectable cardiac output. There are many different heart rhythms that can prevent the heart from effectively pumping blood. The heart may be beating too fast, or not beating at all. Asystole is the complete absence of any electrical activity in the heart and the type of cardiac arrest with the worst prognosis. When someone goes into asystole (i.e. flatlines) and stays in asystole despite CPR, adrenaline and IV fluid resuscitation their chances of survival go from slim to astronomical. It was not the wrong decision to cease CPR and let Sherlock die.

Why didn’t the doctors just shock Sherlock?

Contrary to popular belief you cannot shock a flatline. In fact there are only two types of cardiac arrest rhythms you can shock: ventricular tachycardia and ventricular fibrillation, neither of which look anything like a flatline on an ECG. For every other kind of rhythm the only way to help the patient is to do CPR, give adrenaline and reverse the cause of the arrest.

Why did Sherlock spontaneous get better after they stopped CPR?

Regaining electrical activity after a short period of asystole is not rare, but in most cases the heart still doesn’t work. It is a rhythm known as pulseless electrical activity. The ECG trace looks exactly like a normal ECG but there isn’t a pulse.

However from how quickly Sherlock recovered the use of his muscles after regaining electrical activity – I would say that he almost immediately established cardiac output.

Cases like Sherlock’s are very rare but they do exist. I have managed to find two case reports of them thus far. It is sometimes called the Lazarus Effect.

The Lazarus Effect

For every person who has ever spontaneously revived from asystole, there is always a long detailed debated about why and how.

Of course, we don’t get to see what the doctors did to Sherlock before they turned away but the protocol for managing a cardiac arrest is standardised throughout all hospitals. Therefore the main reason why Sherlock spontaneously regained cardiac output is all to do with the cause.

There are eight common reversible causes of cardiac arrests: the four Ts: tamponade, tension pneumothorax, toxins, thrombosis and the four Hs: hypovolaemia, hypoxia, hyper/hypokalaemia, hypothermia. There are other less common causes as well but during a cardiac arrest those are the eight main thing that we aim to find out and to reverse if present.

My theory is that Sherlock lost a great deal of blood both before getting to hospital and then on the surgical table. The cause of his cardiac arrest was most likely hypovolaemia.

The liver is a very vascular organ and a bullet wound would cause significant bleeding, especially if it hit the largest vein in the body which happens to run behind the liver. Additionally, the program is right to say that the bullet acts like a cork, thus when the bullet has being removed it can be very hard for the subsequent bleeding to be controlled on the operating table.

Sherlock would have been given a large amount of both IV fluid and blood to resuscitate him from the point the ambulance arrived. However he was probably losing as much, if not more, blood as they were putting in. It would have been only after the surgeons got the blood flow under control and repaired his inferior vena cave which carries blood back to heart, that he would start feeling the benefits of the fluid/blood being given.

However Sherlock is a fit young man with plenty of physiological reserve. His body can compensate for a large volume of blood loss without really dropping his blood pressure. This means that in the heat of the moment, doctors may not realise just how serious Sherlock’s blood loss is because his blood pressure remains relatively stable. Unfortunately when he reaches the limits of his reserve, he crashes spectacularly.

Sherlock’s blood pressure drops dramatically and the volume of blood returning to his heart to reduced to almost nothing. This means that the heart no longer has anything to pump into the lungs or out into the rest of the bloody and Sherlock goes into cardiac arrest.

The doctors then started CPR but without an adequate blood volume, Sherlock would not show any signs of improvement despite aggressive use of adrenaline. It can take quite a long time for Sherlock receive enough fluid/blood to regain cardiac output because there is a limit on the speed at which fluid/blood can be given even into his veins because of the size of the tube (cannula).

Sometimes when CPR is stopped it actually gives a chance for the heart to fully relax. Once the heart dilates and fills with enough blood, it can start pumping again automatically, which is what happened to Sherlock.

Sidenote - More Morphine Please

One very frequent question I have been asked is “why do the doctors give Sherlock morphine when he uses heroin? Would it not make him addicted?”

What I’d like to ask is: “why wouldn’t we give Sherlock morphine?”

Firstly it is unethical and unhealthy to leave anyone in pain, drug addicts included. Pain adversely affects wound healing, it increases the stress response and decreases the immune system, which makes it easier for the wound to become infected. After the operation, the first priority is to control the pain in the most effective way possible. Ibuprofen or paracetamol is not going to touch post-operative pain, Sherlock needs something much stronger.

Opiate/opioid analgesics are the most potent painkillers we have and putting Sherlock on a morphine pump he can control is the most effective way of keeping his pain to a minimum. Unfortunately Sherlock kept turning the morphine down, probably because he needed to think clearly but it wasn’t doing his recovery any favours. Although that wasn’t quite as bad as self-discharging early and chasing down a trained assassin.

Bleeding out

It is not surprising that Sherlock collapses after his conversation with John and Mary. The adrenaline of the situation was probably the only thing keeping his blood pressure up and his pain sense down. As soon as the tension was partial resolved, Sherlock crashed again. He was probably working extremely hard to keep himself upright by the end of the conversation and he knew he would not last much longer. I find it very poignant that Sherlock forced himself to hold on until the very end when he knew the ambulance would come so as to minimise disruption to the high sensitive conversation John and Mary were having.

I feel that this is definitely a sign that Sherlock has progressed along his path as archetypal hero.

Tags: character: john watson, character: mary morstan, character: sherlock holmes, episode: his last vow, meta: mycroft holmes, meta: sherlock holmes

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