Fun with Magnets
Updated: Jul 4
Friday 3rd July 2020
Figures for 2nd July
UK COVID Deaths 89 / Total 44,042
James Cook Hospital – Total COVID deaths – 254
All COVID cases within South Tees Hospitals Trust – 7
James Cook Critical Care COVID cases – 3 (2 ventilated)
James Cook Critical Care non-COVID cases – 48
A frustrating day at work today. We are seeing more and more non-COVID patients as the hospital continues to adapt to new ways of working. More routine surgery is taking place and we are starting to see more and more patients attending for clinic visits and procedures. Face masks, hand-gel and social distancing are changing the landscape somewhat but the hospital is starting to look more and more like it did before the pandemic.
Sadly, this is not true for the Intensive Care Units. Currently the few COVID patients we have are being treated in isolation rooms whilst the main units are full of ‘regular’ patients. We are still wearing PPE routinely whilst spending time in these areas, despite the fact that the patients are testing negative for COVID-19.
There are two reasons for this. Firstly, it’s to protect patients and secondly, it’s to protect staff. Whilst all these patients have tested negative, there is a still a small chance that they could still have the virus and be infectious. The incidence of these ‘false negative’ tests may be anywhere between 2 and 30%, depending on if the test was taken too early, the type of test and the technique used to swab the nose and throat.
We have a very reliable virology laboratory service at our hospital and if we suspect a patient has clinical features consistent with COVID-19 then we will test them a second or third time before allowing them to leave isolation. However, there is always a chance that a positive patient could slip through the net. Patients admitted to hospital may also be in the early stages of an infection and not become infectious until a few days later. The earlier you swab a patient, the more likely you are to produce a false negative result.
So, there is a theoretical risk of such patients later infecting staff, or worse, other vulnerable patients. This risk is amplified in the ICU where if a patient’s breathing circuit becomes disconnected, there is a risk of aerosolising a fine mist of virus-ridden particles into the air. These particles can remain afloat for up to 20 minutes. It’s a bit like walking past the perfume and beauty counter in a department store whilst they spray perfume or aftershave at you, only more evil.
So, ICU patients continue to be thought of as possibly infective and staff have to wear PPE in such areas, just to be on the safe side. This creates problems when trying to take a patient out of the ICU. Such problems are particularly significant when taking an ICU patient for an MRI scan.
An MRI scanner is essentially a ridiculously powerful magnet. It is contained inside a huge electro-magnetic shield or Faraday Cage to avoid electromagnetic interference. As you approach the MRI scanner the magnetic field strength increases dramatically. Bringing any metallic object into the scanning room can be extremely dangerous. People have died when objects such as oxygen cylinders have rapidly accelerated toward the MRI scanner and hit patients causing fatal head injuries. The internet contains many pictures of items like floor buffers that have been sucked into MRI scanners. These have been brought into the room by cleaning staff by mistake. This can be an expensive mistake as well as quite alarming for the poor cleaner.
The other danger comes from metallic objects within a patient’s body. Things like brain aneurysm clips, metal stents inside blood vessels, pacemakers or even small metal fragments following an eye injury can move under the influence of the magnet. Metallic items can also heat up and cause burns as the magnetic field induces an electrical current in the object.
All this means that great care has to be taken before any patient can undergo an MRI scan. The problems faced in scanning an ICU patient are many. Nearly every piece of equipment on the ICU contains metal. You cannot take the ventilator, the monitor or any infusion pumps that deliver medication with you into the MRI room. The scanner room does contain an anaesthetic machine which incorporates a ventilator and some monitoring equipment. This equipment is classified as ‘MRI compatible’, meaning it is made of non-ferrous metals such as aluminium, titanium, brass, or aluminium bronze alloy. Such equipment tends to be very expensive.
We have one MRI-compatible ventilator for us to use but otherwise, the ICU patient has to be disconnected from all equipment, transferred onto a special non-metallic trolley and wheeled into the MRI room before being placed inside the scanner. During this time the patient remains unmonitored and unventilated until they are connected to the MRI-compatible equipment. Infusion pumps have to be connected to the patient via extremely long drug giving sets or lines and the pumps have to stay outside the room, remote from the patient in the MRI Control Room. The giving sets normally pass from the control room into the scanner room through purpose-built holes in the electromagnetic shield called ‘wave guides’. We usually observe the patient, the monitor and the ventilator from the control room in order to access the infusion pumps and avoid the extremely noisy scanner room where ear-plugs or ear-defenders have to be worn.
You can see how taking a very sick ICU patient for an MRI scan is far from straightforward. It is not a place where you want anything to go wrong.
One of our young trauma patients needed an MRI scan of his spine today to make sure he had not sustained an injury to his spinal cord. He has tested negative for COVID-19 but we are continuing to take precautions. This means we have to enter the MRI room in PPE. Unfortunately, the ventilated hood systems are not MRI-compatible and most face-masks contain ferromagnetic metal in the nose piece or staples. When in the MRI room, these masks will pull away toward the scanner, compromising the fit. My colleague, the ever-exuberant Caroline is the only ICU Consultant working today who has been fit-tested to wear a mask that has no such metallic components and is the only one of us that can accompany our patient into the scanner room.
The other problem is that she can’t enter the MRI Control Room as she will be wearing PPE. This means there is no way that she can observe the patient’s monitor for the next hour. The drug giving sets cannot pass through the wave guides as the control room would then be in communication with the scanner room. If the breathing circuit became inadvertently disconnected then the control room and all the staff within could potentially be contaminated. The only way around this is to seal the corridor outside the scanner, prop the scanner door open a little, run the drug giving sets through the kink in the door and operate the infusion pumps from the corridor.
The only way we can make this safe is for me to stay in the control room and watch the monitoring equipment. I can let Caroline know if there is a problem. She will stay in the corridor and operate the infusion pumps based on the information I give her. She remains dressed in PPE so she can enter the scanning room in a hurry if there is a problem.
If this sounds elaborate and overly complicated, then that’s because it is. This one scan takes most of the afternoon and evening to organise and perform. The MRI staff are accommodating as ever and thanks to the two Andy’s help, things go without a hitch. In the end, our patient appears not to have damaged his spinal cord so after all that carry-on, at least its good news.
Tomorrow is the first day the pubs are allowed to open since lockdown began. We are expecting the hospital to be busy as a result of the celebrations. Apparently, pubs are allowed to open from 6am if they wish. What a great idea! If I get up early then I can sink a few pints at the Rudds Arms before work tomorrow which should make the day go a lot smoother…
MRI Scanners: What could possibly go wrong?