Welcome to The Plague Pit – issue number 4

In this issue, I’ll be writing about how our COVID-19 patients ‘present’ i.e. what brings them to the hospital. I’ll explain some of the things we do early on to support and treat them once they arrive.

I feel a bit rough, Doc….

A month ago, the World Health Organisation published data on the first c100,000 cases of COVID-19. They concluded that in 80% of patients, infections are mild or asymptomatic.[1] For the other 20% of patients, though, the infection is severe – producing a viral pneumonia. The inflammation caused by the virus damages the walls of the small air sacs in the lungs (alveoli) and impedes the usual passage of oxygen from alveoli into the small blood vessels nearby.

This sort of damage is not unique to COVID-19. Several other viruses produce similar effects [2] and, in any case, this visual evidence is only available at post-mortem. Doctors generally prefer to make a diagnosis sooner than this. To do so, this is what we do:

(1) Take a history from the patient to establish the symptoms (what the patient describes)

(2)  Conduct an examination of the patient to establish the signs (our objective observations)

 (3) Select suitable investigations and review the results

Doctors taking a history usually start with the presenting symptoms – the ‘Why are you here?’ question.  

Do you think it’s coronavirus?

An early report from Wuhan describes the presenting symptoms and signs in hospitalized COVID-positive patients. [3] Nearly all new patients had a fever, and three quarters of them came with a cough. Later on, a third of patients developed breathing difficulties, or ‘dyspnoea’ symptoms – typically about seven days after admission. Dyspnoea usually comes with a sign – tachypnoea (breathing faster than the usual 12-18 breaths/minute).

Doctors ‘elicit’ symptoms and signs in a new patient to help them find out what’s wrong – to establish a diagnosis. But COVID-19  symptoms and signs are unfortunately rather non-specific. In other words, lots of other diseases cause patients to cough, or have a fever. Several workmates of mine developed COVID-type symptoms early in the pandemic, but then tested COVID-negative. They may have had a different virus. One thought, in hindsight, that her cough may have been due to hay fever.

Given the risks to ourselves and other patients, we treat a patient who presents with a recent history of cough and fever as COVID-positive, until specific tests prove otherwise. More on these tests later.

Symptoms and signs of a disease can help to follow its progress, or the effect of treatment, over time. They may also allow doctors to give a patient an idea of the the prognosis, i.e. the likely future course of the disease. In the Wuhan patients above, dyspnoea was twice as common in patients who went on to die than it was in survivors.

In a pandemic, symptoms have another use. The C-19 COVID symptom tracker’ app (available at https://twinsuk.ac.uk/ ) was developed by researchers at King’s College and released in late March. It was downloaded by 700,000 people within 24 hours. They will report their symptoms through the app, helping researchers track the spread of COVID-19. The aim is to help slow the outbreak. I got the app recently and registered as a health care worker. There are plenty of questions for me about COVID exposure and PPE

What are you going to do, Doctor?

All treatment currently used in COVID patients merely keeps things going while the infection follows its course. There is no cure at present – not even hydroxychloroquine, Donald. I’ll go through some of the things doctors have suggested might be useful, and why, in another issue.

When COVID-19 patients arrive at hospital with dyspnoea or tachypnoea, the oxygen in their blood is often low (‘hypoxia’). We measure this straight away, using a pulse oximeter. It’s a small device that shines light through the fingertip and displays two numbers, the heart rate in beats/minute and the percentage of haemoglobin in the red blood cells that is bound to oxygen (the ‘oxygen saturation’). The physics of the pulse oximeter are interesting and involve something called the isosbestic point. I knew a lot about it for my exams but can’t remember the details now. Thank goodness for Wikipedia: https://en.wikipedia.org/wiki/Pulse_oximetry.

In healthy young adults, oxygen saturation is 95-100%. COVID patients sometimes have minor symptoms but unexpectedly low oxygen saturation. On the other hand, some COVID patients have dyspnoea and tachypnoea but manage to keep their oxygen saturation near normal. Patients like this who arrive in Accident and Emergency are sometimes sent home, after expert review, with an oximeter – returning later if things get worse. In normal times this would be extraordinary. Now, there is a need to conserve hospital beds for the very ill.

O2 near the O2

We start by giving hypoxic patients a higher concentration of oxygen than they are getting from the air (21%), usually through a face mask connected to an oxygen supply. Hospitals mostly store the liquid oxygen they buy in large tanks called Vacuum Insulated Evaporators (VIEs). They are not very pretty – you can usually find them round the back, near the bike sheds. Details of the physics/ engineering are available here: https://en.wikipedia.org/wiki/Vacuum_insulated_evaporator.

Here are the ones just installed outside the new Nightingale Hospital in east London.

Oxygen is piped from the VIEs round the hospital and is available through special sockets in the walls. Flow can be adjusted at the outlet. When we transport patients, ore work in more remote areas of the hospital, we use portable oxygen cylinders instead. Recently, there have been a couple of reports of hospitals running low on oxygen as a result of treating such large number of COVID patients. [4]  I qualified more than three decades ago and I’ve never heard of this before

According to the WHO figures, lung damage in 5% of patients with COVID infection is so severe that they require mechanical ventilation. I’ll write about how that comes about, and the special features of managing ventilated COVID patients next time

The Good Soldier

 

[1] World Health Organization. Coronavirus disease 2019 (COVID-19) Situation Report – 46: 06/03/20. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200306-sitrep-46-covid-19.pdf?sfvrsn=96b04adf_4. Accessed 08/04/20

[2] Liu J et al. Overlapping and discrete aspects of the pathology and pathogenesis of the emerging human pathogenic coronaviruses SARS-CoV, MERS-CoV, and 2019-nCoV. J Med Virol. 2020 May;92(5):491-494. doi: 10.1002/jmv.25709. Epub 2020 Feb 21.

[3] Zhou F et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study. Lancet. 2020 Mar 28;395(10229):1054-1062. doi: 10.1016/S0140-6736(20)30566-3. Epub 2020 Mar 11. Erratum in: Lancet. 2020 Mar 28;395(10229):1038.

[4] Kituno N, Thomas R. NHS rushes to increase oxygen supply as virus cases surge. By Nick Kituno, Rebecca Thomas. Helath Serv ices Journal 5 April 2020. https://www.hsj.co.uk/coronavirus/nhs-rushes-to-increase-oxygen-supply-as-virus-cases-surge/7027323.article. Accessed 06/04/20