Why have doctors cautioned against exposing people, especially those with mild symptoms, to radiation?
The story so far: As doctors try out different protocols to manage patients with COVID-19, Dr. Randeep Guleria, director of the All India Institute of Medical Sciences (AIIMS) and member of the National Taskforce on COVID-19, has cautioned against the use of CT scans indiscriminately to diagnose the disease, especially in the early stages. This exposes individuals to unnecessary radiation, which could be harmful in the long run, he said. A single CT scan is equal to 300 X-rays, Dr. Guleria warned, which may increase the risk of cancer later in life for young people. Doctors and the World Health Organization (WHO) are also cautioning against the use of corticosteroids like dexamethasone, a potent anti-inflammatory drug, for patients who have non-severe COVID-19. Corticosteroids have been proven to benefit patients with moderate and severe infection.
When is a CT scan advised for a COVID-19 patient?
An RT-PCR test is the standard for diagnosis or confirmation of COVID-19. Use of CT for the diagnosis of COVID-19 should be restricted to that subgroup of patients who may have classical symptoms of the illness but have a negative RT-PCR test result. However, a chest CT can be useful in evaluating patients with moderate or severe disease, to identify complications like thromboembolism or pneumomediastinum.
There are certain situations involving COVID-19 patients in which a clinician might depend on a CT scan to arrive at treatment decisions. These include scenarios where a patient may have classical symptoms of COVID-19 but his RT-PCR test is negative, or situations when a CT pulmonary angiogram might be in order to rule out pulmonary embolism in a patient who is on anti-coagulants and steroids and is not showing any signs of recovery. Also, in cases where a patient in the ICU with severe COVID-19 is not showing any improvement and a chest X-ray shows new lesions, a CT appearance might give a clue towards a diagnosis of dangerous COVID-19-associated fungal super-infections like aspergillosis or mucormycosis. In a fourth scenario, a clinician might order a CT chest to rule out spontaneous pneumomediastinum, a life-threatening complication.
“However, these four scenarios together constitute less than 2% of situations where a CT chest is ordered in COVID-19 cases. Rather than CT findings, it is oxygen saturation that is the key to treatment decisions. Yet, in 95% of the cases, CT scan is a misused tool, often prescribed to rule out pneumonia even in mild cases of COVID-19. There is no point in ordering CT early in the course of COVID-19 because even patients with mild severity may have some ground-glass opacities in the lungs, which do not merit treatment and will resolve on their own,” says R. Aravind, Head of Infectious Diseases, Government Medical College, Thiruvananthapuram.
The consensus statement from Fleischner Society, an international, multidisciplinary association for thoracic radiology, states that “imaging is not indicated” in suspected COVID-19 infection with mild clinical features. The statement supports the use of imaging in patients with worsening respiratory status as well as in those with moderate to severe clinical features that are indicative of COVID-19 pneumonia.
To sum up, although CT has been used in assessing the severity of COVID-19 pneumonia, its routine use is not recommended.
Are multiple CT scans harmful?
When indicated, a chest CT should be performed with a low-dose, single-phase protocol using fast scanning techniques to minimise motion artifacts (patient movement leading to subtle errors).
There is no evidence to support the use of routine multi-phase chest CT in patients with COVID-19 pneumonia. Dr. Guleria said according to data from the International Atomic Energy Agency, one CT scan was equivalent to almost 300 to 400 chest X-rays, which put youngsters at substantial risk of cancer in the long term. A study published in the New England Journal of Medicine in 2007 said based on data from 1991 to 1996, 0.4% of all cancers in the U.S. may be attributable to radiation from CT studies and that the current estimate could be in the range of 1.5% to 2%.
Apart from all this, the risks of transmission and contamination faced by radiology technicians and staff every time a COVID-19 patient undergoes diagnostic imaging, especially in an air-conditioned, closed space, cannot be dismissed.
Why are steroids being prescribed for COVID-19 patients?
Even though many doctors in India had started treating seriously ill COVID-19 patients with corticosteroids like dexamethasone much earlier during the pandemic, recommendation on their use from international agencies like the WHO came only in September 2020, following the U.K.’s RECOVERY Trial, which found mortality benefit for patients who received steroids.
In many patients, death occurs following a hyper-immune response (cytokine storm) to the SARS-CoV-2 virus, which damages the lungs and other organs, leading to multi-organ dysfunction syndrome. Corticosteroids like dexamethasone, as anti-inflammatory agents, work by calming down the immune system and preventing the progression of organ damage.
“Steroids are the most potent weapon we have to combat COVID-19. But the therapeutic window for starting steroids has to be spot-on. Determining the timing, dosage and duration is an art which has to be mastered,” says Dr. Aravind.
One of the main concerns is that we do not want to start steroids too early in the illness when viral replication is happening as it might interfere with the immune system’s natural ability to fight back. We also do not want to miss that critical point when steroids can prevent the immune system from unleashing the cytokine storm, he says.
The WHO guidelines say that steroids may be administered to patients whose resting saturation levels are below 94% and whose respiration rate at rest is over 24 per minute. However, steroids can benefit some patients who are not on supplementary oxygen yet but are showing early indications that they might worsen.
Kerala’s guidelines thus talk about recognising exertional desaturation — the fall or depletion in oxygen saturation reading by over 3% from the baseline oxygen levels, post-exercise or after the six-minute walk test — and addressing it at the right time so that interstitial inflammation can be arrested. The walk test requires individuals to walk for six straight minutes, without a pause, on an even surface with an oximeter on the finger. After six minutes, if the oxygen level does not go down, the individual will be considered healthy. But if the oxygen level drops below 93%, or by 3%, or if the individual suffers from breathlessness, then they are advised to seek medical attention.
“We want to pick up patients who are at risk of progressing to hypoxemia at rest. The earliest feature of COVID-19 pneumonia will be interstitial involvement, which leads to a demand-supply mismatch of oxygen. So, patients with normal oxygen saturation (> 94%) at rest in room air and who are clinically stable are put through the six-minutes/40-step walk test. If the oxygen levels drop after the walk test, these patients may be started on low-dose steroids after consulting the pulmonary specialist or a physician to prevent the cytokine storm syndrome,” says Dr. Aravind.
When do steroids become a double-edged sword?
That said, steroids can turn out to be a double-edged sword if the dosage, timing or duration of the drug goes wrong. Steroids are not mandated for all patients and certainly not for mild patients in the early stages of the illness. The trigger for starting steroids has to be exertional desaturation and not the day of illness.
Dr. Guleria had pointed out recently that he was seeing many mild COVID-19 cases where steroids had stimulated viral replication, causing oxygen levels to drop. There is potential harm associated with the long-term use of steroids in a serious COVID-19 patient. This includes a rise in blood glucose levels, which will need to be carefully managed with insulin to prevent secondary bacterial or fungal infections.