What to expect in hospital: from oxygen masks to invasive support
Doctors from Wuhan advised the West to start ECMO ‘sooner rather than later’
COVID-19 patients whose illness is severe enough to be admitted to hospital face a battery of tests and possible treatment options when they arrive.
The most important tests measure blood oxygen levels to understand if the lungs are functioning properly, and blood pressure tests to understand the stress on the heart and wider vascular system.
Treatment options are designed to “support” the patient in fighting off the virus rather than cure them. Patients move through a series of steps, each becoming more invasive and onerous.
Basic oxygen therapy
The most basic form of hospital therapy for Covid victims who have become breathless and are struggling to get enough oxygen into their blood. Patients are fitted with a simple mask and supplied oxygen-enriched air.
Pressurised oxygen therapy
The next step. Patients are fitted with an airtight mask and the oxygen-air mix they receive is pressurised to help them breath. At this stage, monitoring of a patient’s vital signs will become more intense. The patient remains conscious.
Mechanical ventilation
A ventilator pushes air in and out of the lungs. This is an invasive procedure for which the patient is put to sleep, probably on their front to take the weight of the heart off the lungs. The ventilator keeps the patient alive.
Extra Corporeal Membrane Oxygenation (ECMO)
This is the option of last resort. It is used where ventilation can no longer get oxygen through the patient’s lungs and into the bloodstream because the lungs have become too damaged and inflamed. ECMO machines bypass the lungs and oxygenate the patient’s blood outside their body before returning to them. It is similar in concept to the heart bypass machines used during open heart surgery and is one of the most aggressive forms of life support available.
The machines are seen as the “last-chance saloon” of respiratory aid, and Guy’s & St Thomas’ is one of five centres in the UK that offers ECMO for adults. Others include the Royal Brompton and Harefield Hospital (London), Glenfield Hospital in Leicester, Papworth Hospital in Cambridge and Wythenshawe Hospital in Manchester.
The WHO has issued interim guidelines recommending the use of ECMO on Covid-19 patients with acute respiratory distress syndrome – respiratory failure when lungs are so ravaged that ventilation is no longer sufficient. The machines, which costs about £100,000 each, consist of an artificial membrane lung, a pump and a blood warmer – all of which are connected by plastic tubing.
Blood is removed from the body and pumped through the artificial lung, called the oxygenator. As well as
oxygenating the blood, the ECMO machine removes carbon dioxide and warms the blood before then returning it to the patient.
The patient is given an anaesthetic and a cannula is placed directly into the femoral vein on the side of the neck (and internal jugular vein if required), which is then connected to the ECMO circuit.
The removal of blood from the body can cause it to clot, so a blood-thinning drug called heparin is used. This can result in bleeding throughout the body and the need for blood transfusions.
In China, ECMO machines were used on the most severely ill patients, and in a mid-march webinar sponsored by the American College of Cardiology, doctors from Wuhan advised the West to start ECMO “sooner rather than later”.
But ECMO is not a cure; it’s a life-support measure used to provide relief for the lungs and is only suitable for a small number of patients who are otherwise fit and well. The prognosis for anyone put on an ECMO machine is, by definition, poor.
One reason for failure is its impact on the immune system. Along with the known ECMO complications of bleeding, infection risk, seizures and possible severe neurological damage due to loss of blood supply (ischaemia), a substantial decrease in the number and function of vital infection-fighting white blood cells called lymphocytes is common.
An ECMO specialist said: “The procedure is risky, because you’re putting blood through a machine full of synthetic surfaces, something blood normally reacts to and that can cause cellular damage and inflammatory response syndrome. The machine also chews up platelets so there can be damage to red blood cells.”
While many studies showing high survival rates among ECMO patients in different scenarios have been published, little is known about its success with Covid-19.
A small observational study by doctors in China published by the American Medical Association in February showed that five out of six patients (83 per cent) diagnosed with severe Covid-19 receiving ECMO died, but doctors have warned against comparing data between China and the UK.
“That figure will be a reflection on the rates in that particular hospital, but local variables play a factor such as how patients are isolated and managed, and medical protocols that are being followed,” said the specialist.
“It’s difficult to extrapolate any real meaning.”