Dan Martin reflects on his experience of working in ICU during the covid-19 pandemic
All of us are now familiar with the virus that just a few months ago was nameless. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes coronavirus disease 2019 (covid-19), a respiratory illness that has affected the citizens of most countries on in the world.
We assumed that like its predecessors SARS CoV (the original “SARS”) and Middle East respiratory syndrome related coronavirus (MERS Cov), SARS-CoV-2 would lead to acute respiratory distress syndrome (ARDS) in patients for whom covid-19 progressed beyond common, self-limiting symptoms. Intensivists dusted down ARDS protocols and reminded themselves of what evidence existed to guide them through the difficult times they were about to face.
At the beginning of February, when preparations for an outbreak began, we were convinced we knew exactly how to manage critically ill patients with acute respiratory failure secondary to a viral pneumonitis. Our usual strategy is to use invasive ventilation to generate high levels of positive end-expiratory pressure (PEEP), and good evidence supports this approach. While doing this, we try to prevent the total pressure generated during inspiration from reaching excessively high levels, which is often challenging in the typical poorly compliant lungs of a patient with ARDS. We also avoid excessive fluid administration to prevent oedema of the lung tissue, which might further impede gas exchange. We anticipated that extra-corporeal membrane oxygenation (ECMO), used extensively in the influenza A H1N1 pandemic of 2009, would be required en masse to get us through the covid-19 pandemic.
Novel by name, novel by nature. We are now at the end of April and the pathophysiology of covid-19 has taken many of us by surprise. A remarkable degree of hypoxaemia is tolerated by affected patients, with little in the way of respiratory distress; calm, rapid, shallow breathing appears in those affected. Chest x-rays demonstrate patchy bilateral infiltrates, but not of the severity we were expecting. Following intubation, mechanical ventilation is remarkably straightforward in many cases, with relatively high lung compliance in the early stages of the disease. In addition, given the enormous number of patients who have required mechanical ventilation, only a small proportion have received ECMO.
Two elements of this disease have struck many physicians as notable: an anecdotally higher-than-expected incidence of acute kidney injury (AKI) and pulmonary emboli. As our knowledge of covid-19 expands, it is slowly becoming clear that thromboembolic events are common; in the lungs, this may explain the hypoxaemia/imaging mismatch. Hypovolaemia due to over-zealous zero fluid balance in hyperventilating patients with extreme hyperpyrexia may exacerbate AKI. A further contribution to AKI may have been the high levels of PEEP, which increase intrathoracic pressure, reducing venous return to the heart. The observational evidence suggests this package may not represent ARDS as we know it, but rather a novel form of lung injury that requires us to rethink the model, using a little less PEEP and a little more fluid.
Extreme circumstances have prompted ICUs to implement myriad novel approaches. My own ICU has doubled in bed capacity, providing mechanical ventilation in operating theatres and outpatient areas across three separate floors. Anaesthetists have helped us to provide 24-hour care for these expanded ICUs and formed intubation teams to cope with the huge number of deteriorating patients outside of ICU. Nurse-to-patient ratios have moved from 1:1 to 1:4 and beyond. The lost art of proning has returned, where we take a sedated and mechanically ventilated patient, turn them face-down and ventilate them in that position for two-thirds of the day to improve oxygenation. Our surgical colleagues have provided an essential service as proning teams, tirelessly rotating these fragile patients by the clock. Hospital staff from a variety of backgrounds and diver medical technicians have been drafted to support exhausted ICU nurses. All this in the face of dwindling supplies of essential medications and equipment along with oxygen pipelines that were never designed to deliver the amount of oxygen that we currently need to provide.
This effort is far from over. We will, no doubt, be faced with many more unexpected challenges. Perhaps the biggest fear for intensive care physicians is that once new cases eventually stop being admitted, the country will relax and celebrate. We, however, will continue to work for weeks and months beyond this, ensuring that those who survived being treated on a ventilator for covid-19 have minimal lasting effects from that experience. We have yet to know the extent to which they will be affected by critical illness polyneuromyopathy and post-traumatic distress syndrome, or whether the pulmonary inflammation will result in fibrotic changes. All this lies ahead of us. And what of the effect on our staff? Will they be also affected by trauma or moral injury when the dust has settled? We must look out for one another in the aftermath of this extraordinarily novel situation.
As this unique situation develops, we will need to keep an open mind, be prepared to admit that we may have been wrong about some things, and constantly review our approach to tackling this very novel virus.
Daniel Martin, Intensive Care Consultant and Intensive Care Lead for High Consequence Infections Diseases, Royal Free London NHS Foundation Trust. Professor of Perioperative and Intensive Care Medicine, University of Plymouth. Editor in Chief of the Journal of the Intensive Care Society.
Competing interests: Consultancy and Lecture Fees: Siemens Healtineers. Consultancy and Lecture Fees: Edwards Lifesciences.