Ventilatory Support. Study the past if you would divine the future - Confucius
Considerable debate still surrounds the optimal treatment of severely ill patients with COVID-19 as we enter 2021. The different methods of their ventilatory support remain important topics with increasing concerns about possible harm associated with endotracheal intubation and invasive mechanical ventilation. As a consequence, non-invasive positive pressure ventilation, NIPPV, is being increasingly used.
Contrasting opinions with regard to the pathophysiology and management were outlined in two BMJ articles. In an editorial, Wilcox  stated that the ARDS caused by COVID-19 is similar to that from other causes and therefore, the principles underpinning ventilation should also be similar, whilst acknowledging that the arguments for and against early intubation and positive pressure ventilation, PPV, were unresolved. Martin  writing in the same edition, noted that the pathophysiology of COVID-19 had caused considerable surprises, including the higher than expected incidence of acute kidney injury, an increased incidence of thromboembolic events, pulmonary embolus, mismatch in lung perfusion and concerns with regard to high levels of positive end expiratory pressure, increasing intra-thoracic pressure and reducing venous return to the heart. He felt that “extreme circumstances have prompted ICUs to implement myriad novel approaches” and warned that the effort was far from over. A prediction that was chillingly accurate.
Could negative pressure ventilatory support be a “novel approach” to assist in COVID-19 and possible future pandemics?
Throughout most of the 19th century and the first half of the 20th century NPV devices were most commonly used to provide ventilatory assistance. There is more than 100 years of experience and research using negative pressure. Physicians moved from negative to positive pressure ventilation (PPV) in the 1950s , largely because of the shortage of heavy and bulky NPV devices and nursing issues. PPV was not physiologically superior. A common misconception amongst the present generation of anaesthetists, critical care doctors and nurses, is that this form of ventilatory support was only useful for the well-known polio epidemics. In fact, some centres have continued to use, research and modernise whole-body NPV devices, including generating continuous negative extra-thoracic pressure (CNEP) to increase the functional reserve capacity (FRC) instead of using continuous positive airway pressure (CPAP) therapy, and adding negative end-expiratory pressure (NEEP) to NPV to provide an equivalent therapy to the combination of positive end-expiratory pressure (PEEP) with PPV .
Both scientific and clinical evidence suggest that a modern NPV device with an ultra-lightweight torso-only cabinet may provide an effective non-invasive ventilatory alternative to CPAP and HFNO, conserving oxygen supplies [5,6]. Importantly NPV may also be able to prevent escalation of the patient to intubation and PPV by its use in conscious patients, who are able to cough, talk, eat and drink whilst ventilated. NPV simulates natural lung movements, and does not reduce the cardiac output which can occur as noted by Martin  when the venous return is compromised by raised intra-thoracic pressure during PPV .
The ease of manufacture, use of readily available parts (not competitive with PPV devices), low cost and easier nursing and medical management, including the prone position, are important further considerations of particular relevance to low- and middle-income settings, as well as wealthy countries presently being overwhelmed by this crisis.
Never has there been a better moment to study the past if you would divine the future. s.
1. Wilcox S. Management of respiratory failure due to covid-19. Editorial. BMJ 2020;369:m1786
2. Martin D. Novel approaches to intensive care medicine. BMJ Opinion. BMJ 2020;369:190
3. Lassen HCA. A preliminary report of the 1952 epidemic of poliomyelitis in Copenhagen. Lancet 1953;1:37
4. Gorini M, Corrado A, Villella G, Ginanni R, Augustynen A, Tozzi D. Physiologic effects of negative pressure ventilation in acute exacerbation of chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2001;163:1614-1618
5. Corrado A, Gorini M. Negative-pressure ventilation: is there still a role? European Respiratory Journal 2002 20: 187-197 DOI: 10.1183/09031936.02.00302602
6. Coulthard M, Ackerley D, Downie N, Fielding A, Harris J, Hodges E, Howard D, Joesbury I, Lambert H, Lund V, Mckeown D, Patel A, Roberts J, Speight C, Exovent: a study of a new negative-pressure ventilator support device in healthy adults. Anaesthesia 2021 In press
7. Corrado A, Renda T, Chiostri M, Villella G, Augustynen A, Misuri G, Bertini S, Tozzi D, Ginanni R, Maluccio N, Romano SM Cardiac output in normal subjects: negative versus positive pressure ventilation. Rassegna di Patologia dell’Apparato Respiratorio 2017;32:148-155
Professor David Howard, BSc, MBBS, MRCSLRCP, FRCS, FRCS(Ed), Hon GCPS.
Honorary Consultant, Imperial and UCLH NHS Trust Hospitals, London, UK.
48 years NHS service. ENT/Head and Neck Consultant, Royal National Throat, Nose and Ear Hospital (now UCLH), and Charing Cross Hospital, Imperial NHS Trust.
Special Interests - Laryngo-tracheo-bronchial trauma/stenosis, Critical Care, Head and Neck Oncology
Chairman of the Exovent Charity,UK. Charity Commission no.1189967
A group of medics, engineers and supporters who have produced a modern, not-for-profit, negative pressure ventilatory support device.
Competing interests: Chairman Exovent Charity, UK. Charities Commission no. 1189967