The surprising story of how ventilation killed covid19 patients in intensive care.

[Wandering Eyes]

Simon Thornley

16/03/2021

Over a year now into New Zealand’s covid-19 saga, what can we learn from the experience of intensive care units? In the early days, protection of intensive care units and the scarcity of ventilators was a major factor shaping covid-19 policy.

New Zealand students were busy building ventilators, intensive care capacity was a major government concern, and became a key component of the elimination strategy.

The thought, early on, was that covid-19 was a completely new disease and that early mechanical ventilation was necessary in a patient’s treatment to give them a good chance to make it through. Since mechanical ventilation is a medical treatment, it must make things better, acting like a kind of super bellows, taking over when the patient ran out of steam, buying them time as their body beat back the virus.

The reality of intensive care experience has been somewhat different. It is well known that ventilators inflate the lung in an unnatural way, causing ventilator induced lung injury. They are far from a benign intervention and must only be applied sparingly.

Unfortunately, a certain level of jargon is necessary to dive deep into the ventilator story. A crucial measure of lung disease that is important in deciding to ventilate a sick or deteriorating patient is the ability of the lungs to soak up oxygen, known as the Pa0₂:FiO₂ ratio. This is the ratio of oxygen pressure, measured from a patient’s artery relative to the percentage of oxygen being delivered, usually via a mask. This ratio indicates the ability of a patient’s lung to deliver essential oxygen to the body. Usually, values of 150 mmHg to 200 mmHg indicate the need for a ventilator. Early opinions from Wuhan, from Chinese anaesthetists, recommended early intubation, with patients having values as low as 300mmHg indicating need for a tube. In some hospitals, the milder form of breathing support, non-invasive ventilation, was not used due to the fear of spreading the virus to staff. In other areas, such as the US, financial incentives to ventilate were operating.

Early mechanical ventilation has been a spectacular failure, with the best evidence now showing that it did more harm than good. A recent study, published in January 2021, now has the wash-up from experience with 10,362 patients who have had covid-19 in the UK and been in through a critical care unit. These are covid-19 patients at the severe end. Almost 38% (3,933/10,362) of subjects died. The critical comparison was between those who were ventilated and those who were not. For those who were ventilated early, at low severity of lung disease (Pa0₂:FiO₂ = 300mmHg), they had almost twice the rate of death, compared to those who weren’t, after accounting for all other factors. In fact, the most surprising finding was that for any level of lung impairment, those who were ventilated were more likely to die than those who were not. A conservative estimate of the importance of this finding, indicates that it accounted for about 15% or 1/7 of all the study deaths.

Naysayers may point out that the study was an observational one – not a trial – and that the results may be explained by doctors spotting unrecorded adverse factors that led them to put tubes down patients’ throats. An interview with North American intensive care doctors, however, contradicts this interpretation. Doctors spoke of asking patients to get off their mobile phones so they could put them on a ventilator. This was unusual practice, created by the fear of a new disease with an unpredictable course. Ultimately, it was learning to do less, rather than more which reduced mortality rates.

This created a sort of medical self-fulfilling prophecy of a deadly virus. The simplistic fixation on ventilators and the perceived need for them led to excessive use and premature deaths. Together with exaggeration of recording of covid-19 deaths, a vicious circle of fear took hold. The finding that Italy had ~10% of participants in a screening study of several regions of the country with antibodies for SARS-CoV-2 in September 2019, with no excess mortality at the time, strongly indicates that the healthcare and societal response, including lockdowns, were deadlier than the virus ever was.

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