Covid-19: Patients to use pulse oximetry at home to spot deterioration
BMJ 2020; 371 doi: https://doi.org/10.1136/bmj.m4151 (Published 27 October 2020) Cite this as: BMJ 2020;371:m4151Read our latest coverage of the coronavirus outbreak
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Dear Editor and R. Bryant,
Like measuring blood pressure or body temperature, please do not take one-off measurement as a reliable assessment. As you correctly did, try different fingers, make sure the oximeter is not too tight or too loose, you are at rest, and your fingers are relaxed, and the room temperature is moderate, etc.
Also, it is a good idea for anybody in the household to have a baseline when s/he is not ill. As some people [particularly with some chronic medical conditions] will have a saturation lower than the normal range of 95-100% in a normal population. For those people, a drop of 4% from their usual baseline is also significant.
Competing interests: No competing interests
Dear Editor,
My concern is that most home patients are using cheap, $30 devices and readings in my experience jump around, 93-97% in my case, a healthy 76 yr old. No note of reading variability was mentioned. I've told freinds and relative to take several readings on both hands to get a reliable value.
Regards,
R. Bryant
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Dear Editor,
I totally agree with the author. Together with five doctors who have treated a total of several thousand Covid patients in China's first epicentre - Hubei, I have speculated that high COVID mortality in the UK is at least partially caused by under-detected “silent hypoxia” at homes or care homes, and, seemingly paradoxically but actually consequently, low admission rate to Nightingale hospitals [ https://doi.org/10.1093/qjmed/hcaa262 ].
Our commentary also discussed the considerable differences between UK and Hubei [similar in population size and epidemic extent] in detecting silent community/care-home patients, and in admitting those patients to Nightingales [treating just over 154 patients then] or 13,000-bedded Fangcang Hospitals [China’s Nightingales, almost fully used with 12,000 (95%) admissions]. The latter significantly reduced mortality, with only 4,512 deaths directly from Covid, mainly with simple and non-expensive approaches – finger oximeters and oxygen supply to those with SaO2 < 93%.
We therefore suggested that the UK authorities consider a strategical change in configuring and using Nightingales may save thousands of lives in the current resurgence.
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Dear Editor
I agree with many of the comments in responses.
I am chief investigator for an ongoing GP practice study on use of oximetry in the public with COVID-19. Despite an information sheet and a printed image of use, on reading the first returned data sets it was clear people could mix up pulse and oxygen levels. The writing below them indicating which, on the display, is which is small. There is also a potential for reading upside down too.
As medical professionals it is difficult to put ourselves into non-medical shoes. We have taped over the pulse display with much better results (amended through HRA). Oximetry displays require improvement.
Dr Jane Wilcock
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Dear Editor
Torjesen (1) reports that patients with covid-19 at risk of complications but not needing immediate hospital attention are to be given pulse oximeters to use at home to identify deterioration in oxygen saturation (SpO2). NHS England advised further intervention if SpO2 levels began to fall suggesting that if SpO2 fell to 94% or 93% the mortality risk increased to around 13% and to about 28% below that level. The idea is to create “virtual covid wards” of patients at risk and to monitor SpO2 through patients taking readings and relating these to their health teams; “If it starts dropping and particularly goes to 94%, then you’ll potentially take some action, which may include [the patient] being admitted to hospital.”
Greater clinical benefit may be gained by looking at the variability of the SpO2 numbers because the underlying lung pathology produces quite different effects on SpO2 stability. Impaired pulmonary gas exchange is caused by increased right to left shunt and/or reduced ventilation to perfused alveoli (VA/Q). Until recently clinicians could not easily differentiate between these and are unaware that Shunt and VA/Q have quite different effects on the stability of SpO2. An example is shown in two patients A and B breathing air.
https://profjgjones.wordpress.com/
In the left panel is a plot of oxygen partial pressure against oxygen saturation. The red curve is the Oxygen Dissociation curve. When inspired oxygen (PIO2) is plotted against SpO2 the blue curve represents the normal lung and dark green the patient’s curve. The fine vertical line is inspired oxygen pressure at 21 kPa. The curve in Patient A has moved downwards because of a small increase in shunt and the curve in B has moved to the right because of a small decrease in VA/Q (2). Curve B is almost a tangent to the inspired oxygen curve and SpO2 became very unstable varying from >95% to 75% during a 13 hour monitoring period. In curve A the intersection is similar to the normal lung curve and SpO2 has normal stability but in a 90-95% range. In each case SpO2 was monitored continuously and plotted in 30min epochs, each epoch moving vertically. The stable epochs superimpose and are very pointed whereas the unstable epochs are broad and wide ranging.
Differentiating between shunt and reduced VA/Q may well have a specific diagnostic relevance to covid-19 induced pulmonary failure. For example, the primary characteristic observed in covid-19 patients by Gattinoni and others (3) was a dissociation between relatively well-preserved lung mechanics and the severity of hypoxemia. The high respiratory system compliance with a large shunt is virtually never seen in most forms of Adult Respiratory Distress Syndrome. Hypoxemia with relatively high compliance indicates a well-preserved lung gas volume and a reduced VA/Q in this patient cohort.
While a reduced VA/Q may be inferred from SpO2 instability it is preferable to examine the effect of varying inspired oxygen using a Ventimask and using pencil and paper to plot the shape of the PIO2 vs SpO2 curve. This indicates the nature and severity of the underlying gas exchange abnormality. In practice reduced VA/Q and and increased Shunt may co-exist in different proportions giving complex effects on curve shape. A computer algorithm generates a numerical estimate of VA/Q and Shunt from 3-4 SpO2 vs PIO2 data pairs when PIO2 is changed stepwise (4).
It would be interesting to know if outcomes are different for covid-19 patients with predominantly reduced VA/Q compared to those with predominant Shunt.
References.
Torjesen I. Covid-19: Patients to use pulse oximetry at home to spot deterioration. British Medical Journal 2020;371:m4151 | doi: 10.1136/bmj.m4151.
Jones JG, Jones SE. Discriminating between the effect of shunt and reduced VA/Q on arterial oxygen saturation is particularly useful in clinical practice. J Clin Monit 2000; 16: 337-350.
Gattinoni L et al. Covid-19 does not lead to a “typical” Acute Respiratory Distress Syn- drome. Am J Respir Crit Care Med, Articles in Press. Published March 30, 2020 as 10.1164/ rccm.202003-0817LE.
Jones JG, GG Lockwood, N Fung et al. Influence of pulmonary factors on pulse oximeter saturation in preterm infants. Arch Dis Child Fetal Neonatal Ed 2015;0:F1–F4. doi:10.1136/archdischild-2015-308675
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Dear Editor,
Home monitoring of oxygen brings with it the potential to treat with oxygen people at home for whom hospital admission may be undesirable. This would be similar conceptually to using oral antibiotics for people unwell with a chest infection but who prefer to take their chances at home rather than be admitted for intravenous treatment. I would be interested to read about the experiences of those nursing homes who used oxygen concentrators during the last wave of this pandemic.
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Dear Editor,
Tower Hamlets GP Care Group rolled out a pulse oximetry service to all its practices and patients back in April. This allowed many patients who might otherwise have needed hospital assessment or admission to be cared for at home.
One of the key components was the delivery of oximeters to patients through the letterbox, by volunteers on bikes. Not only did this mean that time for direct patient care by GPs and other health professionals could be maximised, without the need to leave the practice to make equipment drop-offs, it also kept staff safe. Sadly, care of older and vulnerable patients at home can no longer be undertaken in the way shown in the photo, particularly if they may have covid, and clearly appropriate PPE is essential.
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Dear Editor,
While I accept the comments of Dr Goh regarding the accuracy of commercially available pulse oximeters, and of the risks of misinterpretation of results I think it unlikely in Covid circumstances that either should be a major worry. Any miscalibration would be consistent, so a trend to developing hypoxia will still be seen. The important positive is that it may enable symptomatic patients to avoid hospital admission if their oxygen saturation remains reasonable, but would be able to seek immediate attention when readings fell.
My only concern is - why has this initiative taken so long to implement? I suggested on 12th May in my blog (https://bamjiinrye.wordpress com) that every household should have a pulse oximeter. On the same day you published a piece by Dr Rammya Mathhew saying the same thing (1). In an email to Chris Whitty on 14th May I wrote
"...If infection with SARS-COV-2 can be prevented from progressing to Covid-19 most deaths will stop. To plan early treatment requires early diagnosis. Key measures are hypoxia and a rising serum ferritin and D- dimer. The widespread distribution of pulse oximeters would provide the perfect early warning system for the former, and hospitalisation for intensive therapy could thus be streamlined."
We bought our oximeter on 1st May. I never had a reply to the email.
It is worth revisiting the major issues surrounding the pandemic at this moment.
Transmission will not be stopped while people fail to socially distance, but the appetite for this, and for full lockdowns, has diminished substantially, not least because the resulting economic outlook has become clearer. Cycling in and out of lockdown is a recipe for economic catastrophe.
A vaccine might become available, but may not work very well. To pin all one's hope on one are wishful thinking. Measuring T-cell immunity on a wide scale would be sensible.
Given these problems of prevention, which are insuperable, we need to concentrate on the treatment of serious Covid-19, which has improved dramatically, not least because at last steroids are being used appropriately, and the virtues of CPAP over mechanical ventilation have been recognised. It has also become clear to me that the best informed specialists for the management of Covid-19 are rheumatologists, because they best understand the immunological processes that result in cytokine storms. Their influence is becoming more apparent, but it is time for the SAGE committee formally to include them on their panel.
Reference
1. 1. Mathew R. Innovation during the pandemic. BMJ, 12th May 2020. https://doi.org/10.1136/bmj.m1855
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Dear Editor, In the Covid times, the single most important device that has helped persons in community to be taken to hospital /health care facility / dedicated centre has been pulse oximeter. Largely confined to ICUs, monitoring rooms and post operative care, the phenomenal rise in usage of pulse oximetry at homes/ domestic setups and community has been a 'covidphenomenon' and assuring /relieving asset at that. For any item of mass / self usage, quality control does matter. Reasonable information /knowledge of the device is vital to prevent both panic / complacency. Few murmurs as feedback are the variable time to obtain stabilised final reading, and the higher heart rate displayed initially. As clinicians, best to advise the patients not to rely exclusively - symptom (s) persistent and progressive call for medical assessment. Dr Murar E Yeolekar, Mumbai.
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Re: Covid-19: Patients to use pulse oximetry at home to spot deterioration
Dear Editor,
Pulse oximeters also show the pulse rate of a person. Pulse rate (PR) rises whenever there is an infection in the body and often, pulse rate is high before we can see the symptoms. Covid-19 enters our body through nasal and oral cavities and the virus comes to life when they come in contact with cells. A lot of people nowadays have pulse oximeters at home. If they regularly check their resting PR and whenever it goes over 100 bpm and they take steam twice a day, wouldn't it drastically decrease the chances of virus dying in our respiratory system?
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