In my specialty of emergency medicine, it seems we have an insatiable need for information about our patients. Many of our patients are speedily attached to the EKG machine, placed on continuous cardiac monitoring, pulse oximetry, and then phlebotomy – the routine bloodletting we do in the service of laboratory testing. Then most of our patients get irradiated, first with regular X-rays and then CT scans. What do we get for these efforts? A correct diagnosis in many cases? Perhaps. Useful information we can share with patients? Sometimes, yes. Better outcomes? We assume so? But do we always make progress when we gather up more data about our patients? That idea lies behind efforts to develop more and better diagnostics. These monitoring devices are increasingly are following us home. For instance these include bracelets and watches that many of our wear on our wrists anyway. Fitbits, Apple watches and the like can diagnose atrial fibrillation, measure sleep, generate an electrocardiogram, and monitor blood oxygen. So is all this monitoring helping us?

A recent study studied whether home monitoring of blood oxygen of outpatient COVID-19 patients using a pulse oximeter generated surprising results. Earlier observational work had suggested that patients do better when they are monitored by home pulse oximeters so that we could identify thise patients in early stages of deterioration. Those patients could be flagged for oxygen treatment and possible medications. After all, identifying patients with low oxygen could identify those who would benefit from supplemental oxygen and keep people from deteriorating, right? How could this not be good and helpful?

Here is what they found: No benefit. Taking measures of pulse oxygen and monitoring them remotely did not result in better outcomes. Although conventional wisdom about COVID-19 made it appear that this strategy would work, having more information about the oxygen status of outpatients did not help patients. In a research letter published this month in the New England Journal of Medicine, home oximetry monitoring did not result in better survival. Specifically, there was “no significant between-group difference in the number of days they were alive and out of the hospital at 30 days.” There were more hospitalizations and longer hospital stays, however. If the goal is helping people survive COVID-19, it was a bust. If the goal is generating larger hospital bills, then maybe they can be considered a success. In truth, we should avoid interventions that simply drive up resource utilization without improving outcomes.

There is some relevant back story here about monitoring oxygen in the ED and the ICU. For those patients with sepsis, invasive monitoring to measure oxygen, along with the strategy of maximizing oxygen delivery, have been a well-documented disappointment.

Consider the central venous oxygen catheter. This ScVO2 catheter was a mainstay of sepsis care for over a decade and it was enshrined in the influential Surviving Sepsis guidelines. And the rationale for measuring central venous oxygen with these catheters? Septic shock was and is thought to be a problem of inadequate blood flow and oxygen delivery to the body’s tissues. Increasing blood flow and oxygen delivery, along with careful oxygen monitoring made sense. The 2001 trial of Early Goal Directed Therapy by Rivers et al, suggested that this strategy was a winner. Problem was, that first trial was done at a single center and involved relatively few patients. Another problem: an earlier trial looked specifically at increasing oxygen delivery by Hayes et al in 1994 showed higher mortality in intervention group for whom oxygen delivery was maximized.

More than a decade later, several large scale multicentered trials were undertaken to specifically designed to set the hypothesis that closely measuring and attempting to increase oxygen delivery would help patients – the ARISE, Promise and PROCESS trials each showed no benefit to this strategy, called “early goal directed therapy”, and no benefit to measuring oxygen by a central venous catheter

Not all monitoring or testing is bad, of course. Some home monitoring devices have supplanted their hospital or clinic equivalents because of the pandemic. Home sleep devices to diagnose disorders of sleep, like obstructive sleep apnea, are more often now the norm. This is because of concerns that PAP (positive air pressure) devices would spray COVID-19 particles in to the air. Whether or not this concern is justified, the use of home sleep monitoring devices has skyrocketed. I think this is a good thing, bringing more monitoring to more people since clinic study availability never quite met the demand, at least in the region where I work. If we look to the future, options for remote monitoring and wearable medical monitoring devices is certain to become cheaper and more available. Will these improve our health and improve disease treatment? Time will tell.

Postscript: Another reason to be cautious with handheld pulse oximeters has to do with their overestimation of oxygenation in dark skinned people. Read this JAMA article about the effect of skin melanization and pulse oximetry.

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Joe Alcock

Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine