Only FDA-approved home pulse oximeters should be used by COVID-19 patients at risk for hypoxia who discharged. Smartphone devices do not give warnings of hypoxia that are accurate enough. Advise patients to look up approved devices on Google. Any saturation level of 92% or less requires urgent ED evaluation. Many COVID-19 patients with lung involvement cannot sense hypoxia, and it can be severe and occur rapidly. Merely instructing a patient to return if his breathing worsens is an insufficient warning.
The ICU technique of placing a hypoxic patient in a prone position is being widely used to care for COVID-19 patients in respiratory distress to improve oxygenation and possibly to avoid intubation. The COVID-19 pandemic has also precipitated a marked increase in home pulse oximetry use, and emergency physicians may be tasked with initiating the process.
Home pulse oximetry was previously used occasionally by patients with hypoxemia or conditions that could produce hypoxemia, usually chronic lung disease. An oxygen saturation below 94% is usually designated hypoxia, but a saturation below 88% is often the benchmark for those with chronic lung disease.
Patients with COVID-19 often suffer from hypoxemia at some time during their course, and detecting it is paramount for managing those who have been discharged after ED evaluation. Instructing patients on the proper use of an FDA-approved pulse oximeter is a relatively new mandate for emergency physicians.
Silent Hypoxia in COVID-19: Pathomechanism and Possible Management Strategy
Rahman A, Tabassum T, et al.
Mol Biol Rep.
2021;48(4):3863
Patients with COVID-19 can develop silent hypoxia in a rather unusual fashion. COVID infections can produce extremely low oxygen saturation levels, but many affected curiously lack dyspnea. This silent hypoxia is poorly understood, and its mechanism is unclear. These patients are at significant risk due to lack of dyspnea and even lack of overt tachypnea in the presence of severe hypoxia. Silent hypoxia occurs in 20-40 percent of COVID patients with pulmonary involvement.
The authors of this report describe a few impossible-to-understand reasons behind silent hypoxia in COVID-19. The authors speculate that the virus may affect the brain and nervous system or a lack of normally occurring hypoxic vasoconstriction may be present. My takeaway is that pulse oximetry is extremely important for managing these patients, especially those discharged from the ED.
Simply telling discharged COVID patients to return if they are experiencing worsening breathing problems may not be enough because rapid deterioration is common, but COVID patients with significant hypoxia may not feel shortness of breath or sense their dyspnea. Pulse oximetry seems to be one way to combat this unsensed deterioration in outpatients.
Remote Management of COVID-19 Using Home Pulse Oximetry and Virtual Ward Support
Greenhalgh T, Knight M, et al.
BMJ.
2021;372:n677
The initial illness advances insidiously for many patients who die of acute COVID-19, leading to pneumonia and the rapid development of the acute respiratory distress syndrome. This silent hypoxia occurs without clinically perceptible symptoms of dyspnea. COVID-19 targets the lungs, and a ventilation-perfusion mismatch is present due to intrapulmonary shunting, loss of lung perfusion regulation, intravascular microthrombi, and reduced lung compliance leading to alveolar collapse. Hypoxia can be severe, and the need for supplementary oxygen predicts a worse outcome. Patients can require a ventilator for weeks. The World Health Organization recently recommended pulse oximetry monitoring at home as part of overall management.
A home pulse oximeter costs about $50 to $80 and is relatively simple to use. Finger pulse oximeters are generally accurate and reliable, but the use of smartphone oximeters is discouraged. A pulse oximeter reading should be taken on a warm finger, with the patient resting and sitting upright. The device should be left in place to stabilize for a minute before confirming the reading. Falsely low readings can occur if the patient’s hands are cold, if he has poor perfusion due to hypotension or cardiac failure, or if the patient is wearing nail polish or artificial nails.
Readings may be falsely low in patients with severe anemia, sickle cell disease, or other hemoglobinopathies. Patients with Black or brown skin are three times as likely as those with white skin to have occult hypoxia by oximeter measurements. The pulse oximeter reading in those with dark skin can be in the normal range when hypoxemia is present. This occurs in about 12 percent of patients but usually only in those with dark skin with saturations below 90%.
These authors stated that the normal range of oxygen saturation is 94%-98% at rest in those without chronic lung disease. A saturation of 92% or lower in COVID-19 patients with normal lungs requires urgent referral to the hospital. Patients with chronic lung disease often have a baseline degree of hypoxia with a saturation of 88%-92%, so knowledge of what is normal for an individual patient is important to determine hospital referral. It is common for saturations to fall up to 3% at night.
Pulse oximetry home use is gaining popularity, and it provides real-time estimates of the arterial blood oxygen saturation in the range of 80%-100%. It gives an early warning of diminished capillary perfusion without the risk and time required for an arterial blood vessel puncture and use of the hospital’s lab. Oximetry relies on the concept that the concentration of an unknown substance (oxyhemoglobin or deoxygenated hemoglobin) dissolved in a solvent (blood) can be determined by the light absorption of these substances. The probe used in the process is a reusable clip containing two photodiodes that produce two wavelengths of light, a red light and an infrared light, which are revealed by a photodetector placed over a pulsatile vascular bed in the fingertip. The vascular bed analyzed by the home device is under the nailbed, not the fat pad.
Pulse oximetry is based on the principle that oxygenated hemoglobin and deoxygenated hemoglobin absorb red and infrared light differently. Pulse oximetry uses spectrophotometry to determine the proportion of hemoglobin saturated with oxygen in peripheral arterial blood. The amount of oxygenated blood is increased with each pulse. The ratio of light absorbance between oxyhemoglobin and the sum of oxyhemoglobin plus deoxyhemoglobin is calculated and compared with previously calibrated direct measurements of arterial oxygen saturation (SaO2) to establish an estimated measure of peripheral arterial oxygen saturation (SpO2).
Oxygenated hemoglobin absorbs greater amounts of infrared light and lower amounts of red light than does deoxygenated hemoglobin. Well-oxygenated blood with its higher amounts of oxygenated hemoglobin appears bright red on visual examination because it scatters more red light than does deoxygenated blood that absorbs red light. Deoxygenated blood with its higher amount of red light-absorbing hemoglobin does not appear bright red on visual inspection.
Prescription pulse oximeters are reviewed and sanctioned by the FDA, and they are tested to confirm accuracy before sale. Over-the-counter oximeters are sold directly to consumers and some are connected to a smartphone, but these are not FDA-reviewed and are not recommended for medical use. The physician should be aware that the patient’s home oximeter may not be an FDA-reviewed device. Check Google for a list of FDA-approved devices.
COVID-19 lung disease patients frequently demonstrate hypoxia out of proportion to dyspnea or distress, and that may increase the utility of pulse oximetry. Oxygen saturation is perhaps the most important indicator of respiratory function. One study found that home pulse oximetry monitoring identifies the need for hospitalization in initially nonsevere COVID-19 patients when a cutoff of SpO2 92% is used. (Acad Emerg Med. 2020;27[8]681; https://bit.ly/3CCnJ0o.) Half of patients who ended up hospitalized had SpO2 <92% without worsening symptoms.
Early Self-Proning in Awake, Nonintubated Patients in the Emergency Department: A Single ED’s Experience During the COVID-19 Pandemic
Caputo N, Strayer RJ, Levitan R
Acad Emerg Med.
2020;27(5):375
This article describes the benefit of placing an ED patient with COVID-19 hypoxia and a low oxygen saturation in the prone position. Hypoxia can be treated with supplemental oxygen often delivered with intubation and positive pressure ventilation, but merely placing the awake patient with ARDS in the prone position decreases the need for intubation and improves outcome. Proning is usually used with admitted patients, but it can be easily instituted in the ED.
The COVID-19 pandemic has produced an unusual condition that has confounded existing disease patterns. Many COVID-19 patients have a low oxygen saturation, often less than 90%, but are not in significant respiratory distress and appear clinically well. These patients have happy hypoxia. The authors of this study reported on using early proning of awake nonintubated hypoxic patients with COVID-19 (oxygen saturation less than 90%) who had no resolution with supplemental oxygen and proning’s effect on oxygenation.
Fifty adult patients with documented COVID-19 who presented to the ED with hypoxia (saturation less than 90%) not improving with supplemental oxygen and who were capable of self-proning were instructed to assume that position. Vital signs were obtained through a standard finger oximeter. The investigators evaluated a change in oxygen saturation prior to proning after five minutes of supplemental oxygen and after proning without a change in inspired oxygen. They included the rate of patients who were proned but then required intubation within 24 hours of ED presentation. Individuals were deemed to have failed proning if they had persistent saturations less than 90% with unresolved tachypnea or worsening of tachypnea with accessory muscle use, altered mental status, or hypercarbia on blood gas analysis. The authors determined the proportion of patients achieving an oxygen saturation of 93% or greater.
These patients were quite ill with a median oxygen saturation of 80% at triage. The saturations improved to 94% (90%-95%) in most patients after five minutes of proning. Thirteen patients (24%) failed to improve or maintain their oxygen saturation with proning. These 13 met the definition of respiratory failure plus clinical signs of respiratory distress within 24 hours of presenting to the ED and required endotracheal intubation.
Proning was combined with rotation. The regimens included 30-120 minutes in the prone position followed by 30-120 minutes in the left and then right lateral decubitus positions, followed by sitting upright. Many patients can prone themselves, and it has no cost and uses no additional personnel or ED resources.
These authors concluded that many patients with moderate to severe hypoxemia related to COVID-19 lung disease demonstrated an improvement in oxygen saturations after being placed prone. Early and frequent proning is recommended in the hope that it will delay or prevent intubation.
Positioning a patient face down on his anterior chest and abdomen to take advantage of physiologic changes can result in improved oxygenation through decreased V/Q mismatch. Its early use in the ED to improve oxygenation and prevent intubation makes sense, but this intervention is not widely used in the ED. The authors did not report the long-term benefit in this study, but it seemed to be helpful in the short term. Proning may be tried in the ED for those who are close to intubation, but they must be monitored closely in case of deterioration while in this position.
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FDA Instructions for Pulse Oximetry Home Use
Multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness and temperature, tobacco use, and nail polish. To get the best reading from a pulse oximeter:
- Follow the manufacturer’s instructions for use.
- Make sure the hand is warm, relaxed, and held below heart level. Remove any nail polish on that finger.
- Sit still and do not move the body part where the oximeter is located.
- Wait a few seconds until the reading stops changing and displays a steady number.
- Record the oxygen level and date and time so changes can be easily tracked and reported to physician.
- A pulse oximetry reading of 92% or less should prompt a patient to seek medical evaluation.
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Dr. Robertsis a professor of emergency medicine and toxicology at the Drexel University College of Medicine in Philadelphia. Read his past columns athttp://bit.ly/EMN-InFocus.
