The condition “is especially bewildering to physicians as it defies basic biology,” said Martin J. Tobin, MD, Loyola Medicine and Edward J. Hines Jr. VA Hospital pulmonologist and critical care specialist, and professor, Loyola University Chicago Stritch School of Medicine. Dr. Tobin is lead author of the study, “Why COVID-19 Silent Hypoxemia is Baffling to Physicians,” appearing recently in the online American Journal of Respiratory and Critical Care Medicine.
“In some instances, the patient is comfortable and using a phone at a point when the physician is about to insert a breathing (endotracheal) tube and connect the patient to a mechanical ventilator,” said Dr. Tobin, “which while potentially lifesaving carries its own set of risks.”
The study included 16 COVID-19 patients with very low levels of oxygen (as low as 50%; normal blood oxygen saturation is between 95 and 100%), without shortness of breath or dyspnea, and found that “several pathophysiological mechanisms account for most, if not all, cases of silent hypoxemia. This includes the initial assessment of a patient’s oxygen level with a pulse oximeter.
“While a pulse oximeter is remarkably accurate when oxygen readings are high, it markedly exaggerates the severity of low levels of oxygen when readings are low,” said Dr. Tobin. “Another factor is how the brain responds to low levels of oxygen. As oxygen levels drop in patients with COVID-19, the brain does not respond until oxygen falls to very low levels—at which point a patient typically becomes short of breath,” he said.
In addition, more than half of the patients had low levels of carbon dioxide, which may diminish the impact of an extremely low oxygen level.
“It is also possible that the coronavirus is exerting a peculiar action on how the body senses low levels of oxygen,” said Dr. Tobin, which could be linked to the lack of smell, experienced by two-thirds of COVID-19 patients.
While acknowledging that further research is needed, the study concludes that “features about COVID-19 that physicians find baffling become less strange when viewed in the light of long-established principles of respiratory physiology.”
“This new information may help to avoid unnecessary endotracheal intubation and mechanical ventilation, which presents risks, when the ongoing and much anticipated second wave of COVID-19 emerges,” said Dr. Tobin.
To learn more about Loyola Medicine, visit loyolamedicine.org.
About Loyola Medicine Loyola Medicine, a member of Trinity Health, is a nationally ranked academic, quaternary care system based in Chicago’s western suburbs. The three-hospital system includes Loyola University Medical Center, Gottlieb Memorial Hospital and MacNeal Hospital, as well as convenient locations offering primary care, specialty care and immediate care services from more than 1,800 physicians throughout Cook, Will and DuPage counties. Loyola is a 547-licensed-bed hospital in Maywood that includes the William G. & Mary A. Ryan Center for Heart & Vascular Medicine, the Cardinal Bernardin Cancer Center, a Level 1 trauma center, Illinois’s largest burn center, a certified comprehensive stroke center and a children’s hospital. Loyola also trains the next generation of caregivers through its academic affiliation with Loyola University Chicago’s Stritch School of Medicine and Marcella Niehoff School of Nursing. Gottlieb is a 254-licensed-bed community hospital in Melrose Park with the newly renovated Judd A. Weinberg Emergency Department, an adult day care program, the Gottlieb Center for Fitness, the Loyola Center for Metabolic Surgery and Bariatric Care and the Loyola Cancer Care & Research facility at the Marjorie G. Weinberg Cancer Center. MacNeal is a 374-licensed-bed teaching hospital in Berwyn with advanced medical, surgical and psychiatric services, acute rehabilitation, an inpatient skilled nursing facility and a 68-bed behavioral health program and community clinics. Loyola Medical Group, a team of primary and specialty care physicians, offers care at over 15 Chicago-area locations. For more information, visit loyolamedicine.org.
About Trinity Health
Trinity Health is one of the largest multi-institutional Catholic health care delivery systems in the nation, serving diverse communities that include more than 30 million people across 22 states. Trinity Health includes 92 hospitals, as well as 106 continuing care locations that include PACE programs, senior living facilities and home care and hospice services. Its continuing care programs provide nearly 2.5 million visits annually. Based in Livonia, Michigan, and with annual operating revenues of $19.3 billion and assets of $27 billion, the organization returns $1.2 billion to its communities annually in the form of charity care and other community benefit programs. Trinity Health employs about 125,000 colleagues, including about 7,500 employed physicians and clinicians. For more information, visit www.trinity-health.org.
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