The COVID-19 pandemic is a rapidly evolving global health crisis. The condition COVID-19 develops as a result of infection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and can cause serious damage to the respiratory system. Damage to the respiratory system can lead to hypoxemia, which is a potentially life-threatening state of low blood oxygen levels.
The incidence and prevalence of hypoxemia in patients with COVID-19 have not been readily documented. Mortality estimates related to hypoxemia are not easily made as research into COVID-19 is on-going and developing along with the pandemic, and deaths resulting from COVID-19 infection are complex and multifactorial.
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What is COVID-19?
COVID-19 (standing for coronavirus disease 2019) is a respiratory disease associated with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a novel coronavirus identified in 2019.
It has a high rate of morbidity and mortality and stopping the spread of the viral infectious disease is complicated by the fact that carriers of the virus can be asymptomatic, meaning they can spread the disease without knowing they have it.
Coronaviruses are present among many animals, and some can infect humans, but SARS-CoV-2 had not been seen in humans before the outbreak in 2019. COVID-19 is spread through respiratory droplets and aerosols when people sneeze, cough, or interact closely with other people.
Those with underlying conditions or advanced age are more at risk of serious complications from COVID-19. There is currently no treatment or cure for COVID-19, and any treatment given to those with COVID-19 is supportive, meaning the person is aided in their breathing and other vital functions while the body fights off the infection itself.
What is hypoxemia?
Hypoxemia is a condition in which there are low levels of oxygen in the blood. It is not to be confused with hypoxia, which is the state of low oxygen levels in the tissues.
Normal blood oxygen levels are usually within the range of 75 to 100 millimeters of mercury (mm Hg).
Hypoxemia can occur because of low oxygen levels in the air, the inability of the lungs to take in and send oxygen around the body, or the inability of the bloodstream to travel to the lungs or take oxygen from the lungs to the rest of the body.
Asthma, chronic obstructive pulmonary disease (COPD), emphysema and acute respiratory distress syndrome (ARDS) are all chronic pulmonary diseases that impair the function of the lungs and reduce the amount of oxygen in the blood.
Recent statistics show that 14 percent of COVID-19 cases are severe, with two-thirds of severe cases being fatal.
COVID-19 is another cause of hypoxemia, which can lead to ARDS in severe cases.
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Hypoxemia in COVID-19
COVID-19 is characterized by the fact that the virus affects multiple types of organs. However, the respiratory system is the worst affected part of the body in infected individuals.
Hypoxemia is associated with more inflammatory markers occurring as a result of COVID-19, such as elevated white blood cell counts, neutrophil counts, and C-reactive protein levels. This meant that acute inflammation in the respiratory system might be responsible for the damage to the lungs and the consequent hypoxemia.
Studies have suggested that more rapid breathing and a decrease in oxygen saturation are indications that the lungs are not allowing carbon dioxide and oxygen to pass to and from the blood to full efficacy, and there is a risk of hypoxemia.
However, there has been a distinct disparity identified between the level of hypoxemia and the proper functioning of the respiratory system. Many patients can be experiencing hypoxemia but have relatively normal respiratory mechanics. This has been dubbed ‘silent hypoxemia’.
The risk of silent hypoxemia is that patients will remain untreated for hypoxemia, or will not seek treatment at all, because they are unaware they are experiencing low blood oxygen levels. This means that, although the lungs may be functioning normally, other organs in the body will not be receiving the amount of oxygen they need.
A 2020 study reported that patients experiencing moderate to severe cases of COVID-19 with SpO2 values of over 90 percent with supplemental oxygen have a very high chance of survival.
This study also suggested that blood oxygen levels are an important clinical measurement in predicting outcomes of COVID-19, and those with blood oxygen levels of 90 percent or less, even with supportive, supplementary oxygen, have an increased risk of death.
Healthcare providers have been giving invasive mechanical ventilation to support a patient’s breathing through tracheal intubation early on in their COVID-19 treatment plans. This decision to intubate early was made because patients with COVID-19 can deteriorate very quickly due to hypoxemia and because it can take a significant amount of time to prepare and perform intubation on COVID-19 patients.
However, it has been found that hypoxemia before intubation is associated with a higher risk of cardiac arrest. Additionally, waiting to intubate a patient may make the intubation process dangerous or lethal to the patient.
Opinions differ on whether early intubation is better for the patient than delayed intubation or avoiding intubation at all. Other options for enhanced respiratory support in severe cases include high flow nasal cannula (HFNC), noninvasive positive-pressure ventilation (NIPPV) and extracorporeal membrane oxygenation (ECMO).
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Summary
Hypoxemia is the state of having low blood oxygen levels. COVID-19 can lead to hypoxemia as a result of damage done to the lungs through inflammatory responses to the viral infection in the respiratory system.
Studies have suggested that those experiencing hypoxemia have a higher mortality risk than those who are able to maintain healthy blood oxygen levels. There are challenges for healthcare providers in spotting which patients may be at risk of hypoxemia, as some patients may present with normal lung function and no outward signs of distress, but their blood oxygen levels may be low.
More research is needed into the relationship between COVID-19 and hypoxemia to accurately give advice and guidance on how to recognize and treat hypoxemia in patients with COVID-19.
References
Further Reading
Assessing COVID-19 vaccine effectiveness against long COVID