Why “Happy Hypoxemia” shouldn’t make you happy?
The COVID-19 pandemic has not only slowed the pace of our lives but also brought some seemingly unusual clinical findings that remain largely unclear to the medical community.
In this blog, I will be discussing one such topic that I found to be interesting yet very critical for the understanding of all healthcare providers which is “Happy Hypoxemia” also called the “Silent Hypoxemia”.
Let’s begin by understanding the terms hypoxia and hypoxemia which are most often interchangeably used.
Hypoxia is a state when the supply of oxygen is insufficient or lower than the normal levels, which eventually affects our daily life activities. Hypoxemia however is a state when there is a low level of oxygen in the blood vessels called arteries.
The common symptoms of hypoxia and/or hypoxemia include shortness of breath(SOB), rapid respiratory rate (RR), and rapid heart rate (HR). The extreme symptoms include confusion, inability to communicate, coma, or even death.
The quick diagnosis of hypoxia and/or hypoxemia is done using a simple device called “Pulse Oximeter”. However, for a clear picture of the actual change in partial pressures of both oxygen versus carbon-dioxide levels the “Arterial Blood Gas Analysis” (ABG Report) is recommended, and if necessary lung functioning is measured using the “Pulmonary Function Tests” (PFT).
In most cases, hypoxia and/or hypoxemia are controllable when the sensation of change in breathing (Dyspnea) experienced or reported by the patient has been immediately recognized by the healthcare provider.
Once the symptom of dyspnea has been recognized its effective management through the delivery of supplemental oxygen using a simple face mask or nasal cannula is administered. In very critically ill patients advanced management is required using mechanical ventilation (intubation) through procedures like tracheostomy or endotracheal methods.
If this was really so simple, then why are physicians and healthcare providers so concerned about the “Happy Hypoxemia” phenomenon.
The questions and concerns arise because of the baffling presentations among some COVID-19 affected individuals.
Hence, the SPO2 level readings (oxygen saturation) should be interpreted with extreme caution among COVID-19 patients because of the possibility of normal SPO2 to be present despite an altered PaO2 (partial pressure of oxygen in arterial blood)and PaCO2 (partial pressure of carbon dioxide in arterial blood) levels.
The pathophysiological determinants underlying the possible mechanisms leading to hypoxia and/or hypoxemia among COVID-19 patients are really strange and more so hard to believe.
A study by Sebastiaan et al.,2020 discusses the arterial hypoxemic changes to occur as a result of intrapulmonary shunting, dysregulated hypoxic pulmonary vasoconstriction, impaired lung diffusion, and formation of intravascular microthrombi among these individuals.
Thus during the initial stages of the virus infection, the respiratory center in the brain is unable to sense or detect any of these arterial hypoxemic changes. The individual appears to be all normal, moving around within the hospital ward, talks to his physician during the rounds, or even scrolls through his mobile phone. Basically the patient is all “Happy” and in a state of absolute “Wellbeing”.
It is exactly at this happy phase of a person where the healthcare providers need to cautiously cross-examine the arterial oxygen changes very minutely as the symptom of dyspnea would be varied with an altered oxygen-sensing mechanism.
In a study by Guan et al.,2020 only 18.7% out of 1099 hospitalized patients with COVID-19 had dyspnea despite low levels of the partial pressure of arterial oxygen to that of a fraction of inspired oxygen (PaO2/FiO2 or P/F ratio). “Happy Hypoxemia” induced by COVID has implications on the health of the individual.
A detailed understanding of respiratory physiology can help in early screening, identification, and delivery of timely treatment among patients.