The pathophysiology of ‘happy’ hypoxemia in COVID-19

Abstract

The novel coronavirus disease 2019 (COVID-19) pandemic is a global crisis, challenging healthcare systems worldwide. Many patients present with a remarkable disconnect in rest between profound hypoxemia yet without proportional signs of respiratory distress (i.e. happy hypoxemia) and rapid deterioration can occur. This particular clinical presentation in COVID-19 patients contrasts with the experience of physicians usually treating critically ill patients in respiratory failure and ensuring timely referral to the intensive care unit can, therefore, be challenging. A thorough understanding of the pathophysiological determinants of respiratory drive and hypoxemia may promote a more complete comprehension of a patient's clinical presentation and management. Preserved oxygen saturation despite low partial pressure of oxygen in arterial blood samples occur, due to leftward shift of the oxyhemoglobin dissociation curve induced by hypoxemia-driven hyperventilation as well as possible direct viral interactions with hemoglobin. Ventilation-perfusion mismatch, ranging from shunts to alveolar dead space ventilation, is the central hallmark and offers various therapeutic targets.

An emergency system for monitoring pulse oximetry, peak expiratory flow and body temperature of patients with COVID-19 at home: Development and preliminary application

“…shunting [2]. The results observed in Figure 6 are in line with that obtained by O'Carroll All rights reserved.…”

Hypoxemia Index Associated with Prehospital Intubation in COVID-19 Patients

“…In COVID-19 ARF, clinical signs may not adequately indicate severity [11]; thus, there is a need to explore other means of severity assessment. Outside the hospital, hypoxemia depth may be assessed by arterial blood gas analysis, especially since COVID-19 patients exhibit lower partial arterial oxygen pressure(PaO2) than SpO 2 [12]. However, during the COVID-19 pandemic, there may be a shortage of blood gas analysis medical devices for prehospital emergency services.…”

“…One peculiarity of respiratory SARS-CoV-2 infection is the presentation of a low respiratory rate (RR) increase despite severe hypoxemia reflected by low pulse oximetry (SpO 2 ) of variable depth depending on the stage of the disease, along with a lack of functional signs and respiratory distress signs [11]. This remarkable disconnect in rest between profound hypoxemia and proportional signs of respiratory distress was named "happy hypoxia" by Dhont et al [12].…”

Increased Red Cell Distribution Width Is Associated With Disease Severity in Hospitalized Adults With SARS-CoV-2 Infection: An Observational Multicentric Study

“…Studies have shown that in patients with Coronavirus Disease 2019 (COVID-19), the severity of hypoxemia is independently associated with in-hospital mortality and can reliably predict admission to the intensive care unit (4). Unfortunately, oxygen saturation is often dissociated from arterial hypoxemia as well as the sense of dyspnea in patients with COVID-19 (5,6). To this end, additional determinants of hypoxemia that are minimally invasive and clinicians' friendly are urgently needed for patients with COVID-19 (7).…”