The Fundamentals of Respiratory Physiology to Manage the COVID-19 Pandemic: An Overview

Abstract

The growing coronavirus disease (COVID-19) crisis has stressed worldwide healthcare systems probably as never before, requiring a tremendous increase of the capacity of intensive care units to handle the sharp rise of patients in critical situation. Since the dominant respiratory feature of COVID-19 is worsening arterial hypoxemia, eventually leading to acute respiratory distress syndrome (ARDS) promptly needing mechanical ventilation, a systematic recourse to intubation of every hypoxemic patient may be difficult to sustain in such peculiar context and may not be deemed appropriate for all patients. Then, it is essential that caregivers have a solid knowledge of physiological principles to properly interpret arterial oxygenation, to intubate at the satisfactory moment, to adequately manage mechanical ventilation, and, finally, to initiate ventilator weaning, as safely and as expeditiously as possible, in order to make it available for the next patient. Through the expected mechanisms of COVID-19-induced hypoxemia, as well as the notion of silent hypoxemia often evoked in COVID-19 lung injury and its potential parallelism with high altitude pulmonary edema, from the description of hemoglobin oxygen affinity in patients with severe COVID-19 to the interest of the prone positioning in order to treat severe ARDS patients, this review aims to help caregivers from any specialty to handle respiratory support following recent knowledge in the pathophysiology of respiratory SARS-CoV-2 infection.

The oxygen dissociation curve of blood in COVID-19

“…Astonishingly, we could find only four short papers with measurements of oxygen affinity in patients with COVID-19 and two commenting letters (PubMed and Google Scholar); an increase in hemoglobin oxygen affinity was detected only in one investigation. Additionally, a review contains only a general description of the oxygen dissociation curve and possible contrary effects (hypocapnia vs. fever), but no data ( 1 ).…”

Hyperbaric Oxygen Therapy For Hospitalized COVID-19 Patients With Moderate To Severe Hypoxia

“…24 Coagulopathic mechanisms leading to microemboli and hemoglobin poisoning affecting its oxygen-carrying capacity may also play a role. [25][26][27] HBOT is thought to reduce in ammatory cytokines and tissue in ammation, as seen in the treatment of radiation injuries, soft tissue wounds, infections, [16][17][18] and therefore, it may also reduce in ammatory cytokines and tissue in ammation seen in COVID-19.…”

Hyperbaric oxygen therapy in overweight and obese patients with COVID‑19

“…Hypoxemia in patients with COVID-19 has been shown to be caused by various mechanisms, mainly hypoventilation, impaired diffusion, shunting in hypoventilated areas and a ventilation-perfusion mismatch. The primary cause of hypoxemia is ventilation-perfusion mismatch due to a lack of ventilation in certain areas, even with adequate blood perfusion of the region (24). Additionally, microemboli are a known complication in patients with COVID-19, which can compromise lung perfusion to regions with a low ventilation-perfusion ratio (24)(25)(26).…”

“…The primary cause of hypoxemia is ventilation-perfusion mismatch due to a lack of ventilation in certain areas, even with adequate blood perfusion of the region (24). Additionally, microemboli are a known complication in patients with COVID-19, which can compromise lung perfusion to regions with a low ventilation-perfusion ratio (24)(25)(26). As the level of hypoxemia has been shown to be associated with mortality in hospitalized patients with COVID-19, it may serve as a prognostic indicator (24,27,28).…”

“…Additionally, microemboli are a known complication in patients with COVID-19, which can compromise lung perfusion to regions with a low ventilation-perfusion ratio (24)(25)(26). As the level of hypoxemia has been shown to be associated with mortality in hospitalized patients with COVID-19, it may serve as a prognostic indicator (24,27,28).…”