**3.5 Hypoxia**

Several COVID-19 patients appeared to have severely low blood oxygen saturation levels [39], leading to hypoxia which causes damage to the tissues [40]. Meanwhile, these patients do not get enough oxygenation via the blood, COVID-19 individuals with hypoxia often do not show much respiratory distress, but they feel alert, and can easily talk [39]. Hence, hypoxia in COVID-19 individuals is often known as "happy"

#### *Neurological Effects of COVID-19 and Its Treatment/Management DOI: http://dx.doi.org/10.5772/intechopen.105730*

or "silent" hypoxia due to its minimal additional effects [39]. In a study by Mortaz et al. COVID-19 participants' RBC had higher amounts of intracellular NO (nitric oxide). This is not due to hypoxia per se, but it could provide protection against the hypoxia reported in COVID-19 patients. Constitutive NO generation in RBCs is mostly dependent on NOS during health, although NO production in hypoxic settings may entail nitrite reduction by deoxyhemoglobin carbonic anhydrase and/ or eNOS itself. Also, COVID-19 participants' RBC had higher amounts of intracellular NO [39].
