Silent hypoxemia

Specialty: Respiratory.

• happy hypoxia
• happy hypoxia
• asymptomatic hypoxemia

Why it occurs

• Severe pneumonia due to SARS-CoV-2 (COVID-19) (the loss of pulmonary hypoxic vasoconstriction and the induction of local microthrombosis cause severe shunting and V/Q imbalance, initially maintaining normal lung compliance that prevents the sensation of dyspnea regulated by mechanorectors)
• Congenital right-to-left intracardiac shunt in adults (such as Eisenmenger syndrome or late-corrected tetralogy of Fallot, where the brain chronically adapts to low levels of PaO2 without triggering severe dyspnea at rest)
• Hereditary multiple pulmonary arteriovenous malformations (hereditary hemorrhagic telangiectasia or Rendu-Osler-Weber syndrome)
• Acute respiratory distress syndrome (ARDS) in the very early initial phase
• Exposure to high altitudes with partial chronic acclimatization (decrease in inspired oxygen pressure without disproportionate dyspneic ventilatory response).

Initial workup

Analytical arterial blood gases (exact determination of PaO2, SaO2, PaCO2 and alveolar-arterial oxygen gradient); Continuous pulse oximetry and constant monitoring; High-resolution chest computed tomography (CT); Bubble echocardiogram; CT angiography of pulmonary arteries.

Standard management

• High flow oxygen therapy — HFNC, high-flow nasal cannula, started at 40-60 L/min with FiO2 titrated to maintain oxygen saturation between 92-96%
• Dexamethasone — 6 mg orally or intravenously once daily for 10 days in COVID-19 pneumonia with oxygen requirements
• Enoxaparin (prophylactic dose of 40 mg subcutaneously per day, or therapeutic dose of 1 mg/kg every 12 hours if associated with suspected microthrombosis or PE).