Pre-brief
“Silent Hypoxemia” is a commonly used term for COVID- 19 patients who have profound hypoxemia but have good lung compliance and lack respiratory distress.
Guan et al reported dyspnea in only 18 % of the more than 1000 patients admitted for COVID-19 with significant hypoxemia.
Different pathophysiological mechanisms have been reported to explain the cause of hypoxemia in patients with COVID-19:
- Leftward move of the oxyhemoglobin dissociation curve.
- Intrapulmonary shunting from non-aerated lung tissues.
- Loss of the hypoxic pulmonary vasoconstriction mechanism.
- Intravascular microthrombi.
During these times, a patient with profound hypoxemia without respiratory distress is considered to have COVID-19 unless proved otherwise. Below we present a case of one such “Silent Hypoxemia”.
The Case
A 28 year-old-female with a history of HFrEF with a pacemaker presents with dizziness and fatigue. Her vitals were stable but had a SpO2 of 82 with a CXR showing b/l infiltrates without any obvious consolidation. COVID19 PCR test was negative but given her hypoxia and a relatively “happy” state, she was initiated on steroids, antibiotics, and COVID-specific therapies.
Day 3 – The patient did not respond to therapy with ongoing hypoxemia.
Day 4 – A Rapid Response for a panic attack in the setting of low SpO2 was activated. She was intubated with COVID-19 precautions. A BAL COVID-19 PCR test sent.
Day 5 – Despite mechanical ventilation, the patient remained hypoxic and hypoxemic. RT increased the PEEP which led to worsening oxygen saturation. POCUS was then performed as an intracardiac shunt was suspected.
POCUS Video Bubble study showing a sub-xiphoid 4 chamber view. A bubble study was performed which shows a significant right to left shunt.
Bubble Study and POCUS
- Intracardiac shunt should be suspected in patients with severe hypoxemia especially when SpO2 gets worse with high PEEP and low blood pressure.
- Bedside bubble study with agitated saline should be performed with a 4 chamber or subcostal view clearly visualizing the left and right atria. TEE can be performed for increased accuracy of the test or if transthoracic windows are poor.
- Bubbles will be first seen in the right atrium. If bubbles are seen in the left ventricle within 3 cardiac beats, it is suggestive of an intracardiac shunt.
- Bubbles seen after 3-5 cardiac cycles are suggestive of an intrapulmonary shunt.
Debrief
- “Silent hypoxemia” is commonly seen in COVID 19 patients.
- Non-COVID-19 ‘silent hypooxemia’ and hypoxemia can also exist in patients with intracardiac and intrapulmonary shunts.
- Not every patient with silent hypoxemia is COVID
References
Right-to-Left Shunts and Saline Contrast Echocardiography Tighe, Dennis A. et al.
CHEST, Volume 138, Issue 2, 246 – 248
