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Sunday, May 16, 2021

Explained: The how and why of oxygen therapy for Covid-19 patients

A huge demand for oxygen has underlined its importance in Covid-19 management. What happens in the body that leads to some patients needing oxygen therapy? What is the protocol for such therapy?

Written by Kaunain Sheriff M | New Delhi |
Updated: May 5, 2021 10:37:34 am
Covid-19, Coronavirus India, Covid-19 Oxygen, Oxygen level covid-19, coronavirus covid oxygen shortage, indian exprss newsQueue to fill cylinders with medical oxygen at a plant in Prayagraj. (PTI)

The ongoing second surge in Covid-19 cases has seen a huge rise in the demand for supplemental oxygen. What makes the gas so vital in Covid-19 management?

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When does a Covid-19 patient need oxygen support?

A small proportion of Covid-19 patients need oxygen support, when shortness of breath progresses to a more acute condition. Most patients with Covid-19 have a respiratory tract infection, and in the most severe cases their symptoms can include shortness of breath. In a small proportion of such cases, this can progress to a more severe and systemic disease characterised by Acute Respiratory Distress Syndrome (ARDS).

How does Covid-19 trigger shortness of breath?

Shortness of breath occurs because of the way Covid-19 affects the patient’s respiratory system. The lungs enable the body to absorb oxygen from the air and expel carbon dioxide. When a person inhales, the tiny air sacs in the lungs — alveoli — expand to capture this oxygen, which is then transferred to blood vessels and transported through the rest of the body.

Respiratory epithelial cells line the respiratory tract. Their primary function is to protect the airway tract from pathogens and infections, and also facilitate gas exchange. And the SARS-CoV-2 coronavirus can infect these epithelial cells.

To fight such infection, the body’s immune system releases cells that trigger inflammation. When this inflammatory immune response continues, it impedes the regular transfer of oxygen in the lungs. Simultaneously, fluids too build up. Both these factors combined make it difficult to breathe. Low levels of oxygen triggered by Covid-19 are inflammatory markers, which include elevated white blood cell counts and neutrophil counts.

Is India witnessing more patients with shortness of breath?

Yes. Data with the National Clinical Registry for Covid-19 shows a new emerging trend during the second wave: shortness of breath is the most common clinical feature among symptomatic hospitalised patients at 47.5%, compared to 41.7% during the first wave. Simultaneously, other symptoms have dropped significantly compared to the first wave: dry cough (5.6% vs 1.5%); loss of smell (7.7% vs 2.2%); fatigue (24.2% vs 11.5%); sore throat (16% vs 7.5%); muscle ache (14.8% vs 6.3%).

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How many symptomatic people now require oxygen?

In India, as of Tuesday, 1.75% of the patients were in ICU beds, 0.40% were on ventilator, and 4.03% were occupying oxygen beds. Since the total active cases have now risen to 20,31,977, the number of patients requiring oxygen beds is significant.

On Monday, members of the national Covid-19 task force said hospital data shows that a significant 54.5% of hospital admissions during the second wave required supplemental oxygen during treatment. This was a 13.4-percentage-point increase compared to the previous wave between September and November, the data from 40 centres across the country shows. However, requirement of mechanical ventilation dropped during the second wave: to 27.8% of admitted patients from 37.3% during the first wave.

Dr Balram Bhargava, DG, Indian Council of Medical Research (ICMR), said there is limited data on why more patients are requiring oxygen, and this needs to be further studied. “This (more patients requiring oxygen) could be explained by the fact that due to the sudden surge of cases there is a panic, people wanted to get admitted to hospitals, therefore oxygen requirement suddenly shot up. But there is limited data from hospital settings and more will have to be looked at. However, oxygen [remains] an important tool in the management of Covid-19 disease, particularly when oxygen saturation has fallen,” Bhargava said.

People purchasing oxygen cylinders for serious home-quarantined patients in Lucknow. (Express Photo: Vishal Srivastav)

In what conditions is oxygen used in Covid-19 clinical management?

According to the clinical management protocol, a person is suffering from moderate disease when he or she is diagnosed with pneumonia with no signs of severe disease; with the presence of clinical features of dyspnea (shortness of breath) and/or hypoxia (when the body is deprived of adequate oxygen supply at the tissue level); fever, cough, including SpO2 (oxygen saturation level) less than 94% (range 90-94%) in room air.

In moderate cases, oxygen therapy is the primary form of treatment: the target is to achieve 92-96% SpO2, or 88-92% in patients with chronic obstructive pulmonary disease. The devices for administering oxygen in moderate disease are nasal prongs, masks, or masks with breathing/non-rebreathing reservoir bags, depending on requirement. The protocol also recommends awake proning (having patients lie on their stomachs) as a rescue therapy to increase oxygenation.

Severe cases are defined in three categories: severe pneumonia, acute respiratory distress syndrome, and sepsis. The clinical management protocol recommends oxygen therapy at 5 litres/min. When respiratory distress and/or hypoxemia of the patient cannot be alleviated after receiving standard oxygen therapy, the protocol recommends that high-flow nasal cannula oxygen therapy or non-invasive ventilation can be considered. “Compared to standard oxygen therapy, High Flow Nasal Cannula Oxygenation (HFNO) reduces the need for intubation. Patients with hypercapnia (exacerbation of obstructive lung disease), hemodynamic instability, multi-organ failure, or abnormal mental status should generally not receive HFNO,” the protocol says.

Does a patient always show Covid symptoms when their oxygen levels drop?

No. According to the FAQs on Covid-19 from AIIMS e-ICUS, sudden deaths have been reported at presentation to the emergency department, as well as in hospital. AIIMS has said that the reasons that have been proposed include a sudden cardiac event, preceding “silent hypoxia” that went unnoticed, or due to a thrombotic complication such as pulmonary thromboembolism.

In silent hypoxia, patients have extremely low blood oxygen levels, yet do not show signs of breathlessness. “In patients with silent hypoxia, the amount of oxygen carried in our blood, otherwise known as blood oxygen level, is lower than expected compared to the other vital signs. Silent hypoxia is not usually an early symptom to occur in Covid-19 patients. They frequently arrive at the emergency room for other reasons, such as muscle aches, fatigue, fever and cough. Typically, when a patient begins to demonstrate silent hypoxia, they already have other Covid-19 symptoms and may be in critical condition,” the American Lung Association says.

It recommends that instead of solely relying on a pulse oximeter, the patient should monitor for gastrointestinal symptoms, muscle soreness, fatigue, and changes in taste and smell as well as the more common initial symptoms such as fever, cough, and shortness of breath.

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