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Silent Hypoxia - "Should I be worried?"

In the past few weeks, you may have read about ‘silent’/ ‘happy’ hypoxia or received distressed calls from your parents asking you to buy a pulse oximeter and/ or oxygen concentrator, just in case “the worst” happens.


Before we consider further, let us first understand the condition of hypoxia and its cause: COVID-19 attacks the lungs directly, affecting the ability of the alveoli (those tiny balloon-like structures) to take up oxygen and remove carbon dioxide. As the immune system fights the infection, fluid as well as pus from dead white blood cells is produced, leading to pneumonia.


Hypoxia then arises when oxygen levels drop, frequently to below 95%. Most people with ‘typical’ pneumonia experience shortness of breath. But the oddest thing about COVID-19 pneumonia? Not all patients had trouble breathing and a great many appeared well even though their chest X-rays were extremely abnormal - hence the silent and seemingly happy patient that is confounding doctors and defying biology.


𝗪𝗵𝘆 𝘄𝗲𝗿𝗲 𝘁𝗵𝗲𝗿𝗲 𝗻𝗼 𝘄𝗮𝗿𝗻𝗶𝗻𝗴 𝘀𝗶𝗴𝗻𝘀 𝗼𝗳 𝗶𝗺𝗽𝗲𝗻𝗱𝗶𝗻𝗴 𝘀𝗲𝘃𝗲𝗿𝗶𝘁𝘆?


Several factors may contribute to the phenomenon. One of them is fever, a prominent feature of COVID-19, which may blunt the ability of the body to respond to low oxygen levels. Experts also believe that in the early stages, gas exchange at the alveoli continues with little issue. Because of minimal carbon dioxide increase, there is no shortness of breath - at least, not yet.


Over time, as oxygen supply becomes inadequate and carbon dioxide levels excessive, the patient breathes harder and faster to compensate for the gas mismatch - without being aware of it. This causes the alveoli to collapse. By the time breathing difficulties are noticeable, the patient would already require use of a mechanical ventilator in hospital.


The potential speed of deterioration brings us to the question of whether we should agree with our parents’ suggestions to equip ourselves, whilst considering some salient points:


First and foremost, ‘silent’ or ‘happy’ hypoxia affects only those with COVID-19, and having the infection does not mean it will definitely occur. Most data show that out of 10 COVID-19 patients, about 3 present to the hospital with hypoxia minus shortness of breath.


Having said that, there is no way of predicting the likelihood of getting silent hypoxia. So how can COVID-19 patients monitor themselves to avoid abrupt worsening?


One easily accessible item enables this - a pulse oximeter. This device is the mainstay in non-invasive oxygen saturation (SpO2) monitoring and can be obtained from almost any pharmacy.


A pulse oximeter is a small, clip-like device that is almost as simple to use as a thermometer. When attached to the fingertip, harmless infrared light beams pass through the skin to check how well oxygen binds to red blood cells. 2 readings are acquired: oxygen saturation and heart rate.


According to the UK’s National Health Service, the following people will benefit most from pulse oximetry monitoring: those diagnosed with COVID-19 AND are either aged 65 and above, or if below 65 years old, are identified as being clinically vulnerable (those at higher risk of severe worsening tend to have lung disease, heart disease, are obese or are active smokers).


If you do decide to buy one, be aware that correct technique as well as appropriate application matters. The accuracy of a pulse oximeter is affected by various factors, such as skin pigmentation and thickness. Even a very cold finger could distort readings. Plus while it is precise when oxygen levels are high, accuracy starts to drop below 90% and reliability worsens at readings below 80%.


Although there is no specific golden number for SpO2 readings, a range of 95 to 100% is widely accepted to be healthy levels. Ensuring that readings are consistent is equally important.


And as for oxygen concentrators, there is only one thing the public should know: these should not be used without medical supervision. In other words, unless you have been told by your doctor to get one, an oxygen concentrator is highly unnecessary, and inappropriate use could do more harm than good.


Ultimately, the decision to get either item depends largely on true need: a pulse oximeter is highly recommended for COVID-19 positive patients who have opted to isolate at home whereas oxygen concentrators are certainly beneficial IF they are medically prescribed.


To make it easier for Mom and Dad to take in all this information, simply share these take-home messages with them

  1. A pulse oximeter should not be used to detect/ diagnose COVID-19 - a PCR test is still the most accurate diagnostic tool

  2. An SpO2 reading of less than 95% does not necessarily mean you have COVID-19 - this may occur in people with asthma and certain heart conditions

  3. Never rely on SpO2 levels alone - watch out for other unusual signs like progressive weakness and continue monitoring body temperature (persistent fever is concerning)

  4. For hypertensive patients, blood pressure (BP) and heart rate (HR) are also useful indicators of worsening disease - if BP levels start elevating or HR exceeds 100, get help.

  5. If ever unsure, ask your doctor or pharmacist - never rely on unverified information such as forwarded messages by non-medical professionals.

For professional counselling, talk to our pharmacists today!

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