Pulse oximetry

Pulse oximetry, done by an instrument called the pulse oximeter, measures the pulse rate, and the percentage saturation of oxygen in the blood. Pulse oximetry is a useful tool for self-monitoring especially in the situation of the COVID pandemic.

The following are are important points to be kept in mind while doing and interpreting pulse oximetry.

MEASUREMENT PARAMETERS

The pulse oximeter measures the pulse rate, blood oxygen saturation (SpO2), the perfusion index (PI), and in some of the machines, (not all) the respiratory rate (RR).

The pulse rate can normally show a wide variation of 60-110 beats per minute (bpm). It can be further higher in people with anxiety, just after physical activity, or in children.

The oxygen saturation (SpO2) should ideally be maintained >94% at all times.

The perfusion index (PI) shows the blood flow to the finger. It can range between 0.02-20% in the population depending on weak to strong pulse, but for a particular person, it usually has a short, given range which can be determined by repeated readings.

The respiratory rate (RR) is normally between 12-20 breaths/minute but can increase during physical activity. An RR >24 is considered abnormally high indicating shortness of breath, while RR >30 requires immediate oxygen support and medical assistance/hospitalization.

pulse oximetry

TECHNIQUES

Pulse oximetry should be taken in the sitting position with the hand kept at heart level. If been engaged in physical activity, rest for 5 minutes before taking the reading. The index or middle finger should be properly inserted in the pulse oximeter (not partially, upside down or tilted sideways). The oximeter should close appropriately (not too tightly pressed upon the finger, and not too loosely due to damaged spring or closing levers).

Once put on, wait for the waves to be regular, and the reading values to stabilize. This can take up to 30-60 seconds. The highest stable reading of SpO2 should be considered.

Low battery, irregular waves, and rapidly fluctuating readings can imply possible inaccuracy. Constant movement, shaking the finger, or even tremors/shivering can affect the accuracy of the readings. Nail polish and varnishes, especially if dark should preferably be removed. Readings may be inaccurate in the lying position or if hands are cold.

FREQUENCY AND INTERPRETATION

For people who have contact history or symptoms suggestive/suspicious of COVID, or those who are confirmed COVID-positive asymptomatic or symptomatic cases, 4-6 hourly pulse oximetry is recommended. SpO2 value of >94% at all times is considered satisfactory. Lower values are an alarm sign.

For COVID patients being treated in a non-hospitalized/home care setting, pulse oximetry can be done in combination (just before and after) with the 6-minute walk test (performed at normal walking pace), at least once daily. A drop in SpO2 by 5% or more, or absolute fall to <94% after the test is an alarm sign and indicates ‘happy hypoxia’ (masked oxygen deficiency). One should stop walking if experiencing any lightheadedness, breathlessness, or tiredness; Elderly>60 years can perform shorter 3-minute tests).

Lying on one’s belly (prone position) with a pillow under thighs and tummy, for about one hour and taking few deep breaths every 10-15 minutes, can sometimes bring up the oxygen saturation (conscious proning) and is recommended 2-3 times a day.

If the SpO2 value is consistently at 94% or lower in a day, it is recommended to have a medical consultation immediately. If a person is also showing breathlessness or increased respiratory rate >24, arrangement for giving oxygen should be made by shifting to the hospital or if a bed is not immediately available, in an appropriate COVID-care setup, or at home.

SpO2<90% should be considered as an urgency and priority for oxygen therapy and hospitalization.

For people suffering from chronic respiratory diseases without COVID, it is advised to perform pulse oximetry once daily or as advised by their physician. For them, SpO2 cut-off values are typically lower than that of the rest of the population (ideal 92% and above, to maintain with therapy at 88-92%, and oxygen to be administered at <88%).