Difference between SpO2 Scale 1 and 2: Understanding Oxygen Saturation Scales

In the US, the SpO2 scale 1 prevails as the guideline, but in the United Kingdom (UK), two SpO2 scales exist: Scale 1, used with the majority of individuals, and Scale 2, used when an individual receives a diagnosis of hypercapnic respiratory failure or exhibits an increased risk of developing it.

Why the two separate scales? A 2013 research study from David Moore published in the journal Nursing Standards shows that individuals diagnosed with chronic obstructive pulmonary disease (COPD) experience an increased risk of developing acute hypercapnic respiratory failure (AHRF) if administered high-concentration uncontrolled oxygen, something inappropriate to their condition.


Chronic Obstructive Pulmonary Disease

The term chronic obstructive pulmonary disease refers to a disease group involving blockage of airflow and breathing issues. Commonly known diseases such as asthma, chronic bronchitis, and emphysema fall into the COPD category. Doctors have diagnosed about 16 million individuals in the US with a form of COPD. Clinicians suspect many people with COPD go undiagnosed. Although medical science can’t cure COPD, doctors can treat the diseases within the COPD group.

The most common symptom of any form of COPD involves shortness of breath during normal activity, such as walking while doing errands or climbing stairs. Research links COPD with smoking tobacco. Even those who quit smoking experience increased COPD risk. Other environmental influencers include regular exposure to air pollution at home or work. A family history of developing a disease within those in the COPD group increases the likelihood of developing it. Developing a respiratory infection, such as pneumonia, also increases COPD risk.

A doctor determines whether a patient experiences COPD using a spirometry breathing test. Once diagnosed, treatment begins. Both medicine and supplemental oxygen number are among the items a doctor may prescribe, as well as a custom pulmonary rehabilitation program. The doctor typically also prescribes a regular vaccination program that includes annual vaccinations for flu and pneumonia. Additionally, the doctor directs the patient to quit smoking and avoid environmental air pollutants.


Oxygen Therapy in a Prehospital Setting

The supplemental oxygen used in oxygen therapy, combined with medicine and the patient’s pulmonary rehabilitation program, can help the individual manage their disease so they can participate in normal, everyday activities without shortness of breath.

This daily oxygen therapy does not attempt to establish the typical oxygen saturation of a normal, healthy individual. Instead, healthcare practitioners use target saturations of 88 percent to 92 percent for individuals with damaged lungs. For people with COPD, appropriately titrated oxygen therapy prevents future acute exacerbations. 


How SpO2 Scale 1 and 2 Differ from Each Other

In the UK, the National Early Warning Score or NEWS2 system means medical practitioners use two oxygen saturation measurement scales. Let’s look at how they differ.

SpO2 Scale 1 for everyday pulse oximetry measurement

SpO2 scale 1 refers to the existing SpO2 scale used every day. This scoring system applies in most situations and is determined using pulse oximetry via a noninvasive measuring device that slips over the finger, foot, or onto the forehead when monitoring an infant during the birthing process.

On scale 1, we consider a normal reading for oxygen saturation to fall within the parameters of 95 to 100 percent. With any value below 90 percent, we consider the person in need of supplemental oxygen.

SpO2 Scale 2 to assess patients with hypercapnic respiratory failure

SpO2 scale 2 refers to a SpO2 scoring system developed for individuals with an existing diagnosis of hypercapnic respiratory failure or COPD. Used in a clinical setting, this second scale adjusts the desired oxygen saturation to a lower level falling within 88 to 92 percent. If a blood gas analysis reveals the patient has a hypercapnic respiratory failure or an acute exacerbation of COPD, but they have not had a prior diagnosis of it, the clinician would also apply this second scale.


Adjusting the National Early Warning Score from NEWS to NEWS2 to Determine Acute-Illness Severity 

The creation of a second scale for SpO2 also resulted in the updating of the NEWS scoring system. The UK medical industry now uses the National Early Warning Score (NEWS) and NEWS2 systems. Each contains the same six measurements for vital indicators of health:

  • Level of consciousness or confusion
  • Oxygen saturation
  • Pulse rate
  • Respiration rate
  • Systolic blood pressure
  • Temperature

The UK medical community developed the NEWS2 scoring system for use with individuals aged sixteen years old or older.

Apply the SpO2 scoring scale 2 in cases when admitting an individual as a patient and when the patient has the following:

  • Prior blood gas analysis score indicates the need.
  • Current blood gas test score indicates the need.
  • Existing diagnosis includes COPD.
  • Existing diagnosis includes hypercapnic respiratory failure.

Otherwise, apply SpO2 scale 1.

The National Early Warning Score helps prevent clinical deterioration, which can lead to in-patient morbidity and mortality. Early signs of clinical deterioration include changes in respiratory rate, oxygen saturation, diastolic and systolic blood pressure, temperature, heart rate, and conscious/mental status.


Properly Applying SpO2 Scale 2

To properly apply the SpO2 scale 2, note the decision to use the second scale in the patient's clinical chart. Cross out whichever scale does not apply on the measurement recording sheets in the patient chart. This ensures the various nurses and physicians will opt for the correct scale.

The updated SpO2 scale, as depicted on the National Early Warning Score chart, provides an area to record whether a patient’s readings refer to their natural, unassisted breathing or their readings while receiving oxygen. It also offers specific areas for the recording of any oxygen delivery device used and the rate of oxygen delivery.

The amendments to SpO2 scale 2 ensure that patients who need supplemental oxygen can more easily meet satisfactory oxygen saturations accounting for their reduced capacity. When treating a patient with COPD, chronic hypercapnic respiratory failure, or the acute illness form, calculate their aggregate National Early Warning Score, then add a weighting score of two (2).

Also, record both the mode of oxygen delivery and the device used for delivery. Continue to record the rate of oxygen flow (L/min) to accurately define the amount of oxygen the patient receives. ​Use the appropriate BTS device codes to document the oxygen delivery system.​


Problems with Application

According to a recent article in the journal Thorax, a little more than one-third of patients admitted to UK hospitals had the incorrect SpO2 scale applied to their case. Most patients did not have an arterial blood gas test performed, the test the medical community considers the gold standard for determining whether the individual needs scale 1 or scale 2 applied to their supplemental oxygen.

The Thorax study considered patients experiencing hypercapnic respiratory failure who were admitted to a medical ward at Leicester Royal Infirmary. Researchers built the sample for the study using Nervecentre, an electronic patient records system that notes tests performed, treatments administered, and vital demographic data, such as age and gender. The researchers considered patients admitted during the months of May and June 2022. They analyzed the following outcome measures:

  • Arterial blood gas test (ABG) performed/not performed
  • Venous blood gas test (VBG) performed/not performed
  • Correct use of NEWS2 Scale 1
  • Correct use of NEWS2 Scale 2

During the two-month period of the study, Leicester admitted 53 patients meeting the criteria. The study sample group consisted of 58 percent males and 42 percent females. Their ages ranged in years from 47 to 96, with a mean age of 76 years.

Prospective trials involving patients revealed that the medical personnel at the hospital weren’t ordering the tests that would indicate whether to use SpO2 scale 1 or scale 2. Doctors ordered ABG for only 11 percent of the 53 patients at admittance and ordered VBG for 62 percent. Only 6 percent of patients had both ABG and VBG tests, while 9 percent had neither.

A lack of information led to the use of the wrong scale in the application of the National Early Warning Score. The medical personnel placed 75 percent of patients on scale 1 and the remaining 25 percent on scale 2.

In sum, the resulting analysis of all patient records revealed that 28 percent of the patients placed on Scale 1 belonged to Scale 2, and 31 percent of the patients placed on Scale 2 belonged to Scale 1.

Testing each patient with an ABG test at admittance provides the baseline needed to determine whether to use scale 1 or 2. Because the early warning score provided using National Early Warning Score influences all treatment decisions, obtaining the needed baseline for an accurate assigning of SpO2 scale 1 or 2 results in more accurate decision-making overall.

The medical staff can more suitably monitor supplemental oxygen. Recognizing that a patient exhibits COPD-like symptoms can result in the use of Scale 2 and its lower “normal.” This can lead to appropriate supplemental oxygen instead of administering high-flow oxygen.

Not all patients present themselves at a hospital during acute exacerbations of asthma or COPD. Admittance for another reason can preclude knowing acute illness severity, making tests more important. Conduct intake tests, including ABG and VBG, to determine which SpO2 scale to use.