Short answer: British Thoracic Society guidance sets a saturation target of 94 to 98 percent for most acutely ill adults, and 88 to 92 percent for people with COPD or other risk of hypercapnic respiratory failure until blood gas results are known. Exam questions test whether you prescribe a target, use the right device and escalate.
The two targets
The British Thoracic Society (BTS) guideline for oxygen use sets out target ranges. Oxygen is treated as a drug with a target, not as something to give until a patient looks pink.
This is exam-preparation revision, not clinical guidance. In practice, follow your own organisation’s policies and the current guideline, and check doses and thresholds against them.
- 94 to 98 percent: acutely ill adults not at risk of hypercapnic respiratory failure.
- 88 to 92 percent: people with known COPD or another risk factor for hypercapnic respiratory failure, until blood gas results are available.
Why a lower target
Some people with long-standing lung disease depend partly on a raised carbon dioxide level and can retain more of it when given high oxygen. The result can be drowsiness and acidosis. That is why exam questions put a drowsy patient with COPD on high-flow oxygen as the wrong answer. A blood gas guides adjustment: if carbon dioxide is normal, the usual target may apply. See blood gas interpretation.
Devices and monitoring
Controlled oxygen is given through a device that delivers a known concentration, such as a Venturi mask, when a tight target matters. For people at risk of hypercapnia, BTS guidance starts with a 24 or 28 percent Venturi mask, then adjusts to the target. Check saturation, breathing rate, work of breathing and conscious level, and escalate if oxygen needs rise or the patient tires.
Acute asthma: severity features
The BTS and SIGN asthma guideline (SIGN 158) lists features of acute severe asthma: peak flow 33 to 50 percent of best or predicted, inability to complete sentences in one breath, respiratory rate of 25 or more and heart rate of 110 or more. Life-threatening features include peak flow below 33 percent, oxygen saturation below 92 percent, a silent chest, cyanosis, poor respiratory effort, arrhythmia, low blood pressure, exhaustion or altered consciousness.
The guideline warns that a patient may not look distressed. Any severe or life-threatening feature means call for senior help at once. Oxygen, a short-acting bronchodilator and systemic steroids are central, as your protocol directs.
How exams test it
Look for questions that give a saturation and a history, then ask the first action. The safe thread: assess airway and breathing, give oxygen to the right target, use the prescribed bronchodilator, monitor, and escalate with SBAR. Silent chest and drowsiness are red flags, not signs of improvement. Also check that you know your prescribing rules, see medication safety.
A worked exam scenario
Invented for teaching. A man with known COPD arrives with breathlessness. His saturation is 84 percent on room air. He is sleepy and a little confused. What is the best first oxygen action?
The best action is to give controlled oxygen through a device that delivers a known concentration, aim for the lower target range, monitor closely, call for senior help and arrange a blood gas. High-flow oxygen through a non-rebreather mask is the tempting wrong answer. Sleepiness is a warning that carbon dioxide may be high, and it needs escalation.
Prescribe, record and review
BTS guidance treats oxygen like any drug: it should be prescribed with a target range, the device and flow should be recorded and the saturation should be checked and charted. If the target is not met, or the patient needs more oxygen over time, that change is a reason to escalate. Questions on documentation often reward a recorded target and a dated review over a vague note.
Other patients on the lower target
BTS guidance lists risk factors for hypercapnic respiratory failure beyond COPD, such as chronic lung disease, chest wall deformity, neuromuscular disease and obesity-related breathing problems. Exams may describe a patient with one of these without naming COPD, so read the history. If the patient has a card that records a target from earlier admissions, use it. When in doubt, aim for the lower range until a gas is available, then adjust on the result. Always reassess, because a patient can move from one risk group to another as the illness changes.
Frequently asked questions
This article is general educational guidance, not official advice. Exam rules, fees and timelines are set by the Dubai Health Authority and the test provider and can change, so always confirm the latest details on their official channels.
Last updated .