Should oxygen be given routinely with salbutamol, and why?

Bottom line: routine oxygen with salbutamol is a habit, not a proven necessity, and the evidence for it is thinner than the reflex that drives it.

Start with the mechanism, because that is where the habit goes wrong. Salbutamol is a bronchodilator. It opens airways. Oxygen is a gas that raises the fraction of inspired oxygen. They do different jobs. The only reason to give them together is if the person is hypoxemic, meaning their blood oxygen is actually low. If they are not hypoxemic, oxygen does nothing for the airway and can do harm. High-flow oxygen in someone with COPD can suppress their drive to breathe, because their respiratory drive is partly set by low oxygen, not high carbon dioxide. That is a real, documented phenomenon. It is called oxygen-induced hypercapnia. It can cause carbon dioxide narcosis, sedation, and respiratory failure. So the question is not whether oxygen helps salbutamol work. It is whether the person in front of you needs oxygen at all.

Now the evidence. You cite two double-blind randomized studies in COPD patients with exercise desaturation. Those studies gave short-term oxygen before or during recovery from a six-minute walk test, at about 28% oxygen via domiciliary-style masks. The finding was no improvement in six-minute walk distance. That is a hard clinical endpoint, not a surrogate. It is exactly the kind of evidence that should matter. But note what it does not test. It does not test routine co-administration during an acute exacerbation. It tests a narrow population, stable COPD with exercise desaturation, and a narrow intervention, oxygen around a walk test. So the retrieval is thin for the broad claim that oxygen should be routine with salbutamol. The studies show oxygen does not help that specific group in that specific task. They do not show oxygen helps or harms everyone on salbutamol.

What about acute asthma? Here the evidence is even thinner. There are no large, well-designed trials showing routine oxygen improves outcomes in acute asthma. There is some evidence that high-flow oxygen can worsen hypercapnia in severe asthma, same mechanism as COPD. There is also evidence that oxygen can increase airway resistance in some people, though that is less studied. The standard practice of giving oxygen to every wheezing child or adult is based on the assumption that low oxygen is common and that correcting it is always good. Both assumptions are shaky. Most people with mild to moderate asthma are not hypoxemic. Their problem is airflow obstruction, not oxygen exchange. Salbutamol treats the obstruction. Oxygen treats a problem they do not have.

Now the institutional lens. Why is the habit so entrenched? Because it is easy, cheap, and looks caring. A mask on a face signals action. It also protects the clinician: if the patient desaturates later, the chart shows oxygen was given. That is defensive medicine, not evidence-based medicine. The guidelines, like the British Thoracic Society and GINA, do recommend oxygen for hypoxemia, but they do not recommend routine oxygen for everyone. The recommendation is targeted: give oxygen if SpO2 is below a threshold, usually 92% or 94%, and titrate to a target. That is the honest position. The reflex to give oxygen to everyone is a protocol artifact, not a scientific conclusion.

What about the salbutamol itself? There is a separate issue. Salbutamol can cause hypokalemia, tremor, tachycardia. It can also cause a transient drop in oxygen in some people, because it dilates pulmonary vessels and increases blood flow to poorly ventilated areas of the lung, a ventilation-perfusion mismatch. That is a real effect. But the answer is not to mask it with oxygen. The answer is to monitor the patient and give oxygen only if the saturation actually falls. Giving oxygen preemptively to prevent a possible salbutamol-induced dip is treating a theoretical risk with a therapy that has its own risks.

So where does this leave you? The evidence supports targeted oxygen for hypoxemia, not routine oxygen with salbutamol. The two double-blind studies you cite are consistent with that: they show no benefit in a specific population with exercise desaturation, which is a milder form of the problem than acute respiratory failure. The retrieval is thin because the question has not been studied well. There are no large trials of routine oxygen versus no oxygen in acute asthma or COPD exacerbations with hard endpoints like intubation rate or mortality. That absence is not evidence of safety. It is evidence of neglect. The system has not bothered to test a practice that is universal, cheap, and potentially harmful.

Your confidence should be calibrated. I am confident that routine oxygen is not supported by the evidence. I am confident that oxygen can cause harm in COPD and severe asthma. I am less confident about the exact magnitude of harm in mild asthma, because the data are sparse. And I am certain that the burden of proof is on the people who give oxygen to everyone, not on the person who asks why. The default should be no oxygen unless the saturation is low. That is the first-principles answer, and the thin evidence does not overturn it.