As the title says, what are contraindications of providing a patient oxygen in the emergency system outside of hospitals?
Clearly if there's a risk of fire, then giving oxygen outside the hospital risks fire. And in neonates, high flow oxygen can cause oxygen toxicity.
If there is no such risk, then the main objection is that by removing the hypoxic respiratory drive in patients with hypercapnic respiratory failure the patient then stops breathing.
The risks of oxygen therapy are oxygen toxicity and carbon dioxide narcosis. Pulmonary oxygen toxicity rarely occurs when a fractional concentration of oxygen in inspired gas (FiO2) lower than 0.6 is used; therefore, an attempt to lower the inspired oxygen concentration to this level should be made in critically ill patients.
Carbon dioxide narcosis occasionally occurs when some patients with hypercapnia are given oxygen to breathe. Arterial carbon dioxide tension (PaCO2) increases sharply and progressively with severe respiratory acidosis, somnolence, and coma. The mechanism is primarily the reversal of pulmonary vasoconstriction and the increase in dead space ventilation.
With particular reference to those prone to respiratory failure, the BTS 2008 guidelines state
Some patients with COPD and other conditions are vulnerable to repeated episodes of hypercapnic respiratory failure. In these cases it is recommended that treatment should be based on the results of previous blood gas estimations during acute exacerbations because hypercapnic respiratory failure can occur even if the saturation is below 88%. For patients with prior hypercapnic failure (requiring non-invasive ventilation or intermittent positive pressure ventilation) who do not have an alert card, it is recommended that treatment should be commenced using a 28% Venturi mask at 4 l/min in prehospital care or a 24% Venturi mask at 2–4 l/min in hospital settings with an initial target saturation of 88–92% pending urgent blood gas results. These patients should be treated as a high priority by emergency services and the oxygen dose should be reduced if the saturation exceeds 92%. [Grade D]
In addition to circumstances where an oxygen source would itself be a hazard for external reasons, and in those with chronic type 2 respiratory failure as pointed out in Graham Chie's answer; there is a move away from providing supplementary O2 in those with myocardial infarction (in line with AVOID, which assessed both pre- and in-hospital supplementation, and DETO2X-AMI)
In an update to the BTS Guideline for Oxygen Use in Adults in Healthcare and Emergency Settings (July 2017), this is stated as:
Myocardial infarction and acute coronary syndromes
Most patients with acute coronary artery syndromes are not hypoxaemic and the benefits/harms of oxygen therapy are unknown in such cases. Unnecessary use of high concentration oxygen may increase infarct size.
-- Table 3, Conditions for which patients should be monitored closely but oxygen therapy is not required unless the patient is hypoxaemic; emphasis mine.
Other conditions listed in this table include:
- stroke ("Most patients with stroke are not hypoxaemic. Oxygen therapy may be harmful for non-hypoxaemic patients with mild–moderate strokes")
- Hyperventilation or dysfunctional breathing
- Most poisonings and drug overdoses
- Poisoning with paraquat or bleomycin ("Patients with paraquat poisoning or bleomycin lung injury may be harmed by supplemental oxygen.")
- Metabolic and renal disorders
- Acute and subacute neurological and muscular conditions producing muscle weakness
- Pregnancy and obstetric emergencies ("Oxygen therapy may be harmful to the fetus if the mother is not hypoxaemic")
(I have included rationale where potential harm could be considered a contraindication)
Of course, not all of these are necessarily going to be offered supplementary oxygen outside of a hospital setting.
This guideline does apply to paramedics and other out-of-hospital users:
1.2 Intended users of the guideline and target patient populations
This guideline is mainly intended for use by all healthcare professionals who may be involved in emergency oxygen use. This will include ambulance staff, first responders, paramedics, doctors, nurses, midwives, physiotherapists, pharmacists and all other healthcare professionals who may deal with ill or breathless patients.