Emergency Oxygen Therapy

Emergency Oxygen Therapy 

This features in an educational article in the BMJ this week. Oxygen used to be given routinely for a wide range of acute medical presentations, however increasingly it is only being recommended if the patient is hypoxaemic. Oxygen should be prescribed and given in a controlled manner. A number of publications in the medical literature have raised concerns about the risks of insufficient or excessive oxygen therapy. The main indication for oxygen therapy in an emergency setting is to protect patients from the harmful consequences of hypoxaemia.

The common acute medical presentations can be broadly categorised into those who require high concentration oxygen in all cases, those likely to require oxygen therapy, and those where patients are likely to need controlled oxygen.

1) High Flow O2 in all cases - Shock, sepsis, major trauma, anaphylaxis, cardiac arrest, carbon monoxide or cyanide poisoning.

2) O2 Therapy (Aim sats 94-98%) - Pneumonia, asthma, acute heart failure, PE

3) Controlled O2 (Aim sats 88-92%) - Exac. of COPD, acute illness in CF, acute illness in patients with obesity hypoventilation syndrome or morbid obesity, or with chronic neuromuscular / musculoskeletal conditions.

The following are common medical emergencies where oxygen was given routinely in the past but is now only advised if the patient is hypoxaemic:

MI/ACS, survivors of cardiac arrest with ROSC, sickle cell crisis, obstetric emergencies, most poisonings and metabolic/renal disorders with tachypnoea due to acidosis (Kussmaul breathing). In acute stroke, there is uncertainty in the literature as to whether routine oxygen supplementation actually improves outcomes and these patients should only be given oxygen to maintain saturations within the normal range (94-98%).

Approximately half of UK hospital patients receiving oxygen therapy do not have a prescription for this treatment or any valid written documentation. There is no evidence that oxygen therapy can relieve 'breathlessness' in non-hypoxaemic patients with acute illness. High concentration of oxygen in patients with acute exacerbations of COPD increases the risk of hypercapnic respiratory failure. High concentrations of oxygen has also been shown to increase the risk of hypercapnia in acute asthma and pneumonia.

Venturi masks are a useful way of delivering controlled oxygen to a patient. They are available in five types: 

24% O2, Blue, 2 litres

28% O2, White, 4 litres

35% O2, Yellow, 8 litres

40% O2, Red, 8 litres

60% O2, Green, 15 litres

If oxygen requirements increase, the patient requires a medical review and the underlying cause of the increased requirements should be sought. Beware that in some cases, pulse oximetry may be misleading (eg. in carbon monoxide poisoning). Clinical signs such as tachypnoea and chages in other vital signs may occur before a change in oxygen saturations.

Finally, it is very important to recognise that hypoxia is a sign of underlying illness (problem with gas transfer or regulation of respiratory activity) and not a disease in itself. Blind treatment of hypoxia may lead to a delay in identification of an underlying life threatening condition.