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Oxygen therapy in primary care

Mark Levy
MB ChB FRCGP
Editor
General Practice Airways Group
GPIAG Senior Lecturer
Department of General Practice
Aberdeen University
Member
Royal College of Physicians Working Party on Provision of Domiciliary Oxygen Therapy
Part-time GP London
E:marklevy@animalswild.com
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It is not uncommon to encounter conditions such as acute asthma and pneumonia and acute cardiac events such as angina or myocardial infarctions in general practice. These result in life-threatening hypoxia, yet many surgeries do not have oxygen on the premises. Even fewer GPs carry an emergency supply of oxygen in their cars. Why is this? Is it the cost? Oxygen is relatively inexpensive - it costs about £120 per year to maintain two or three cylinders (one for the car). The more likely reason is, in my opinion, ignorance of the uses and means of acquiring oxygen for the practice. In this short article, I will hopefully persuade many of my colleagues to think seriously about providing oxygen for their patients.
In general practice oxygen is prescribed in cylinders; however, if expected usage is above a threshold (usually 15 hours a day over a prolonged period), an oxygen concentrator is more cost-effective. Portable oxygen cylinders (which are carried by the patient) are also prescribable, although these need to be initiated by specialist hospital departments. There is little research on the prescribing patterns and cost-effectiveness of oxygen used in the community; yet nearly £30 million is spent on this drug annually in the UK. 
Measurement of oxygen saturation (SpO(2)) with a pulse oximeter should be standard practice in the surgery. Oxygen saturation is useful in acute situations and assists the GP or practice nurse in management decisions. For example, after nebulising a child with a bronchodilator, SpO2 levels below 92% indicate a need for admission to hospital.
 
Common indications for prescribing oxygen in primary care
Patients presenting to a GP with acute respiratory or cardiac problems are often hypoxaemic; oxygen is indicated while waiting for the ambulance, which may take time during high-demand periods. I once had to treat a 23-year-old acute asthmatic woman in her home during a busy December in London. Her oxygen saturation levels dropped to 84% at times, and the ambulance took 45 minutes to get to us; without oxygen, that woman could have died.

Acute asthma
High-dose b(2)-agonist bronchodilators, oral steroids and oxygen are used to treat patients with acute asthma. High-dose b(2)-agonist bronchodilators can be administered via a metered-dose inhaler, either alone or ideally via a large-volume spacer device. Alternatively a nebuliser can be used, driven by an air compressor or preferably via high-flow oxygen (over 6 litres/min). The potential risk of making the patient hypoxaemic through delivery of bronchodilators using an air-driven compressor, from ventilation/perfusion mismatch, is significant; furthermore, air will not improve the low oxygen saturation levels in patients with acute asthma. (1) Therefore oxygen is the preferred driving gas for delivering nebulised medication. 
Other acute conditions where oxygen administration is indicated include patients presenting with acute myocardial infarction, cardiac arrhythmias and chest infections with severe hypoxia. In cases where the GP is called to attend to patients with head injuries, for example road traffic accidents outside the surgery, oxygen may be lifesaving while waiting for an ambulance to arrive.

Chronic prescription of oxygen
Chronic prescription of oxygen includes long-term oxygen therapy (LTOT) in the home, ambulatory oxygen therapy and short-burst oxygen therapy, for example for patients with episodic breathlessness.(2) All three of these indications require thorough assessment by a respiratory specialist physician. For example, for patients with chronic obstructive pulmonary disease (COPD), LTOT should be prescribed only when the PaO(2) is less than 7.3kPa (55mmHg) when breathing air during a period of clinical stability. GPs are often inappropriately contacted by junior hospital staff requesting oxygen prescription for patients due to be discharged. Oxygen should be prescribed only if the above criteria are met, usually at least four weeks after discharge from hospital.(2)
There are a number of other chronic diseases for which oxygen prescription is appropriate. These include interstitial lung disease, obstructive sleep apnoea, pulmonary hypertension, pulmonary malignancy and chronic heart failure. However, each of these patients should be assessed by a specialist before LTOT is prescribed. A report by the Royal College of Physicians provides a detailed overview of the indications for and assessments required for prescribing domiciliary oxygen in the community.(2) It is an excellent resource for those planning healthcare provision. Primary care trust board members would be well advised to study it closely.

Obtaining oxygen supplies
Full details on oxygen prescription, including UK suppliers of oxygen and concentrators (listed by region), are available in the Drug tariff.(3) Initial orders should be for two 1,340-litre cylinders for the surgery (ie, one spare) plus a high-flow regulator (up to 15 litres/min). The standard regulator provides only 2 or 4 litres/min, which is insufficient to drive a nebuliser (that requires at least 6 litres/min), and also insufficient should 100% oxygen be required in cases of severe trauma. Therefore a high-flow regulator (up to 9 or 15 litres/min) should be purchased. These cost about £110 and need to be renewed every five years. A smaller 300-litre cylinder with a high-flow regulator for the car is invaluable, for example when stopping at a road traffic accident or administering emergency treatment at home before the paramedics arrive. Oxygen-giving sets also need to be prescribed (or bought for surgery use). These consist of tubing to connect the cylinder to a mask - 24% or 28% masks are usually supplied. It is also helpful to have a 100% (with rebreathing or reservoir bag) mask available. GPs need only purchase one of each and then replace them (as they are single-patient use only) from the paramedics' supply when referring a patient to hospital.

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References

  1. Gleeson JG, Green S, Price JF. Air or oxygen as driving gas for nebulised salbutamol. Arch Dis Childhood 1988;63:900-4.
  2. Rudolf M, Wedzicha W, Calverley P, et al. Domiciliary oxygen therapy services. Clinical guidelines and advice for prescribers. A report of the Royal College of Physicians. London: Royal College of Physicians; 1999.
  3. National Health Service England & Wales. Drug tariff. London: Stationery Office; (published every month).

Resources
General Practice Airways Group
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British Lung Foundation
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British Thoracic Society
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E:bts@brit-thoracic.org.uk
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National Asthma Campaign
T:020 7226 2260
F:020 7704 0740
W:www.asthma.org.uk
National Asthma Campaign Scotland
T:0131 226 2544
F:0131 226 2401
National Respiratory Training Centre
T:01926 493313
F:01926 493224
E:enquiries@nrtc.org.uk
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Respiratory ERC
T:0151 529 2598
F:0151 529 3943

Forthcoming conferences
December 2002
British Thoracic Society Winter Meeting, London
June 2003
GPIAG Annual Congress