Uses and dangers of oxygen therapy : report of a sub-committee of the Standing Medical Advisory Committee.
- Scotland. Standing Medical Advisory Committee
- Date:
- 1969
Licence: Public Domain Mark
Credit: Uses and dangers of oxygen therapy : report of a sub-committee of the Standing Medical Advisory Committee. Source: Wellcome Collection.
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![mask at a flow rate of | and 2 litres/minute respectively. For the severe chronic bronchitic who has hypercapnia as well as arterial desaturation, it is potentially dangerous to give oxygen much in excess of these concentrations because of the risk of hypoventilation and carbon dioxide narcosis. Since it is con- sidered unwise to give more than 30% oxygen to these patients at sea level without careful supervision, it would be equally unwise to give them more than 35% oxygen at 5,000 ft. or 40% at 10,000 ft. Any patient suffering from an acute exacerbation of chronic bronchitis is unsuitable for air travel because oxygen therapy at that stage of the illness is Baer seapet a difficult without the added complication of altitude. 125. Central cyanosis due to heart disease results either from the secondary effects of heart disease on the ventilation and perfusion of the lungs or from direct anatomical shunting of blood from the right to the left side of the heart. In either case carbon dioxide retention is very unlikely and consequently higher concentrations of oxygen can be given without fear of carbon dioxide narcosis. It is obvious that patients in heart failure, from whatever cause, should not travel by air until maximal improvement in their condition has been obtained by treatment. Even then, the additional stress and excitement of travel together with the reduced arterial oxygen tension due to altitude, may be enough to precipitate failure. It is advisable, therefore, that a special request be made for a provision of oxygen during the flight. 126. In patients with an anatomical shunt, additional oxygen will not correct the cyanosis, but it should be sufficient to prevent an important fall in the saturation of arterial blood at altitude, if the oxygen tension is on the steep part of the oxyhaemoglobin dissociation curve. This applies particularly to the transport of patients, often young children, with cyanotic congenital heart disease from one country to another where investigation and surgical repair of the cardiac lesion is contemplated. Special arrangements will have to be made for very young children and since oxygen tents and oxycots are considered to be dangerous in long-distance, scheduled aircraft because of the fire hazard, small sized oxygen masks must be provided. For older patients, oxygen can be given through a correctly fitted Polymask at a flow rate of 6 litres/minute which provides an inspired concentration of about 60% oxygen (Chapter 11). If this uses up oxygen too rapidly and necessitates an excessive weight of cylinders, the use of a mask with a reservoir bag and a valve to prevent re- breathing would help to conserve oxygen that is otherwise wasted during the expiratory phase of respiration. An alternative would be to supply oxygen through a demand valve on inspiration only, and to ajust the regulator to allow dilution of the oxygen with cabin air according to the altitude and the patient’s requirements. 127. If the blood supply to any organ is impaired, the amount of oxygen available for metabolism is not necessarily less when the arterial oxygen tension falls. This is because, under these circumstances, the extraction of oxygen from blood flowing through the organ may become more complete. However, the penetration of oxygen into tissue that is very poorly perfused depends on the oxygen tension gradient and this is inevitably reduced as the arterial PO, falls. Furthermore, in the case of heart muscle, oxygen extraction from the coronary blood is already fairly complete, so that the coronary venous blood is normally only about 20% to 30% saturated with oxygen. This does 4]](https://iiif.wellcomecollection.org/image/b32175152_0049.jp2/full/800%2C/0/default.jpg)
