To the Editor

We are stimulated to respond to a letter appearing in a recent APSF Newsletter, (1992, volume 7, page 19), entitled “Supplemental oxygen for M.A.C. cases: Is it valuable? Is it a hazard?’ by D.M. Penndorf. Ms. Penndorf highlights what is indeed a problem when lightly sedated patients for ophthalmological surgery under local analgesia are placed beneath drapes. It is most uncomfortable for the patient to he totally covered in drapes and indeed hazardous unless some way of supplying oxygen and promoting carbon dioxide removal is provided. There is also, as Ms. Penndorf notes, a further potential hazard of fire due to the high oxygen concentration beneath flammable drapes.

We have gone some way toward solving these problems by the simple use of a battery operated air blower. The drapes are tented up over a light plastic moulding (an IV pole or ‘ether screen’ would do just as well) to which runs a tube supplying between 6 and 8 1 /min of 100% oxygen. The blower supplies room air through a one inch diameter flexible pipe resting alongside the plastic moulding at a flow rate of 3 3.5 1 /min. This reduces the Ukehhood of an excess accumulation of oxygen, enhances carbon dioxide removal, and further lessens any sense of claustrophobia by the stream of fresh cool air. Theoretically, the inspired oxygen concentration could be adjusted within limits by altering the flow rate of the supplemental oxygen and measured using a fuel cell oxygen analyser (or similar) placed near to the patient s face.

The blower which we have found to be very suitable is manufactured by Stackhouse Inc., El Segundo, California. It is compact, light in weight and operated by a rechargeable battery. It is marketed as a part of their ‘Freedom Mark III’ surgical helmet system. It is not expensive and can be purchased separately.

We have found this technique useful in more than 1,000 patients to date.

Brian J. Pollard, M.D

Janis Shaw, M.D.

Department of Anaesthesia

The University of Manchester, England