To the Editor

Each month we care for 75-100 patients having cataract surgery under M.A.C. at our surgical center. Before we had SaO2 monitors available, we used the anesthesia circuit resting on the patient’s chest to fill the space under the drapes with oxygen during surgery. This did not prevent desaturation when the patients were sedated. I placed an FiO2 monitor under the drapes near the patient’s face and monitored FiO2 both with and without supplemental 02. The difference was rarely greater than 2-3%.

I decided that I would put an oxygen nasal cannula on the patient, taping it to the cheeks, well out of the surgeon’s way. The improvement was dramatic and now, 2 liters/min. oxygen suffices in all but the most compromised patients. This has improved our safety, saves a lot of money and reduces the very real risk of fire with large volumes of oxygen under the drapes.

I was concerned that such a low flow of oxygen would not suffice to displace unwanted C02 from under the drapes, resulting in re-breathing. I placed the C02 monitor near the face of several patients before and after the drapes were placed. The C02 level did rise a few percentage points after the drapes were placed. I am not convinced that this does any harm.

One surgeon insists on a suction catheter under the drapes to evacuate C02, but his patients do no better than patients of the six other surgeons who do not, as far as I can tell.

Stephen R. Shuput, M.D.

Intermountain Surgical Center Salt Lake City, UT