To the Editor:—

Williams and Tomlin 1evaluated a device combining a Bitegard (Gensia Automedics, Inc., San Diego, CA) and a bilateral nasal cannula in patients undergoing cataract surgery.

Although bilateral nasal cannula oxygen supplementation is commonly used during cataract surgery, there is little need for this technique. During eye surgery, drapes are sealed around the eye and cover the patient. The drapes are impenetrable and confine gases completely. If oxygen is insufflated at 2–4 l/min at any point  under the tented drapes, the concentration will increase to 30–50% throughout the confined atmosphere. Nasal cannulae will only create facial irritation and additional expense.

Cataract surgery with regional or topical anesthesia should be pain free. Modest sedation is appropriate. The problem is not hypoxia, but build-up of exhaled carbon dioxide under the drapes and rebreathing thereof. Ventilation is needed to dilute the carbon dioxide, and this can be provided by insufflation of oxygen or compressed air, or by applying suction at any point under the tented drapes.

Williams AR, Tomlin K: The modified Bitegard: a method for administering supplemental oxygen and measuring carbon dioxide (letter). A NESTHESIOLOGY 1999; 90: 338–9