Awake Capnograph Improves

Steven J. Derrick, C.R.N.A.

To the Editor

I would like to submit the following letter in reference to two specific articles in the APSF Newsletter, Spring, 199 1. “ASA Standards Amended,” by John H. Eichhorn, M.D. and “Capnography Se-en Advantage to Awake Patients,” by Dean L. Melnyk, M.D., Ph. D. and Shep Cohen, M.D.

Capnographic monitoring for monitored anesthesia care (MAC)/intravenous sedation is rapidly becoming a reality with the development of several sampling devices designed specifically for the purpose of end-tidal C02 monitoring in the awake patient. However, all currently available products are not capable of optimal continuous end-tidal gas sampling in this situation. All of these capnographic sampling devices lack the capability to appropriately sample oral breathing as well as nasal breathing.

During MAC procedures concurrent monitoring of end-tidal C02 from both the mouth and nose revealed that approximately 40% of the patients alternate between oral, nasal and simultaneous oral/nasal modes of breathing (unpublished data). A sampling device that monitors nasal or oral breathing only, will frequently underestimate the true end-tidal C02 when a majority of the breathing is taking place at the non-sampled airway passage. This can lead to the misinterpretation of ventilatory adequacy when in fact, hypoventilation exists. All existing capnographic devices for sedation cases are only capable of monitoring either the nose or the nose and mouth simultaneously. To date, there is no device available which is capable of discriminate sampling of all possible modes.

A new capnographic monitoring device does provide for this capability in the sedated patient. It will also allow for concurrent 02 administration if desired and is no more invasive than an oxygen nasal cannula. This product should be available by the Fall of 199 1. It should provide more accurate end-tidal C02 monitoring during sedation and a safer anesthetic for the patient.

Steven J. Derrick, C.R.N.A. West Mifflin, PA