To the Editor:-It is routine to monitor end-tidal carbon dioxide concentration during anesthesia, whenever possible. During sedation using spontaneous respiration via native airways, carbon dioxide monitoring allows for verification of air exchange and respiratory rate, excluding mere motion against an obstructed airway. Nasal cannulae increase ambient oxygen concentrations, and coupled with blunt metal 18-gauge cannulae (Lifeshield-Abbott list #11302; Abbott, Abbott Park, IL), provide inexpensive carbon dioxide detection in the expired air also (Figure 1). Because the 18-gauge cannula is blunt, retrograde insertion into the cannula prong opening facilitates the creation of the desired perforation site in the cannula tubing wall. The 18-gauge cannula is then removed, turned 180 [degree sign], and reinserted into the created perforation to clinically monitor expired carbon dioxide. The blunt, stiff metal shaft closely matches prong length, prevents kinking, protects against finger-stick injury during insertion, and will readily/atraumatically retract to within the nasal cannulae, should the tip press against nasal mucosa. The length of 18-gauge protrusion from the nasal cannulae (different manufacturers) can be securely minimized if desired via tape application to the oxygen tubing or 18-gauge hub, or both. The 18-gauge cannula can be repeatedly reinserted without problem if dislodged to provide safe, cost-effective, single-use, and consistent carbon dioxide sampling during oxygen administration via nasal cannula.
Paul Kempen, M.D., Ph.D.
Associate Professor; Department of Anesthesiology; University of Pittsburgh School of Medicine; 200 Lothrop Avenue; UPMC Presbyterian Hospital; Suite B 208.7; Pittsburgh, Pennsylvania 15213;Pkempe@POL.NET
(Accepted for publication September 21, 1998.)