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A Nasal Catheter for the Measurement of End-Tidal Carbon Dioxide in Spontaneously Breathing Patients: A Preliminary Evaluation
Mohamed Samy Abdel Raheem, MD, DA (UK), FRCA, CCT, and Olaa M. Wahba, MD
BACKGROUND: Several devices have been proposed to monitor end-tidal carbon dioxide tension (PETCO2) in spontaneously breathing patients; however, many have been reported to be inaccurate. Wedesigned this study to investigate the accuracy of a balloon-tipped nasal catheter in measuring PETCO2 in nontracheally intubated, spontaneously breathing patients. METHODS: The catheter was assembled using a 14-F rubber Foley catheter, a tracheal tube pilot balloon, and the plastic sheath from an 18-gauge needle. The catheter was connected to the sampling tube of a gas analyzer. PETCO2 and PaCO2 weredetermined simultaneously in 20 otherwise healthy postsurgical patients while receiving oxygen. RESULTS: The mean PETCO2 PaCO2 difference was 4.4 1.6 (SD) mm Hg with a correlation coefficient r 0.87 (P 0.001). CONCLUSION: Our results suggest that a balloon-tipped nasal catheter can provide a simple, easy, and reliable method for PETCO2 measurement in nontracheally intubated, spontaneously breathingpatients. (Anesth Analg 2010;110:1039 –42)

easurement of end-tidal carbon dioxide tension (Petco2) is now common not only during anesthesia and procedural sedation but also in intensive care, postoperative anesthetic recovery, and emergency care.1 Although measuring Petco2 in intubated patients is technically easy, it can be difficult to obtain accurate values in the postanesthetic care unitwhen patients are no longer intubated.2 Petco2 and respiratory waveforms from a capnograph can provide vital information about CO2 retention and respiratory depression and can serve as an apnea monitor in spontaneously breathing patients.3 The measurement of Petco2 is frequently used as an approximation of arterial carbon dioxide (Paco2); however, in the absence of tracheal intubation, it isdifficult to obtain end-tidal gases. Many devices have been proposed for measuring Petco2 during simple oxygen administration in spontaneously breathing, nontracheally intubated patients.4 – 6 However, cannulae threaded into the posterior nasopharynx frequently obstruct.7 Nasal oxygen cannulae have been modified to form “oronasal cannulae” that give reliable measurements of Petco2. Nevertheless, thesehave not been examined quantitatively.8 Moreover, the uses of modified nasal cannulae for Petco2 measurements (with oxygen flowing through the cannulae) are reported to be inaccurate.9,10 In a trial to accurately measure Petco2 in spontaneously breathing patients receiving supplementary oxygen, we have assembled a balloon-tipped nasal catheter that could

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possibly avoid the inaccuraciesreported when using similar devices. Therefore, this study was performed to investigate the accuracy and reliability of a balloon-tipped nasal catheter to measure Petco2 in otherwise healthy, nonobese, spontaneously breathing patients.

METHODS
This prospective study was approved by the ethics committee, Faculty of Medicine, Asyut University. It was conducted on 20 ASA physical status Ipostoperative patients who underwent orthopedic (internal fixation), plastic (skin grafting), or vascular (varicose vein stripping) limb surgery. A written informed consent was obtained from all patients before inclusion in the study. Patients were excluded from the study if they had a body mass index 30, a history of chronic respiratory, cardiac or metabolic disease, nasal operation, epistaxis, nasalobstruction, or obstructive sleep apnea. Having undergone limb surgical procedures, all patients received a standard anesthetic technique: an IV induction followed by inhalation-based maintenance of anesthesia with analgesia provided by boluses of fentanyl with/without local anesthetic infiltration at the end of the procedure. After tracheal extubation, patients were kept in the postanesthesia care...