A Comparison of the Detection of Hypoventilation During Deep Sedation Utilizing Nasal End Title CO@ Versus Transcutaneous CO2 Measurement Techniques

The estimation of the partial pressure of carbon dioxide (PCO2) in the arterial blood is used to judge the adequacy of ventilation during spontaneous and controlled ventilation. Although the gold standard for monitoring PCO2 remains arterial blood gas sampling, this requires an invasive procedure and provides only an intermittent estimate of what is frequently a continuously changing value. The solution to this problem has been the development and validation of accurate noninvasive monitoring techniques which provide a continuous intraoperative estimate of PCO2.The most commonly used noninvasive technique to monitor PCO2 is measurement of the end tidal CO2 (PECO2) . However, sampling errors and patient -related issues such as ventilation-perfusion mismatch, patient positioning or decreases in pulmonary blood flow may influence the accuracy of PECO2 monitoring (1-3). Nasal capnography has been proved to be an accurate monitor during the post-operative period (4) but its ability to accurately detect hypoventilation associated with deep sedation has not been studied. According to the American Society of Anesthesiologist standards for basic monitoring, continuous capnography is required for all patients undergoing general anesthesia but it is optional for MAC/sedation cases. The need for CO2 monitoring has been studied by other medical specialties that use procedural sedation, including gastroenterology (12) and emergency medicine (13, 14) and many specialties now recommend capnography as a standard monitor. Patients receiving supplemental oxygen may experience significant persistent hypoventilation leading to progressive hypercarbia and acidosis which may go undetected for a significant time interval since the routinely monitored SpO2 may be maintained within normal range. A recent study has shown that despite the fact that end tidal CO2 is reliable in detecting apnea , increasing oxygen flow rates decrease the amplitude of measured CO2, probably via dilution, making