Analysis of capnogram during patient-controlled sedation with propofol or midazolam in healthy volunteers

Jung-Man Lee1, Kwang-Suk Seo2, Hyun Jeong Kim2
1 Department of Anestheisology and Pain Medicine, Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Seoul, Korea, Republic of
2 Department of Dental Anesthesiology, Seoul National University Dental Hospital, Seoul, Korea, Republic of


ABSTRACT
Background and Goal of Study: For safe sedation, capnogram should be important. However, some limitations such as high false positive and high false negative on detecting the respiratory depression still exist in using capnogram. Therefore, accurate algorithm should be needed for safe sedation. The purpose of this study was to analyze the capnogram obtained from nasal cannula during patient-controlled sedation (PCS)　with propofol or midazolam in healthy volunteers for algorithm to monitor capnogram.

Materials and Methods: This retrospective observational study was based on data from the registered study (KCT0001618) at Seoul National University Dental Hospital for a new protocol development of PCS for dental treatment. Total of 60 patients were enrolled. Each patient was randomly assigned to 6 groups according to drug and dose used in the PCS. We converted the digital data of partial pressure of carbon dioxide from each patient into analyzable waves with a signal analysis processing program. Respiratory depression was defined to no wave during more than 30 seconds in capnogram or an event of SpO2 < 90%. We defined ‘capnographic inspiratory time (cTi)’ and ‘capnographic expiratory time (cTe)’ based on the peak velocity of increasing and decreasing of partial pressure of carbon dioxide. Also, we defined the value of ‘cTi:cTe’ as ‘capnographic I:E ratio’. We analyzed the ‘capnographic I:E ratio’ on the change of respiratory pattern in each volunteer.

Results and Discussion: All data from total of 60 volunteers were analyzed in the study. When observation period of each volunteer was divided to three parts of ‘Before PCS’, ‘Consciousness during PCS’, and ‘Unconsciousness during PCS’, the capnographic I:E ratios of all volunteers were 1:1.10 ± 0.35, 1:1.09 ± 0.23, and 1:0.93 ± 0.17 respectively. It was significantly lower in ‘Unconsciousness during PCS’ period than other periods (p < 0.001). Forty-nine respiratory depressions were observed in 21 volunteers. For 21 volunteers who experienced respiratory depression, standard deviation of capnographic I:E ratio during respiratory depression periods was significantly higher than during normal breathing periods (0.24 ± 0.10 vs. 0.28 ± 0.69, p = 0.001).
Conclusions: Quantification analysis of capnographic I:E ratio could help in improving the diagnosis of respiratory depression. Also, it could be helpful in predicting of significant desaturation. In the future, capnogram can be a more useful monitoring tool for safety of patients during sedation.