A Study of Capnography Monitoring During Monitored Anaesthesia Care (MAC)
Capnography Monitoring During Monitored Anaesthesia Care (MAC)
Background: MAC alone or with local anaesthesia accounts for a relatively high percentage of anaesthesia services now a days. Capnography is a non-invasive monitoring device that closely approximates the arterial carbon dioxide (CO2) levels and thus the ventilatory status of the patients. Objectives were to detect adverse respiratory events by observing the trend in respiratory rate (RR), EtCO2 value, SpO2 value and found association between them. Subjects and Methods: Total 60 patients of age 14-65 years of either sex posted for elective procedures carried out under MAC were included in this study. The study investigator (who did not participate in the patient care) was present throughout each procedure and recorded all the data. The sedation provider was blinded to the capnography data throughout the procedure. At any time during the procedure if SpO2 dropped to ? 90% or RR ?8 breaths/min or EtCO2 ?45 mm Hg, it was considered as respiratory depression and absence of EtCO2 waveform for ?15 seconds was considered as apnoea. During the study whenever EtCO2 value was ?60 mm Hg or respiratory rate dropped to ?6 breaths/min, the study investigator had informed to the sedation provider for timely intervention. Results: Main anaesthetic agent used in the study was Inj. Propofol with average dose 1.7 mg/kg and Inj. ketamine 1mg/kg which is safe dose for sedation. Out of 60 patients of the study, total 27 patients (45%) fulfilled either of the pre-defined RD criteria along with apnoea episodes in study. Out of these 27 patients, apnoea (absence of EtCO2 waveform) episodes were detected only by the capnography in 6 (10%) patients. There was total 8 episodes of apnoea in this study, 4 were of < 15 seconds duration and 4 episodes were of ? 15 seconds duration in whom the sedation provider was informed by the study investigator for the safety of patients. When we correlated all the 3 parameters, SpO2 detected RD in 22 patients within 20 minutes of starting procedures. Whereas RR and EtCO2 detected RD in 5 and 7 patients respectively either alone or with other parameters. Out of those 27 patients total 25 required interventions. While in rest 33 patients without respiratory events (RE), 11 patients required intervention. When we compared interventions in patients with RE and without RE, p value was <0.001, hence, RE patients required more interventions compared to non-RE patients. Conclusion: Though, the value of capnography in monitoring ventilation in patient undergoing procedure under sedation is well appreciated, we could identify few cases of respiratory depression by sole capnography as compared to pulse oximetry. Also, the anaesthesiologists providing sedation were vigilant and able to provide timely intervention in study. Thus, capnography cannot replace clinical observation methods and pulse oximetry in identifying respiratory events. But its value cannot be neglected also, as capnography serves as a warning monitoring tool by instantly drawing anaesthesiologists attention.
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