Abstract
AIM: To determine whether a newly developed respiratory rate monitor can practically and accurately monitor ventilation under propofol sedation in combination with standard monitoring. METHODS: Patients [American Society of Anesthesiologists (ASA) Classification I-III] scheduled for elective colonoscopy under propofol sedation were monitored with a new device that measures the respiratory rate based on humidity in expired air. Patients with clinically significant cardiac disorders or pulmonary disease and patients requiring emergency procedures were excluded from study participation. All of the patients also received standard monitoring with pulse oximetry. This was a single-center study conducted in a community hospital in Switzerland. After obtaining written informed consent from all subjects, 76 patients (51 females and 25 males) were monitored during colonoscopy under propofol sedation. The primary endpoint was the occurrence of any respiratory event (apnea or hypopnea). Apnea was defined as the cessation of breathing for a minimum of 10 s. Significant apnea was defined as the cessation of breathing for more than 30 s. Hypopnea was defined as a reduction in the respiratory rate below 6/min for a minimum of 10 s. Any cases of significant apnea triggered interventions by the endoscopy team. The interventions included withholding propofol, verbal stimulation of the patients, and increased oxygen supplementation or the chin lift maneuver. A secondary endpoint was the correlation of apnea or hypopnea with hypoxemia (measured as a decrease in SaO2 of at least 5% from baseline or less than 90%). RESULTS: At least one respiratory event was detected in thirty-seven patients (48.7%). In total, there were 73 respiratory events, ranging from one to six events in a single patient. Significant apnea (> 30 s) occurred in five patients (6%). Only one episode of apnea led to a relative SaO2 reduction (from 98% to 93%) after a 50 s lag time. No event requiring assisted ventilation was recorded. Our analysis revealed that the total propofol dose was an independent risk factor for respiratory events (P = 0.01). Artifacts developed with the same frequency with the new device as with conventional pulse oximetry. Compared with pulse oximetry alone, this new monitoring device detected more respiratory events and may provide earlier warning of impending respiratory abnormalities. CONCLUSION: Apnea commonly occurs during endoscopy under sedation and may precede hypoxemia. We recommend this respiration rate monitor as an alternative to capnography to aid in detecting ventilatory problems.