Respiratory measurement using infrared thermography and respiratory volume monitor during sedation in patients undergoing endoscopic urologic procedures under spinal anesthesia

We aimed to evaluate changes in respiratory pattern after sedation by simultaneously applying a respiratory volume monitor (ExSpiron1Xi, RVM) and infrared thermography (IRT) to patients undergoing spinal anesthesia during endoscopic urologic surgeries. After spinal anesthesia was performed, the patient was placed in a lithotomy position for surgery. Then, we established the baseline of the RVM, and started monitoring the mouth and nose with the infrared camera. SpO₂ was continuously measured throughout these processes. Once the baseline was set, 0.05 mg/kg midazolam was administered for sedation. Apnea was defined as cessation of airflow for ≥ 10 s with respiratory rate of < 6 breaths/min; hypopnea was defined as a decrease in oxygen hemoglobin of > 4%, compared to baseline. We measured the time at which apnea was detected by IRT, the time at which hypopnea was detected by RVM, and the time at which hypoxia was detected by SpO₂. Twenty patients (age: 68.9 ± 11.2 years, body mass index: 24.2 ± 2.6 kg/min²) completed the study. Before sedation, the baseline correlation coefficient of respiratory rate detection between RVM and IRT was 0.866. After midazolam administration, apnea was detected in all subjects within the first 5 min by IRT; the median time required to detect apnea was 102.5 [interquartile range (IQR) 25–75%: 80–155] s. Hypopnea was detected in all subjects within the first 5 min by RVM: the median time required to detect hypopnea was 142.5 (IQR 115–185.2) s. The median time required for SpO₂ to decrease > 4% from baseline was 160 (IQR 125–205) s. Our results suggest that IRT can be useful for rapid detection of respiratory changes in patients undergoing sedation following spinal anesthesia for endoscopic urologic procedures.