Comparison of transcutaneous and endtidal CO2 -monitoring for rigid bronchoscopy during high-frequency jet ventilation

Objective: To compare endtidal and transcutaneous respiratory monitoring of high-frequency jet ventilation (HFJV) in rigid bronchoscopy. Both techniques provide a noninvasive measurement of pCO(2). Methods: High-frequency jet ventilation was applied via a rigid bronchoscope. Driving pressure (DP) was initially adapted to ensure normal ventilation. It was then changed twice by +/-30% from the initial value. Endtidal and transcutaneous data were compared with arterial blood gas monitoring (ABG). Results: Results were analyzed separately for the time just after changing the driving pressure (10 min) and the remaining time until the next change of the driving pressure (4 min). The first part was called the dynamic phase, and the second part the steady-state phase. Correlation coefficient between endtidal capnography and ABG was 0.96 for the steady state and 0.94 for the dynamic phase, respectively. Bland-Altman analysis revealed a bias of -0.21 kPa with limits of agreement (LOA) 1.63 kPa for the steady state and -0.25 kPa, 2.08 kPa for the dynamic phase, respectively. Correlation coefficient between transcutaneous monitoring and ABG for the steady state phase was 0.83, and was 0.72 for the dynamic phase. Bland-Altman analysis resulted in a bias of -0.89 kPa with LOA - 3.84 kPa during steady state and 0.92 kPa, 4.06 kPa for the dynamic phase, respectively. Conclusion: Endtidal capnography offers accurate respiratory monitoring of HFJV. Transcutaneous monitoring showed a good correlation to ABG only during steady-state conditions. For the dynamic phase the accuracy was significantly lower. Thus, we cannot recommend transcutaneous respiratory monitoring for the specific indication of rigid bronchoscopy using HFJV.