Invasive Respiratory Monitoring in Surgery

Once a satisfactory sedation level was achieved, a nasopharyngeal airway was inserted. PetCO₂ monitoring was performed using an infrared CO₂ analyzer (Avance CS², GE Healthcare, Madison, WI, USA) by inserting a sample line into the nasopharyngeal airway to minimize the potential under-detection of exhaled gas due to airway obstruction (Figure 1). The radial artery on the non-operated side was cannulated to monitor continuous arterial blood pressure and sample arterial blood for gas analysis. PtcCO₂ was measured using a TCM4^TM device (Radiometer, Copenhagen, Denmark). The transcutaneous monitoring technique was standardized by applying a probe on the forearm ipsilateral to the non-operated lung in the lateral decubitus position (Figure 1). Before placement, the device was calibrated ex vivo as per the manufacturer’s recommendations. Then, the skin surface where the electrode was placed was swabbed with alcohol to facilitate disc adhesion. Subsequently, the probe was mounted on the electrode with the working temperature set to 42 °C to arterialize the capillary blood flow in the skin. The subsequent in vivo calibration was based on the results of the first ABGA performed after a 10-min equilibration period from the time of the placement of probe on the patient for stabilization of the measurement [14 (link),15 (link)].