Study objectives: Transcutaneous CO2 pressure (Ptcco2) and transcutaneous O2 pressure (Ptco2) measurements are routinely used in pediatric ICUs in order to avoid serial arterial punctures. The aim of this study was to determine the value of Ptcco2 assessment during the evaluation of home ventilation in 12 adult patients with COPD or restrictive respiratory failure in the stable state (mean [± SD] basal Paco2, 48.8 ± 8.3 mm Hg) who were treated by mask or tracheotomy-mediated ventilation.
Methods: After radial catheter insertion, patients were instructed to breathe spontaneously for 40 min and then to receive ventilation for 40 min according to their individual home ventilation modalities. An in vivo calibration was performed in the initial stage of the study in order to optimize the arterial Pco2 and Ptcco2 values. Every 5 min, transcutaneous measurements were performed and simultaneously compared with arterial values.
Measurements and results: Ptcco2 and Ptco2 were correlated with arterial values (p < 0.0001) except for Paco2 values of > 56 mm Hg and Pao2 values of > 115 mm Hg. During ventilation, Paco2 decreased ≥ 4 mm Hg in seven patients. Ptcco2 variations recorded during consecutive 5-min periods while the patient received mechanical ventilation were well correlated with the arterial variations (p = 0.0033), with a delay of < 5 min.
Conclusion: Ptcco2 values and variations accurately reflected Paco2 values and variations during mechanical ventilation. However, the accuracy of these data seems to be restricted to patients with Paco2 values of < 56 mm Hg.