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Accuracy and precision of three different methods to determine Pco2 (Paco2 vs. Petco2 vs. Ptcco2) during interhospital ground transport of critically ill and ventilated adults.

BACKGROUND
Interhospital transportation of critically ill and mechanically ventilated patients represents a common, yet difficult problem. Three different methods to determine Pco2 during transport are available: arterial blood gas analysis (Paco2), end-tidal (Petco2) and transcutaneous (Ptcco2) measurement. The aim of the present study is to analyze accuracy and precision of those different methods simultaneously in critically ill and ventilated adults during interhospital transport.


METHODS
Patients scheduled for interhospital transport were investigated after approval of the local ethics committee in the prospective study. Pco2 was determined five times in each patient during the transport simultaneously by (1) arterial blood gas analysis (Paco2[Immediate Response Mobile Analyzer, IRMA]), (2) end-tidal (Petco2), and (3) transcutaneous (Ptcco2) measurements. The results were compared with an in-hospital reference measurement performed by an ABL 625 blood gas analyzer (Paco2[ABL625]). For statistical analysis the Bland-Altman method was used. A p < 0.05 was considered statistically significant.


RESULTS
One hundred seventy data sets (Paco2[IRMA], Paco2[ABL625], Petco2, Ptcco2) were obtained in 34 patients (61 years +/- 16 years old; 19 male patients, 15 female patients). The mean Paco2(ABL625) was 43.2 mm Hg +/- 8.8 mm Hg ranging from 24.9 mm Hg to 72.4 mm Hg. Bland-Altman analysis revealed a bias and precision of -0.6 mm Hg +/- 2.5 mm Hg for the arterial blood gas analysis with the mobile IRMA device and -0.6 mm Hg +/- 7.5 mm Hg for the transcutaneous measurement (p > 0.05). Bias and precision (-5.3 mm Hg +/- 6.1 mm Hg) of endexpiratory CO2-measurement differed significantly (p < 0.003) when compared with the reference.


CONCLUSIONS
During interhospital transport Paco2(IRMA) and Ptcco2 provide the best accuracy when compared with the reference measurement. Patients who either require a tight control of Pco2 or endured lengthy transportation could benefit greatly from the combination of expiratory capnography with mobile arterial blood gas analysis or the transcutaneous measurement of Pco2.