Background The measurement of gastric–arterial partial CO₂ pressure difference (PgCO₂–PaCO₂  =  PCO₂ gap) with gastric tonometry may help us to monitor the stability of circulation. However, it is very difficult to follow up the condition with frequent acid-base examinations, especially in the case of neonates. In our present examinations we wanted to compare the conventional PCO₂ gap with alternative gaps of PETCO₂ gap (PgCO₂–end-tidal carbon dioxide) and tCO₂ gap (PgCO₂–transcutaneous CO₂).

Methods Gastric tonometric examinations were performed with a new, balloon-free tool developed at our department. PaCO₂ was determined with an acid-base automate, PETCO₂ and PgCO₂ were measured with a side stream capnograph and tCO₂ was determined with a Radiometer Copenhagen transcutaneous blood gas monitor. We performed prospective pilot studies on ventilated neonates requiring intensive care (PETCO₂ gap study: n  =  24, 14 surviving, seven non-surviving patients, weight: 1930 ± 1136 g; tCO₂ gap study: n  =  10, weight: 2471 ± 774 g, all surviving patients). Student’s t test and Pearson’s correlation were applied as statistical methods.

Results The PETCO₂ gap was higher than conventional PCO₂ gap (12.0 ± 9.9 versus 6.1 ± 9.9 mm Hg, p<0.01) whereas there was no significant difference between the tCO₂ and conventional PCO₂ gaps (1.1 ± 5.8 versus 0.1 ± 7.7 mm Hg). There were significant correlations (p<0.01, r  =  0.58) between any two of the four PCO₂ parameters.

Conclusions According to our findings the PETCO₂ and possibly also tCO₂ gaps may be used as methods of continuous estimation of splanchnic perfusion. However, because of the difficulties in the technique of the measurement of tCO₂ and PETCO₂ in neonates, the conventional PCO₂ gap should not be abandoned.