Measurement technique and variation in intramucosal pH.

We have calculated gastric intramucosal pH (pHi) from Trip catheter saline tonometered samples in two patients undergoing ventilation using four different sampling techniques, each repeated five times. pHi was calculated from measurement of PCO2 in tonometered saline (TCO2). TCO2 was measured immediately, and then at 6-min intervals for 30 min. Variation in measurement was greatest for capped syringes stored at room temperature, and least when stored uncapped on ice. TCO2 always decreased significantly within 12 min. The mean difference in pHi (all sampling techniques) over 30 min was 0.1005 pH units. The results indicate that the calculated pHi was subject to variation as a result of both the method of sample storage and delay in measurement. An error of +/- 0.1 pH units may have clinically important implications if pHi is used to monitor either severity of illness or efficiency of resuscitation.