Evaluation of the 5-French saline paediatric gastric tonometer

Objective: To evaluate the paediatric 5-French (Fr) saline-filled gastric t onometer. Design: (a) In vitro comparison of saline bath reference pCO(2) w ith tonometric pCO(2) measured by normal saline-filled and phosphate-buffer ed saline-filled 5-Fr tonometers, and by a recirculating gas tonometer. (b) In vivo comparison of gastric intramucosal pCO(2)i, measured by normal sal ine-filled 5-Fr tonometer (NST) and simultaneously by recirculating gas ton ometer (RGT) in ten paediatric intensive care patients. (c) In vivo compari son of pCO(2)i measured simultaneously by 2 NST 5-Fr tonometers, before and after enteral feeding, in ten paediatric intensive care patients. Measurem ents and main results: (a) Twenty consecutive measurements of pCO(2) were m ade at constant reference pCO(2) of 19, 38, 56, and 75 mmHg (2.5, 5.0, 7.5, and 10.0 kPa), respectively. The NST tonometer underestimated reference pC O(2) by mean bias (limits of agreement) of 58 % (20 %), and the phosphate-b uffered saline-filled tonometer by 6 % (26 %). The RGT showed mean bias 5.7 % with narrow limits of agreement (1.5 %). (b) In 50 paired (NST vs. RGT) in vivo measurements over pCO(2)i range 23-73 mmHg (3.0-9.7 kPa), the NST u nderestimated RGT pCO(2)i by a mean bias of 10 mmHg (1.3 kPa), with limits of agreement + / -10 mmHg (1.5 kPa). This resulted in NST consistently over estimating pHi and underestimating pCO(2) gap (both P < 0.001). (c) One hun dred simultaneous paired NST measurements were assessed (50 without, and 50 with enteral feeding). The mean biases (limits of agreement) were identica l in the fasted and fed states 0.4 +/- 6 mmHg, with no difference between t he fed and fasting states (P = 0.7). Conclusions: There are inherent proble ms in the methodology of saline tonometry, which adversely affect the accur acy and reliability of the 5-Fr paediatric gastric tonometer in comparison to recirculating gas tonometry.