Gastric tonometry:: in vivo comparison of saline and air tonometry in patients with cardiogenic shock

Measurement of gastric intramucosal pH (pHi) has been advocated to assess gastric perfusion. Regional Pco(2) (rPco(2)) values are measured using saline tonometry (rsPco(2))and more recently using air tonometry (raPco(2)). We compared 237 measurements of saline and air tonometry in 19 consecutive, severely ill patients (mean age 59 (range 31-76) yr, 19 males, APACHE 11 22+/-7) with cardiogenic shock. Equilibration period was set to 90 min. Nineteen independent paired samples of mean raPco(2) and mean rsPco(2) of each patient showed good correlation (r=0.93, P < 0.001). Mean raPco(2) was 6.5 (1.8) kPa and mean rsPco(2) 6.8 (2.4) kPa. Pco(2) measured by saline was significantly higher than that measured by air (P < 0.05). Bland and Altman analysis showed a bias (mean rsPco(2)-mean raPco(2)) of 0.3 kPa and a precision of 1.2 kPa. Agreement between the two methods decreased with increasing rPco(2) concentrations. Although air tonometry of rPco(2) is a promising technique, a systematic disagreement with saline tonometry at high rPco(2) values requires further investigation and cautious interpretation of these values.