Changes in p(i)CO(2) reflect splanchnic mucosal ischaemia more reliably than changes in pH(i) during haemorrhagic shock

Background: Gastric tonometry is intended to reveal alterations in splanchn ic perfusion and oxygenation. Based on the tonometric measurement of gastri c mucosal partial pressure of carbon dioxide (PCO2) and the simultaneous de termination of arterial blood gas parameters (bicarbonate concentration [HC O3-] pH and pCO(2)), several parameters can be calculated. Aims: To identif y the most suitable tonometric parameter [gastric mucosal pH (pH(i)), intra mucosal PCO2 (p(i)CO(2)), the difference between tonometric and arterial pC O(2) concentrations (PCO2 gap), [H+] gap] that reliably reflects gastric hy poperfusion and hypoxia during severe haemorrhagic shock. Design: Randomise d, controlled experimental study. Methods: An artificial stenosis of the le ft anterior descending coronary artery (LAD) was induced. Subsequently, the animals were haemorrhaged to a mean arterial pressure of 45 mmHg, which wa s maintained for 60 min. Measurements and main results: Tonometric measurem ents were performed in 17 land-race pigs before and after induction of LAD stenosis and after haemorrhagic shock. P values obtained using the Wilcoxon signed-rank testing were used to compare the level of significance for the tonometric parameters and the corresponding arterial blood gas values [art erial pCO(2) (PaCO2), [HCO3-], arterial pH (pH,)]. While induction of criti cal coronary stenosis did not provoke any changes, all parameters changed s ignificantly during haemorrhagic shock. The lowest P value was found for pH i (P=0.00013) followed by [H+ gap] (P=0.0005). P values higher by a factor of ten were found for PCO2 gap (P=0.00119) and were highest for PiCO2 (P=0. 00562). P values of the corresponding arterial blood gas parameters were lo wer by a factor of ten than the P value of PiCO2. Conclusion: pH(i), PCO2 g ap and [H+] gap are considerably influenced by changes of systemic arterial blood gas values. This is demonstrated by lower P values of the correspond ing arterial blood gas values in comparison with PiCO2. Therefore pHi, PCO2 gap and [H+] gap seem to indicate more likely systemic changes, whereas Pi CO2 appears to reflect disturbances of regional gastric tissue perfusion an d oxygenation more reliably than any other derived tonometric parameter.