Changes in piCO2 reflect splanchnic mucosal ischaemia more reliably than changes in pHi during haemorrhagic shock

Background: Gastric tonometry is intended to reveal alterations in splanchnic perfusion and oxygenation. Based on the tonometric measurement of gastric mucosal partial pressure of carbon dioxide (PCO2) and the simultaneous determination of arterial blood gas parameters (bicarbonate concentration [HCO3-] pH and pCO(2)), several parameters can be calculated. Aims: To identify the most suitable tonometric parameter [gastric mucosal pH (pH(i)), intramucosal PCO2 (p(i)CO(2)), the difference between tonometric and arterial pCO(2) concentrations (PCO2 gap), [H+] gap] that reliably reflects gastric hypoperfusion and hypoxia during severe haemorrhagic shock. Design: Randomised, controlled experimental study. Methods: An artificial stenosis of the left anterior descending coronary artery (LAD) was induced. Subsequently, the animals were haemorrhaged to a mean arterial pressure of 45 mmHg, which was maintained for 60 min. Measurements and main results: Tonometric measurements 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 [arterial pCO(2) (PaCO2), [HCO3-], arterial pH (pH,)]. While induction of critical coronary stenosis did not provoke any changes, all parameters changed significantly during haemorrhagic shock. The lowest P value was found for pHi (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 lower by a factor of ten than the P value of PiCO2. Conclusion: pH(i), PCO2 gap and [H+] gap are considerably influenced by changes of systemic arterial blood gas values. This is demonstrated by lower P values of the corresponding arterial blood gas values in comparison with PiCO2. Therefore pHi, PCO2 gap and [H+] gap seem to indicate more likely systemic changes, whereas PiCO2 appears to reflect disturbances of regional gastric tissue perfusion and oxygenation more reliably than any other derived tonometric parameter.