Changes in p_iCO₂ reflect splanchnic mucosal ischaemia more reliably than changes in pH_i during haemorrhagic shock

Abstract.

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 pCO₂), several parameters can be calculated. Aims: To identify the most suitable tonometric parameter [gastric mucosal pH (pH_i), intramucosal pCO₂ (p_iCO₂), the difference between tonometric and arterial pCO₂ 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 pCO2 (p_aCO₂), [HCO₃ ^–], arterial pH (pH_a)]. 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 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 p_iCO₂ (P=0.00562). P values of the corresponding arterial blood gas parameters were lower by a factor of ten than the P value of p_iCO₂. 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 p_iCO₂. Therefore pH_i, pCO₂ gap and [H⁺] gap seem to indicate more likely systemic changes, whereas p_iCO₂ appears to reflect disturbances of regional gastric tissue perfusion and oxygenation more reliably than any other derived tonometric parameter.