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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 (pCO(2)) and the simultaneous determination of arterial blood gas parameters (bicarbonate concentration [HCO(3-)], pH and pCO(2)), several parameters can be calculated., Aims: To identify the most suitable tonometric parameter [gastric mucosal pH (pH(i)), intramucosal pCO(2) (p(i)CO(2)), the difference between tonometric and arterial pCO(2) concentrations (pCO(2) 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(a)CO(2)), [HCO(3-)], 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 pCO(2) gap (P=0.00119) and were highest for p(i)CO(2) (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(i)CO(2)., Conclusion: pH(i), pCO(2) 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(i)CO(2). Therefore pH(i), pCO(2) gap and [H+] gap seem to indicate more likely systemic changes, whereas p(i)CO(2) appears to reflect disturbances of regional gastric tissue perfusion and oxygenation more reliably than any other derived tonometric parameter.

The influence of severe acute normovolemic hemodilution (ANH) on myocardial contractility (MC) was investigated in 14 splenectomized, anesthetized dogs. MC was assessed by the maximum rate of left ventricular pressure increase (LVdp/dt(max)), end-systolic elastance (Ees), and preload recruitable stroke work (PRSW) (conductance catheter, left ventricular pressure-volume relationship). Measurements of myocardial perfusion and oxygenation (radioactive microsphere technique) assured comparability of the model to previously performed studies. Global and regional myocardial blood flow increased significantly upon hemodilution with preference to midmyocardium and subendocardium. This resulted in preservation of both myocardial oxygen delivery and consumption after ANH. Myocardial oxygen extraction as well as coronary venous Po2 were unaffected by ANH, while coronary venous lactate concentration decreased, indicating that myocardial oxygen need was met. LVdp/dt(max) decreased significantly after hemodilution (2278 +/- 577 vs 1884 +/- 381 mm Hg/s, P < 0.01), whereas Ees and PRSW increased significantly (1.76 +/- 0.54 vs 2.15 +/- 0.75 mm Hg/mL, P < 0.05, for Ees and 33 +/- 14 vs 45 +/- 14 mm Hg.mL, P < 0.05, for PRSW). While the decrease of LVdp/dt(max) most likely reflects ANH-induced changes of ventricular pre- and afterload, the increase of Ees and PRSW indicates a true increase of myocardial contractility during ANH in anesthetized dogs.