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Inter-relation between splanchnic ischaemia measured by air-tonometry and renal function

Background and goal of study

Air tonometry is a common method to examine splanchnic hypoxia, which often is a predictor of severe clinical complications such as sepsis or renal failure. Urodilatine is one of the indicators of renal function. A retroperspective case–control study was conducted considering whether there is an inter-relation between splanchnic ischaemia and renal function.

Patients and methods

After approval of the local ethics commitee, 39 intensive care patients have been studied. The age of the patients diverged from 37 to 98 years (median age 64 years). Hemodynamic variables, including continuous cardiac output, air-tonometric variables via a nasogastric tube (Tonocap Datex, Helsinki, Finland), arterial lactate, urine production, heart rate, central venous pressure (CVP) and mean arterial pressure, were measured every hour. Furthermore, renal values, such as urodilatine, ANF and urine excretion have been assessed after 6, 7 and 8 hours.

The increase of the CO2 gap values within the first 6 hours was determined by curve estimation and correlated (bivariate correlation) with indicators of renal function using Spearman's rho and Pearson correlation. The CVP increase within the first 6 hours was assessed similar to the CO2 gap increase.

Results and discussion

Between air tonometry values and renal function, a significant contiguity (P < 0.05) was found.

A bivariate correlation level of -0.356 (P = 0.039) between the CO2 gap increase and urine urodilatine assessed after 7 hours resulted. Spearman's rho was -0.358 (P = 0.044) between the CO2 gap increase and urodilatine extraction, and was 0.407(P = 0.014) between the CO2 gap increase and urine excretion after 7 hours.

The strongest correlation was found between the CO2 gap increase and the urodilatine–creatinine ratio (-0.503, P = 0.012). There was no correlation between CO2 gap increase and serum creatinine. There also was no appreciable inter-relation between CVP increase and CO2 gap increase (Pearson = 0.000, P = 0.999; Spearman's rho = 0.047, P = 0.778).

Furthermore the time of ventilation correlates positively with the CO2 gap increase (0.326, P = 0.043).


This study suggests the CO2 gap increase to be a predictor for decreasing urodilatine values indicating renal failure. Therefore air tonometry is helpful, tendentially detecting deterioration of renal function as sign of multiorgan failure.

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Henniger, A., Brunkhorst, F., Reinhart, K. et al. Inter-relation between splanchnic ischaemia measured by air-tonometry and renal function. Crit Care 8 (Suppl 1), P172 (2004).

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