PCO2 ELECTRODES AT THE SURFACE OF THE KIDNEY DETECT ISCHEMIA

Background: Under ischaemic (anaerobic) conditions there will be an ac cumulation of CO2 in the tissue secondary to a build up of protons tha t is buffered by HCO3-. We reasoned that CO2 could be measured at the surface of the kidney by PCO2 electrodes to detect ischaemic condition s. Methods: Anaesthetized, mechanically ventilated pigs (25-30 kg) wer e investigated. Two acute porcine models, one of haemorrhagic shock an d one of renal artery stenosis were used. Renal blood flow was gradual ly decreased, either by successive episodes of bleeding through the ar terial cannula or by successive snaring of the renal artery. Results: In both models we found that with decreased blood flow but maintained aerobic metabolism (supply independence) PCO2 both at the surface of t he kidney and in the renal vein increased by 2-3 kPa. Thus, the tissue -venous PCO2 difference did not change much. At DO2 crit, i.e., at the transition to supply-dependent O-2 consumption, the tissue PCO2 start ed to increase rapidly, as did the tissue-venous PCO2 difference. This is compatible with the notion that a hallmark of ischaemia is decreas ed ability of the blood to transport away waste products because the c ontact between large parts of tissue and blood is virtually non-existe nt. In the renal artery stenosis model kidney surface PCO2 values rose from a baseline of 6.6+/-0.6 kPa (mean+/-SEM) to a value near DO2 cri t of 10.6+/-0.8 kPa, reaching a final value of 29.9+/-3.5 kPa at no fl ow. PCO2 in the renal vein, however, reached a maximum of only 8.2+/-0 .6 kPa. Numbers very similar to these were also found in the haemorrha gic model. The urine production decreased before the onset of ischaemi a. When surface PCO2 values increased sharply indicating ischaemia, th e urine production was zero. Lactate production by the kidney correlat ed very well with increasing tissue PCO2 values further corroborating that anaerobic metabolism was detected with the electrodes. Conclusion : We conclude that PCO2 electrodes placed at the surface of the kidney detect renal cortical ischaemia. (C) Acta Anaesthesiologica Scandinav ica 40 (1996)