[Evaluation of cerebral perfusion during aortic clamping and cross-clamping in patients undergoing resection for abdominal aortic aneurysm. A study with transcranial doppler].

OBJECTIVE

To evaluate the cerebral blood flow parameters assessed by transcranial Doppler during aortic cross-clamping and unclamping in patients undergoing abdominal aortic aneurysmectomy.

METHODS

Invasive intraoperative monitoring of mean arterial pressure (MAP) and PaCO2, and right middle cerebral artery (RMCA) monitoring of blood flow parameters (mean velocity "Vm" and pulsatility index "PI") by transcranial Doppler were performed as well as evaluation of the four parameters during these subsequent periods: pre-cross-clamping, pre-unclamping, unclamping and 1-5-10-20 minutes after abdominal aortic unclamping.

RESULTS

No significative changes of MAP, PaCO2, Vm and PI were noticed during the aortic cross-clamping period (77.5 +/- 18.5 SD minutes). During aortic unclamping Vm and MAP decreased (64 +/- 20 vs 52 +/- 20 cm/sec, p < 0.05, and 101 +/- 8 vs 80 +/- 15 mmHg, p < 0.01, respectively). At the 1th post-unclamping minute there was an increase from pre-unclamping values of Vm (75 +/- 20 cm/sec, p < 0.05) and PaCO2 (42 +/- 1.5 vs 36 +/- 2 mmHg, p < 0.05), with persistent reduction of MAP (92 +/- mmHg, p < 0.05), even more evident at the 5th post-unclamping minute (Vm = 93 +/- 25 cm/sec; PaCO2 = 46 +/- 1.2 mmHg, p < 0.001, and MAP returned to pre-unclamping value), in which there was also a decrease of PI (0.65 +/- 0.16 vs 0.78 +/- 0.2, p < 0.05). At the 10th minute Vm (83 +/- 24 cm/sec, p < 0.02) and PaCO2 (41 +/- 1.5 mmHg, p < 0.05) increments were present together with persistent reduction of PI (0.69 +/- 0.17, p < 0.05), while at the 20th post-unclamping minute also Vm, PaCO2 and PI returned to their pre-unclamping values.

CONCLUSIONS

The Vm decrease at aortic unclamping might correlate with the acute changes in MAP (blood steal hypovolemia) and is likely due to an inadequate cerebral autoregulatory response to abrupt MAP changes. The arterial CO2 increase after aortic unclamping could lead to a dilation of cerebral arterioles and a rise of CBF (increase of Vm and decrease of PI). Transcranial Doppler is a simple and reliable technique for the monitoring of cerebral blood flow parameters and seems to be quite suitable for the recognition and the quantification of changes in these parameters induced by surgical manoeuvres able to produce hemodynamic instability.