Cerebral haemodynamics in internal carotid artery trial occlusion

Abstract

The purpose of this study was to analyse the cerebral haemodynamic changes brought about by trial occlusion of the internal carotid artery (ICA). Sixteen patients with surgically inaccessible cerebral aneurysms, carotid cavernous fistulas or neck neoplasms were monitored with transcranial Doppler ultrasonography (TCD) during 90-120 s angiographic ICA balloon occlusion or ICA closure with a Selverstone clamp. The blood velocity (V) was registered continuously in both middle cerebral arteries (MCA) while the pulsatility index (PIMCA) and haemodynamic tension (Uhem MCA) were calculated. ICA closure led to an instantaneous drop in the ipsilateral VMCA, PIMCA and Uhem MCA. The VMCA thereafter increased gradually until reaching a stable level. The subjects were grouped into those with initial drops in VMCA to > or = 60% of pre-occlusion value (group 1) and those that fell to < 60% (group 2), respectively. In group 1 autoregulatory mechanisms made the PIMCA decline further, while the Uhem MCA remained unaltered during ICA closure. In group 2, however, the PIMCA did not change further, while the Uhem MCA increased slightly. The cerebral haemodynamic features during ICA test occlusion were thus essentially different in the two groups. On re-opening the ICA, there was an overshoot in VMCA and Uhem MCA. Contralaterally, the VMCA was increased during ICA occlusion. Seven of the patients later had their ICA closed permanently. While none of five group 1 patients developed haemodynamic complications, two group 2 individuals experienced haemodynamic stroke. Assuming ICA sacrifice is feasible when test occlusion results in an ipsilateral initial reduction in VMCA to > or = 60% of pre-occlusion value, the corresponding limit for the Uhem MCA is > or = 40%. In the pre-operative evaluation of the haemodynamic risk related to ICA loss, TCD emerges as a reliable method. It also seems to allow for the reduction of test occlusion time to 90-120 s.

Monitoring Balloon Test Occlusion of the Internal Carotid Artery with Transcranial Doppler

“…Its main limitation is the inadequate temporal bone acoustic window in some patients, which renders TCD impossible to perform 24 . The published series report a decrease in PS-V MCA < 30% relative to baseline during the occlusive period as a consistent predictive value of clinical tolerance 2,[17][18][19] , with no false negatives. The PSV MCA is considered an estimate of regional blood flow 25 , specifically during the first seconds after balloon inflation, while MCA diameter and territory are constant and before cerebral autoregulation takes place 2,25,26 .…”

“…A PSV MCA reduction > 40% is thought to correspond to a tissue perfusion of approximately 30 ml/100 g/min, a threshold to symptom occurrence in quantitative CBF studies 4,16,19 . To date, no patients with predicted tolerance to ICA occlusion by TCDmonitored BTO (PSV MCA drop < 30%) have suffered haemodynamic infarction after definite occlusion 2,[17][18][19]27 . However, the risk of thromboembolism after arterial occlusion warrants antithrombotic prophylaxis 6 .…”

“…However, the risk of thromboembolism after arterial occlusion warrants antithrombotic prophylaxis 6 . Some authors also advocate the use of minimal occlusion times by implementing TCD monitoring 2,18 with the BTO. Since the haemodynamic response to ICA occlusion is immediate and can be evaluated by TCD, the classic extended occlusion times required for clinical symptoms to develop may no longer be necessary.…”

“…Since the haemodynamic response to ICA occlusion is immediate and can be evaluated by TCD, the classic extended occlusion times required for clinical symptoms to develop may no longer be necessary. In fact, Sorteberg et al 18 reported 86% sensitivity and 93% specificity (positive predictive value of 86%) of TCD analysis of the first seconds after carotid occlusion. With shorter occlusion times, procedure safety and patient comfort could be improved 2 .…”

“…Among these, transcranial Doppler (TCD) stands out as a non-invasive bedside method providing real-time monitoring of cerebral haemodynamics that can accurately identify patients at risk of delayed ischaemic sequelae 2,[17][18][19] . Despite the advantages of TCD and the absence of a universally accepted method to monitor the BTO, its potential is not yet widely recognized.…”