Intracranial Hemodynamics in Endovascular Exclusion of Cerebral Arteriovenous Malformations from Blood Circulation: Intraoperative Monitoring

Semenyutin V.B., Nikitin P.I., Bukhaev I.M., Alexeev V.V.

Russian Polenov Neurosurgical Institute Saint Petersburg, Russia

Development of modern technologies, used for superselective embolization of arteriovenous malformations (AVM), resulted in possibility of their radical exclusion from blood circulation [2, 6, 7, 8, 15]. The most informative parameters of such exclusion were found out [4, 5, 13, 14, 16, 18] and surgical tactics of multi-stage operations was determined [1, 9, 25, 26]. At the same time there are several unsolved problems, connected with ischemic complications, which develop in a postoperative period and lead to disability of operated patients [9, 17, 22, 23]. In such a situation intraoperative monitoring of intracranial circulation at all stages of superselective embolization of AVM acquires more and more importance.

The most frequent method of reducing a rate of complications due to ischemia, following AVM embolization, is preliminary estimation of afferent vessels and their functional significance by administration of barbiturates with a short-term effect (Amobarbital, Bryetal, Sodium Thiopental, Amytal, etc.) into an examined vessel. Focal neurologic symptoms, watched in a short period of time after it, are indicative of functional significance of this vessel. However, this test has considerable limitations under conditions of anesthesia [8, 21]. Besides, one should always keep in mind a possible side effect of an administered drug. Thus, this test cannot be regarded as highly informative.

Simulation of cerebral hemodynamics of patients with AVM demonstrated dependence of blood pressure (BP) in afferent vessels on a degree of shunting and a volume of blood, flowing through AVM [11, 12, 19]. An afferent vessel diameter was dependent on volumetric blood flow velocity in it [20]. Use of up-to-date technologies in microsurgery, in particular microcatheters for embolization, allows to measure BP in afferent vessels. It appears, that its value with taking into account the above-mentioned conditions can be an index of functional significance of AVM's afferent vessels.

The Study Goal

Possibility of estimating functional significance of an afferent vessel of AVM by direct measurement of blood pressure in it during intraoperative monitoring of intracranial hemodynamics.

Materials and Methods

There were 21 patients with cerebral AVM of the 3rd-5th grade according to Spetzler, Martin [24]. They underwent 29 superselective embolizations (1 intervention - 15 cases, 2 interventions - 4 cases; a three-stage operation was performed in 2 patients). Magic STD 1.8F microcatheters (Balt, France) were used.

A universal algorithm of operations for AVM was worked out by us some time ago. Surgical technique of multistage superselective embolizations of AVM is presented in Fig.1.

A system of intraoperative monitoring included bilateral recording of linear blood flow velocity (BFV) in major arteries of preferential (in relation to AVM) and contralateral (taking no part in blood supply of AVM) vascular regions with transcranial Doppler (Multi Dop X), and direct measurement of systemic blood pressure (SBP) in a femoral artery and BP in afferent vessels of AVM (Mingograph M-34). A diameter of AVM's afferent vessels and initial segments of arteries of a preferential vascular region were determined with the help of angiography and a calibrated marker of a microcatheter for superselective embolization. An index of flow in arteries of a preferential region was calculated on the basis of a special formula [10]. Sodium Thiopental (30-50 mg) was administered through a microcatheter before each embolization with the purpose of estimating functional significance of an afferent vessel [8]. A barbiturate test (BT) was considered to be positive in appearance or augmentation of neurologic symptoms. It was regarded to be negative in the absence of any changes in a neurologic state.

Results and Discussion

BT was carried out after catheterization of an afferent vessel and stabilization of recorded indices of intracranial hemodynamics. It was done in accordance with an algorithm, presented in Fig.1.

BT was negative in 22 cases. BP in afferent vessels varied from 11 up to 43 mm Hg, which made 17-49% of SBP. A diameter of afferent vessels was within the range of 1.8-3.8 mm (2.4±0.4 mm). Mean BFV in initial segments of arteries of a preferential vascular region was equal to 119±32 cm/s. A calculated value of a flow index in these arteries was 516±160 ml/min. BP in exclusive afferent vessels, feeding AVM only, did not exceed 50%, when volumetric blood flow in them was 50 ml/min. It was in compliance with data, computed on a model [11]. Thus, the value of BP in afferent vessels was indicative of their low functional significance in all 22 cases. Maybe, variability of this index was dependent on (a) different volume of blood, flowing through examined afferent vessels and (b) possible participation of AVM's afferent vessels in feeding functionally insignificant areas of the brain, which was confirmed by BT values. There were no complications in a postoperative period after AVM embolization (complete exclusion of AVM's part from blood circulation via examined afferent vessels), performed in these 22 cases. Data of intraoperative monitoring, recorded in one patient during superselective embolization of AVM, are given in Fig.2. Exclusion of AVM from circulation was accompanied by reduction of BFV in an artery of a preferential region up to the level of BFV in an artery of a contralateral side, which did not take part in supplying AVM with blood. BP in an afferent vessel increased after the first administration of an embolizing substance. However, according to the worked out criteria of radical exclusion of AVM [3], its value was insufficient. It was confirmed by angiographic examinations. The second embolization led to increase of BP up to the level, corresponding to radical exclusion, which was confirmed angiographically.

BP in afferent vessels of 4 patients with positive BT varied within the limits of 56-73 mm Hg, which made 51-81% of SBP. A diameter of afferent vessels was not more than 3 mm (2.0-2.6 mm). Mean BFV in initial segments of arteries of a preferential region was 137±31 cm/s. A calculated value of a flow index in these arteries was equal to 568±122 ml/min. According to calculated values and data of BT, blood supply of functionally eloquent cerebral structures by these afferent vessels was partial. We did not perform embolization of AVM via these afferent vessels.

BT was negative in 3 cases. However, monitoring of intracranial hemodynamics was indicative of functional significance of an afferent vessel. BP in afferent vessels ranged from 42 up to 55 mm Hg, which made 54-76% of SBP. A diameter of afferent vessels was within 2.5-2.6 mm. Mean BFV in initial segments of an artery of a preferential region was 125±23 (96-152) cm/s. A calculated value of a flow index in these arteries was 611±108 (465-724) ml/min. Nevertheless, taking into account a leading position of BP in determining indications for surgical intervention, superselective embolization was made in all 3 cases. It resulted in complete exclusion of AVM's part from blood circulation via examined afferent vessels. There was augmentation of neurologic symptoms in all 3 patients in an early postoperative period (3-4 hours after operation). They manifested themselves in hemiparesis, motor aphasia and hemianopsia. Development of these complications could be connected with an effect of anesthesia or individual sensitivity of a patient to barbiturates, used in BT.

Mean values of recorded and calculated indices, watched in positive and negative BT, are given in Fig.3. There was reliable difference in a mean value of BP in afferent vessels. When groups of patients with a negative (25.1±8.6 mm Hg) and positive (66.0±6.4 mm Hg) BT were compared, it turned out, that difference in this index was characterized by the highest reliability, i.e. p<6.6´10-9. Comparison of relative values of this index showed that reliability of this difference was even higher. BP in afferent vessels of patients with a negative BT was reliably higher (p<0.0003) in cases with postoperative complications (47.7±5.4 mm Hg). It did not differ much from values, obtained in patients with a positive BT. We failed to find reliable difference in calculated values of a flow index in arteries of a preferential region (p>0.4).

Comparative analysis of results of determining functional significance of AVM's afferent vessels on the basis of BT and BP, recorded during intraoperative monitoring, shows, that a value of BP in afferent vessels is no less informative than a value of BT. In our opinion, use of BP in afferent vessels for estimation of their functional significance has several advantages. Among them one can mention simple, reliable and quick obtaining of quantitative data on functional significance of AVM's afferent vessels, absence of contraindications in any AVM localization and possibility of its assessment at any stage of anesthesia.

Thus, a value of BP in an afferent vessel of AVM, recorded during intraoperative monitoring of intracranial hemodynamics, can be used for estimation of both radical exclusion of AVM and vessel's functional significance. A system of intraoperative monitoring with measurement of BP in afferent vessels of patients with cerebral AVM of different localization allows to achieve considerable reduction of complications, increasing a risk of invalidism, in superselective embolization, performed via these vessels.

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