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Ann Thorac Surg 2005;79:139-146
© 2005 The Society of Thoracic Surgeons
eref A. Küçüker, MDb
ta
, MDb
uz Tademir, MDb
a Department of Anesthesiology and Reanimation, Ankara, Turkey
b Cardiovascular Surgery Clinic, Turkiye Yuksek Ihtisas Education and Research Hospital, Ankara, Turkey
Accepted for publication June 11, 2004.
* Address reprint requests to Dr Erdemli, Turkiye Yuksek Ihtisas Education and Research Hospital, Department of Anesthesiology and Reanimation, 06100, Shhiye, Ankara, Turkey (E-mail: erdemli{at}tr.net).
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Abstract |
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METHOD: Fifteen consecutive patients (mean age of 53 ± 3.3 years) underwent surgical reconstruction of aortic arch with antegrade selective cerebral perfusion through the right brachial artery. We monitored maximum, minimum and mean blood flow velocities of bilateral middle cerebral arteries using the transcranial Doppler technique at four different time periods: after induction of anesthesia, during cardiopulmonary bypass, during antegrade selective cerebral perfusion, and after termination of cardiopulmonary bypass. We compared the results of brachial cannulation group with aortic group.
RESULTS: Following induction, no significant differences were observed in the right and left middle cerebral artery blood flow velocity measurements in and between the groups. During cardiopulmonary bypass, Vmax and Vmean decreased significantly in both groups. When two groups were compared there was a significant decrease in the left Vmax values of brachial group (p = 0.048). In-group comparisons revealed that Vmax values were lower in left middle cerebral artery than right middle cerebral artery in brachial group (p = 0.002). With the initiation of antegrade selective cerebral perfusion in brachial group, significant decrease occurred in Vmax and Vmean when compared with cardiopulmonary bypass values. When left and right sides were compared, although Vmin values remained similar, Vmax and Vmean values decreased significantly in the left side (p = 0.001 and p = 0.003, respectively). After cardiopulmonary bypass, in both groups, all values restored to initial values and indicated no difference between left and right middle cerebral artery in the groups as well as between the groups. No neurologic deficit was observed in any patient postoperatively.
CONCLUSIONS: Antegrade selective cerebral perfusion through the right brachial artery, as a method of cerebral protection for aortic arch repair, seems to provide adequate perfusion for both right and left cerebral hemispheres.
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Introduction |
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Antegrade selective cerebral perfusion through cannulation of the right brachial artery has been routinely used in our clinic since 1996 [3]. Although ASCP, through the cannulation of the brachial artery, is gaining acceptance for cerebral protection there are some questions to be answered: whether cerebral perfusion through left hemisphere is adequate, whether the perfusion through the circle of Willis is enough, and how we can recognize the insufficient perfusion of the left hemisphere?
Aaslid and colleagues [5] first introduced the use of transcranial Doppler (TCD) ultrasonography to monitor blood flow velocity in the basal cerebral arteries in 1982. This noninvasive, inexpensive, and easy method has the advantage of estimating the blood flow indirectly within given intervals and duration of time. Accordingly, we evaluate and compare the safety and efficacy of bilateral middle cerebral artery (MCA) blood flow during ASCP through the right brachial artery using the TCD technique and investigate the relationship between those measurements and postoperative neurologic outcome.
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Material and Methods |
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Verification of effective collateral perfusion through both the carotid and vertebrobasiler arterial systems, including the middle cerebral arteries, the basilar artery, the vertebral arteries, the extra of internal carotid arteries, were documented with TCD before the operation. Demographics and operative data are presented in Table 1. Institutional ethic committee approval and informed patient consent was obtained from all patients.
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The cardiopulmonary bypass (CPB) circuit consisted of roller pump, cardiotomy reservoir, arterial filter and a membrane oxygenator (Medos Hilite 7000, Stolberg, Germany) with integrated heat exchanger. The circuit was primed with 700 mL lactated Ringer's solution, of mole/L sodium bicarbonate, and 5000 IU heparin. The 
-stat approach was used during hypothermia. Arterial blood gases were monitored and measured at 37°C with a blood gas analyzer. Blood electrolytes, glucose and osmolality were monitored and kept within normal ranges; perfusion pressure was maintained at 50 to 70 mm Hg. Hematocrit level was maintained at greater than 20% during whole CPB period.
Transcranial Doppler
Following intubations, two 2.5-MHz pulse-wave ultrasonography transducer were positioned over the left and right temporal sound window to monitor the maximum (Vmax), minimum (Vmin), and mean (Vmean) blood flow velocities of the cerebral blood flow of the bilateral MCA. As we used 2.5-MHz transthoracic probe of HP Sonos 1000 Ultrasound device (Hewlett Packard, Palo Altos, CA), it was too large to be used with ready-made probe holders. So we used a tube holder attached to the surgical table and fixed the probe in order to press strongly enough on the temporal bone. This device maintained adequate contact on upper zygomatic arc region called temporal window during the procedure. In order that, we could measure blood flow velocities of both right and left middle cerebral arteries continuously. Common carotid arteries compression tests were used in all patients for reliable assessment of the anterior and posterior communicating arteries functional patency. Each carotid artery was compressed for three to five cardiac cycles, to assess the collateral function of the anterior and posterior communicating arteries and to determine the peak systolic velocity decrease in the MCA in both hemispheres. We did not determine any inadequate collaterals of the communication artery in these tests. But, we observed closed temporal window in 2 patients, and therefore we could not test collaterals in these patients. In these patients for the control of adequate selective cerebral perfusion, we used EEG and followed the spontaneous blood flow from the left subclavian artery. After verifying the patency of communicating arteries, we have proceeded to monitor MCA blood velocities at four different time periods; after induction of anesthesia (T1), during CPB (T2), during ASCP (only in brachial group; T3), and following termination of CPB (T4).
Operative Technique
Operative technique used was described in our previous published study [3]. Briefly, dissection and cannulation of the right upper brachial artery was done before median sternotomy. A medial longitudinal incision is made along the bicipital groove into the axillary fossa. The incision is carried down to the fascia of the biceps after identifying its medial border. The muscle is then retracted anteriorly; the neurovascular bundle appears under a thin aponeurotic sheath, which is then opened. After heparin administration, arterial soft clamps are placed proximal and distal to the cannulation site. The artery is cannulated with a nonwire-reinforced venous return catheter (California Medical Laboratories, Irvine, CA), the tip of which is trimmed to 16 to 18Fr diameters according to the size of patient's brachial artery. The catheter is gently inserted into the artery, as its tip is positioned 5- to 7-cm proximal to the arteriotomy. The cannula is then connected to the CPB circuit as usual for any arterial return cannula.
Full-length sternotomy was performed in all patients, and a bistage single venous cannula was positioned in the right atrium for the venous return. Myocardial protection was provided with intermittent antegrade and retrograde cold blood cardioplegia and topical cooling. CPB is instituted with 2.0 to 2.2 L/min/m2. For patients having a body surface area (BSA) above 2 m2, to prevent high-pressure gradients along the cannulation site we preferred not to increase the flow above 4.5 L/min. When rectal temperature has reached 26°C, flow of the arterial return through the upper brachial artery cannula is adjusted to 500 to 600 mL/min (8 to 10 mL/kg/min). The innominate, left common carotid, and, occasionally, the left subclavian artery (but only if the returning blood interferes with suturing) are clamped with soft vascular clamps. We believe leaving the left subclavian artery unclamped will not lead to steeling of cerebral blood due to small size of vertebral and posterior communicating arteries but will serve as a siphon to prevent brain edema during ASCP. Besides, free blood flow through left subclavian artery indirectly indicates blood flow passage from right hemisphere to left hemisphere through communicating arteries. Then, cross-clamp on the aorta is released. All arch reconstructions and distal anastomosis were performed with open aortic anastomosis technique while low-flow perfusion through the upper brachial artery continued. Open distal anastomosis technique was the preferred method for ascending aneurysms as well since all ascending aneurysms of this cohort were reaching the origin of innominate artery and applying the cross clamp proximal to the innominate artery would influence the security of the distal anastomosis. After terminating the distal repair the flow through the upper brachial artery cannula is increased gradually as the soft clamps on the brachiocephalic vessels are released. Air is removed from the vessels and grafts, which are then filled with blood, and the distal graft is cross-clamped. Normal flow rate is reached through the upper brachial artery cannula and rewarming is begun in accordance with the time necessary for proximal repair.
Neurological outcome and postoperative complications were evaluated and recorded in the intensive care unit (ICU).
Statistical Analyses
Measured values are given as mean ± standard deviation. Statistical analysis was performed using SPSS for Windows (version 10.1.1) statistical program (SPSS, Inc, Chicago, IL). Student's t test was used to compare two different independent group's means in parametric and Mann-Whitney U test in nonparametric variables. For paired samples the t test was used to compare right and left measurements means in parametric and Wilcoxon signed ranks test in nonparametric variables in the same groups. Analysis of variance with repeated measures test was used to compare three and four different times' measurements in parametric variables, and Friedman test in nonparametric variables. Post hoc multiple comparison test was also performed after analysis of variance with repeated measures and Friedman tests. A p value less than 0.05 was considered as significant in all of the tests.
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Results |
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Right and left MCA blood flow velocities measured by TCD and expressed as Vmax, Vmin, and Vmean are shown in Tables 2, 3, and 4, respectively, which correlate to the study groups: brachial and aortic groups.
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After the weaning of CPB, Vmax and Vmean values restored to initial values and showed no difference in Vmax measurements of left and right MCA within the groups (p = 0.625, p = 0.365) as well as between the groups (p = 0.398, p = 0.513).
When we examined the period of ASCP (that is only for the brachial group); we noticed the decrease in all velocity measurements. We observed that the left MCA Vmax and Vmean values were lower than the right MCA values (p = 0.001, p = 0.003 respectively), whereas Vmin values demonstrated no difference when compared with each other (p = 0.239).
Figures 1 and 2 illustrate velocity changes of brachial group at four different time periods. No major or temporary neurologic dysfunction was observed in both groups and all patients were discharged from hospital without any complication.
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Comment |
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Sakurada and associates [10] compared the effect of retrograde cerebral perfusion, ASCP, and hypothermic circulatory arrest on cerebral functions of mongrel dogs using SEP and concluded that ASCP was the safest method for arch reconstruction that requires cerebral protection for 90 minutes.
In our surgical technique, the right brachial artery is cannulated and low-flow ASCP is instituted during aortic arch repair. Because the brachiocephalic vessels are not directly cannulated, this modified technique is simple, decreases the risk of embolization, and provides better surgical exposure by not cluttering the field with cannulas and lines [3].
Tanaka and coworkers [11] suggested in an animal study that the safe range of flow rates for cerebral perfusion during moderate hypothermia is greater than 50% of the physiologic level with a carotid arterial pressure of about 30 mm Hg or more. In experimental and clinical studies, during hypothermic CPB, cerebral blood flow (CBF) appears to be adequate with pump flow of 1 to 1.6 L/min/m2 at 28°C and as low as 1 L/min/m2 at 21 to 25°C [12]. Both studies used somatosensory evoked potential measurements to evaluate the efficacy of cerebral function at different levels of flow rates. Finally, they claimed that flow rate rather than perfusion pressures per se influence the cerebral function during CPB. Thus, the effect of varying pump flow rate on CBF during hypothermic CPB depends on the integrity of blood pressure autoregulation. During hypothermic CPB, CBF decreases proportionately less than other organ blood flows as pump flow rate is reduced [13]. During antegrade selective cerebral perfusion high pressure and high flow may result in postoperative complications as brain edema caused by the loss of cerebral autoregulation during hypothermia [11]. We, therefore, preferred the low-pressure and low-flow method guided with neuromonitoring, as Tanaka and coworkers [11] proposed, with CBF rate measurements that permits autoregulation and protection against ischemia or hyperperfusion.
The concept of unilateral selective cerebral perfusion may arise concern about the adequacy of preservation for contralateral hemisphere. The two vertebral arteries and two internal carotid arteries supply the brain, and an extensive anastomosis (the circulus arteriosus) exists between them. The anterior communicating artery joins the two anterior cerebral arteries to each other; behind the basilar artery divides into the two posterior cerebral arteries, each of which is joined to the internal carotid artery of the same side by the posterior communicating artery (Fig 3). Hypothetically the absence of one of the three communicating arteries in the circle of Willis should not carry hypoperfusion risk since the blood from the right brachial artery will perfuse the whole brain through vertebral, basilar, and internal carotid arteries. The only case in which a potential hazard for contra-lateral lobe hypoperfusion exists is the absence of both anterior and left posterior communicating arteries. Hoksbergen and colleagues [14], in their transcranial duplex study investigating the influence of collateral function of the circle of Willis on 46 cases, mentioned this combination to occur in 1 patient. Because we couldn't find any other article mentioning this combination in the medical literature, we presume that this kind of incidence should be very rare than the 2% proposed by Hoksbergen and associates [14]. However, even in such a case, only the frontal and temporal parts should become affected [15]. Consequently, when suspected the insufficiency of collateral circulation, additional cannulation for perfusion through the left common carotid artery is an easy method to overcome the dilemma.
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Tanoue and coworkers [18] had studied the retrograde cerebral perfusion (RCP) and ASCP with TCD and found that retrograde MCA flow velocities during RCP could be measured in only 3 patients and were 6%, 20%, and 21% of MCA flow velocities before CPB. In the other 12 patients in the RCP group, retrograde MCA flow velocities during cerebral perfusion could not be detected. However, MCA flow velocities could easily be measured in 16 patients of the ASCP group, and the average velocity was 43.8% ± 35.8% of MCA flow velocity before CPB.
In our series, TCD measurements demonstrated that during induction, no significant differences were observed in the right and left MCA blood flow velocity measurements in and between the groups.
During CPB, in the aortic group, no difference was observed between the left and right side. In the brachial group, right-sided Vmax values were statistically higher than left side after the initiation of CPB. This is comprehensible because, in the aortic group cerebral hemispheres obtain same amount of blood through right and left carotid arteries, but in the brachial group, while right carotid artery gets direct flow, left carotid artery is probably receiving less flow due to vortex currents around its origin.
At the onset of ASCP in the brachial group, comparison between the left and right side, demonstrated that Vmin values remained similar, whereas Vmax and Vmean values showed further decrease on the left side. At close attention to the results and percentile changes of blood flow velocities, we presume that Vmean value is the most reliable and comprehensible measurement to monitor the cerebral perfusion during CPB and ASCP. Due to nonpulsatile pump flow during bypass, Vmin and Vmax values can be affected from many independent factors such as length and elastance of connecting tubes, squeezing amount of pump head, etc. In view of this reason, we have proposed that Vmean should be considered as a better indicator of blood flow estimation. As well, Nuttall and colleagues [19] clearly determined the correlation of MCA mean velocity and cerebral blood flow during nonbypass and two hypothermic bypass flow conditions. However, probable reasons that cause changes in Vmin and Vmax need further research.
A reduction of blood flow at the left side was observed after the on set of ASCP. Nevertheless, TCD revealed that the blood flow never stopped and this reduced flow as far as our neurological results concerned, is satisfactory to maintain the metabolism of the left hemisphere. However, one may question a situation where additional left common carotid artery perfusion is necessary to protect the left hemisphere in terms of the discrepancy of the blood flow velocity. Because no neurologic event was observed in this study, we cannot state a critical level for the left MCA flow velocity. Certainly cessation of free blood flow through left MCA in the surgical field is an indication for additional left hemispheric perfusion. In case of a significant drop for left MCA flow velocity when compared with the right side, level of hypothermia, estimated time required for the distal repair and surgeons‘ own observation about the amount of returning blood by left common carotid artery at the onset of ASCP should be the guiding points for using additional perfusion through left common carotid artery.
The presented study cohort had relatively short periods of cerebral low blood flows. In 1 patient, after 81 minutes ASCP, we found satisfactory results. Hence, favorable neurological outcomes of this cohort may not be totally attributable to our ASCP technique. However, in a report covering 104 patients recently published by our group using the ASCP technique with longer periods of cerebral low-flow periods (mean duration range), the total neurological incidence rate was 1.9% [3]. We also investigated postoperative neurocognitive functions testing both right and left hemispheres among a different cohort of 22 patients and we did not observe any loss of neurocognitive function when compared with preoperative test results [20].
In conclusion, ASCP through the right brachial artery, as a method of cerebral protection for aortic arch repair, seems to provide adequate perfusion for both right and left cerebral hemispheres. TCD ultrasonography is a very satisfactory tool to confirm the adequacy of the blood flow to left hemisphere during unilateral antegrade cerebral perfusion. We deem that this noninvasive technique may further contribute to neurological safety obtained by the use of antegrade cerebral perfusion.
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Acknowledgments |
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TopAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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References |
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TopAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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demir O, Sartas A, Küçüker , Özatik MA, ener E. Aortic arch repair with right brachial artery perfusion Ann Thorac Surg 2002;73:1837-1842.This article has been cited by other articles:
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= Vmax; 
= Vmin; 
= Vmean; ASCP = antegrade selective cerebral perfusion; CPB = cardiopulmonary bypass.)
