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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3734_Библиотеки_им_академика_М_И_Перельмана
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C. V. Ghincea et al.
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Fig. 1 Common routes of arterial cannulation for the initiation of cardiopulmonary bypass on
acute aortic syndrome. (a) Right axillary cannulation using a tube graft sewn end-to-side. (b)
Innominate artery cannulation using a tube graft sewn end to side. (c) Direct aortic cannulation
using the Seldinger technique and epiaortic ultrasound/transesophageal echo to verify true lumen
access (d) Right axillary cannulation using the Seldinger technique. (e) Right common carotid
cannulation using a tube graft sewn end-to-side. (f) Left common carotid cannulation using a tube
graft sewn end-to-side. Due to potentially complex dissection anatomy multiple arterial cannulation options must be considered with the goal perfusing the true lumen via the most feasible and
expeditious route. In addition to the routes depicted in this gure, femoral artery and left subclavian cannulation are other options which can be utilized. In rare and what ought to be considered
salvage cases, the aorta can be transected and cannulated directly, or cannulation can be achieved
through the apex of the heart
Femoral Cannulation
Femoral cannulation has been traditionally preferred for rapid access and early
cooling. Differential neurological outcomes have not been demonstrated for femoral cannulation versus other sites [3]. Femoral cannulation, especially using a percutaneous approach, is a safe strategy. The pitfalls of femoral cannulation include
potential difculty with accessing the true lumen and the need for separate cannulation to provide cerebral perfusion during circulatory arrest.
Evolving Cannulation Complexity andStrategy
As comfort with circulatory arrest has grown, our institution has become bolder
with cannulation choices. In cases where the innominate artery is spared of dissection, free of signicant atherosclerosis, and a hemiarch replacement is planned, the
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authors will frequently cannulate via 10mm graft sewn end-to-side to the innominate artery with a partial occlusion clamp. However, this takes more time than
routinely stated, so it has become less utilized institutionally. As more aggressive
total arch replacement has become more commonplace, the authors favor central
aortic cannulation (into the true lumen) when possible using transesophageal and
epiaortic ultrasound guidance and a modied Seldinger technique (Fig. 1c) [4].
Simultaneous imaging is critical to conrm true lumen perfusion. While cooling,
we proceed to split arterial perfusion and bypass the brachiocephalic vessels using
a multibranch graft, as shown in Fig.2, that is later connected to a branch of the
arch graft.
The experience from Emory has shown the benet of washout from retrograde
cerebral perfusion (RCP) washout of debris from arterial manipulation during the
cooling period. When using RCP, a 24 French cannula is placed in the superior vena
cava immediately prior to circulatory arrest period with a Rummel tourniquet above
the Azygous vein take off. This will be removed immediately after circulatory arrest
so as not to obstruct venous return from the upper half of the body. The authors have
used the SVC cannula for drainage in the context of bicaval cannulation and RCP
but this conguration requires multiple connections to the cardiopulmonary bypass
circuit. Institutionally we have begun to take advantage of both retrograde and antegrade perfusion during circulatory arrest. Specics of perfusion management during the circulatory arrest period will be discussed later in the chapter.
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Neuromonitoring/Neurophysiological Intraoperative Monitoring
Collectively termed neurophysiological intraoperative monitoring (NIOM), the
most commonly employed modalities for monitoring neurologic function during
aortic arch surgery include EEG, somatosensory evoked potentials (SSEP), motor
evoked potentials (MEP), and cerebral oximetry by near-infrared spectroscopy
(NIRS), as depicted in Fig.3. The argument for overall NIOM use is early detection
of neuromalperfusion. Measures can be instituted at this early point to reverse or
minimize effects of the malperfusion such as suction embolectomy, adding arterial
cannulation sites to watershed areas, or even simple measures like hemodynamic
augmentation with increased central blood pressure. Opponents to NIOM suggest
this monitoring leads to a lot of noise with false positive signals. The authors have
found that while there is some noise, when the neuromonitoring is combined with
clinical perspective, the information can be valuable for preserving neurologic
patient outcomes [5].
Electroencephalography
Continuous EEG monitoring remains the primary NIOM modality utilized by the
authors for all cases involving the aortic arch or hypothermic circulatory arrest,
including hemiarch replacement. Although requiring specialized equipment,
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Fig. 2 Common routes of cannulation for cerebral perfusion during circulatory arrest. (a) For
retrograde cerebral perfusion a right-angle cannula is placed into the superior vena cava above the
insertion of the azygous vein. (b) The innominate artery can be cannulated either percutaneously
(as shown in the gure) or using a graft sewn end-to-side to the vessel. (c) Upon initiation of circulatory arrest, once the aorta has been transected, the ostia of the innominate and left common
carotid arteries can be directly cannulated with balloon tipped catheters. (d) The right axillary
artery can be cannulated either percutaneously (as shown in the gure) or using a graft sewn endto-side to the vessel. (e) With an already established alternate route of arterial cannulation for
cardiopulmonary bypass, the innominate and left common carotid arteries can be sequentially
debranched from the arch and sewn to a multibranch graft that is also connected to the bypass
circuit, allowing for split arterial perfusion between the upper and lower body, and bilateral antegrade cerebral perfusion during circulatory arrest. In addition to the options depicted in this gure,
right or left common carotid artery cannulation remain available for establishing unilateral antegrade cerebral perfusion, as shown in Fig. 1
C. V. Ghincea et al.
additional set-up, and a dedicated neuromonitoring team intraoperatively, EEG can
provide useful information especially in the case of acute aortic syndrome repair.
When possible, without causing delay in denitive repair, the authors advocate its
use routinely.
A reference EEG following induction of anesthesia but before cooling during
CPB is obtained as a baseline. Anesthetic agents can dramatically inuence electrocerebral activity, however it is important to establish the reference prior to the effects
of hypothermia or any surgical manipulation. These objective data may be particularly important in the case of acute aortic syndrome with antecedent neurological
injury or an imperfect or unreliable clinical neurological exam. Continuous EEG
monitoring is maintained throughout the period of cardiopulmonary bypass.
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MEP
SSEP
EEG
MEP
Stimulator
EEG
NIRS
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SSEP
Stimulator
Fig. 3 Neurophysiological intraoperative monitoring (NIOM) is a term that refers to multiple
modalities that are employed to actively monitor neurological function and perfusion during surgery for aortic dissection. These modalities include electroencephalography (EEG), motor evoked
potentials (MEPs), somatosensory evoked potentials (SSEPs), and near infrared spectroscopy
(NIRS). EEG utilizes multiple detector electrodes placed on the patient’s scalp to monitor cerebral
electrical activity. MEPs are produced by transcranial stimulation of the motor cortex with peripherally placed detectors to read a response. SSEPs are produced by peripheral electrical stimulation
with transcranial detection of somatosensory cortical response. NIRS use scalp monitors to determine regional cerebral oxygen saturation
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C. V. Ghincea et al.
Electrocerebral activity follows a predictable pattern as cerebral hypothermia deepens and serves as surrogate for cerebral metabolism and energy consumption. Burst
suppression typically develops between 15.7°C and 33.0°C [6, 7] with progression
to complete electrocerebral inactivity (ECI) occurring between 12.5 °C and
27.2°C.Surface and body temperature measurements have been demonstrated to
poorly correlate with brain temperature. There also exists signicant individual
variability between temperature and electrocerebral activity [8]. Therefore, for a
particular patient, extrapolating a prediction of cerebral metabolism based on core
temperature or duration of cooling alone remains unreliable, highlighting the utility
of continuous EEG monitoring for real-time acquisition of electrocerebral activity.
This degree of monitoring seems especially pertinent when using more moderate
degrees of hypothermia. In the authors experience, EEG has been very useful to
determining adequate cerebral protection before circulatory arrest, and when used
in combination with SSEPs and MEPs, has identied intraoperative stroke including areas of malperfusion from cannulation/dissection mismatch, when differential
pressures exist between brain and systemic perfusion, or embolization. All of these
instances were dealt with quickly with prompt reversal of the malperfusion, but
would have resulted in prolonged regional ischemia without the neuromonitoring
in place.
Cerebral Oximetry/Near Infrared Spectroscopy
While more commonly used in pediatric cardiac surgery, there is increased adoption
of cerebral oximetry monitory by NIRS in adult cardiac [9] and aortic arch surgery
[10, 11]. Attractive features of cerebral oximetry include its relative ease-of-use,
ubiquity, simplied read-out, and real-time feedback. Regional ScO2 levels generally increase from baseline during the period of cooling reaching a plateau prior to
initiation of cerebral circulatory arrest after which they decline until cerebral perfusion is restored. Non-invasive cerebral oximetry historically has poor correlation
with jugular bulb saturation [12] and limited data exist to suggest absolute saturation values to correlate with development or prevention of clinical neurological
injury. Therefore, cerebral neuroprotection or perfusion strategies based on NIRS
data alone remain nebulous. However, the reference to baseline and changes in symmetry may be helpful to identify problems intraoperatively that are related to altered
perfusion. The identication of a sudden decreased in left sided cerebral regional
saturation with initiation of selective antegrade cerebral perfusion through the
innominate artery prompting subsequent conversion to a bilateral antegrade cerebral perfusion strategy is an example of directly actionable feedback that may be
provided by NIRS monitoring. This has been exceeding helpful in the development
of a protocol for selective arterial perfusion during hypothermic circulatory arrest
with moderate hypothermia. Balanced oximetry suggests selective perfusion
through one carotid is sufcient, but a drop in the contralateral saturations suggests
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a need for bilateral perfusion. While this may add nothing for short circulatory
arrest times below 15–20min, prolonged circulatory arrest times may benet from
increasing unilateral ow and pressure or even from adding a perfusion cannula to
the opposite carotid.
Prevention ofFurther Neurological Injury
Temperature Management
Hypothermia remains the cornerstone of any cerebral protection strategy when periods
of altered cerebral perfusion are anticipated during repair of acute aortic dissection.
Analogous to other systemic tissue beds, neuronal cellular metabolic rate and oxygen
consumption are dependent on tissue temperature via reductions in enzymatic activity.
Experimentally, cerebral metabolic activity has been shown to decrease initially by
6–7% per degree Celsius below 37 degrees [13]. This roughly correlates to a separate
descriptor of temperature modulated tissue metabolism, the Q10 rule, which describes
an approximately 50% reduction in metabolic rate for every 10 degree decrease in
temperature [14]. The effects of tissue temperature on neuronal survival have be
exploited by aortic surgeons for the purpose of circulatory arrest for decades, however
recommended temperature nadirs and adjunctive strategies continue to evolve.
In order to more accurately classify temperature strategies in aortic arch surgery,
a consensus denition of hypothermia stratied into 4 categories has been devised
[15], as shown in Table1 [16]. Profound hypothermia (≤14°C) is sufcient without
adjuncts to induce electrocerebral inactivity (ECI) in approximately 80% of patients.
Whereas deep hypothermia (14.1–20°C) falls within a steeper section of TemperatureECI curve and produces ECI with more individual variability, roughly 20–80% predicted. Moderate and mild categories of hypothermia are less likely to yield ECI and
correspond to shorter predicted protection times during hypothermic circulatory
arrest [6, 15]. The safety of deep hypothermic circulatory arrest (DHCA) strategies
whereby the patient is systemically cooled until ECI prior to “straight” circulatory
arrest for periods up to 30min have been demonstrated during aortic arch surgery in
a number of large series [8, 17–19]. A large study of 394 patients who underwent
Table 1 Temperature and predicted circulatory arrest protection time
Category Temperature (°C) HCA time (min)
Profound ≤14 30–40
Deep 14.1–20 20–30
Moderate 20.1–28 10–20
Mild 28.1–34 <10
HCA hypothermic circulatory arrest
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arch repairs with this strategy showed no diminished cognitive function and a hypoperfusion-specic stroke rate of 1.8%, with an overall stroke rate less than 5% [20].
Despite both historical evidence and contemporary outcomes from Yale supporting the safety of a DHCA strategy, there are drawbacks to deep hypothermia that
provide vigor for alternate methods using more moderate degrees of hypothermia.
The main disadvantages to lower temperatures include longer durations of cardiopulmonary bypass needed for systemic cooling/rewarming and associated consequences. However, temperature specic issues such as hypothermia induced
coaguloapathy may increase perioperative blood loss and the need for transfusion as
well as the rate of reoperation for bleeding [21–23].
In order to achieve similar or superior neurological outcomes with warmer systemic and cerebral temperatures, adjunctive perfusion strategies and more efcient
operative techniques are aimed at reducing time spent with relative cerebral hypoperfusion. It is the author’s position that there is no truly “safe” duration of circulatory arrest regardless of temperature nadir or adjunctive measures that can ensure
cerebral protection for all patients. Minimizing, ideally eliminating, time spent in
sub-physiological cerebral perfusion remains our goal for all aortic procedures.
Compared with elective aortic arch repair, acute dissection with or without antecedent injury remains a risk factor for neurological injury, further highlighting the need
for speed in this particular patient group.
C. V. Ghincea et al.
Adjunctive Cerebral Perfusion During Systemic
Circulatory Arrest
Retrograde Cerebral Perfusion
The technique of retrograde cerebral perfusion exploits the anatomical lack of valves
between the superior vena cava and the cerebral venous vasculature allowing perfusate
to ow retrograde to the brain. A 24 french or similar cannula connected to the arterial
limb of the CPB circuit is placed into the SVC within the chest and the SVC encircled
by a snare above the azygous insertion (Fig.4a). With the tourniquet cinched, the cerebral venous system can be selectively pressurized though the SVC cannula. RCP Flow
has traditionally been targeted in the range of 100–300ml/min at 10–12°C.The authors
transduce venous pressure through the side-arm of an introducer placed by anesthesia
in the right internal jugular vein and increase ow to the achieve a venous pressure of
25mmHg. Frequently RCP ows >500ml/min are required to achieve pressure target
of 25mmHg and to observe retrograde ow from the innominate and left common
carotid ostia. Signicant oxygen and glucose delivery to the brain have not been demonstrated during RCP [24], so this technique in isolation is frequently coupled with
deeper levels of hypothermia or shorter circulatory arrest periods. However, RCP does
provide ongoing regional cooling, lowering cerebral metabolic demands even further.
Additionally, RCP may “ush” out the arterial system of both air and possibly particulate emboli. Proponents of RCP cite the avoidance of additional arterial manipulation
to minimize both local arterial injury and propagation of emboli [25].
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Fig. 4 In patients undergoing total arch replacement, the authors’ preference is central aortic cannulation into the true lumen using the Seldinger technique and epiaortic ultrasound/transesophageal echo verication. During cooling, the innominate and left common carotid arteries are
debranched from the aortic arch using a vascular stapler and sewn to a multibranch graft connected
to a separate arterial line from the bypass circuit. In this way, unilateral cerebral perfusion is maintained during the relatively brief time it takes to sew the contralateral anastomosis, with bilateral
cerebral perfusion maintained once both anastomoses are complete. This provides split upper and
lower body perfusion prior to initiation of circulatory arrest
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Antegrade Cerebral Perfusion
In order to precisely mimic natural cerebral blood ow during systemic circulatory
arrest, antegrade perfusion must be established to all three arch vessels to supply
both carotid arteries and both vertebral arteries. However, a number of ACP techniques with more limited antegrade access have been successfully described [26].
Most commonly, especially in the case of hemiarch replacement, is selective antegrade cerebral (sACP) perfusion via the innominate artery. Access for innominate
sACP can be accomplished in a number of ways—percutaneous innominate cannulation (Fig.4b), a graft conduit anastomosed end-to-side to the innominate, ostial
balloon-tipped cannulation through an open arch (Fig.4c), or axillary cannulation
(Fig.4d) with occlusion of the proximal innominate artery. The Circle of Willis is
incomplete in up to 70% of the population (LF), however sufcient extracranial collaterals exist in the vast majority of patients allowing antegrade perfusion through
the innominate artery to supply both cerebral hemispheres. Similar collaterals allow
clamping of the innominate artery or the common carotid proximal to the bifurcation without regional malperfusion. However, a known incomplete Circle of Willis
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or signicant ipsilateral carotid stenosis may represent relative contraindications to
this technique. During innominate sACP, perfusate ow is established around
6–10ml/kg/min and increased or decreased to maintain a mean arterial pressure of
40–60mmHg as measured in a right upper extremity arterial line [3]. Bilateral ACP
strategies require access to both the left common carotid as well as the innominate
and are more typically employed during total arch replacement (Fig.4e). Despite
the intuitive sense that bilateral ACP would be more physiological than sACP, studies have failed to demonstrate superior neurological outcomes or decreased mortality with this technique [27].
Neuroprotection asaFunction ofRepair Technique andPerfusion
Strategies: Buffalo Trunk Technique—Shaggy Aorta Protocol (RCP/ACP)
The technique for total arch replacement with frozen elephant practiced at the
University of Colorado is a modication of the FET utilizing a separate branched
graft for the brachiocephalic vessels and a branched graft–stent graft construct for
arch and proximal descending aortic reconstruction. Longer durations of deep
hypothermic circulatory arrest have been associated with worse postoperative neurologic dysfunction including stroke in patients undergoing arch replacement [28,
29]. The Buffalo Trunk technique [30] represents the authors efforts to minimize
(ideally to eliminate) the period of cerebral, spinal, and systemic ischemia through
operative and technical efciency. Combined with optimizing cerebral perfusion by
replacing dissected arch vessels, the Buffalo trunk procedure and other similar operations represent a method of neuroprotection as a function of the dissection repair
strategy and technique.
In cases of dissection extending into the head vessels, our practice is to identify
the extent of dissection and replaced the portion of the involved common carotid
arteries up to the level of the internal and external bifurcation through an extended
or separate cervical incision if necessary. The more severely affected side is typically debranched rst in an end-to-end fashion to a separate trifurcated branched
graft which is connected to a “Y’d” arterial limb of the cardiopulmonary bypass
circuit. The contralateral side is subsequently debranched while perfusion is continued from the previously repaired side. A separate branched graft for the supraaortic
vessels allows an independent connection to the cardiopulmonary bypass circuit
and enables bilateral antegrade cerebral perfusion independent from body perfusion
(Fig.2). Central or peripheral cannulation is performed and CPB instituted prior to
brachiocephalic debranching in order to begin the process of systemic cooling and
creates some mild cerebral hypothermia during clamping of head vessels. A shunt
during either carotid or innominate artery anastomosis is not typically needed due
to contralateral perfusion through an intact circle of Willis and other arterial collaterals. Electroencephalography, cerebral oximetry by near-infrared spectroscopy,
and other non-invasive neuromonitoring are used continuously to monitor for
changes during a test occlusion of the head vessel and while proximally occluded
for debranching. Early separation of the innominate and left common carotid
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arteries from the aorta in this technique may theoretically reduce the risk of anterior
circulation emboli. However, with an anomalous left vertebral artery originating
from the arch, the posterior circulation remains at risk, highlighting the importance
of minimizing excessive aortic manipulation.
Patients are systemically cooled to moderate levels of hypothermia (20–28°C)
as the arch vessels are debranched. Following separation of the innominate and left
common carotid from the aortic arch, a guidewire is advanced from the groin into
the proximal transverse arch. Intravascular ultrasound is performed to identify the
dissection anatomy and conrm true-lumen wire placement. Exchange for a stiff
guidewire will serve as a rail for FET deployment into the true lumen. Transesophageal
echo and uoroscopy may be used as adjuncts to assess wire positioning, but do not
supplant the need for IVUS to prevent a wire path that could traverse multiple
fenestrations.
In acute aortic dissection, the authors will employ a “shaggy aorta” protocol for
cerebral perfusion consisting of a 3-min period of RCP followed by subsequent
ACP for the remaining duration of systemic circulatory arrest. The sequential combination of both cerebral perfusion adjuncts aims to optimize cerebral hypothermia,
provide a short period of deairing and ushing of potential emboli, and sufcient
oxygen and metabolite delivery. Arterial line management for both hemiarch and
total arch operations utilizing the “shaggy aorta” protocol are shown in Fig.5.
During systemic circulatory arrest, the aortic arch is transected and the Buffalo
trunk graft-stent graft construct is advanced into the proximal descending thoracic
aorta antegrade over the guidewire. The stent graft is released from the construct
and further advanced until the proximal edge is ush with the cut edge of the divided
aorta. An external felt strip, the aortic wall, the surgical graft, and the proximal end
of the stent graft are incorporated in a single running external suture line comprising
the distal anastomosis. Systemic circulation is recommenced though the perfusion
limb of the aortic graft. The left subclavian artery and the separate branched graft to
the innominate artery and LCCA are anastomosed to the aortic graft after completion of additional procedures to the aortic root and myocardial reperfusion. The
completed arch replacement is shown in Fig.6.
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Pharmacological Neuroprotection
Various pharmacologic agents have been evaluated for their neuroprotective properties with regard to aortic surgery. These drugs act through a range of mechanisms
which include the following categories: cardiovascular modulators, antiinammatories and immunomodulators, antioxidants, anti-apoptotic agents, drugs
reducing neuronal excitotoxicity, drugs that reduce metabolic demand, and osmotic
agents or diuretics to reduce tissue swelling. The literature on pharmacological neuroprotection is vast resulting in signicant confusion as both agonists and inhibitors
of certain receptors, or pathways, have demonstrated efcacy in different studies.
For example, modulators of vascular tone can improve cerebral or spinal cord
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