# Aortic Arch Surgery: Cerebral Protection Strategies

## Overview

Aortic arch surgery is among the most technically demanding procedures in cardiothoracic surgery, requiring interruption of cerebral blood flow during the repair. The choice of cerebral protection strategy directly impacts neurologic outcomes. This chapter covers open arch replacement techniques, cerebral perfusion methods, temperature management strategies, and the evidence supporting current best practices.

## Indications for Arch Surgery

### Elective

Elective arch surgery is indicated for aortic arch aneurysm exceeding 5.0-5.5 cm (or exceeding 4.5 cm in connective tissue disorders), chronic dissection with aneurysmal degeneration of the arch, and penetrating aortic ulcer or intramural hematoma involving the arch.

### Emergent

Emergent indications include acute Type A dissection with arch involvement or an arch entry tear, ruptured arch aneurysm, and (rarely) traumatic arch disruption.

## Arch Anatomy and Zones

### Arch Branch Vessels

The three great vessels arising from the arch are the **innominate (brachiocephalic) artery**, which supplies the right common carotid and right subclavian arteries, the **left common carotid artery**, and the **left subclavian artery**. Variant anatomy is present in 20-30% of patients and includes common origin of the innominate and left carotid, aberrant right subclavian artery (lusoria), and bovine arch configuration.

### Ishimaru Landing Zones (for Endovascular)

The Ishimaru classification divides the aortic arch into zones for endovascular planning. **Zone 0** is the ascending aorta proximal to the innominate artery. **Zone 1** lies between the innominate and left common carotid arteries. **Zone 2** lies between the left common carotid and left subclavian arteries. **Zone 3** is the proximal descending aorta distal to the left subclavian. **Zone 4** is the mid-descending aorta.

## Types of Arch Repair

### Hemiarch Replacement

Hemiarch replacement involves replacing the undersurface (lesser curvature) of the arch, with the distal anastomosis beveled from the lesser curvature to the greater curvature while preserving the origins of the arch branch vessels. This is the most common arch procedure performed, particularly for acute Type A dissection. It requires shorter circulatory arrest times than total arch replacement and is adequate when the arch is not aneurysmal and the primary tear is in the ascending aorta.

### Total Arch Replacement

#### Island Technique

In the island technique, the arch branch vessels are kept on a common island of aortic wall that is sewn to an opening in the arch graft. This approach is simpler and faster than individual reimplantation but has the disadvantage that the island tissue may be diseased, especially in dissection or connective tissue disorders.

#### Branched Graft Technique

A prefabricated four-branch graft (such as the Terumo Aortic Plexus) allows individual reimplantation of each arch vessel to dedicated branches of the graft. This eliminates diseased arch wall tissue and enables sequential clamping and perfusion of branch vessels, allowing partial CPB flow restoration after each branch is connected and thereby reducing total brain ischemia time.

### Frozen Elephant Trunk (FET)

The frozen elephant trunk is a hybrid prosthesis with a conventional woven Dacron proximal segment and a stented distal segment. The stented portion is deployed into the true lumen of the descending aorta under circulatory arrest, facilitating aortic remodeling in the descending aorta (especially for dissection) and providing a landing zone for future TEVAR if needed. Available devices include the Thoraflex Hybrid (Terumo Aortic) and E-vita Open Plus (Jotec). The risk of spinal cord ischemia from extensive aortic coverage is a significant concern.

### Arch Repair Techniques Comparison

| Technique | Indication | Circulatory Arrest Time | Key Advantages | Key Risks |
|-----------|-----------|-------------------------|----------------|-----------|
| Hemiarch replacement | Type A dissection (ascending tear), non-aneurysmal arch | Short (15-25 min) | Simpler; lower risk; adequate for most dissections | Does not address arch disease |
| Total arch (island technique) | Arch aneurysm, arch tear | Moderate-long | Simpler than branched | Diseased island tissue may degenerate |
| Total arch (branched graft) | Arch aneurysm, dissection with diseased arch | Moderate (sequential perfusion) | Eliminates diseased tissue; sequential branch perfusion | Technically complex |
| Frozen elephant trunk | Complex arch + descending disease | Moderate-long | Addresses both zones in one operation; facilitates future TEVAR | 2-5% spinal cord ischemia risk |

### Elephant Trunk (Classical)

The classical elephant trunk is a two-stage approach. The first stage involves arch replacement with a free-floating graft ("trunk") left in the proximal descending aorta. The second stage involves descending or thoracoabdominal repair via left thoracotomy, using the trunk as a proximal landing zone. A limitation is that some patients never undergo the second stage due to intercurrent events.

## Cerebral Protection Strategies

### Deep Hypothermic Circulatory Arrest (DHCA)

In DHCA, the patient is cooled to 14-18 degrees Celsius (nasopharyngeal or tympanic temperature) and all circulation is arrested. Brain metabolic rate decreases 6-7% per degree Celsius; at 18 degrees Celsius, metabolism is approximately 15% of baseline. The safe arrest time is 25-40 minutes, with shorter being better. The advantages are simplicity (no additional cannulation required) and provision of a bloodless field. The disadvantages include prolonged cooling and rewarming (which extends CPB time), increased neurocognitive dysfunction with arrest times beyond 30-40 minutes, and coagulopathy from prolonged hypothermia.

### Antegrade Cerebral Perfusion (ACP)

ACP involves selective perfusion of one or both carotid arteries during circulatory arrest. **Unilateral ACP** perfuses the innominate or right axillary artery and relies on the circle of Willis for contralateral brain perfusion. **Bilateral ACP** perfuses both the innominate and left common carotid via direct cannulation or balloon perfusion catheters. ACP allows moderate hypothermia (24-28 degrees Celsius), which reduces cooling and rewarming time and associated coagulopathy. Flow rates of 10-15 mL/kg/min target right radial artery pressure of 50-70 mmHg. Near-infrared spectroscopy (NIRS) monitoring provides continuous cerebral oximetry for both hemispheres. The advantages are an extended safe arrest time beyond 60 minutes, reduced coagulopathy, and shorter CPB time. The disadvantages are additional cannulation complexity and risk of embolization from direct vessel cannulation.

### Retrograde Cerebral Perfusion (RCP)

RCP perfuses the brain via the SVC (reverse flow through the cerebral venous system) at low flow rates of 200-300 mL/min with SVC pressure of 20-25 mmHg. It flushes debris from arch vessels, maintains brain hypothermia, and has a simple setup. However, it is unclear how much nutrient flow actually reaches the brain due to venous valves and arteriovenous shunting, and it is not a substitute for ACP for prolonged arrest times. RCP is used primarily as an adjunct to DHCA rather than as standalone cerebral protection.

### Cerebral Protection Strategies Comparison

| Strategy | Temperature | Safe Arrest Time | Advantages | Disadvantages |
|----------|------------|-------------------|------------|---------------|
| DHCA alone | 14-18°C (deep) | 25-40 min | Simple; no extra cannulation; bloodless field | Prolonged CPB; coagulopathy; neurocognitive dysfunction if > 30-40 min |
| Unilateral ACP | 24-28°C (moderate) | > 60 min | Shorter CPB time; less coagulopathy; adequate for hemiarch | Relies on circle of Willis (incomplete in 20-30%) |
| Bilateral ACP | 24-28°C (moderate) | > 60 min | Both hemispheres perfused; best for total arch | More complex cannulation; embolization risk |
| RCP (adjunct) | Used with DHCA | Adjunct only | Flushes debris; maintains brain hypothermia | Uncertain nutrient delivery; not standalone |

### Current Best Practice

**ACP at moderate hypothermia (24-28 degrees Celsius)** is the most widely adopted strategy at high-volume centers. Bilateral ACP is preferred for total arch replacement when arrest times exceed 30 minutes. Unilateral ACP via the right axillary artery is adequate for hemiarch cases with shorter arrest times. DHCA alone remains acceptable for short arrest times (less than 25-30 minutes) in hemiarch cases.

<image>Diagram of cerebral protection strategies during aortic arch surgery. Three panels illustrate: (A) Deep hypothermic circulatory arrest -- pump is off, patient cooled to 18 degrees C, no cerebral perfusion, with a clock showing safe arrest time of 25-40 minutes. (B) Unilateral antegrade cerebral perfusion -- arterial inflow via the right axillary artery perfuses the right hemisphere directly and the left hemisphere via the circle of Willis, with moderate hypothermia (24-28 degrees C) and NIRS monitoring on both hemispheres. (C) Bilateral antegrade cerebral perfusion -- separate perfusion of the innominate and left carotid arteries via balloon perfusion catheters or direct cannulation, providing bilateral brain perfusion during total arch replacement. Each panel labels the temperature target, flow rates, and pressure goals.</image>

## Temperature Management

### Temperature Targets

**Deep hypothermia** (14-18 degrees Celsius) is used for DHCA alone. **Moderate hypothermia** (24-28 degrees Celsius) is used with ACP and is the most common current practice. **Mild hypothermia** (28-32 degrees Celsius) for arch surgery is controversial and used by some experienced centers with ACP.

### Cooling and Rewarming

Cooling is performed at 1 degree Celsius per minute on CPB, avoiding a gradient greater than 10 degrees Celsius between arterial blood and patient temperature. Rewarming proceeds slowly at less than 0.5 degrees Celsius per minute, and hyperthermia (overshoot above 37 degrees Celsius) must be avoided because it worsens neurologic injury. The target temperature for separation from CPB is 36 degrees Celsius.

### Monitoring

**Nasopharyngeal temperature** is the best surrogate for brain temperature. **Bladder or rectal temperature** reflects core body temperature but lags behind brain temperature. **Bilateral NIRS** provides continuous cerebral oximetry and alerts to asymmetric or inadequate cerebral perfusion. **EEG** can confirm electrocerebral silence to verify adequate cooling and is used at some centers.

## Neurologic Outcomes

### Stroke

The overall stroke rate for arch surgery is 3-8%, varying with extent and complexity. Risk factors include prolonged arrest time, atherosclerotic arch, age, and prior stroke. ACP reduces stroke risk compared to DHCA alone for prolonged arrest times.

### Temporary Neurologic Dysfunction (TND)

Postoperative confusion, agitation, and delirium constitute temporary neurologic dysfunction, which is typically reversible. It occurs in 10-20% of cases and is more common with DHCA alone and longer arrest times. TND may be reduced with ACP and moderate hypothermia.

### Spinal Cord Ischemia

The risk of spinal cord ischemia increases with FET procedures that cover extensive descending aortic segments, with a paraplegia rate of 2-5% with FET. Prevention strategies include CSF drainage, limiting the stented segment length, and maintaining distal perfusion pressure.

<image>Intraoperative view of total arch replacement using a four-branch Dacron graft. The illustration shows the four-branch graft with individual anastomoses to the innominate artery, left common carotid artery, and left subclavian artery (three branches), with the fourth limb serving as the arterial inflow cannula during CPB. The proximal anastomosis to the ascending aorta and distal anastomosis to the proximal descending aorta are shown. Bilateral ACP is depicted with perfusion catheters in the innominate and left carotid branches. NIRS pads are shown on the patient's forehead. Temperature and flow parameters are listed.</image>

## Clinical Pearls

Antegrade cerebral perfusion at moderate hypothermia (24-28 degrees Celsius) has become the dominant cerebral protection strategy and should be the default approach for arch surgery at training programs. Right axillary artery cannulation is the preferred arterial access because it provides true lumen flow (in dissection) and serves as the conduit for unilateral ACP during arch repair. Bilateral NIRS monitoring is essential — a unilateral drop exceeding 20% from baseline should prompt investigation, including contralateral carotid perfusion catheter adjustment and repositioning. Hemiarch replacement is sufficient for most Type A dissections when the arch is not primarily diseased, while total arch replacement should be reserved for arch tears, arch aneurysms, or planned FET procedures. The frozen elephant trunk has revolutionized management of complex arch and descending aortic pathology by addressing both zones in a single operation, but it carries a 2-5% spinal cord ischemia risk. Rewarming above 37 degrees Celsius must be avoided because hyperthermia dramatically worsens neurologic injury in the post-arrest brain. The circle of Willis is incomplete in approximately 20-30% of patients — this is why bilateral ACP is preferred over unilateral ACP for prolonged arrest times during total arch replacement.

## References

- **Czerny M, Schmidli J, Adler S, et al.** 2024 EACTS/STS Guidelines for the management of acute and chronic aortic diseases. *Eur J Cardiothorac Surg.* 2024;65(1):ezad426.
- **Tian DH, Wan B, Bannon PG, et al.** A meta-analysis of deep hypothermic circulatory arrest versus moderate hypothermic circulatory arrest with selective antegrade cerebral perfusion. *Ann Cardiothorac Surg.* 2013;2(2):148-158.
- **Shrestha M, Martens A, Kruger H, et al.** Total aortic arch replacement with the frozen elephant trunk technique. *Ann Thorac Surg.* 2015;99(2):421-427.
- **Spielvogel D, Etz CD, Silovitz D, et al.** Aortic arch replacement with a trifurcated graft. *Ann Thorac Surg.* 2007;83(2):S791-S795.
- **Yan TD, Bannon PG, Bavaria J, et al.** Consensus on hypothermia in aortic arch surgery. *Ann Cardiothorac Surg.* 2013;2(2):163-168.