202412092222

Status:

Tags: vascular, CTS

aortic aneurysm

A true aneurysm of the aorta is a permanent dilatation at least 50% greater than its original size involving all wall layers

A pseudoaneurysm is a rupture through the layers of the aorta held together by blood and surrounding tissues

A dissection is a disruption of the intimal layer of the aorta, with bleeding within the wall.

Untreated aneurysms of the descending and thoracoabdominal aorta exceeding 6 cm in diameter have a 14.1% annual rate of rupture, dissection, or death.
The 5 yr survival of patients managed conservatively is 10–20%

Diameter of AAA Annual rupture risk Additional risk factors for rupture
<4 cm 0% Rate of expansion (>0.5 cm in 6 months)
4–4.9 cm 0.5–5% Continued smoking
5–5.9 cm 3–15% Uncontrolled hypertension
6–6.9 cm 10–20% Female sex associated with higher risk of rupture for a given diameter AAA
7–7.9 cm 20–40%
≥8 cm 30–50%

Indications:

Thoracoabdominal aortic aneurysms (TAAAs) are described using the Crawford classification according to the location of aneurysmal sections

Pre-op

Pre-op assessment

Risk models have been used but are somewhat limited in their prediction for an individual and are not recommended by NICE

Initial resus for ruptured AAA

Optimisation:

Pre-op optimisation of vascular patients
undiagnosed COPD
short acting bronchodilator → long acting
steroid responsive: course of steroid prior to surgery

Smoking cessation
incentive spirometry
peri-op physio
Prehabilitation
A Cochrane review of RCTs comparing the impact of preoperative exercise interventions versus usual care in people having AAA repair was unable to ascertain whether prehabilitation reduced 30-day mortality, pulmonary complications, re-intervention rates or postoperative bleeding.
It may however, reduce cardiac and renal complications

Statins are protective both in the long term (reducing cardiovascular risk) but also in the perioperative period

Aspirin is continued but thienopyridine derivatives such as clopidogrel should generally be stopped in advance of open surgery due to the association with excessive bleeding and contraindication to neuraxial blockade

recent PCI → d/w cardiac

current recommendations state that initiation of β-blockers should not be considered routine in those undergoing vascular surgery and should be only started if indicated on a case-by-case basis.

Key trials on Open vs EVAR for AAA

overall: lower peri-oip mortality but survival benefits lost in following years & ↑ re-intervention rates

EVAR I, the Dutch DREAM trial and the American OVER trial concluded that although EVAR offered lower operative and 30-day mortality rates there was no survival advantage at the 5-year endpoint.
EVAR was associated with ↑ risks of

follow-up study of EVAR-1 demonstrated ↑ all cause and aneurysm-related mortality figures in the EVAR group from 8 years following follow up. This was in part attributed to secondary aneurysm sac rupture.

ACE trial demonstrated similar 30-day mortality rates between the two interventions

In 2014, the IMPROVE trial failed to prove any significant difference in 30-day mortality between EVAR and open surgery in patients with ruptured AAA.
However, those that survived who underwent EVAR

Complications from EVAR may be ↓ ∵

The ongoing ACTION-1 trial is comparing whether ACT guided heparinisation results in more optimal coagulation than 5000 IU as a single dose and although focusing on OR, it should be applicable to EVAR

Anaesthetic technique

The anaesthetic technique for open AAA repair is built on the foundations of maintaining

Monitoring

5 lead ECG ∵ ↑ risk of CAD

Urine output and temperature monitoring are important in this group of patients, particularly when considering the pathophysiological effects of cross-clamping.

Cardiac output monitoring in combination with goal-directed fluid therapy was shown to improve postoperative outcome in high-risk general surgical patients. To date, the evidence sup-porting the use of cardiac output monitoring in open aneurysm repair is lacking
The reliability of the oesophageal Doppler and arterial pressure waveform analysis is invalidated when the aorta is clamped

BIS has garnered some support in recent times. It has been suggested that monitoring depth of anaesthesia using electroencephalographic data allows more accurate titration of anaesthetic agents without increasing the risk the awareness
Avoiding excessive doses of anaesthetic agents would be beneficial in this group of patients prone to significant haemodynamic changes, but this has yet to be proven

Evidence is emerging that suggests BIS-guided anaesthesia may be associated with a ↓ incidence of postoperative cognitive dysfunction (POCD)

Other essential equipment:
rapid infusion device
Cell salvage
POC devices e.g. VHA

Conduct of anaes

The potential cardioprotective effects of volatile anaesthetics found in cardiac surgery were not replicated when volatiles were compared with total intravenous anaesthesia (TIVA) for patients undergoing elective AAA repair

Low tidal volume ventilation with high positive end-expiratory pressure (PEEP) is associated with a reduction in post-operative pulmonary complications

PROVAR trial failed to demonstrate an improvement in intraoperative or postoperative respiratory function when using different lung protective ventilatory strategies in patients undergoing open abdominal surgery

Active warming measures should be employed to avoid the associated risks of hypothermia (oxygen consumption, myocardial dysrhythmias, coagulopathies, and postoperative wound infections). Lower body warming during aortic cross-clamping should be avoided

EA

For those undergoing open repair an epidural plus general technique has better outcomes than general plus systemic analgesia

Postoperative analgesia is usually managed with a thoracic EA that is sited before induction. Some anaesthetists prefer not to commence the epidural infusion until the end of surgery, after haemostasis and haemodynamic stability has been achieved

sympathetic blockade associated with epidural analgesia will necessitate vasopressor therapy if commenced early after aortic clamp release

Limited evidence does support the use of thoracic epidural analgesia both in terms of

EOT

MTP should be initiated whilst blood is sent for full cross-match (minimum 8–10 units)

Permissive hypotension and the avoidance of aggressive fluid resuscitation prior to cross-clamping minimizes surges in BP that could cause dislodgement of an intact thrombus and avoids further dilution of already depleted clotting factors

SBP of 70 mmHg is advocated provided the patient shows no signs of altered conscious state or cardiac ischaemia

RSI w/ Arterial line, & patient prepped & draped
The aim is to minimize the time between induction and application of the aortic cross-clamp

Heparinization is not usually required

Blood products

Blood loss during open aneurysm repair is highly variable

Contributing factors include those relating to the aneurysm and those relating to the surgery
Larger aneurysms, those with more complex anatomy and those associated with a hostile abdomen are associated with an increased risk of bleeding

Haemorrhage may result from

Pre-op anaemia treated

Ideally, blood products should be transfused when haemostasis has been achieved and after the aortic cross-clamp has been released

Ideally the anesthetist should aim for

Aortic cross clamping

Surgery involving aortic arch

DHCA

Repair of the aortic arch involves interruption to the cerebral blood supply necessitating the use of CPB with deep hypothermic circulatory arrest (DHCA). Cerebral perfusion may be maintained antegrade via cannulation of arteries as they branch from the aortic arch or via the arterial line into the right axillary, subclavian, or innominate artery, or retrograde via cannulation of the internal jugular vein.

Hypothermia is an effective technique for the protection of the central nervous system and other viscera in the presence of reduced or absent blood flow. The lower temperature reduces tissue metabolic activity and attenuates the inflammatory response to reperfusion.
The core temperature is allowed to decrease spontaneously with additional cooling from the heater/cooler on the CPB circuit. Application of topical cooling to the head is performed in some centres to minimise passive warming, although the benefits of this have been extrapolated from studies in animals. Where used, particular care should be taken to protect the patient's eyes

Opinions vary on the degree of hypothermia required. Deep hypothermia (14.1–20°C) allows 20–30 min of safe circulatory arrest time compared with 10–20 min where moderate hypothermia (20.1–28°C) is used

Profound cooling contributes to morbidity through the development of coagulopathy and an increased inflammatory response.

Anaes considerations

Invasive arterial blood pressure monitoring via the right radial artery ensures continued assessment should the aortic cross-clamp be applied proximal to the left subclavian artery.
If the right axillary artery is used for antegrade cerebral perfusion, a left radial arterial catheter may be required

Temperatures measured within the nasopharynx have been shown to most accurately reflect cerebral temperature, and monitoring is usually via probes positioned in the nasopharynx and either rectum or bladder

Pharmacological protection of the brain and spinal cord is used variably as an adjunct to hypothermia, as there is little consistent evidence.
Drugs occasionally administered include

Near-infrared spectroscopy is increasingly used during surgery involving the aortic arch to provide continuous, real-time non-invasive monitoring of anterior cerebral oxygenation. The proportion of light absorbed attributable to oxygenated and deoxygenated haemoglobin within the cerebral cortex is calculated using adhesive diodes on the forehead. Intracerebral oxygen saturation (rSO2) is calculated and should be maintained within 25% of baseline.
Inadequate cerebral perfusion should prompt assessment of cannulation sites; increased flow rate within the CPB circuit; optimised haemoglobin concentration; and, if necessary, increased hypothermia and Pco2 to promote vasodilatation.

Surgery involving descending aorta

Where a clamp can be placed distal to the left subclavian artery and there is to be no interruption to the cerebral blood supply, the use of partial left heart bypass (PLHB) is preferable

Anaes considerations

OLV
neuromonitoring

A left-sided DLT is used for ease of positioning, although external compression of the left main bronchus by the enlarged aorta may preclude this, and a right-sided DLT or single-lumen tube with bronchial blocker may be required

An arterial catheter is sited in a femoral artery, in addition to the right radial artery, to allow monitoring of distal perfusion pressure

A central venous catheter and percutaneous introducer sheath are inserted into the left internal jugular vein; insertion into the right may lead to problems with kinking once the patient is positioned

Spinal cord protection

Paraplegia after thoracic aortic surgery is a devastating and life-limiting complication, reported to occur in 4–16% of cases overall and in up to 50% of Extent II aneurysms

Perfusion insufficiency may be 2/2

Aortic cross clamping

Replacement of diseased sections of aorta requires temporary or permanent interruption of arterial collaterals, leading to spinal cord ischaemia and subsequent reperfusion injury.
Ischaemia causes spinal oedema, hyperaemia, and inflammation, thus increasing the CSF pressure (CSFP) and compromising spinal cord perfusion pressure (SCPP).

Risk factors for spinal cord ischaemia include

interventions to ↓ risk of spinal cord ischaemia, including

Monitoring may be

Spinal cord blood supply

The superior source vessels are branches from the left subclavian and vertebral arteries, which form the anterior and posterior spinal arteries.
Throughout its length the anterior spinal arteries receive supply from the paired intercostal and lumbar segmental arteries and then caudally from branches of the inferior mesenteric, internal iliac, and sacral arteries

reverse flow from spinal arteries may both contribute to extraprosthetic leaks after the placement of sealed or occlusive stent grafts (type II endoleaks) and ‘shunt’ blood from the spinal circulation by a low-resistance pathway

Lumbar drain

Cerebrospinal fluid drainage is effective because acute changes in the spinal cord in response to ischaemia or reperfusion may result in oedema and increased CSF pressures during the procedure and for 48–72 h (or even longer) afterwards

CSFP is maintained at 10–15 mm Hg
CSF is drained to maintain this at rates up to 20 ml/h
Monitoring of CSFP and drainage continue for up to 72 h after surgery.

An SCPP target of 70 mm Hg is used in most centres, requiring a CSFP of less than 15 mm Hg and a minimum MAP of 80 mm Hg
Where there is evidence of spinal cord ischaemia, the SCPP and MAP target can be increased in 5 mm Hg increments

The spinal drain consists of a transduced intrathecal catheter inserted at the level of L3–4 or L4–5 to reduce the risk of direct spinal cord damage

IONM

Paraplegia caused by spinal cord ischaemia significantly dampens the lower-limb potentials when compared to those of the upper limb.
MEPs disappear in the presence of neuromuscular blocking agents, and volatile anaesthetics also cause dose-dependent depression of the MEP at doses within the range used in clinical practice

TIVA is preferred if MEPs are to be used

SSEPs, although less frequently used, allow monitoring of the posterior ascending sensory columns, and are not affected by neuromuscular blocking agents or volatile anaesthetic agents.

A ↓ in MEP amplitude >50% should prompt reinsertion of intercostal arteries into the graft along with measures to improve spinal cord perfusion.
A MAP >80 mm Hg and distal aortic pressure >60 mm Hg are targeted.
Haemoglobin concentration should be maintained at or above 100 g/L
CSF may be drained at 20 ml/h
The decision for surgical intervention is usually made within 3–5 min of the change in the neurophysiological variables.

Post-op

In most cases, the aim is for primary extubation at the end of surgery and transfer to HDU/ICU

Ensure peripheral pulses are checked in lower limb for early detection and treatment of thrombosis and ischaemia before extubation.

Indications for a period of post-operative ventilation include

The requirement for organ support often depends on

multimodal analgesia to allow early weaning
→ to facilitate neuro assessment

?EA
vs spinal opioid via lumbar drain

Post-op complications

Postoperative organ dysfunction is particularly common in

Neuro complication : rare
Disruption of the arterial supply to the spinal cord during cross-clamping can result in ischaemia and paraplegia

Preoperative placement of a cerebrospinal fluid (CSF) drain may be deemed necessary in patients deemed to be high-risk or spinal cord ischaemia

In general, the risk is extremely low and maintenance of adequate perfusion pressure with postoperative monitoring for evolving neurology is sufficient

Other less common postoperative complications include

Abdominal compartment syndrome is caused by combination of

References

Perioperative Management of Thoracic and Thoracoabdominal Aneurysms - BJA Ed

Spinal Cord Protection in Aortic Endovascular Surgery - BJA Ed

Anaesthesia for Open Abdominal Aortic Surgery - A&ICM

Anaesthesia for Ruptured Aortic Aneurysm - A&ICM