Aortic Dissection CPB Strategies
On this page
Direct answer
Type A dissection makes cannulation itself the first operation: femoral arterial return, perfusing retrograde up a dissected aorta, may fill the false lumen and steal the true — so contemporary strategy favours axillary or innominate cannulation (antegrade true-lumen flow through a graft), direct true-lumen cannulation under echo, or cerebral-first strategies that cool to deep hypothermia at 18-20 degrees before any arrest. Cerebral protection during circulatory arrest uses selective antegrade cerebral perfusion — commonly about 10 mL/kg/min at 20-28 degrees with right radial pressure roughly 50-70 mmHg — or retrograde cerebral perfusion through the superior vena cava at 20-30 mmHg. Bilateral NIRS is the perfusionist's real-time referee of which lumen is actually being perfused, and a unilateral desaturation during bypass is a malperfusion alarm, not a monitor artefact.
What you must remember
- Cannulation hierarchy: axillary/innominate artery (side-graft, antegrade true-lumen flow) is the common default; direct ascending true-lumen cannulation under epiaortic or transoesophageal echo is an alternative; femoral return is a fallback compromised by false-lumen pressurisation and distal malperfusion risk.
- The lumen question governs everything: perfusing the false lumen kills the coronaries and the brain — verify true-lumen position on echo and watch the pressure trace and NIRS after every cannulation move.
- Cooling for arrest: nasopharyngeal 18-20 degrees C, with uniform cooling time before arrest; pH-stat management during cooling is common in many dissection programmes for its even cerebral cooling.
- Cerebral perfusion during arrest: selective antegrade cerebral perfusion at roughly 10 mL/kg/min (right radial pressure commonly 50-70 mmHg, or via innominate graft), or retrograde via SVC at 20-30 mmHg — antegrade generally supports longer safe arrest.
- Bilateral NIRS is non-negotiable: asymmetric or bilateral falls direct investigation of cannula position, perfusion route and cerebral perfusion strategy in real time.
- Rewarming discipline: slow, gradient-limited rewarming after arch reconstruction, vigilance for distal malperfusion as the flap repositions; femoral retrograde rewarming is again suspect.
- Perfusionist's drug and blood plan: dissections bleed — anticipate coagulopathy with viscoelastic testing, fibrinogen concentrate or cryoprecipitate planning, cell salvage and rapid transfusion pathways.
- Coronary ostium involvement may convert the operation to a root/Bentall procedure — the perfusionist plans cardioplegia routes (direct ostial, retrograde) before the surgeon announces it.
An acute type A, decided in minutes
A 49-year-old with tearing chest and back pain, CT confirming a Stanford type A dissection to the iliacs. Induction and sternotomy are the anaesthetic and surgical acts; the perfusion act is the cannulation conference: the right axillary artery is grafted for arterial return — antegrade, true-lumen, and the route that doubles as selective cerebral perfusion during arrest. Venous drainage via the right atrium. On bypass, cooling begins toward 18 degrees nasopharyngeal with pH-stat gas management, and both NIRS traces hold — true-lumen flow confirmed. Under circulatory arrest, antegrade cerebral perfusion runs about 500 mL/min through the axillary graft with right radial pressure mid-50s; the arch is opened, the tear found and repaired with a hemiarch. Twenty-six minutes of arrest, NIRS flat and symmetric throughout. Rewarming is slow, gradient under 10 degrees; the haemoconcentrator runs because the haematocrit and the temperature have to end in the right places together. The record shows the strategy as a sequence of decisions — cannulation route, cooling depth, cerebral protection, rewarming — which is exactly how the examiner will ask for it.
How the exam frames it
The favourite theory question is "arterial cannulation strategies in acute aortic dissection", and the marks sit in the reasoning: why femoral return is second-class (retrograde flow can pressurise the false lumen and worsen malperfusion), why axillary is default (antegrade, true-lumen, convertible to cerebral perfusion), and what confirms true-lumen perfusion (echo, pressure behaviour, NIRS). The viva then moves to cerebral protection during circulatory arrest: antegrade at about 10 mL/kg/min versus retrograde SVC at 20-30 mmHg, with the arrest temperature 18-20 degrees. Indian context: acute type A surgery concentrates in large tertiary and dedicated aortic centres, and many Indian programmes built their experience with retrograde cerebral perfusion before adopting selective antegrade — a chronology examiners themselves lived through, so quoting both with the trade-offs (antegrade supports longer arrest; retrograde is simpler and de-airs) sounds like training rather than textbook rental.
Frequently asked questions
Why is axillary arterial cannulation preferred in type A dissection?
It delivers antegrade flow into the true lumen, avoids retrograde false-lumen pressurisation seen with femoral return, and can serve as the route for antegrade cerebral perfusion during arrest.
What flow and pressure define antegrade cerebral perfusion?
Commonly about 10 mL/kg/min at 20-28 degrees C, monitored with a right radial pressure around 50-70 mmHg through an axillary or innominate graft.
What pressures govern retrograde cerebral perfusion via the SVC?
Superior vena caval pressure held around 20-30 mmHg, with the head vessels; generally supports shorter arrest durations than selective antegrade perfusion.
What does a unilateral NIRS drop during dissection repair suggest?
Malperfusion — the cannula or flap is compromising one carotid territory — prompting immediate echo reassessment of cannula position and perfusion strategy.
Why does dissection repair demand a major blood product plan?
Long deep-hypothermic runs, open arch surfaces and preoperative anticoagulation-consumptive state drive coagulopathy — viscoelastic-guided fibrinogen, platelets and rapid transfusion pathways are prepared before the arch opens.