Decannulation Techniques
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Direct answer
The first cannula in is the last cannula out: decannulation reverses the initiation order — the venous cannula comes out first (its purse-string snugged as the anaesthetist gives volume back through the circuit), then, once protamine is running or complete and the field is dry, the arterial cannula is removed last, preserving the team's route for transfusion of residual pump blood and for instant re-initiation until the very end. Aortic sites are repaired with the pre-placed purse-string sutures, femoral sites either closed surgically or with percutaneous closure devices over a wire, with distal limb perfusion checked immediately. The perfusionist's contribution is volume stewardship — giving back circuit blood judiciously, or processing it through the cell saver — and vigilance: decannulation bleeds, air enters where cannulae exit, and a sudden collapse during protamine is the drug's territory.
What you must remember
- Order and its logic: venous out first, arterial last — the venous purse-string closes, the heart fills from the circuit, and the arterial cannula remains the lifeline for transfusion and rapid return to bypass until protamine is well underway.
- Protamine choreography: many surgeons decannulate the venous side as protamine begins and remove the arterial cannula only after the reversal is substantially given — balancing the clot risk in a cannulated aorta against the risk of needing the pump again.
- Give-back arithmetic: the residual circuit volume is transfused to the patient via the arterial cannula in judged aliquots, watching filling pressures and the heart on echo; hypervolaemia is its own complication.
- Residual blood options: process remaining circuit blood through the cell saver (heparin removed, plasma lost) or reinfuse with additional small protamine cover per unit policy — the choice is documented.
- Aortic site repair: purse-string sutures placed at cannulation are tied down, sometimes reinforced; the site is inspected for bleeds and, rarely, addressed for late stenosis or pseudoaneurysm.
- Femoral decannulation: open repair with direct closure or a percutaneous closure-device strategy (often pre-closed with sutures before cannulation), wire maintained until haemostasis is confirmed, distal pulses and perfusion checked immediately.
- Air discipline at exit: cannula removal moments are de-airing moments — ventilation held per surgeon preference, root venting available, echo watching.
- Perfusionist's stance until the end: the circuit stays primed, clamped and ready until the surgeon releases it; the record closes with decannulation times and residual volume disposition.
The give-back, decided at the console
Separation has gone well; the heart ejects on modest support; roughly 1,200 mL of blood sits in the oxygenator and reservoir, and it belongs to the patient. The negotiation is haemodynamic: the anaesthetist calls for volume in 100 mL aliquots, watching central venous pressure, mean pressure and the transoesophageal echo — the ventricle small gets blood, the ventricle full gets nothing and a vasodilator instead. Protamine begins; the venous cannula is removed once reversal is established. For the last 700 mL the choice is explicit: direct reinfusion through the arterial cannula is faster but carries heparinised prime; processing through the cell saver returns washed red cells at 55 per cent haematocrit with no heparin, at the cost of plasma and platelets — protocol, bleeding and product availability decide. The arterial cannula comes out last, its purse-string tied, the site inspected.
Where the exam probes
The guaranteed viva question is "which cannula is removed first and why", and the pass answer is the reasoning, not the order: venous first because the arterial route is the lifeline for volume and re-initiation until protamine is safely established. The second probe is residual pump blood: asked "what do you do with the blood in the circuit", weak answers say "give it back"; trained answers give both routes — direct reinfusion with extra protamine accounting, or cell-saver processing — with what each contains and lacks. Indian boards add texture: femoral closure devices are a cost line many centres weigh against open repair, product availability shapes the coagulation tail of the evening, and late aortic-site complications — bleeding, pseudoaneurysm, stenosis — appear as one-mark questions.
Frequently asked questions
Which cannula is removed first and why?
The venous cannula — the arterial cannula remains as the route for transfusing residual circuit volume and for rapid return to bypass until protamine reversal is well established.
How is residual pump blood managed at the end of the case?
Transfused in judged aliquots via the arterial cannula watching filling pressures, or processed through the cell saver to washed red cells — each option's heparin and component profile is weighed and documented.
How is the aortic cannulation site closed?
With the purse-string sutures placed at cannulation, tied as the cannula exits, reinforced as needed, and inspected for bleeding before closure.
What are the femoral decannulation options?
Open surgical repair, or percutaneous closure devices (often pre-placed before cannulation), keeping a wire until haemostasis is confirmed and checking distal pulses and limb perfusion immediately.
Why does the perfusionist keep the circuit ready after decannulation?
Until the chest is closing, the team retains the ability to re-heparinise and re-initiate bypass within a minute — the circuit is broken down only when the surgeon releases it.