ECMO Cannulation

Induction, the dangerous moment - by now the patient is hypoxemic, acidotic and holding a pressure only on maximal catecholamine drive, so a dose that is routine in the elective room produces arrest here. Cut it hard and give it over minutes, not seconds.

Pressors before the hypnotic - have the vasopressor and inotrope infusions titrating before the first drug goes in, not drawn up beside you. Ketamine or etomidate gives the smallest hemodynamic footprint, and even those get reduced.

Already sedated in intensive care - most arrive intubated, so the job is deepening safely rather than inducing. Do not re-induce out of habit; add opioid and hypnotic in increments, and confirm tube position yourself before you lose the head to the drapes.

Veno-venous versus veno-arterial - veno-venous supports oxygenation only, so the native heart still ejects and the trace stays pulsatile. Veno-arterial supports the circulation, so pulsatility flattens, pressure becomes pump flow against resistance, and oximetry and cuff readings turn unreliable.

Right radial, right hand - in femoral veno-arterial support put the arterial line in the right radial artery and the oximeter on the right hand. Both come off the innominate artery, the first vessel off the arch, so they are the closest thing you have to a brain sample.

Differential hypoxemia - retrograde femoral flow meets poorly oxygenated blood ejected forward by the recovering heart, so the brain can run desaturated while the legs read fully saturated and a left radial line reads beautifully. Escalate ventilator support or push for conversion.

Wire confirmation before dilation - echo shows the wire in the right atrium or vena cava rather than a hepatic vein or coiled in the ventricle. If the pressure falls off as the cannulas go in, look for pericardial fluid and a distending abdomen before reaching for norepinephrine.

Full paralysis for dilation - it stops movement and, more importantly, abolishes the spontaneous inspiratory effort that generates negative intrathoracic pressure and can entrain air down an open large-bore venous tract.

Carbon dioxide correction rate - once flow starts the ventilator drops to lung rest and the membrane clears carbon dioxide faster than the body buffers it, and a precipitous fall causes cerebral vasoconstriction. Ask for sweep gas to come up gradually.

Flow onset step change - veno-arterial support unloads the right heart and imposes retrograde afterload on the left, so expect either sudden hypertension or vasoplegic hypotension as the prime dilutes your pressors. Treat line chatter as preload, not as a reason for more speed.

Anticoagulation, not a recipe - many of these patients are already bleeding or coagulopathic and some centers cannulate with a reduced bolus or none. Use your unit's written protocol, confirm the target with the perfusionist, and have blood products present before you start.

The cannulated leg - a femoral return cannula occludes most of the lumen and everything distal lives on collateral flow, and a sedated patient cannot tell you the leg hurts. Document a baseline before draping and keep the limb visible for calf oximetry or Doppler checks.

No wake-up at the end - plan a paralyzed, sedated, monitored transfer and treat the move itself as the highest-risk part, because cannula migration is exsanguinating. Give one person the cannulas to own, and hand over which arterial line and oximeter site to interpret.

Extracorporeal membrane oxygenation drains venous blood through a large-bore cannula, drives it across a membrane oxygenator that adds oxygen and strips carbon dioxide, and returns it to the patient. Where it returns defines everything else. Veno-venous ECMO returns oxygenated blood to the right atrium, so the circuit supports gas exchange only and the native heart still has to generate the whole cardiac output; its signature inefficiency is recirculation, where freshly oxygenated blood is drained straight back into the circuit instead of passing through the systemic circulation. Veno-arterial ECMO returns blood into an artery, usually the femoral, so the circuit supports oxygenation and circulation together and runs in parallel with whatever the native ventricle still ejects. That retrograde aortic flow raises left ventricular afterload, and the watershed where circuit flow meets native flow is what produces differential oxygenation.

Decision and configuration - the team picks veno-venous for isolated respiratory failure and veno-arterial for cardiogenic shock, refractory arrhythmia, or arrest. The choice is made before anyone touches the patient, because it dictates cannula sizes, which vessels are opened, and what the anesthesia monitoring has to look like.

Site selection and vessel imaging - femoral vein, internal jugular vein, and femoral artery are the usual peripheral targets; a dual-lumen single cannula in the right internal jugular is an alternative for veno-venous support. Ultrasound sizes the vessel first, because a cannula wider than the artery guarantees distal ischemia.

Access technique - most adult cannulation is percutaneous by Seldinger technique under ultrasound. Surgical cutdown is used when the vessel is small, calcified, or cannot be found, and central cannulation directly into the right atrium and aorta is used when the chest is already open or peripheral flow is inadequate.

Wire placement and confirmation - the guidewire is tracked into the inferior vena cava or right atrium and its position is confirmed by transesophageal echocardiography or fluoroscopy before any dilator goes over it. This is the single most important safety step of the procedure: a dilator or cannula railroaded over a malpositioned wire is what perforates a vessel, the right atrium, or the right ventricle.

Systemic heparinization - a heparin bolus is given before the cannulas go in, per the institution's ECMO protocol, so the circuit does not clot as blood first contacts the membrane and tubing.

Serial dilation and cannula insertion - the tract is dilated up in steps to accept cannulas that are far larger than a standard central line. This is the point of maximal bleeding risk in an anticoagulated patient, and of air entrainment into an open large-bore venous tract.

Circuit connection and de-airing - the cannulas are connected to the primed circuit with the lines clamped, all air is cleared, and the clamps come off in a coordinated sequence with the perfusionist.

Initiation of flow - pump speed is brought up gradually while drainage, line pressures, and arterial waveform are watched. Chattering of the drainage line means the circuit is outrunning venous return and needs volume or a lower speed.

Distal perfusion cannula - in femoral veno-arterial ECMO a small antegrade cannula is placed into the superficial femoral artery below the arterial cannula, so the leg is still perfused past a vessel that is now largely occluded by the return cannula.

Position confirmation and securing - final cannula tip positions are documented by echocardiography or chest radiograph, the cannulas are sutured and dressed heavily, and limb position is fixed. Cannula migration during transfer is a lethal complication, not a nuisance.

Extracorporeal cardiopulmonary resuscitation is a different animal from an elective cannulation. You are cannulating during ongoing chest compressions, so the field moves, transesophageal echocardiography images between compressions, and there is no induction to give because the patient is in arrest. Your job narrows to airway confirmation, capnography as a marker of compression quality and of return of circulation, drug delivery, and keeping the resuscitation algorithm running while the cannulating team works. Amnesia matters as circulation returns, so have sedation drawn up and ready to give the moment flow is established; awareness during and immediately after eCPR is a recognized and preventable harm.

A large share of these cannulations happen outside the main operating room, in intensive care, the catheterization lab, or the emergency department. Treat it as a full off-site anesthetic: bring your own airway equipment and a working suction, confirm the oxygen supply and scavenging before you commit, know where the nearest defibrillator and blood fridge are, and make sure every infusion pump is on the same side of the bed as you and running on battery that will survive a transfer. The single most common off-site failure is drug and equipment access, not clinical judgment.

The circuit changes pharmacokinetics from the moment it is connected. Priming volume abruptly increases the volume of distribution and dilutes whatever is circulating, including the vasopressor infusion, and the oxygenator membrane and tubing sequester lipophilic, highly protein-bound drugs, so propofol, fentanyl, midazolam, and dexmedetomidine all lose apparent potency on ECMO. Expect sedation and analgesia requirements to climb after initiation and titrate to effect on the monitor and on a sedation score rather than reusing the pre-cannulation infusion rates.

Left ventricular distension is the complication people forget to look for in veno-arterial ECMO. The retrograde arterial flow raises afterload on a ventricle that may not be able to open the aortic valve, so blood backs up, the ventricle distends, pulmonary edema worsens, and stasis in the left heart risks thrombus. Watch for loss of aortic valve opening and a rising pulmonary artery diastolic pressure or worsening pulmonary edema, and raise it with the team early, because the fixes are theirs: inotropic support, an intra-aortic balloon pump, an Impella, or a surgical vent.