Complications related to Arterial cannulation

Establishing arterial cannulation (usually aortic) is one of the most important events in cardiopulmonary bypass. Commonly used arteries are the Ascending aorta, femoral artery, axillary artery and rarely the iliac arteries ,descending thoracic or abdominal aorta and sometimes the carotid artery in neonatal ECMO. Arterial vascular access can give rise to major complications that can make CPB hazardous.

=Ascending aortic cannulation= It is necessary to cannulate the aorta in a nonatheromatous area and with the blood pressure in a normal range.

Aorta with atheroma
This can cause dislodgement of atheromatous plaques.


 * An epicardial ultrasound is more sensitive compared to manual palpation which has actually found to be neither specific or sensitive.
 * Careful minimal handling is required in such cases or another cannulation site may have to be chosen.
 * If an atheromatous plaque is found on incision it may be wiser to close that hole and cannulate elsewere rather than shoving a cannula through an incision in a plaque.
 * If there is extensive atheromatous plaques consideration for doing an anaortic OPCAB with arterial grafts with inflow from the IMA's or resection of the aorta or an aortic endartercetomy or a sucker atherectomy of loose atheroma's may have to be planned.
 * Consider cannulation of the axillary artery in very atheromatous aortas if you are not accustomed to OPCAB, then perform CABG "On-Pump- beating heart".

Hypertensive aorta

 * The blood pressure must be reduced when trying to cannulate the aorta . Trying to cannulate an aorta which is tense can cause an arterial dissection or tears that can rapidly extend the confines of the purse string.

Management of such a tear
This may require
 * Packing / digital control while


 * A larger purse string can be placed - if the tear is really limited. With the pressure lowered a side clamp may be placed and precise location of the lumen, and placement of the cannula and repair of any lateral tear may be done.


 * It may be wise to use a pledget if placing additional purse strings. care must be taken to avoid an "iatrogenic coarctation".


 * An alternate site (for eg femoral artery ) is exposed to allow CPB establishment.


 * Further planning is based on whether a cross clamp can be placed above the tear and if so it can allow a precise repair/ patching. If not the patient must be prepared for total circulatory arrest to allow precise repair of the torn edges and this may even require patching if the tissues are under tension or even replacement of a part of the ascending aorta or arch depending on the extent of the tear.

=Cannulation of a hypotensive aorta= This represents another set of problems - while a single purse string can be placed easily the problem is in insertion of the cannula. The cannula tends to push the anterior wall to the posterior wall frustrating attempts to cannulate the aorta.
 * It is best to put a wide purse string and release any old purse strings (if tied). The opening made in the aorta by stabbing the aorta is made wide intentionally and is widened with an artery forceps deliberately and the cannula is placed without forcing through the bleeding incision under vision with the purse string kept loose.
 * An alternative is to side clamp the aorta and after opening the aorta place the cannula under direct vision.
 * Cannulation of the soft aorta using a guide wire is a useful techniquein this situation. Several companies make a cannula-guidewire set that can be used.

=Complications related to the methodology of ascending aortic cannulation= There are diffferent methods of cannulation of the ascending aorta nad each of these can be associated with various complications.

Stab cannulation
This is a common method of cannulation. Basically a controlled stab inside the aorta is made with either a no 11 or 15 blade and this allows a cannula to be slipped in. A common mistake is to place too small an incision causing a dissection or a controlled tear. Actually if a forceps is used to hold the upper flap and a slightly oblique cut is used, a clean cut can be made into the aorta with virtually no bleeding and precise introduction of the cannula can be done slowly in a unhurried manner. Some surgeons serially dilate the opening with Hegar's or an artery forceps. This has to also be done carefully to prevent an uncontrolled tear.

Scratch and cannulate
This method requires serially incising the aorta 'upto the intima. This is seen as a bluish streak while incising the media. The tip of the cannula is then ently forced agains t this nad cannulation can be done. This may be problematic if the aorta is floppy and hypotensive like in an aorta in a case which has arrested. Rough manipulation can cause a dissection especially if care has not been tken to incise down to the intima and damage can also occur to the posterior wall if rough "shoving" introduction is done. If the cannula does not go in easily, withdrawal of the cannula, careful inspection is requiredand usually the cause is due to an improper incision failing to rech the intima.

Clamp incise and cannulate
This requires the application of a purse string either prior or after application of a side clamp. The aorta is opened and this can allow precise application of a purse string through a precise hole. The cannula is placed under vision as the clamp is being released. This method requires quick placement of the purse string if not placed before and cannulation as the side clamp can cause hypotension if it occupies a significant portion of the aorta. This method has to be obviously be avoided in atheromatous aortae. Clamp induced dissection is a distinct possibility by this method.

Recognition of intraoperative dissection
Dissection on cannulation can be recognized by
 * Bluish swelling of the aorta
 * Bleeding from the needle holes
 * Increasing line pressure and if perfusion is maintained falling venous reservoir volume

Management

 * STOP THE PUMP


 * CANNULATE AN ALTERNATE SITE . All open heart patients should have their femoral arteries painted for easy access in case of an intraoperative dissection. A useful alternative is to cannulate the LV apex with a wire reinforced straight cannula (20-22 Fr) in an adult and guide it via the aortic valve and this ensures perfusion of the true lumen in an emergency.


 * Rapidly cool to at least 22 degrees The anesthesiologists should prepare for Total circulatory arrest.


 * Give Head low position, open the aorta and assess. If there is a distinct tear it can be resected and patched or sutured. GRF glue/Bioglue can be conveniently used. An easy alternative is to invert the aortic adventitia and use it (Floten Flap). A patch of a Zero porosity graft or Pericardium can be used. If the damage is extensive and not glueable, resection and replacement of the ascending aorta basically involving the whole entry site will be required.. Circulation can be started with deep head low position (Trendlenburg) and slowly fill the aorta to de-air it. Retrograde cerebral perfusion can help in deairing.After this during rewarming the proposed surgical procedure can be done. Cerebral protective measures have to be maintained postoperatively.
 * Avoid cerebal hyperthermia

Post cannula removal bleed
The best thing even in thin aortae is to '''avoid piercing through and through when taking a purse string. Care taken initially goes a really long way.''' If a thin problematic aorta is suspected femoral cannulation may be wiser to minimize aortic manipulation.



A Marfan aorta must be pledgetted'''. It just hasn't got intrinsic strength of its own.''' The aortic cannulation site may bleed after removal of the cannula especially if the aorta is thin. Management includes
 * Use a pericardial/Teflon pledget on the third Z stitch if there is bleeding.


 * One important thing is that if there is bleeding it is important to cut open the surrounding adventitia to prevent a "blue bleb" dissection. The subsequent bites can imbricate this lifted adventitial along with or without a pledget as an autologous reverse adventitial flap (something like a reverse Floten flap.)


 * One little trick is to make a longer strip of pericardium (roughly more than double the regular pledget. Use one end as a pledget and take the needles through the tissue and then pass the needles into the remaining part of the pericardium. This folds up the pericardium and acts as a local patch which works very well.

A Caveat to managing this is to REDUCE THE PRESSURE


 * Head up and SNP usually works and it is good to get the pressures below 90 and better still in the 60's.


 * If the dP/dT is really high based on the vigorousness of cardiac contractions temporary rapid ventricular pacing at 150 -200 beats ]


 *  Temporarily clamping / snugging the IVC causes the BP to drop over 20-30 seconds and then it can be released as soon as the stitch is placed and tightened and the BP returns with resitution of preload.


 * a short period of fibrillation - defibrillation may be used conveniently.

If it still persist there is tension on the aorta and then you must consider patching it - either with a large piece of pericardium over the whole area or femoral bypass with open patching.

Relevant links include Massive hemorrhage

=Femoral artery cannulation= Femoral artery cannulation can be elective as in redo's or may be emergent. This is a less popular method (though historically the first method used) because of a higher incidence of complications. Complications can occur during vascular exposure, cannulation and perfusion. Percutaneous cannulation is associated with additional problems

Complications during femoral vascular exposure

 * The femoral arteries are typically exposed by a longitudinal incision in the femoral triangle.
 * It is easily exposed when the pulse is well felt but can be difficult to feel in a hypotensive patient. An initial skin incision and a rolling movement with the fingers over the tissues usually allows the femoral artery to be felt like a firmer "cord" like structure or even allow palpation of the pulse which may have not been felt through the skin.
 * The relation "VAN" from medial to lateral is a useful mnemonic - vein artery nerve.
 * The saphenous vein if seen can be a good guide as the femoral artery will be lateral to it.
 * The common femoral artery needs to be canulated and thus the vessel above the profunda needs to be exposed. This may require retraction of the inguinal ligament in case the profunda origin is high.
 * As a rule in any vascular exposure adequate proximal and distal control with tapes using Blalock - Pott loops or tourniquets must be used
 * If the artery is really small,
 * Iliac or axillary artery cannulation may have to be considered.
 * Suturing a prosthetic graft as a side arm for perfusion may also be an option if the femoral arteries are small or look friable.


 * It is wise to use cautery to burn any femoral lymphatics as they can cause troublesome lymphorrhea postoperatively.

Arteriotomy and cannulation

 * The cannulation can be by means of a deliberate transverse arteriotomy /purse string. The transverse arteriotomy allows a clean controlled opening of the artery and allows cannulation under vision. This arteriotomy needs to be precisely repaired after closure avoiding any narrowing.


 * The cannula must be adequately wetted / lubricated and introduced Bevel down and not up to allow easy cannulation without dissecting the femoral artery.


 * A longitudinal purse string can be placed through which an arteriotomy with cannulation can be performed or a Seldinger technique can be used. A theoretical advantage with this method is the possibility of pericannula perfusion of the distal limb though arterial vasospasm around these large cannulae may actually limit the amount of practical distal perfusion.  Removal of the cannula must be followed by tightening of the purse string and if there is any suspicion of luminal compromise, the purse strings may be loosened after clamping above and below the artery and the margins may have to be debrided and repaired by direct suture / a venous pericardial/prosthetic patch.


 * FREE PULSATILE FLOW MUST COME FROM THE CANNULA WHEN TRANSIENTLY OPENED The force of ejection must be brisk and it is convenient to remember that 1mm Hg = 13.6 cm of water so a patient with a pressure of 100 mm Hg systolic can actually eject to a height of approximately 13.6 metres !! (to put it in perspective). If it doesn't gush well there is a block somewhere

Fixing the cannulae

 * It is very important to securely fix the femoral cannulae and tubing. The snuggers can be tied to the femoral cannula so that dislodgement does not occur.
 * The femoral arterial line must be the most caudad tubing when the lines are received by the assistant and are fixed to the table.
 * A full loop of the arterial line should be made and securely fixed to the drape so that inadvertent traction will only cause traction and narrowing of the loop rather than causing traction on the cannula.
 * When suturing the loop to the drapes, it is important not to puncture the arterial cannula.
 * No sharp instrument should be placed over the drape covering the femoral arterial cannulation site. Inadvertent exsanguination can result !!

Complications during percutaneous cannulation

 * Percutaneous cannulation requires a Seldinger technique.


 * Preoperative localization with a hand held Doppler may be easily done and a Duplex scan can identify potential problenms in these patients for eg small femoral arteries, localized disease/atheroma's etc.


 * It is always wise to keep a femoral arterial line to monitor femoral pressure and this can be emergently used to pass relevant guidewires and dilators to cannulate percutaneously. It is preferable not to leave only a guidewire in place as this can migrate internally and may also be inadvertently be left behind !!!


 * A tortuous aorta may preclude femoral cannulation percutaneously.


 * A small femoral artery may tear and cause extensive damage requiring a either direct or cross femero femoral graftingdepending on the nature of injury.


 * The percutaneous cannula must be left behind and acts as an an obturator till the femoral artery is formally exposed and the artery is repaired.

Retrograde femoral dissection
Femoral perfusion can be associated with a retrograde dissection.(Retrograde femoral dissection)

THIS MAY NOT BE ASSOCIATED WITH A HIGH LINE PRESSURE. The dissection may extend into the retroperitoneum which can easily accommodate liters of fluid without an increase in pressure.

AN UNEXPLAINED FALL IN VENOUS RESERVOIR VOLUME in a patient with a femoral or iliac cannula should immediately make the surgeon and the perfusionist think of a intra operative dissection with retroperitoneal extension.

If this occurs then immediate exposure of the abdominal aorta via a laparotomy and cannulation of the abdominal aorta after precise identification of the true lumen or ascending aortic /axillary cannulation may have to be attempted. A TEE can at times show the dissection

Distal limb Ischemia
This can occur if the artery is cross clamped / snugged or vasospasm around a percutaneously placed artery.

It is imperative to always pass a Fogarty catheter down the cannulated limb prior to closing the artery.

If a very long period of femoral perfusion (&gt; 6 hours) is planned then it may be wise to suture a side arm graft to the femoral arteriotomy and cannulate the graft allowing antegrade perfusion of the limb.

An alternative is to do a cross femero femoral graft distal to the cannulation site if a long period has elapsed and the cannula has originally been placed via a formal arteriotomy and snared and prolonged perfusion is required for whatever reason.

If a long period of Ischemia has already occurred controlled reperfusion of the limb may be done using papaverin or Diltiazem with mannitol and an initial warm normoxic perfusion at a low pressure can be done followed by normal perfusion.

The cannulated limb must be monitored continuously postoperatively and if required an embolectomy or a fasciotomy may be required.

=Axillary artery / Subclavian artery cannulation= This is being increasing used in aortic arch surgery. Important points include - There is a good video describing direct cannulation at. It requires real player to see the video.
 * Direct cannulation should be done gently to avoid tears.
 * A graft if sutured end to side allows good perfusion with lesser chances of damage to the artery and can easily be over sewn.
 * Dissection should be careful to avoid damaging the brachial plexus.
 * Ipsilateral and opposite radial artery pressures can document bilateral upper limb perfusion and also indirectly Innominate perfusion.

=Innominate artery cannulation= Innominate artery cannulation is gaining popularity in cases which would otherwise require circulatory arrest. This allows antegrade cerebral circulation to be performed. Methods It is wise to use a pediatric (Castaneda type) of micro clamp to partially calamp the innominate to cannulate it. A Hemashield or Goretex graft can be sutured to the innominate and a cannula can be passed through.the graft. This ensures good perfusion without compromising the lumen. Bone wax can be rubbed on the needle holes if Goretex is used to prevent troublesome needle hole bleeding.
 * Direct cannulation
 * Cannulation through a graft
 * Endoluminal cannulation- This can be done with a retrograde cannula placed via an Octopus multihead and cannulae can be placed in all 3 arch vessels to allow antegrade cerebral perfusion till the cerebral island or the branched grafts are attached. Care to deair while passing the catheters needs to be done. A short burst of retrograded perfusion can be used to advantage.

=Iliac artery cannulation= This is an alternative to femoral cannulation.
 * Advantages
 * Less chances of infection and troublesome lymphorrhea
 * Less incidence of wound complications


 * Disadvantages
 * Deeper location of vessels
 * Should be avoided in patients with ascites or significant TR where venous bleeding can be very troublesome.

It is exposed through a "Lanz" type of incision (like that for an appendicectomy on the relevant side) Muscles may be split or minimally divided and the peritoneum is swept away. Care to sweep away the Ureter should be taken. Vessels are looped and taped. The rest of the technique is the same as femoral cannulation.

=Rarer forms of arterial cannulation= These rare forms of cannulations are often done in select cases or in emergent situations. They can be an important quiver in the surgeons armamentarium

Prosthetic aortic graft cannulation
If femoral artery is cannulated for repair of aortic dissection, the cannula is transferred to the aortic graft following repair to establish antegrade arterial flow. On removal, the site is prone to bleed.

Technique to reduce bleeding on removal of cannula from the prosthetic graft
 * Linear cut in the graft
 * Run two separate 5-0 polypropylene simple sutures along each edge
 * Each suture line run in opposite direction
 * The two free tails at each end passed through torniquets.
 * Insert the cannula.
 * On removal, both suture ends tied.

Trans LV apical cannulation
This is indicated in
 * Aortic dissection especially intraoperative


 * Arch +descending aneurysms when being approached via a left thoracotomy

Technique

 * The LV apex is lifted up after placing Lap pads or a Deep Pericardial Retraction Suture (DPRS) as is placed in OPCAB.
 * A 3/0 Prolene suture with Teflon/Pericardial pledget is placed as a U suture and a snugger is placed. The site selected must be as apical as possible but avoiding fat.
 * An epicardial incision is placed within the U stitch. An artery forceps / vascular dissection forceps is then passed through this incision and is used to dilate the incision into the LV cavity.
 * A wire reinforced cannula (A straight 22-24 Fr venous cannula works very well in an emergency) is passed through the incision and guided through the aortic valve into the aorta an can be palpated there.. The snuggers are tightened and a safety tie is placed over the snugger to prevent inadvertent dislodgement and the heart is placed back into the pericardial well.
 * The free flow from the cannula is confirmed and connected to the arterial line after deairing.


 * TEE or an epicardial Echo confirms true lumen perfusion.

Removal
Removal is done after CPB by pulling the DPRS with steep head low and left tilt of the table allowing the apex to come up. The cannula is removed and the snugger is tightened. An over and over second layer is pre-placed and the first suture is tightened thereafter.

At times if ascending aortic replacement has been done the cannula can be shifted to the new site and the apex may be closed on CPB.

It is wise to have an alternative option for cannulation in ind if there is any bleeding from the LV apex - this is rare if the cannulation site is done in an area of muscle avoiding all stitches through fat.

Cranial placement of the LV apical stab can damage the base of the anterior papillary muscle of the mitral valve. and should be avoided.

Abdominal /Descending Thoracic aortic cannulation
Abdominal aortic cannulation is rarely done and this may have to be done when there has been a dissection of the femoral /iliac artery after its cannulation. This retrograde dissection may mandate cannulation of the abdominal aorta. The technique briefly involves doing a full midline incision, a medial visceral gut rotation after incising the peritoneum over the left paracolic gutter and placing an the infrarenal aorta is cannulated. This can be done between clamps to identify the true lumen if required. Care has to be taken to choose a soft spot and to avoid "pikn,.npe stem" portions of aorta as this can lead to troublesome bleeding that may eventually need endartrectomy / replacement of the aorta.

Descending thoracic aortic cannulation is usually done in an emergency situation when a left thoracotomy has been done.This can be done when doing a closed mitral valvotomy (when emergent CPB has to be instituted or when doing a thoracic aneurysm is being done. In the latter case this may be used to cannulate the aorta above and below an aneurysm to allow placement of a shunt or active bypass across the clamped segment. It is important to obtain control of proximal and distal segments and to remember that back flow from intercostal arteries will be present even if the segment is clamped.

Carotid artery cannulation
The carotid artery is usually used only in children for ECMO either in an emergency or when being done in a case where a sternotomy is not being contemplated (for eg neonatal respiratory distress syndrome.) This should be avoided in adults as the intercerebral circulation may not be as good as in neonates.If this has to be done in an adult it is preferable to suture an end to side graft to allow antegrade cerebral flow. Innominate artery cannulation is preferable alternative as it is larger and can often accomodate direct cannulation.

Exsanguination cannulation
This is done for example in a ruptured dissection when the sternum is open. . The IVC and SVC is clamped and suckers are allowed to suck whatever blood is pouring into the venous reservoir. The aorta is now flaccid and aorta is opened and directly cannulated under vision. If properly done this can be achieved in 1-2 minutes.

Trans scar cannulation using a Seldinger technique in a partially opened sternum
In the case of catastrophic sternal re-entry with damage to the RV a needle can be used to access the aorta and via a Seldinger technique a percutaneous aortic cannula can be placed and suction bypass or CPB  can be initiated to prevent exsanguination. After further dissection the cannula can be secured or repositioned.