**3. ECMO circuit configuration**

### **3.1. Cannulation strategies**

Initial cannulation strategies for long-term ECMO are identical to short-term ECMO support, with the goal of achieving adequate blood flow to support gas-exchange requirements, while minimizing recirculation between the cannulae. For patients with isolated respiratory failure, venovenous cannulation is possible. If hemodynamic support is required, or if there is significant pulmonary hypertension, venoarterial ECMO may be necessary. For the expeditious initiation of ECMO, percutaneous cannulation of femoral and jugular vessels is preferred, as it allows for initiation of ECMO at the bedside in a rapid manner.

As the patient's tenure on ECMO becomes prolonged, however, cannulation must not only provide appropriate cardiopulmonary support but must also provide long-term stability and allow for rehabilitation with possible ambulation. In general, long-term femoral cannulation is not preferred due to infectious risk as well as relative limit to mobility associated with access to the femoral vessels.

For isolated respiratory support, early transition to a double-lumen internal jugular cannula (Avalon Elite®), placed under echocardiographic or fluoroscopic guidance, has proven to be beneficial in many centers. Since the double-lumen internal jugular cannula allows for full mobility of the lower extremities, these patients are able to ambulate and undergo physical therapy with the goal of limiting deconditioning. This double-lumen cannula does impose a restriction to flow, however, and careful patient selection is required.

For patients with cardiogenic shock or pulmonary hypertension, the cannulation options are more limited. In principle, the cannulae must provide venous drainage as well as return of oxygenated blood to the arterial system with adequate return pressure to provide end-organ perfusion. In the acute cannulation of patients with cardiopulmonary collapse, the common femoral artery is the preferred vessel for arterial cannulation in adults. Of note, the presence of the arterial cannula in the common femoral artery can compromise distal limb perfusion, and insertion of a distal perfusion catheter is often required. Unfortunately, the groin access required for cannulation of the common femoral artery limits mobility and may be deleterious to rehabilitation.

would be considered long term (21 days). Reports of patients being supported on venoarterial ECMO for prolonged durations do exist in the literature, however. In one study, a patient unable to wean from cardiopulmonary bypass following re-do sternotomy and aortic valve replacement was supported with venoarterial ECMO for 33 days postoperatively before being successfully weaned and decannulated [11]. Unfortunately, this patient ultimately suffered a cerebrovascular accident and died in a high-dependency unit. In a cohort of 98 patients receiving ECMO for refractory cardiogenic shock, Rousse et al. reported a median duration of ECMO use of 8 days, with the maximum duration of 81 days [12]. This cohort suffered 50% mortality, with 30% of patients recovering to normal cardiac function, 13% of patients receiv-

The decision to provide long-term ECMO support for these patients is largely dependent on their presumed recovery path, and it is the patients who are poor candidates for VAD support who are typically supported on venoarterial ECMO in the long term. These patients must be aggressively medically optimized, as the goal of the ECMO therapy is in recovery of native cardiac function prior to decannulation. Indeed, some patients will not recover native cardiac function, will never become transplant candidates, and are unsuitable for VAD as a destination therapy. Management of these patients is a significant challenge both medically and ethi-

Initial cannulation strategies for long-term ECMO are identical to short-term ECMO support, with the goal of achieving adequate blood flow to support gas-exchange requirements, while minimizing recirculation between the cannulae. For patients with isolated respiratory failure, venovenous cannulation is possible. If hemodynamic support is required, or if there is significant pulmonary hypertension, venoarterial ECMO may be necessary. For the expeditious initiation of ECMO, percutaneous cannulation of femoral and jugular vessels is preferred, as

As the patient's tenure on ECMO becomes prolonged, however, cannulation must not only provide appropriate cardiopulmonary support but must also provide long-term stability and allow for rehabilitation with possible ambulation. In general, long-term femoral cannulation is not preferred due to infectious risk as well as relative limit to mobility associated with

For isolated respiratory support, early transition to a double-lumen internal jugular cannula (Avalon Elite®), placed under echocardiographic or fluoroscopic guidance, has proven to be beneficial in many centers. Since the double-lumen internal jugular cannula allows for full mobility of the lower extremities, these patients are able to ambulate and undergo physical therapy with the goal of limiting deconditioning. This double-lumen cannula does impose a

ing a heart transplant, and 7% of patients transitioned to VAD therapy.

cally, and the family must frequently be updated in the plan of care.

it allows for initiation of ECMO at the bedside in a rapid manner.

restriction to flow, however, and careful patient selection is required.

**3. ECMO circuit configuration**

218 Advances in Extra-corporeal Perfusion Therapies

**3.1. Cannulation strategies**

access to the femoral vessels.

Although there is no commonly accepted cannulation site for long-term venoarterial access, one reported technique is cannulation of subclavian vessels [13]. This technique is reported to provide adequate flows and improved ambulation options. Technically, this cannulation method requires a small infraclavicular incision, anastomosis of a synthetic arterial graft with the subclavian artery in an end-to-side fashion, and direct insertion of the cannula into the arterial graft. Naturally, decannulation from this arrangement requires a surgical procedure with either explant or close ligation of the arterial graft.

In cases where there is right heart dysfunction or severe pulmonary hypertension, venoarterial ECMO through femoral vein and femoral artery is the traditional means of decompressing the right ventricle. In patients with a congenital atrial septal defect, a less invasive technique can be employed, in which a dual-lumen cannula is placed under fluoroscopic or echocardiographic guidance [14]. This goal of this configuration is to direct the oxygenated blood returned from the ECMO circuit through the atrial septal defect and into the left atrium, thus reducing the blood delivered through the right ventricle. This configuration promotes ambulation, as the dual-lumen venovenous cannula is inserted through the internal jugular vein. Both animal and human studies have shown success with creation of an atrial septostomy in conjunction with venovenous ECMO for the treatment of pulmonary hypertension [15]. If this technique cannot provide adequate right ventricular unloading, central cannulation is required, with two primary configurations.

The first central cannulation technique involves venous drainage from the right atrium and return of oxygenated blood into the pulmonary artery. Technically, this is accomplished through a median sternotomy or thoracotomy, with insertion of the venous drainage cannula into the right atrial appendage, and a synthetic arterial graft is anastomosed to the main pulmonary artery in an end-to-side fashion. The arterial cannula is inserted into this graft. In the patient with pulmonary hypertension, this configuration requires that the ECMO circuit pumps against this high-resistance pulmonary vasculature. This is rarely an issue, however, as even the vasculature of severe pulmonary hypertension has a lower driving pressure than systemic arterial pressure, and modern ECMO circuits have little difficulty driving blood through the systemic circulation. One major advantage of this configuration is that it places the arterial return in the main pulmonary artery, benefiting from the systemic-embolus protection afforded by the pulmonary vasculature. Additionally, cannulae can be tunneled out of the subcutaneous tissues and skin without access to upper or lower limbs, promoting mobility.

Central cannulation between the right atrium and left atrium can also be a strategy to mitigate pulmonary hypertension or right heart dysfunction [16]. In this case, venous blood is drained from the right atrial appendage, passed through the ECMO circuit for gas exchange, and oxygenated blood is returned to the left atrium. Again, cannulae for this technique can be tunneled allowing for mobility. Unfortunately, the invasiveness of the thoracotomy or median sternotomy is required, and there is no "pulmonary filter" to mitigate the consequences of ECMO circuit embolism, with a theoretical increase in the risk of stroke.

with long-term cannulation in an ovine model, evidence of impending cannula failure has been

Extracorporeal Membrane Oxygenation (ECMO) for Long-Term Support: Recent Advances

Due to the prolonged duration of component use in patients on long-term ECMO, component failure is a realistic possibility. Catastrophic failures, such as component rupture and hemorrhage, are managed through emergent circuit exchange. As such, a primed backup circuit

More gradual failures can occur in both the pump and the oxygenator, requiring exchange of these components. For the pump, failure can occur due to thrombus formation (typically on the impeller or bearing) causing decreased pump performance and increased hemolysis. This can be detected by trending pump rotational speed, blood flows, and plasma-free hemoglobin (PFH). A PFH level of approximately 10 mg/dL is generally acceptable, with a level over 50 mg/dL suggestive of excess hemolysis [18]. Rapid changes in PFH are perhaps more informative than the absolute value, and any rapid increase in PFH should be investigated. Of note, it is critical that blood samples be obtained gently while measuring PFH, as hemolysis

Oxygenator failure can occur as a result of several conditions. The most acute failure is rupture of the fiber bundle, allowing sweep gas to enter the blood path and placing the patient at risk for an air embolism. Slow decline in oxygenator performance can occur due to protein deposition on the membrane, condensation buildup inside the gas passage, or the development of thrombus within the oxygenator. Condensation buildup can be prevented by periodically increasing the sweep gas to a high flow rate (10 LPM) for several seconds to blow the condensate into the

a prolonged period. A flashlight can be used to examine the oxygenator (and tubing) for thrombus. Any thrombus visible on the oxygenator outlet side is impetus for oxygenator exchange, as this thrombus is at risk of embolization. Any other thrombus greater than 5 mm or enlarging may also warrant component or circuit exchange [17]. Finally, oxygenator performance may slowly decline as a result of protein deposition on the membrane. There is no reliable test to identify this as the cause of poor oxygenator performance, thus any oxygenator that cannot generate an exhaust oxyhemoglobin saturation of at least 95% is a candidate for exchange [18].

The use of ECMO for long-term support can lead to any number of complications. Although a multitude of complications can occur during long-term ECMO support, the typical complications are related either to cannulation, anticoagulation, concomitant organ failure, or infection. A meta-analysis by Cheng et al. reports complication rates on 1866 adult patients receiving ECMO as rescue therapy for the treatment of cardiogenic shock [18]. The rates of complications from this analysis are as follows: lower extremity ischemia—16.9%, lower extremity fasciotomy or compartment syndrome—10.3%, lower extremity amputation—4.7%, stroke—5.9%, neurologic complication—13.3%, acute kidney injury—55.6%, kidney injury

by maintaining this high sweep for

http://dx.doi.org/10.5772/intechopen.76506

221

detected (and repaired) on multiple occasions (unpublished data) (**Table 2**).

can occur during sample acquisition causing an erroneously high reading.

**3.2. Circuit maintenance and component exchange**

should be available for emergent exchange at all times.

exhaust. Care must be taken not to reduce the patient's CO2

**4. Complications**

In a long-term ECMO patient, physicians may need to transition between cannulation sites, due to changes to patient's support needs, desire to promote mobility, as well as cannulation site complications such as infection, hemorrhage, or inadequate distal perfusion. Continuous reevaluation of the appropriateness of cannulation must be performed, as a highly mobile patient on venovenous ECMO will likely fare better than a bedbound patient supported by a venoarterial configuration. Additionally, long-term ECMO patients may suffer unusual cannulation site and hardware complications. The securing sutures of cannula must be frequently examined, as they may pull from the skin or break during long-term support. Additionally, cannulae are subject to prolonged periods of fatigue, which may lead to early failure. In this author's experience


**Table 2.** Possible cannulation sites.

with long-term cannulation in an ovine model, evidence of impending cannula failure has been detected (and repaired) on multiple occasions (unpublished data) (**Table 2**).

#### **3.2. Circuit maintenance and component exchange**

Central cannulation between the right atrium and left atrium can also be a strategy to mitigate pulmonary hypertension or right heart dysfunction [16]. In this case, venous blood is drained from the right atrial appendage, passed through the ECMO circuit for gas exchange, and oxygenated blood is returned to the left atrium. Again, cannulae for this technique can be tunneled allowing for mobility. Unfortunately, the invasiveness of the thoracotomy or median sternotomy is required, and there is no "pulmonary filter" to mitigate the consequences of

In a long-term ECMO patient, physicians may need to transition between cannulation sites, due to changes to patient's support needs, desire to promote mobility, as well as cannulation site complications such as infection, hemorrhage, or inadequate distal perfusion. Continuous reevaluation of the appropriateness of cannulation must be performed, as a highly mobile patient on venovenous ECMO will likely fare better than a bedbound patient supported by a venoarterial configuration. Additionally, long-term ECMO patients may suffer unusual cannulation site and hardware complications. The securing sutures of cannula must be frequently examined, as they may pull from the skin or break during long-term support. Additionally, cannulae are subject to prolonged periods of fatigue, which may lead to early failure. In this author's experience

**Site**

Lengthy, OR High Bedside Systemic Requires fluoroscopy

Lengthy, OR High OR Systemic Possible limb

Lengthy, OR High OR Pulmonary Requires chest

Left atrium Lengthy, OR High OR Systemic Requires chest

Aorta Lengthy, OR High OR Systemic Requires chest

Low Bedside vs. OR Systemic Possible limb

Low Bedside Pulmonary

High Bedside Pulmonary

**Comments**

or transesophageal echocardiography for

ischemia, Consider distal perfusion catheter

ischemia, vascular complications

exploration for bleeding

exploration for bleeding

exploration for bleeding

positioning

ECMO circuit embolism, with a theoretical increase in the risk of stroke.

**Drainage Return Cannulation Mobility Decannulation Embolization** 

Jugular vein Rapid,

Jugular vein Rapid,

Femoral artery Rapid,

Jugular vein with atrial septostomy

220 Advances in Extra-corporeal Perfusion Therapies

Subclavian or axillary artery

Pulmonary artery

**Table 2.** Possible cannulation sites.

bedside

bedside

bedside

Femoral vein

Jugular vein

Jugular vein

Femoral vein

Subclavian vein

Right atrium

Right atrium

Right atrium Due to the prolonged duration of component use in patients on long-term ECMO, component failure is a realistic possibility. Catastrophic failures, such as component rupture and hemorrhage, are managed through emergent circuit exchange. As such, a primed backup circuit should be available for emergent exchange at all times.

More gradual failures can occur in both the pump and the oxygenator, requiring exchange of these components. For the pump, failure can occur due to thrombus formation (typically on the impeller or bearing) causing decreased pump performance and increased hemolysis. This can be detected by trending pump rotational speed, blood flows, and plasma-free hemoglobin (PFH). A PFH level of approximately 10 mg/dL is generally acceptable, with a level over 50 mg/dL suggestive of excess hemolysis [18]. Rapid changes in PFH are perhaps more informative than the absolute value, and any rapid increase in PFH should be investigated. Of note, it is critical that blood samples be obtained gently while measuring PFH, as hemolysis can occur during sample acquisition causing an erroneously high reading.

Oxygenator failure can occur as a result of several conditions. The most acute failure is rupture of the fiber bundle, allowing sweep gas to enter the blood path and placing the patient at risk for an air embolism. Slow decline in oxygenator performance can occur due to protein deposition on the membrane, condensation buildup inside the gas passage, or the development of thrombus within the oxygenator. Condensation buildup can be prevented by periodically increasing the sweep gas to a high flow rate (10 LPM) for several seconds to blow the condensate into the exhaust. Care must be taken not to reduce the patient's CO2 by maintaining this high sweep for a prolonged period. A flashlight can be used to examine the oxygenator (and tubing) for thrombus. Any thrombus visible on the oxygenator outlet side is impetus for oxygenator exchange, as this thrombus is at risk of embolization. Any other thrombus greater than 5 mm or enlarging may also warrant component or circuit exchange [17]. Finally, oxygenator performance may slowly decline as a result of protein deposition on the membrane. There is no reliable test to identify this as the cause of poor oxygenator performance, thus any oxygenator that cannot generate an exhaust oxyhemoglobin saturation of at least 95% is a candidate for exchange [18].
