**5. Equipment of v-a ECMO circuit**

#### **5.1. ECMO circuit**

The ECMO circuit is made of PVC tubing and the diameter of lines varies from ¼ inch for a neonate to ½ inch for pediatric and adult patients. The length of the circuit is kept not more than 2 meters to avoid increasing of resistance within a tube and twisting, but the length should be suitable to allow the movements of the patient by ECMO staff.

Areas of turbulent flow can predispose to clot formation; therefore loop and connectors should be avoided or kept at minimum.

#### **5.2. ECMO cannulas and cannulation techniques**

the likelihood of heart and end organs recovery. If the organs failure is thought to be reversible with ECMO, in such situation the device application is to be encouraged. If the likelihood of recovery of the heart or other end organs is thought to be very low or even impossible, then other factors must be taken into account. In such clinical scenario, the decision to institute ECMO should be based on an experienced ECMO team approach, which has to evaluate the patient's eligibility for heart transplantation or a definitive mechanical assist device (LVAD)

**•** possibilities for myocardial revascularization therapy, such as a coronary artery bypass

The ECMO circuit is made of PVC tubing and the diameter of lines varies from ¼ inch for a neonate to ½ inch for pediatric and adult patients. The length of the circuit is kept not more than 2 meters to avoid increasing of resistance within a tube and twisting, but the length should

Areas of turbulent flow can predispose to clot formation; therefore loop and connectors should

**•** possibilities for heart transplantation or LVAD implant as destination therapy;

implant as destination therapy.

276 Principles and Practice of Cardiothoracic Surgery

**4.1. Indications for v-a ECMO**

**•** Age of patient and body surface area;

grafting or coronary angioplasty;

**4.2. Contraindications for v-a ECMO**

**•** disseminated malignancy;

**•** known severe brain injury;

be avoided or kept at minimum.

**•** aortic dissection aortic incompetence.

**5. Equipment of v-a ECMO circuit**

**•** graft vs. host disease;

**•** advanced age;

**5.1. ECMO circuit**

**•** sufficient medical expertise in the field of ECMO;

**•** status of central organs such as kidney, liver, and brain.

Contraindications to the institution of v-a ECMO include [20]:

**•** unwitnessed cardiac arrest or cardiac arrest of prolonged duration;

be suitable to allow the movements of the patient by ECMO staff.

The following factors need to be evaluated for the indications [19]:

Cannulation is one of the most challenging aspects of ECMO. Peripheral percutaneous approach [6, 21 is the most used in cardiogenic shock and cardiac arrest [7, 22] because is quicker with less bleeding complications and easier decannulation. (Figure 2).

**Figure 2.** Peripheral cannulation for V-A ECMO.

The open surgical approach is considered for patients with severe peripheral vascular disease or for patients with postcardiotomy syndrome or failure of weaning from cardiopulmonary bypass [23, 24] (Figure 3). The open or central cannulation has more complications such as bleeding, infections, and mediastinitis.

**Figure 3.** Central cannulation for V-A ECMO

Percutaneous cannulas are usually made of polyurethane (Figure 4) and they are inserted using the Seldinger technique (Figure 5).

**Figure 6.** Distal leg perfusion to restore the blood flow.

(Figure 7).

dental trauma.

**5.3. Pumps**

the superficial femoral artery is lower than 50 mmHg.

Some Authors [25] suggested to insert a catheter for a distal perfusion if the mean pressure of

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Alternative arterial approach, such as axillary arterial cannulation, has been reported [26]

**Figure 7.** Cannulation of right axillary artery (tube on the right). Cannula is tunneled below the skin to protect by acci‐

Whatever the type of approach cannulation is considered, it requires always a highly skilled medical staff, usually a cardiac or vascular surgeon, who are able to undertake this procedure under often very difficult conditions as the patients are so unstable or even in cardiac arrest.

The pump pushes the blood through the oxygenator and then back to the patient. The most used pump in adult patients is the centrifugal pump. These pumps consist of a pol‐ ycarbonate housing with a one-point sapphire bearing linked to a magnetic field, which create a vortex flow at an adjustable rate (Figure 8). Vortex creates a negative pressure in

**Figure 4.** Percutaneous arterial cannulas (right) and percutaneous venous cannulas (left).

**Figure 5.** Percutaneous cannula insertion by Seldinger technique.

The size of the cannulas depends on the size of the patient; usually the arterial cannula ranges between 17 Fr to 21 Fr and the venous cannula ranges between 21 Fr and 25 Fr. Cannulas of sufficient size are required to support high blood flow with low resistance. Local complica‐ tions, particularly at the site of peripheral insertion of VA-ECMO can occur, of which the most concerning is leg ischemia. For this reason all attempts the limb perfusion is restored, after noted the absence of anterior and posterior tibial artery flow, by inserting a 9-Fr catheter distally to the arterial cannula by means of vascular ultrasound scan as soon as possible after ECMO implantation (Figure 6).

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**Figure 6.** Distal leg perfusion to restore the blood flow.

Percutaneous cannulas are usually made of polyurethane (Figure 4) and they are inserted using

**Figure 4.** Percutaneous arterial cannulas (right) and percutaneous venous cannulas (left).

**Figure 5.** Percutaneous cannula insertion by Seldinger technique.

ECMO implantation (Figure 6).

The size of the cannulas depends on the size of the patient; usually the arterial cannula ranges between 17 Fr to 21 Fr and the venous cannula ranges between 21 Fr and 25 Fr. Cannulas of sufficient size are required to support high blood flow with low resistance. Local complica‐ tions, particularly at the site of peripheral insertion of VA-ECMO can occur, of which the most concerning is leg ischemia. For this reason all attempts the limb perfusion is restored, after noted the absence of anterior and posterior tibial artery flow, by inserting a 9-Fr catheter distally to the arterial cannula by means of vascular ultrasound scan as soon as possible after

the Seldinger technique (Figure 5).

278 Principles and Practice of Cardiothoracic Surgery

Some Authors [25] suggested to insert a catheter for a distal perfusion if the mean pressure of the superficial femoral artery is lower than 50 mmHg.

Alternative arterial approach, such as axillary arterial cannulation, has been reported [26] (Figure 7).

Whatever the type of approach cannulation is considered, it requires always a highly skilled medical staff, usually a cardiac or vascular surgeon, who are able to undertake this procedure under often very difficult conditions as the patients are so unstable or even in cardiac arrest.

#### **5.3. Pumps**

The pump pushes the blood through the oxygenator and then back to the patient. The most used pump in adult patients is the centrifugal pump. These pumps consist of a pol‐ ycarbonate housing with a one-point sapphire bearing linked to a magnetic field, which create a vortex flow at an adjustable rate (Figure 8). Vortex creates a negative pressure in the pump head and this negative pressure pulls blood into the pump and then the blood is pushed towards the oxygenator.

**Figure 9.** V-A ECMO circuit with polymethilpentene oxygenator (blue case)

sole.

inlet and the outlet of oxygenator and the pressure drop (Figure 10).

Recently a new miniaturized system for V-A ECMO was introduced in the clinical practice. The system has the console directly connected with the oxygenator and the blood pump, which are integrated to each other. The console has a touch screen where is possible to monitor continuously several parameters such has hematocrit, hemoglobin, SVO2, resistance at the

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**Figure 10.** On the left the miniaturized V-A ECMO system (Cardiohelp by Maquet); on the right the particular of con‐

This system is very useful because of his reduced dimension and weight (the weight of console is about 10 Kgs); for this reason this system can be used for transportation of V-A ECMO

patients within the different sites of the hospital or from hospital to other hospital.

**Figure 8.** Centrifugal pump.

#### **5.4. Oxygenators**

The silicone membrane has been the principal artificial lung used for ECMO for many years and introduced in the clinical practice by Kolobow [27] and Bartlett [28]. The silicone oxygen‐ ators were used until the diffusion of microporous hollow fibers oxygenators in the 90s. The silicone surface is homogeneous and does not contain micropores, which can cause plasma leakage. However, the silicone oxygenator has a very large membrane surface to ensure adequate gas exchange and needs both high prime volume and high pressure drop; moreover, the procedure to optimize the efficacy of the oxygenator is cumbersome and lengthy, requiring a CO2 gas flush. The hollow-fiber polypropylene membrane oxygenators had advantages over the silicone oxygenators, such as high gas exchange efficiency with a smaller change surface, lower prime volume, and lower pressure gradient. However, this generation of oxygenators has micropores causing plasma leakage for periods more than 6 hours, thus reducing the gas exchange. Recently, a new generation of poly-methylpentene (PMP) membrane oxygenators have been introduced with the aim of allowing longer support without the complications linked to the hollow-fiber oxygenators, such as plasma leakage [29] (Figure 9).

The adjunct equipment that completes the ECMO system includes a heat exchanger for tem‐ perature regulation, monitors that measure blood flow, venous and arterial saturation, hem‐ atocrit, and other variables. ECMO systems also can measure circuit pressures and changes in circuit resistance. Additional safety features include continuous monitoring of venous drainage and air detection.

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**Figure 9.** V-A ECMO circuit with polymethilpentene oxygenator (blue case)

the pump head and this negative pressure pulls blood into the pump and then the blood

The silicone membrane has been the principal artificial lung used for ECMO for many years and introduced in the clinical practice by Kolobow [27] and Bartlett [28]. The silicone oxygen‐ ators were used until the diffusion of microporous hollow fibers oxygenators in the 90s. The silicone surface is homogeneous and does not contain micropores, which can cause plasma leakage. However, the silicone oxygenator has a very large membrane surface to ensure adequate gas exchange and needs both high prime volume and high pressure drop; moreover, the procedure to optimize the efficacy of the oxygenator is cumbersome and lengthy, requiring a CO2 gas flush. The hollow-fiber polypropylene membrane oxygenators had advantages over the silicone oxygenators, such as high gas exchange efficiency with a smaller change surface, lower prime volume, and lower pressure gradient. However, this generation of oxygenators has micropores causing plasma leakage for periods more than 6 hours, thus reducing the gas exchange. Recently, a new generation of poly-methylpentene (PMP) membrane oxygenators have been introduced with the aim of allowing longer support without the complications

linked to the hollow-fiber oxygenators, such as plasma leakage [29] (Figure 9).

The adjunct equipment that completes the ECMO system includes a heat exchanger for tem‐ perature regulation, monitors that measure blood flow, venous and arterial saturation, hem‐ atocrit, and other variables. ECMO systems also can measure circuit pressures and changes in circuit resistance. Additional safety features include continuous monitoring of venous

is pushed towards the oxygenator.

280 Principles and Practice of Cardiothoracic Surgery

**Figure 8.** Centrifugal pump.

drainage and air detection.

**5.4. Oxygenators**

Recently a new miniaturized system for V-A ECMO was introduced in the clinical practice. The system has the console directly connected with the oxygenator and the blood pump, which are integrated to each other. The console has a touch screen where is possible to monitor continuously several parameters such has hematocrit, hemoglobin, SVO2, resistance at the inlet and the outlet of oxygenator and the pressure drop (Figure 10).

**Figure 10.** On the left the miniaturized V-A ECMO system (Cardiohelp by Maquet); on the right the particular of con‐ sole.

This system is very useful because of his reduced dimension and weight (the weight of console is about 10 Kgs); for this reason this system can be used for transportation of V-A ECMO patients within the different sites of the hospital or from hospital to other hospital.
