Inguinal Cannulation for Establishing Extracorporeal Circulation in Adult Porcine Model

Summary

This article describes the establishment of extracorporeal circulation via inguinal cannulation and explains the advantages and disadvantages associated with this technique.

Abstract

Due to the similar size ratios, adult porcine models are suitable for cardiovascular and circulatory physiology studies on extracorporeal circulation. As standard, the connection to the cardiopulmonary bypass (CBP) is established via a sternotomy and cannulation of large vessels. However, problems can arise during methodical implementation, for example, due to a small situs, vessels that are difficult to see, or vascular anomalies with a small aorta. An iatrogenic aortic rupture can lead to the termination of the experiment. Therefore, there is a need for further, safe access via the inguinal vessels. A heart-lung machine with a disposable set (hollow fiber oxygenator with a perfusion capacity of up 3,5 l/min) is used in the in vivo trial. For inguinal cannulation, the femoral artery and vein are dissected in the right groin. A 14-16 French (Fr.). Edwards Heartport cannula and a 22-Fr. SAP femoral cannula is used for cannulation. Cannulation is performed using the Seldinger technique. Inguinal cannulation resulted in significantly fewer aborted experiments in the large animal trials and allowed better relief of the heart during dissection. Inguinal cannulation to establish an extracorporeal circulation in a large animal model trial represents a safe approach. It results in minimal trauma to the aorta and improved visibility in the thorax. In addition, this access enables minimally invasive cardiac surgery. The focus is also on the ethical aspects of animal experiments and the associated experimental success.

Introduction

In vivo pig models are suitable for cardiovascular and circulatory physiology studies due to their comparable anatomical and physiological properties. Establishment of extracorporeal circulation is also unproblematic due to the size and weight ratios. This means that extensive studies on various issues can be carried out in vivo. This applies in particular to studies on the use of a heart-lung machine and the associated establishment of an extracorporeal circuit^1,2. The goal of the method presented here is to provide an experimental platform for extracorporeal circulation in pigs using groin vessels. This provides a less invasive approach compared with central cannulation via a median sternotomy. Additionally, groin vessel cannulation is increasingly used for minimally invasive cardiac surgery and temporary mechanical circulatory support^3,4. So, this method can be useful for research specifically focusing on these areas.

When establishing an extracorporeal circuit, the aorta and the atrium are used as standard for cannulation. Access via the aorta in particular can be complicated by morphological changes in the aortic tissue, a short ascending aorta, or an enlarged heart in a small situs, which obstructs the view of the aorta (Figure 1A-B). In pigs, the aorta is often particularly small, short, and located dorsally to the main pulmonary artery. The risk of iatrogenic aortic rupture by manipulation during cannulation may be the consequence. Therefore, another safe arterial and venous access is necessary. This can be obtained by cannulation of the femoral vessels. In large animals (genus domestic pig), the inguinal vessel diameters range between 6 and 8 mm (common femoral artery) and between 10 and 12 mm (femoral vein). In order to ensure sufficient organ perfusion in the test animal (40-60 kg), use a 14-16 Fr. Edwards cannula (Figure 2A) for arterial cannulation and a 22 Fr. Sorin cannula (Figure 2B) for venous cannulation⁵.

Protocol

All large-animal experiments on pigs (age 3-4 months; sex: male and female; weight 40-60 kg; domestic pigs), after thorough review, were approved by the Karlsruhe Regional Council on October 10, 2022, under file number 35.-9185.81/G-96/22. This is a terminal procedure; all animals were euthanized at the end of the procedure.

1. Anesthesia and animal preparation

1. Premedication is always carried out at our faculty in the Interfaculty Biomedical Research Facility. Premedicate the laboratory animal with 0.075 mL/kg midazolam hydrochloride (5 mg/mL) and 0.225 mL/kg ketamine (100 mg/mL) before taking it to the operating room.
2. Place an indwelling venous catheter in the ear vein, through which to administer analgesia with 0.56 mg/kg bw/0.5 h piritramid and a volume of Sterofundin 1/1.
3. Fixate all extremities with a gauze bandage on the operating table.
4. Attach a 5-lead ECG to the thorax and abdomen for rhythm analysis, a temperature probe rectally, and a pulse oximeter to the nasal mucosa for monitoring^6,7,8,9.

2. Intubation and ventilation

1. Secure the airway by intubation and initiate pressure-controlled ventilation.
2. Use the following ventilation settings under pressure control using a respirator. The initial settings are as follows:
   FiO₂ 0.6-0.8
   Respiratory rate of 12-18/min
   Respiratory minute volume of approx. 0.2 L/min/kg
3. Using these settings, aim at a CO₂ of 35-40 mmHg, a paO₂ of 150-200 mmHg, and a normal respiratory metabolism with a pH of 7.35-7.45. Evaluate the ventilation regularly with blood gas analyses^7,8,9.

3. Maintenance of anesthesia

1. Maintain anesthesia with sevoflurane 1.5% (administered via the ventilator) or propofol 1%, 8 mg/kg bw/h. If the depth of anesthesia is insufficient, increase the sevoflurane dose to 2.0 % or administer a propofol bolus of 2-4 mg/kg bw. Signs of insufficient anesthesia include intraoperative awakening, pain reactions, movement, the animal breathing along, rapid heart rate, arterial hypertension, etc. Dexpanthenol is used to prevent dryness of the conjunctiva of the eyes^7,8,9,10.

4. Arterial pressure measurement and large central venous access

1. For arterial monitoring, open the left groin (the procedure is as described in section 5.4.), expose the femoral artery, and insert a pressure catheter by means of a puncture. The pressure curve is displayed using a pressure transducer.
2. Aim at a mean arterial pressure (MAP) of 50-60 mmHg⁶. To maintain MAP, administer volume or norepinephrine.
3. Secure the large-lumen volume access externally by open preparation of the jugular vein. This catheter has two volume accesses: one for volume substitution and one for central venous pressure monitoring (8-12 mmHg). This pressure, as well as the arterial pressure, is displayed via the transducer.
4. Insert a transurethral indwelling catheter to assess urine output. Balance the volume using a urine bag⁶.

5. Operative procedure

1. Before beginning the surgical procedure, mark the areas to be operated (standardized access routes in cardiac surgery) on with a water-insoluble pen (incision guide; Figure 3). Cover all non-relevant areas with blue surgical drapes.
2. Prepare the operating table with all instruments (Figure 4).
3. Median sternotomy
   1. Perform a longitudinal skin incision above the sternal midline, then divide the subcutaneous layers, pectoral muscle, and sternal periosteum using electrocautery.
   2. Expose the sternal midline for the median sternotomy. Make sure the jugular fossa and the xiphoid process are well defined, and dissect the retrosternal surface bluntly using a finger.
   3. After that, divide the sternum longitudinally with a sternal saw. Ensure hemostasis by using electrocautery on the periosteum and applying bone wax. Insert the sternal retractor.
   4. Expose the underlying fatty tissue and the thymus. Open the pericardium longitudinally and place pericardial stay sutures (mersiline 0) to create a pericardial well.
   5. Inspect the situs and the heart carefully. The final steps take place after the inguinal cannulation. First, mobilize the ascending aorta and the pulmonary artery and place a purse-string suture (polypropylene 4,0 RB-1) for the cardioplegia cannula.
   6. Dissect the aorta free circumferentially in the area to be clamped¹¹.
4. Preparation of inguinal vessels
   1. Perform a longitudinal incision on the skin (inguinal) and cut through the fatty skin tissue using electrocautery (Figure 5A-H). Expand the tissue with a tissue retractor.
   2. Dissect along the muscle gracilis and the muscle adductor femoris fascia with dissecting scissors to expose the femoral artery and vein between the muscles. Then loop the vessels with a red and blue rubber band.
   3. To secure the cannula in the vessel, loop a silk thread around the vessel and secure it with a tourniquet¹².
5. Cannula position : To better understand the intravascular cannula position, position the venous and arterial cannulas on the test animal (see illustrative diagram, Figure 6)¹².
6. Venous cannulation
   1. Use a 22 Fr. Seldinger cannula and a puncture set for cannulation of the femoral vein. The puncture set consists of a 180 cm long wire, a puncture cannula, and dilators (Figure 7A).
   2. The schematic is shown in Figure 8A-E¹². Place a purse string suture with Polypropylene 5.0 RP-2 and puncture the vein with an 18 GA puncture cannula.
   3. Insert the wire into the vessel (femoral vein) via the cannula using the insertion aid. Make sure that the wire can be pushed back and forth loosely.
   4. Advance the wire into the superior vena cava. The position can be checked by palpation or an echocardiogram.
   5. Remove the cannula and lightly compress the puncture site with a gauze (avoid blood loss). Carefully dilate the puncture site with the various dilators (start with the smallest); the wire must be kept taut at all times.
   6. Thread on the cannula and push the lower, taut wire into the vessel up to the atrial level and loop the tobacco pouch suture. When the thorax is open, the position of the superior vena cava must be checked. This is necessary to drain the venous blood from the superior and inferior vena cava and to adequately relieve the heart.
   7. Secure the cannula to the tobacco pouch suture with silk. Carefully pull out the wire and cannula inlet, vent with antegrade blood, and clamp with a tube clamp. Then connect the cannula to the 1/2"connector and the 1/2" 3x32 tube of the CPB.
7. Arterial cannulation
   1. Use a 14-16 Fr. Seldinger cannula and a puncture set for cannulation of the femoral artery. The latter consists of a 100 cm long wire, a puncture cannula, and dilators (Figure 7B).
   2. The procedure is the same as for venous cannulation¹². Prepare the purse string sutures (4-0 polypropylene RB-1) and insert the puncture cannula.
   3. Insert the wire over the cannula and remove the cannula. Dilate the puncture site with the individual dilators (12 Fr. and 14 Fr.) and insert the arterial 16 Fr cannula.
   4. Remove the wire and inlet, deflate retrogradely, and clamp. Then connect the cannula to the 3/8" connector and the 3/8" 3x32 tube of the heart-lung machine and fix it to the tissue.
8. Connection to the cardiopulmonary bypass
   1. After having connected the cardiopulmonary bypass to the inguinal vessels, initiate the extracorporeal circuit (Figure 9A and Video 1). Due to the small difference in height between the venous cannula and the reservoir, venous drainage frequently needs to be supported by active suction. This suction is approx. -60 to -80 mmHg and is generated by a roller pump. Visualize the suction by measuring the pressure on the venous tube using a pressure transducer^13,14,15.

Results

The change in cannulation type for establishing extracorporeal circulation, from thoracic central cannulation to inguinal cannulation, did not result in iatrogenic aortic rupture in animal experiments (Table 1). The background to this is an animal study in which 18 pigs per group were operated on. In the first 15 procedures, six pigs suffered iatrogenic aortic rupture after central cannulation, which is why the experiment was discontinued. The mortality rate was 40%. In the remaining 21 procedures, the c...

Discussion

Experimental cardiac surgery is indispensable today. Possible objectives include assessing left ventricular pump function under the administration of various drugs and their pharmacokinetic properties, optimizing surgical procedures, and optimizing perfusion in extracorporeal circulation. Adult pig models are very well suited for this purpose due to their cardiovascular and physiological characteristics.

In extracorporeal circul...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dexpanthenol 5%	Bayer	PZN AT-2424276	Anaesthesia
HLM Set Trilly AF Kinder	Eurosets	AG71155	Heart lung machines disposable set
Ketamin 5mg/ml	Pfizer	PZN 01395650	Anaesthesia
Mersilene 0	Ethicon	R844	pericardial stay sutures
Midazolam 5mg/5ml	Hameln	PZN 05918501	Anaesthesia
Perkutanes Einführkit 100 cm	Maquet	PIK 100	Arterial puncture set
Piritramid 15mg/ml	Piramal	PZN 01312724	Anaesthesia
Polypropylene 4,0 RB-1 (Prolene)	ETHICON	8710H	Tobacco pouch seam on the vessel
PotiSite Arterial Perfusion Cannula 16 Fr.	Edwards	FLK0012	Arterial inguinal cannula
Propofol 1% 200mg/20ml	Fresenius KABI	PZN 18116200	Anaesthesia
RAP Femoral Venous Cannula 22 Fr.	LivaNova	200-100	Venous inguinal cannula
Revas Access Kit Dual Lumen 180 cm	Freelife	FLK0012	Venous puncture set
Seide 75 cm	Resorba	G850N	to fix the cannula around the vessel
Sevofluran 100% /V/V) 250ml	SEVOrane	PZN 03796821	Anaesthesia
Silikon-Loops 2,5 mm blue	SERAG Wiessner	SL27	for the preparation of the vein
Silikon-Loops 2,5 mm red	SERAG Wiessner	SL26	for the preparation of the artery
Sterofundin ISO 1/1 E ISO	B/BRAUN	PZN 01078955	Volume
Tourniquet Kit 7 Fr.	Medtronic	79005	for attaching the cannulas to the vessel