Low-Diameter Mesocaval Shunt Miguel A. Mercado, Hector Orozco

(1)

Low-Diameter Mesocaval Shunt

Miguel A. Mercado, Hector Orozco

Introduction

The mesocaval shunt decompresses portal hypertension with an interposition graft between the superior mesenteric vein (SMV) and the inferior vena cava (IVC).

Popularized by Drapanas in the 1970s, it has had several proponents since, and most highlight that it is a shunt performed remote from the hepatic hilus. Similar in phy- siology to a side-to-side portacaval shunt, a mesocaval shunt diverts all portal ﬂow if

≥12 mm diameter, while if 8–10 mm diameter some prograde portal ﬂow is maintained.

Indications and Contraindications

Indications

^■

Variceal bleeding refractory to endoscopic treatment

■

Child’s A and B patients

Contraindications

^■

Advanced liver disease (Child’s C)

■

Mesenteric venous thrombosis

Investigations

History: variceal bleeding

Absence of advanced liver disease Laboratory studies: Child’s A/B class

Vascular imaging: Ultrasound with Doppler

Angiography with venous phase imaging if SMV patency is questioned

Preparation

■

Elective operation preferred

■

Stabilize from acute bleed – Correct coagulation – Diurese ascites

– Improve nutrition status

(2)

Procedure

STEP 1 Access and mobilization

The abdomen is entered through a large median or transverse incision, to obtain adequate exposure of the whole cavity. A retractor (Thompson, Omni-Tract) is placed with blades that expose the root of the mesentery in the inframesocolic compartment.

Traction of the transverse colon up and forward of the mesentery (caudal) exposes the third portion of the duodenum. The peritoneum is incised, in a semicircular fashion, from the root of the mesocolon to the ligament of Treitz. Only lax adhesions are usually found with occasional small veins that need electrocoagulation. The duodenum is freed completely.

The peritoneum is cut at the root of the mesentery, exposing the lymphatics (usually dilated and hypertrophied) that surround the mesenteric vessels. Chronic lymphatic hypertension produces ﬁbrosis that makes dissection difﬁcult. It is necessary to ligate all these structures in order to avoid postoperative lymph leakage. Also, small dilated veins can be found.

Complete dissection of the anterior and right lateral aspect of the superior mesen- teric vein is done. All the vessels from the uncinate process of the pancreas (variable in length, diameter and distribution) are carefully dissected and ligated. The dissection is continued cephalad to the neck of the pancreas. The middle colic vein is ligated.

Caudally, the dissection is continued down to the conﬂuence of the ileocolic branch (which in many instances can be preserved). In some instances the ileocolic artery crosses over at this level; it can usually be retracted, but if necessary it can be ligated.

It is necessary to dissect free the mesenteric vein 4–5cm in length. Also, it is important

to dissect the whole circumference of the vessel in order to comfortably place the

vascular clamp.

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STEP 2 Preparation of the inferior vena cava

The infrarenal IVC is dissected free, after removing the lax areolar tissue that surrounds

it. Some small veins are found that have to be suture ligated. It is not necessary to dissect

the vessel in its whole circumference since it is easy to place the vascular clamp on the

anterior wall of the IVC due to its width and low intravascular pressure.

(4)

STEP 3 Venotomy of the vena cava

Retractors are placed to separate the duodenum (cephalad), the right colon (lateral) and the small intestine (caudal). Lymph nodes around the aorta can be observed; this is the limit of the medial dissection.

A Satinsky clamp is placed and a longitudinal venotomy is done approximately

12–14mm in length using DeBakey scissors, in order to obtain an oval venotomy.

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STEP 4 Suture on the caval side

A ring reinforced polytetraﬂuoroethylene (PTFE) 10-mm graft is cut in tangential fashion in order to obtain a 12 - to 14-mm opening for anastomosis. If the decision to place a wider graft has been made, a wider venotomy must be performed.

Using a 5-0 vascular Prolene suture placed at each angle, the graft is sewn with a running suture (Figure 4). The suture is placed from outside. An everted suture is advised at this point in order to minimize exposure of rough areas in the vascular lumen.

When the suture is completed, the graft is ﬁlled with heparinized saline.

(6)

STEP 5 Preparation and suture on the mesenteric side

A Satinsky clamp is placed on the superior mesenteric vein and a semicircular cut of the

vein is done with Potts scissors (Figure 5). This incision favors the position of the graft

in the right and slightly posterior aspect of the vein. Using a 5-0 Prolene suture, each

angle is placed and the PTFE graft is approximated close to the vein. The length of the

graft has to be cut according to the position of the duodenum.

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STEP 6 Completing the suture

The anastomosis is completed using a continuous suture. The posterior layer is done

from within the lumen, so that the ﬁrst stitch places the needle inside the lumen

(Figure 6). When the posterior aspect is completed, the needle is brought outside

and then the anterior layer of the anastomosis is done. An everted suture is advised.

(8)

STEP 7 Release of the clamps

When the suture is complete, the vascular clamp in the inferior vena cava is released ﬁrst followed by the vascular clamp in the mesenteric vein. Usually a small amount of bleeding at the suture line is observed. This resolves spontaneously with the application of dehydrated cellulose and mild pressure.

STEP 8 Final position

The ﬁnal position of the graft. The duodenum is allowed to rest over the graft and the

peritoneum is closed over the graft. No drainage is left and the abdominal wall is closed

in standard fashion.

(9)

Postoperative Tests

■

Daily laboratory studies

■

Shunt study prior to discharge – Ultrasound

– Possible angiography

Postoperative Complications

■

Early:

– Liver failure – Shunt thrombosis

■

Late:

– Liver decompensation – Encephalopathy – Shunt thrombosis

Tricks of the Senior Surgeon

■

Injection of water around the vessels, through a small oriﬁce when the vessel is identiﬁed, allows separation of dissection planes, making the dissection easier.

■

Circumferential dissection of the mesenteric vein permits an easier mobilization of the vessel. Fixed segments of the wall can produce small tears of the vessel at the time of clamping and when traction to the vessel is done.

■

When the posterior face of the mesenteric anastomosis is performed, it is impor- tant to maintain the graft close to the vein. Traction to the graft when the ﬁrst stitches are placed can produce tears in the vein wall and loss of substance.

■

Low-Diameter Mesocaval Shunt Miguel A. Mercado, Hector Orozco

Low-Diameter Mesocaval Shunt

Miguel A. Mercado, Hector Orozco

Introduction

The mesocaval shunt decompresses portal hypertension with an interposition graft between the superior mesenteric vein (SMV) and the inferior vena cava (IVC).

Popularized by Drapanas in the 1970s, it has had several proponents since, and most highlight that it is a shunt performed remote from the hepatic hilus. Similar in phy- siology to a side-to-side portacaval shunt, a mesocaval shunt diverts all portal ﬂow if

≥12 mm diameter, while if 8–10 mm diameter some prograde portal ﬂow is maintained.

Indications and Contraindications

Indications

Variceal bleeding refractory to endoscopic treatment

Child’s A and B patients

Contraindications

Advanced liver disease (Child’s C)

Mesenteric venous thrombosis

Investigations

History: variceal bleeding

Absence of advanced liver disease Laboratory studies: Child’s A/B class

Vascular imaging: Ultrasound with Doppler

Angiography with venous phase imaging if SMV patency is questioned

Preparation

Elective operation preferred

Stabilize from acute bleed – Correct coagulation – Diurese ascites

– Improve nutrition status

Procedure

STEP 1 Access and mobilization

The abdomen is entered through a large median or transverse incision, to obtain adequate exposure of the whole cavity. A retractor (Thompson, Omni-Tract) is placed with blades that expose the root of the mesentery in the inframesocolic compartment.

Caudally, the dissection is continued down to the conﬂuence of the ileocolic branch (which in many instances can be preserved). In some instances the ileocolic artery crosses over at this level; it can usually be retracted, but if necessary it can be ligated.

It is necessary to dissect free the mesenteric vein 4–5cm in length. Also, it is important

to dissect the whole circumference of the vessel in order to comfortably place the

vascular clamp.

STEP 2 Preparation of the inferior vena cava

The infrarenal IVC is dissected free, after removing the lax areolar tissue that surrounds

it. Some small veins are found that have to be suture ligated. It is not necessary to dissect

the vessel in its whole circumference since it is easy to place the vascular clamp on the

anterior wall of the IVC due to its width and low intravascular pressure.

STEP 3 Venotomy of the vena cava

Retractors are placed to separate the duodenum (cephalad), the right colon (lateral) and the small intestine (caudal). Lymph nodes around the aorta can be observed; this is the limit of the medial dissection.

A Satinsky clamp is placed and a longitudinal venotomy is done approximately

12–14mm in length using DeBakey scissors, in order to obtain an oval venotomy.

STEP 4 Suture on the caval side

A ring reinforced polytetraﬂuoroethylene (PTFE) 10-mm graft is cut in tangential fashion in order to obtain a 12 - to 14-mm opening for anastomosis. If the decision to place a wider graft has been made, a wider venotomy must be performed.

Using a 5-0 vascular Prolene suture placed at each angle, the graft is sewn with a running suture (Figure 4). The suture is placed from outside. An everted suture is advised at this point in order to minimize exposure of rough areas in the vascular lumen.

When the suture is completed, the graft is ﬁlled with heparinized saline.

STEP 5 Preparation and suture on the mesenteric side

A Satinsky clamp is placed on the superior mesenteric vein and a semicircular cut of the

vein is done with Potts scissors (Figure 5). This incision favors the position of the graft

in the right and slightly posterior aspect of the vein. Using a 5-0 Prolene suture, each

angle is placed and the PTFE graft is approximated close to the vein. The length of the

graft has to be cut according to the position of the duodenum.

STEP 6 Completing the suture

The anastomosis is completed using a continuous suture. The posterior layer is done

from within the lumen, so that the ﬁrst stitch places the needle inside the lumen

(Figure 6). When the posterior aspect is completed, the needle is brought outside

and then the anterior layer of the anastomosis is done. An everted suture is advised.

STEP 7 Release of the clamps

STEP 8 Final position

The ﬁnal position of the graft. The duodenum is allowed to rest over the graft and the

peritoneum is closed over the graft. No drainage is left and the abdominal wall is closed

in standard fashion.

Postoperative Tests

Daily laboratory studies

Shunt study prior to discharge – Ultrasound

– Possible angiography

Postoperative Complications

Early:

– Liver failure – Shunt thrombosis

Late:

– Liver decompensation – Encephalopathy – Shunt thrombosis

Tricks of the Senior Surgeon

Injection of water around the vessels, through a small oriﬁce when the vessel is identiﬁed, allows separation of dissection planes, making the dissection easier.

Circumferential dissection of the mesenteric vein permits an easier mobilization of the vessel. Fixed segments of the wall can produce small tears of the vessel at the time of clamping and when traction to the vessel is done.

When the posterior face of the mesenteric anastomosis is performed, it is impor- tant to maintain the graft close to the vein. Traction to the graft when the ﬁrst stitches are placed can produce tears in the vein wall and loss of substance.

When bleeding is observed at the anastomotic suture line, it is better to wait until

it stops spontaneously. Placing new stitches can be troublesome because the wall

is under tension and a larger hole can be made.