Microsurgical technique for femoral vascular access in the rat

Graphical abstract

. Soft tissue is dissected to expose the femoral neurovascular bundle. nn. nerves; A., artery; V., vein; L., lymphatics.   Following distal ligation using 4-0 braided silk suture, tension is applied to the suture threads using a needle holder (or hemostat), which is allowed to gently rest on the edge of the operating table (a custom-made block sitting atop the lab bench) and a temporary vascular clip is then applied distal to the vena profunda femoris to achieve proximal control. yet important point for facile performance of the procedure, especially for insertion of the arterial catheter.
Proximal control is then obtained via a vascular clip applied immediately distal to the vena profunda femoris (Fig. 5). One to two millimeters proximal to the distal ligation site, a venotomy is made through the upper half of the vessel circumference at a 45 angle using iridectomy scissors (Fig. 6). During catheter insertion, the stopcock is opened in the direction of the catheter proper and a fluid bubble should be present at the catheter's tip in order to prevent introduction of air emboli to the vascular system. The catheter is inserted through the venotomy and advanced to the vascular clip ( Fig. 7). At this point, the stopcock is locked in the direction of the catheter. The proximal control vascular clip is then removed and the catheter advanced distally towards the level of the inguinal ligament (Fig. 8). The catheter is secured to the femoral vein proximally and distally with 3 single knots using 4-0 braided silk suture (Fig. 8).
If proximal and distal control are applied in the aforementioned manner, bleeding is not observed during venotomy or catheter insertion, but there is infrequently very slow oozing when advancing following removal of the proximal vascular clip. If observed earlier, it may be due to the proximal vascular clip being placed proximal to the vena profundal femoris. Rapid securing of the catheter to the vessel is necessary should this occur. Confirmation of catheter patency is achieved by unlocking the catheter, withdrawing $0.2 ml of venous blood then flushing with $1 ml.
In order to prevent absorption of lactic acid and tissue breakdown products consequent to the ensuing ischemia resulting from femoral arterial catheterization, the lymphatics can be separately excluded from the circulation (shown) or alternatively included in the knots used to secure the femoral venous catheter (Fig. 9). The lymphatic duct is ligated proximally and distally, transected with iridectomy scissors, and the field is inspected for lymphatic leakage proximally and distally (Fig. 10). In our experience, lymphatic leakage is never observed. Should it occur, the proximal and distal ends should be sought and ligated individually, especially if neural recordings are to be performed in this region.
Femoral arterial access is obtained following femoral venous access. Lateral retraction of the     femoral artery exposes the arteria profunda femoris, immediately adjacent to the vena profunda femoris (Fig. 11). Following distal ligation, tension is applied to the suture thread ends in the same manner as described previously for the femoral vein. Proximal vascular control is achieved by applying a temporary vascular clip immediately distal to the arteria profunda femoris (Fig. 12). An arteriotomy is made 1-2 mm proximal to the distal ligation and the catheter (open) is inserted and advanced to the vascular clip. Greater resistance is met when inserting the catheter intra-arterially than intravenously and the initial insertion will only permit the tip. The intra-arterial catheter is then advanced to the proximal clip by pulling the arterial wall over the catheter, having both secured with surgical instruments; this is distinct from venous catheter insertion, which is introduced quite easily. The stopcock is locked in the direction of the catheter, the proximal control vascular clip is removed, and the catheter is further advanced to the inguinal ligament. If proximal and distal control are applied in the aforementioned manner, bleeding is never observed during arteriotomy, catheter insertion, or advancement. The catheter is secured proximally and distally using 3 single knots (Fig. 13). Confirmation of catheter patency is assured by observing arterial pulsations at the interface between the artery and distal catheter tip when the catheter is unlocked. As an option, a small amount of blood may be withdrawn and a similar amount flushed, but this may introduce a small amount of heparin into the animal, which could result in mild factor coagulopathy complicating further surgical preparation. We are typically sufficiently reassured of arterial catheter patency by visualizing normal arterial pulsations when the catheter is unlocked. A Ringer-Locke soaked cottonoid is placed in the femoral region to replace removed soft tissue bulk and the incision is closed using continuous 4-0 braided silk suture to prevent fluid loss to the environment and leakage during intraoperative changes in animal position for further pre-experimental microsurgical preparation (Fig. 14).

Conclusion
We present our microsurgical technique for femoral venous and arterial access in the rat. It is important to identify the deep branches of the femoral artery and vein in order to optimally place proximal vascular control. It is important to introduce the catheter with a fluid bubble at the tip in Fig. 11. Lateral retraction of the femoral artery exposes the arteria profunda femoris, adjacent to the vena profunda femoris. Fig. 12. Following distal ligation, tension is applied to the suture used for the same and a vascular clip is applied distal to the arteria profunda femoris to achieve temporary proximal vessel occlusion. Fig. 13. An arteriotomy is made immediately proximal to the distal ligation and a catheter (open) filled with heparin (300 U/L) in Ringer-Locke inserted and advanced to the vascular clip. The catheter is closed, the vascular clip is removed, and the catheter is further advanced towards the inguinal ligament. The catheter is secured proximally and distally using 3 single knots. order to prevent the introduction of air emboli and to ensure a continuous column of blood, with the latter of critical importance for obtaining an accurate recording of the arterial pressure waveform.

Funding
Drexel University College of Medicine.