Chronic catheterization of blood vessels in the rat is often required for administration of substances, obtain blood sample over a period of time or for direct conscious blood pressure measurements. Femoral arterial catheterization of the rat and corresponding measurements of blood pressure in the conscious animal will be demonstrated.
In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically implanted catheters permit a researcher to effectively and humanely administer substances, perform repeated blood sampling and assists in conscious direct measurements of blood pressure and heart rate. Once the catheter is implanted long-term sampling is possible. Patency and catheter life depends on multiple factors including the lock solution used, flushing regimen and catheter material. This video will demonstrate the methodology of femoral artery and venous catheterization of the rat. In addition the video will demonstrate the use of the femoral venous and arterial catheters for blood sampling, drug administration and use of the arterial catheter in taking measurements of blood pressure and heart rate in a conscious freely-moving rat. A tether and harness attached to a swivel system will allow the animal to be housed and have samples taken by the researcher with minimal disruption to the animal. To maintain patency of the catheter, careful daily maintenance of the catheter is required using lock solution (100 U/ml heparinized saline), machine-ground blunt tip syringe needles and the use of syringe filters to minimize potential contamination. With careful aseptic surgical techniques, proper catheter materials and careful catheter maintenance techniques, it is possible to sustain patent catheters and healthy animals for long periods of time (several weeks).
1. Prior to Starting Surgical Procedure
Note: Prior to beginning any animal procedures ensure that you have obtained the appropriate permission through your institution/organization. As with all survival surgeries, make sure that the surgery is performed under sterile conditions and the appropriate pain medication and antibiotics needed are used for a successful outcome.
2. Preparation of Surgical Areas for Catheter Placement
3. Tunneling the Catheter
4. Inserting the Catheters into the Femoral Vein and Artery (Figure 3)
5. Surgical Wrap-up
–For long-term maintenance replace catheter saline solution with 20 U/ml heparin/saline.
6. Maintenance of Catheter (Sterile gloves should be worn during procedure)
7. Blood Sampling (Sterile gloves should be worn during procedure)
Clamp the catheter with padded forceps.
8. Drug Infusion
9. Blood Pressure and Heart Rate Sampling
10. Representative Results
A representative blood pressure measure was taken from a conscious freely moving animal and is presented in Figure 4. Phenylephrine (3 ug/kg, iv), an alpha 1 adrenergic receptor agonist, was administered into the femoral vein line to increase blood pressure, while simultaneously measuring blood pressure from the femoral arterial line. Phentolamine (4 mg/kg, iv), a nonselective alpha-adrenergic antagonist, was then administered to lower blood pressure.
Figure 1. Blunt dissection of tissue. With the rat on his back, you will have made approximately a ½ inch (12 mm) incision on the angle of the hind leg and using blunt scissors or hemostats you will blunt dissect the connective tissue to expose the femoral artery and vein.
Figure 2. Separation of femoral artery and vein from connective tissue.
Figure 3. Catheter placement. Using Vanna micro-dissecting scissors place a small incision approximately ¼ of the way through the vessel at a 45 degree angle (top) and place fine-tipped forceps into the incision and using another pair of forceps feed the catheter into the vessel (middle). Lastly, upon completion of the placement of the catheter suture the catheter in place (bottom).
Figure 4. Representative blood pressure measure taken from a conscious freely moving animal.
Arterial and vein catheterization have historically been used to both acutely and chronically monitor blood pressure, sample blood and deliver substances in the experimental rat animal model1-4. A major benefit of these surgical instrumentations is that it allows monitoring procedures, including, blood sampling, drug administration and blood pressure monitoring, to be conducted with minimal disturbances and/or stress to the animal1. Numerous investigators have written protocols and have specific methodologies by which their laboratory performs the surgical procedure5-8. The video and illustrations demonstrate what our laboratory has found to be successful with regards to the femoral arterial and venous catheterization procedure.
Rats are commonly used in the laboratory for a multitude of scientific studies due to their small size and convenience in handling. There are several locations where a chronic catheter can be placed within an animal, including the jugular vein, abdominal aorta, carotid artery and femoral artery, to name a few. The rat femoral location for chronic catheterization results in increased length of catheter patency and had the fastest recovery of pre-surgical animal weight compared to other catheter locations9.
Numerous investigators have used indwelling catheters for acute as well as chronic blood sampling1-5,11-13. In many studies multiple blood draws are required of an animal and external cannulation/catheterization is one methodology that is advantageous due to its non-traumatic nature; moreover it can be done while the animal is conscious, thus is not limited by the effects of anesthetics and also the animal can be freely moving1,10. The best method by which to obtain blood samples and to measure stress hormones in rodents has been long debated6,13. With regards to pharmacokinetic studies, catheterization of the research animal permits repeated blood sampling with minimal restraint when using a chronically implanted catheter system. In addition, studies have shown reduced basal concentrations of adrenaline, noradrenaline and dopamine in the plasma of freely moving rats (jugular catheter) compared to animals that have been handled (30 seconds) and or restrained (5 minutes)14. An additional method by which to discern increases in stress is by measuring plasma corticosterone levels. Previously it was suggested that even following three to four days of surgical recovery times that plasma corticosterone levels were elevated in the chronic cannulated rat15. However, recent improvements in methodology have determined that there are no differences in baseline plasma corticosterone levels in the jugular vein cannulated rats compared to uncannulated rats16. In addition, HPLC methodology for corticosterone analysis also revealed that corticosterone levels are elevated by restraint stress; however, stable after jugular catheterization16.
An additional use of chronic catheterization is the measurement of blood pressure and heart rate in rodents. There are multiple methodologies that are utilized to measure the blood pressure and heart rate in the rat; these include the non-invasive tail cuff methodologies, radiotelemetry procedures and direct indwelling catheters. Each method has its advantages and disadvantages, which are described in detail in other publications. Indwelling fluid-filled catheters can be implanted into multiple arteries within the rat. The femoral artery is but one artery that can be used for this measure. For blood pressure/heart rate measures, the distal end of the catheter is connected to a calibrated pressure transducer . The catheter can be housed in a protective spring that is connected to a swivel to allow free movement of the animal, or attached to a button surgically implanted to the animal. Indwelling catheters have the advantage of minimizing the long-term stress on the animal17,18. In addition the materials are inexpensive, calibration is easy for pressure measures and continuous long-term measures can be obtained under conditions of relatively low stress for numerous weeks19. We would be remiss if we didn’t mention that there are disadvantages to this technique, including, it is a surgically invasive technique, maintenance of the catheter is required to maintain patency, damage to the artery due to the implantation of the catheter and the potential of infection to name a few.
For chronic measures of blood pressure direct recordings from chronically-implanted arterial catheters are more technically challenging but are more accurate and can be done continuously without disturbing the animal. Tail-cuff measurements are less accurate; however they do not require surgery and can also be repeated. Tail-cuff methodologies do require handling as well as heating of the animal to dilate the tail vessels to facilitate the detection of the pulse20. Handling and the added heat stress can affect blood pressure measurements, thus not providing truly accurate measures. Moreover, the non-direct tail-cuff method does not permit easy simultaneous blood sampling or drug administration.
An additional method by which direct measure can be achieved is using telemetric methodology. Telemetry allows high-quality recordings of blood pressure (and other measures) continuously for long periods of time in conscious freely moving animals without restraint or anesthetics18. However, telemetry devices while ideal are very costly. When compared to telemetry, catheterization benefits include: decreased “setup” and operational costs, the ability to readily administer drugs and easily take blood samples in conscious freely moving animals. The administration of drugs and substances, and obtaining blood samples from the research animal can be done while minimally disturbing the animal, thus minimizing stress to the animal and allowing for a more accurate measure.
The authors have nothing to disclose.
The authors wish to acknowledge Dr. Andrew King, PhD and Katrina King for the contribution of the illustrations. NIH grant: R00HL087927.
Name | Typ | Company | Catalog Number |
Arterial Catheter | Consumable | SAI Infusion | RFA-01 |
Venous Catheter | Consumable | Scientific Commodities, Inc. | BB518-20 & BB31785-V/2 |
27g 1/2″ Blunt Needle | Equipment | Integrated Dispensing Solutions, Inc. | 9991113 |
23g 1/2″ Blunt Needle | Equipment | Integrated Dispensing Solutions, Inc. | 9991109 |
PowerLab/8SP | Equipment | ADInstruments | ML765 |
Quad Bridge | Equipment | ADInstruments | ML118 |
LabChart 7.2 | Software | ADInstruments | |
BP Transducer with stopcock & Cable | Equipment | ADInstruments | MLT844 |
Single Channel Swivel | Equipment | Instech | 375/22PS |
Single Axis-Counter Balance Swivel Mount | Equipment | Instech | CM375BP |
Covance Infusion Harness | Equipment | Instech | CIH105 |
Table Top Isoflurane Anesthesia Unit | Equipment | Protech International, Inc. | 61020 |
Rodent Anesthesia Mask | Equipment | Protech International, Inc. | RAM-02 |
Rodent Induction Chamber | Equipment | Protech International, Inc. | RIC-01 |
Anesthesia Gas Filter Canister | Equipment | Protech International, Inc. | 80120 |
Tabletop Laminar Flow Hood | Equipment | Sentry Air Systems, Inc. | SS-200-WSL |
Oster Golden A5 | Equipment | Oster Professional Products | 78005-140 |
Fiber Optic Light with Dual Gooseneck Guide | Equipment | LW Scientific, Inc. | ILL-1502-DGG1 |
Deltaphase Isothermal Pad | Equipment | BrainTree Scientific | 39DP |
Cotton-Tipped Applicators | Consumable | Solon Manufacturing Company | 36200 |
Gauze Sponges 2″x2″ | Consumable | Kendall Curity | 2146 |
5-0 Nylon Suture | Consumable | Ethicon | 661G |
4-0 Silk Suture | Consumable | Deknatel | 8-S, 136075-0208 |
Tissue Adhesive | Consumable | 3M | 1469SB |
Splinter & Fixation Forceps | Equipment | George Tiemann & Company | 160-55 |
Student Tissue Forceps | Equipment | Fine Science Tools, Inc. | 91121-12 |
Micro Forceps/Bracken Forceps | Equipment | George Tiemann & Company | 10-1942 |
Extra Fine Graefe Forceps | Equipment | Fine Science Tools, Inc. | 11152-10 |
Olsen-Hegar Needle Holder | Equipment | Fine Science Tools, Inc. | 12002-12 |
Student Halsted-Mosquito Hemostat | Equipment | Fine Science Tools, Inc. | 91308-12 |
Rochester Pean Forcep | Equipment | Biomedical Research Instruments, Inc. | 31-1640 |
Student Surgical Scissors | Equipment | Fine Science Tools, Inc. | 91402-12 |
Dumont Forceps | Equipment | Fine Science Tools, Inc. | 11251-35 |
Micro Dissecting Scissors | Equipment | George Tiemann & Company | 160-210 |
Strabismus Scissors | Equipment | Fine Science Tools, Inc. | 14075-11 |
Hartman Hemostat | Equipment | Fine Science Tools, Inc. | 13003-10 |
Tissue Scissors | Equipment | George Tiemann & Company | 160-150 |
Retractor | Equipment | Custom Made |