Some years ago, we used similar techniques for intra-arterial BP recording in conscious unrestrained and untethered rats. Details of our technique can be found in the following publications: Am J Physiol Heart Circ Physiol 275:H1290-H1297, 1998 and Am J Physiol Heart Circ Physiol 292:H2506-H2512, 2007. In particular, we constructed polyethylene catheters [a PE-10 (2 cm length, 0.28 mm ID, 0.61 mm OD; Clay Adams, Parsippany, NJ) fused to a PE-50 (15 cm length, 0.58 mm ID, 0.96 mm OD; Guerbet, Louvres, France)] filled with heparinized 0.9% NaCl (50 U/ml). The catheter was inserted into the lower abdominal aorta via the left femoral artery to record distal (peripheral) aortic BP. The catheter was tunneled subcutaneously under the skin of the back to exit between the scapulae and was plugged with a short piece of stainless steel wire. After 24 h of rest, the catheter was attached to another PE-50 (15–20 cm). At least 2 limits must be highlighted: 1) whatever the diameter of the catheter, its tends to be obstructed with coated blood even if its filled with heparinised physiological saline. 2) Catheterisation of femoral artery leads to a heavier surgery than catheterizing carotid artery, as one have to tunnel the catheter through all the length of the back of the rat. Nowadays, the best way to record arterial BP is using telemetry, although this technique is very expensive.

Recording of the real pressure in invasive animal model depends to the sensitivity of your pressure transducer. In addition, when the diameter of the tubing is reduced or its length is increased will decrease the quality of recording (i.e the pressure you record will be lower than the real pressure).

Millar catheter is better for this kind of recordings

In some our experiments we used similar technique as Hubert Dabire described earlier. We cannulate the femoral artery and the vein and if we need to record the BP in conscious animals we use the tunnel under the skin and fix our cannulas on the back exactly between the scapulaes. We usually use PE Tubing 0.96*0.58mm (Microtube Extrusions). From our experience we can say that this particular size of tubes give you a nice real BP recording. All the best in your research!

I highly recommend Millar Micro-Tip pressure cathters for carotid artery and jugular vein BP measurements. In our experience, the PE-50 tube through the femoral artery tends to clot eventhough we flush with heparinised saline solution. The surgical procedure tends to elevate lactate levels, but these decline after 30-60 mins. Bw

we using PE-50 all the  time for blood pressure recording for  femoral  and carotid  and Micro-renathane  tubing from Braintree Scientific Inc. for Jugular vein  just make sure flash line few time during baseline recording. As Hubert Dabire  mentioned  telemetry recording is one of the best option for BP recording .

we start to using Fiber optic system (FISO) for BP recording in mice and it is amazing !

As Hubert Dabire commented telemetry really is the best method for monitoring BP. Sure its a little more expensive initially than a tethered system, but overtime you would use far less animals and find much more accurate data from a smaller group size, thus reducing long term study costs. With telemetry subjects are freely moving and you can gain a continuous profile whilst even monitoring more than just the BP, Temperature, Activity, ECG are all possible at the same time from a single device. I know a number of researchers at your facility already carrying out telemetry studies and would be happy to connect you, additionally I'm also available for a more in-depth chat if you would like? Feel free to DM me and I can also share some sepsis paper titles you maybe interested in.