Intracranial Pressure Monitoring In Nontraumatic Intraventricular Hemorrhage Rodent Model

This protocol describes a method to measure intracranial pressure, mean arterial pressure, and cerebral perfusion pressure following non-traumatic intraventricular hemorrhage in rodents. Intracranial and mean arterial pressures can be measured accurately and reliably with a fiber-optic sensor inserted into the rat’s cortex and femoral artery respectively. The techniques described here are translated into the clinical setting when patients with intraventricular hemorrhage require invasive intracranial pressure monitoring.

Goals of this study were to establish an IVH animal model with objective monitoring of ICPs, MAPs, and CCPs following intraventricular IVH, so that the authors can apply this further in future experiments that will focus on the effects of ICPs induced by IVH on subsequent memory dysfunction. Major struggles may include precision, as fiber-optic sensors are small. Femoral artery dissection could also pose a challenge for some, particularly those not used in microsurgical skills.

After anesthetizing the rat, insert rectal thermometer to monitor the temperature continuously. Clip the hair on the head and the femoral region, and prep the skin with three alternating scrubs of Betadine and 70%alcohol prior to surgery. Aspirate any accumulated respiratory secretions by temporarily removing the rat from the ventilator and aspirating the secretions with PE-50 tubing connected to a 10-milliliter syringe.

Protect the eyes with sterile artificial tears eye ointment. Before the scalp incision, inject local bupivacaine into the skin and subcutaneous tissues. Place the rat in a prone position on a stereotactic frame and ear bar it.

Make a 1.5-centimeter scalp incision along the midline with a 15 blade scalpel. Apply mild pressure with gauze for hemostasis. Using a sterile cotton tip applicator, separate the periosteum from the skull until the bregma landmark is visible.

Locate and mark out bregma using stereotaxis, and mark out the location of two bilateral burr holes 1.4 millimeters lateral and negative 0.9 millimeters posterior to the bregma. Using a handheld drill, create these two small cranial burr holes in the right and left hemispheres. Irrigate any excess bone chips with sterile lactated Ringer’s solution.

In the right hemisphere, position a 22-gauge guide cannula at the level of the burr hole to insert the 28-gauge needle through the cannula to the depth of the right lateral ventricle to create intraventricular hemorrhage. Connect the fiber-optic pressure sensor to the readout unit. Turn on the readout unit, and ensure the units selected are in millimeters of mercury.

Then prime the sensor by submerging its tip into a small beaker with lactated Ringer’s solution until the readout unit reads out zero and is ready to use. In the left hemisphere, gently insert the pressure sensor to two to three millimeter depth into the cortex for real-time monitoring of ICP. After insertion of the ICP monitor, turn the lower trunk of the rat for easy access to the left thigh and groin area.

After sterile preparation and local bupivacaine administration, make a 1.5-centimeter skin incision over the hindlimb with a 15 blade scalpel. Dissect the left femoral artery superficially with a hemostat and then deeper layers using forceps with fine tips under a microscope. Identify the deep blue femoral vein to help locate the adjacent artery.

Tie off the distal femoral artery using a 3-0 silk suture and place a temporary metal clip on the proximal portion of the femoral artery. Have a second fiber-optic pressure sensor connected to the readout unit already primed. Insert the pressure sensor into the PE-50 tubing, which is inserted into a Tuohy Borst that is then closed.

Connect the Tuohy Borst to a three-way stopcock connected to a one-millimeter syringe at one end and a 22-gauge needle with PE-50 tubing at the other end. Under the microscope, make a two-millimeter femoral arteriotomy with micro scissors, and cannulate it with PE-50 tubing connected to the rest of the setup. Aspirate 500 microliters of blood using a one-millimeter syringe, and turn the three-way stopcock to have the pressure sensor read MAP.

Prime the 28-gauge intraventricular needle connected to PE-50 tubing with the aspirated blood for IVH animals and lactated Ringer’s for the vehicle control animals. Then insert this needle into the guide cannula to the depth of the right lateral ventricle. Using 100 microliters per minute rate, inject the blood, or 200 microliters sterile lactated Ringer’s solution into the right lateral ventricle by pumping the one-millimeter syringe with the thumb.

Monitor and record ICP, arterial blood pressure, and rectal temperature. Monitor and record the post-injection ICP and MAP values. After completing the intraventricular injection, withdraw the PE-50 tubing containing the pressure sensor inserted into the femoral artery, and apply the temporary clip to the femoral artery to prevent bleeding.

Tie off the proximal portion of the femoral artery using the 3-0 silk suture and close the femoral incision in an interrupted fashion using 3-0 silk. Remove the guide cannula with the intraventricular needle in the ICP monitor. Seal the burr holes with bone wax.

And close the cranial incision with 3-0 silk suture interruptedly. Apply topical bupivacaine to the incision, and inject 0.5 milligrams per kilogram of carprofen. Do not leave animals unattended until they have regained sufficient consciousness to maintain sternal recumbency.

Allow rats to fully recover after surgery under supervision and return them to their home cages with free access to food and water after recovery. Excluding the sham group, ICPs increased significantly during intraventricular injection in IVH and vehicle control groups. ICPs were higher in the IVH group compared to vehicle control.

The ICPs then quickly decreased and normalized within five minutes post-intraventricular injection in those animal groups. It was observed that MAPs stayed similar throughout the procedure, whereas CPPs decreased during intraventricular injection of either blood, or lactated Ringer’s solution. Vital steps of the surgery include correct location and drilling of burr holes and femoral arteriotomy.

The steps mentioned above should be followed closely to ensure that sensors perform their job in reading the pressure changes accurately.