gms | German Medical Science

Accurate measurement of intracranial pressure (ICP) in small animals is challenging. Mostly, conventional pressure transducers connected to intraventricularly located microcatheters are used. However, these systems have proven inaccuracy in detecting rapid changes of ICP. Recently, the accuracy and sensitivity of a new fiberoptic pressure microprobe has been demonstrated for cardiovascular measurements. For cerebral measurements we evaluated the practicability of this microprobe in rats for high ICP using a weight drop trauma model (i), and for low ICP using artificial cerebrospinal fluid (aCSF) injections into the basal cisterns (ii).

Male wistar rats (250-350g) were anesthetized using inactin (100μg/ml, 0.1ml/100g body weight). The new microprobe (Samba-Sensor, OD 0.38mm, Samba-Sensors, Gothenburg, Sweden) protected by a PE tubing (OD 0.8, ID 0.4 mm) was inserted via a parietal burr hole into the parietal cortex of male wistar rats and fixed to the skull with dental cement. Arterial and venous microcatheters (OD 0.8, ID 0.4 mm) were placed into the femoral vessels for monitoring of macrohemodynamic parameters. Sensors were connected to a multiparameter monitoring apparatus with sampling rates of 1024-2048 hertz. Rats were placed under a weight drop device and several intensities applied (10, 20, 30, 40, and 100cm; bolt-weight, 500g) (i), or received intermittent bolus injections of 0.1 ml aCSF. Data were digitally stored on a personal computer and rewiewed using customized software packages of National Instruments and Microsoft Corp.

Baseline ICP values after probe insertion showed interindividual differences of 30 mmHg caused by persistent counterpressure of the surrounding tissue to the sensor membrane, which is located at the tip of the sensor. In the trauma model, a dose dependent increase of intracranial peak pressures (duration, 2 ms) was found ranging from 169 ± 81 mmHg to 409 ±122 mmHg at 20 cm or 50 cm height of fall, respectively (mean ± SD). ICP’s showed posttraumatic oscillations with a maximum duration of 10 ms at 50 cm height of fall. After injection of aCSF, ICP increased to 150% compared to baseline values and showed increased amplitudes of ICP oscillations due to reduced brain compliance.

The new fiberoptic pressure microprobe is able to measure rapid ICP changes at different pressure ranges. With its small size it may preferentially be used in small animals. However, practicability is limited due to the high fragility of the sensor membrane and its location on the tip of the sensor.