Isolated Brain Trauma in Cats Triggers Rapid Onset of Hypovolemia

Hemodynamic instability responsive to fluid resuscitation is common after a traumatic brain injury (TBI), also in the absence of systemic hemorrhage. The present study tests if an isolated severe TBI induces a decrease in plasma volume (PV).

The study was performed in three groups of anesthetized and tracheostomized male cats (n = 21). In one group (n = 8), the cats were prepared with a cranial borehole (10 mm i.d) used to expose the brain to a fluid percussion brain injury (FPI) (1.90-2.20 bar), and two smaller cranial boreholes (4 mm i.d) for insertion of an intracranial pressure (ICP) and a microdialysis catheter. To differentiate the effect of FPI from that of the surgical preparation, a sham group was exposed to the same surgical preparation but no FPI trauma (n = 8). A control group had no brain trauma and no surgical preparation (n = 5). PV was determined by a ¹²⁵I-albumin dilution technique. PV, electrolytes, pH, BE (base excess), hematocrit (Hct), P_aO₂, and P_aCO₂ were measured at baseline and after 3 h. Mean arterial pressure (MAP) was measured continuously. ICP was measured in the FPI and the sham group.

In the FPI group, PV decreased by 11.2 mL/kg from 31.7 mL/kg (p < 0.01) with a simultaneous increase in Hct and decrease in pH. In the sham group, PV decreased by 5.7 mL/kg from 32.7 mL/kg (p < 0.01). The control group showed no PV reduction.

The results support that an isolated severe head trauma triggers a significant and rapid reduction in PV, most likely due to vascular leak.