Brain Blood Volume and Cerebral Hemodynamics in the Anesthetized Rat

Adult male rats (400+ grams) were used for all studies. Nembutal anesthesia was induced via intraperitoneal injection at 40mg/kg and maintained by IV infusion at 8mg/kg/hr. Induction for Halothane was via inhalation in a bell jar at 2.5% in an 80/20 mixture of breathing air/100% 02. Induction with Forane was likewise in a bell jar at 4% Forane in 100% 02. Maintenance for Halothane and Forane was at 1.5–2% in an 80/20 mix of breathing air/02. All animals were mechanically ventilated via tracheostomy. Following placement of femoral arterial and venous catheters, animals were placed in a head frame in the sphinx position. For measurement of ICP and determination of PVI’s, a 26 gauge needle was inserted into the cisternal space and connected to a Camino fiber optic pressure measuring system. Normocarbic conditions (pCO2 30–40 mmHg) were obtained using a respirator volume of 2.5 cc and a rate of 60/min. Hypercarbia (pCO2 > 40 mmHg) was achieved by lowering the respirator rate. After stabilization of blood gases and ICP, 10μl of liquid was injected through a side port via a Hamilton syringe for the PVI measurement.