[Effects of experimental compression of the brainstem on the circulatory and the respiratory parameters in the...

Circulatory and respiratory changes following a mechanical compression of the brainstem of the rabbit were studied. Under light ether anesthesia, the animal was tracheostomized, immobilized by pancuronium bromide, and mechanically ventilated, following which the skull was fixed and suboccipital craniotomy was performed, and finally the brainstem was exposed. The site of compression was selected as (A): 3mm lateral, 3mm rostral, (B): 2mm lateral and (C): 3mm lateral, 3mm caudal, of the obex, respectively. After inhalation of ether was discontinued and elimination of the effect of muscle relaxant was confirmed, the direct compression with glass stick of 0.8mm in diameter was carried out. In each point, vertical compression of 1mm, 2mm and 3mm, was performed stereotaxically. In each depth of the compression, 3 to 4 animals were studied. The blood pressure was measured directly in the femoral artery and the respiratory changes by impedance pneumography. The circulatory changes, biphasic change of arterial pressure and/or transient bradycardia occurred earlier than the respiratory changes in 2mm and 3mm depth of the compression in all 3 points. CO2 response curve with rebreathing method was obtained before and 15 minutes after the compression to evaluate the degree of damage of the medullary respiratory center. The depression of CO2 response curve was observed only in 3mm compression depth at the point (A). It is concluded from this study that excessive invasion of the brainstem during the suboccipital craniotomy under controlled ventilation could be detected through the observation of the changes in circulatory parameters.