Cerebral microembolization. I. Pathophysiological studies.

Unilateral embolization of the brain was performed in cats by intracarotid injection of 10.5 million carbonized microspheres (15 +/- 5 mu). Intracranial pressure increased from 6.1 +/- 1.5 to 14 +/- 2.3 mm Hg within two minutes and continued to rise more slowly to 24 +/- 18.3 mm Hg within four hours. Embolization caused a nonhomogenous distribution of microflow, but initially had no effect on global cerebral blood flow, nor on cortical oxygen tension. Yet, a functional suppression of cortical electrical and metabolic activity occurred. The ipsilateral EEG flattened irreversibly after 15 seconds; the contralateral EEG was transiently suppressed shortly thereafter. Arteriovenous difference of oxygen fell from 10.5 +/- 0.7 to 5.3 +/- 0.6 vol%, and the arteriovenous difference of glucose fell from 11.7 +/- 3.9 to 2.6 +/- 2.1 mg/100 ml as a consequence of reduced oxygen and glucose extraction. Subsequently, severe vasogenic brain edema, secondary ischemia, and severe functional suppression developed between two and four hours.

Technical adjuncts in neurosurgery.

Modifications of several surgical adjuncts are presented: a balanced microscope stand with mouthpiece and hand controls, a piston release operating stool, a support device for resting the surgeon's arms, a table mounted arm with coupling head for attaching self-retaining brain retractors, fish hook retractors, suction tubes, bipolar forceps, aneurysm clips and mobile tip mirrors. Although many of these changes are minor, they considerably facilitate microneurosurgical procedures.

Possible mechanisms for observed pathophysiological variability in experimental spinal cord injury by the method of Allen.

Experimental spinal cord injuries were induced in dogs by dropping calibrated weights through a vented tube onto a small impounder resting on the surgically exposed cord. The motion of the impounder and the drop-mass were recorded by high-speed photography and the resulting data were compared to those obtained from a computer simulation of the dynamics of the injury mechanism. It is concluded that this method of induced spinal cord injuries may yield markedly different degrees of cord compression depending upon the parameters of the animal material and apparatus even when the gm-cm of impact energy is maintained at a constant value. Some approaches to standardization of this injury model are suggested.

Treatment of Jefferson fracture with a halo apparatus. Report of two cases.

Two patients with bursting fractures of the atlas vertebra are presented. The use of a halo apparatus as an effective alternative to bedrest and cervical traction in these patients is discussed. Polytomography was helpful in establishing an accurate diagnosis.

Rapid closed reduction of cervical fracture dislocations.

Indications and a procedure for rapid closed reduction and decompression of cervical fracture dislocations in less than two hours by tong traction are described. Large amounts of weight are utilized. Neurologic damage due either to the large amount of weight or to rapidity of reduction has not been observed. The procedure is advocated in appropriate patients, provided that both sequential neurologic and radiographic monitoring are carried out.

Systemic hypotension in neurosurgery.

The authors review the intraoperative use of elective hypotension to reduce the probability of hemorrhage, to increase pliability of the aneurysmal sac for ease of clip application, and to control hemorrhage. The optimum agent and techniques for lowering systemic blood pressure remain controversial, but trimethaphan, sodium nitroprusside, and halothane have been found most useful. When cerebral blood flow falls below the brain's capacity to autoregulate, distinct time-related alterations occur biochemically and histologically. The profile of prolonged reduced adenosine triphosphate (ATP), low phosphocreatine, low glucose, and elevated lactate and lactate/pyruvate ratio is associated with swelling of perivascular astrocytes and "blebbing" of vascular endothelial cells with subsequent cerebral damage. To prevent permanent alteration it is desirable to observe time constraints and to employ other means of protection such as hypothermia, although the authors believe the latter unnecessary for short hypotensive periods. It has been proposed, but not substantiated, that anesthetics which depress rate of cerebral oxygen consumption but do not affect cerebral ATP level protect the brain from hypotension. Several investigations suggest that halothane, a vasodiltor, satisfies the safety requirement. The most prominent contraindication to halothane, however, is elevation of intracranial pressure. At present hypotensive surgery for aneurysmorrhapy is usually performed when intracranial pressure has returned to normal. Experimentally the electroencephalogram has been observed to show alterations prior to biochemical parameters for following brain vulnerability, so that it conceivably could be an effective monitoring technique during prolonged profound hypotension.

Astrocytic processes: A route between vessels and neurons followingblood-brain barrier injurt.

The fluorescent tracer Evans blue (EB) was studied after circulation time ranging from 30 seconds to 5 minutes following blood-brain barrier (BBB) injuries in 42 dogs. Selective neuronal stainings (sns), associated with BBB injuries, occurred to a high degree. This phenomenon was examined by modifications in existing fluorescence techniques. The mechanism of SNS was seen to lie in an almost imperceptible transport of EB along astrocytic processes connecting SNS with the adjacent vasculature. This report presents visual evidence under pathological conditions, and supports the concept of astrocytic processes as the normal route of transport between blood vessels and neurons. This requires long exposure photomicrographs since the fluorescing material is subtle within the neuroglial processes.