Is it useful to measure supratentorial ICP in the presence of a posterior fossa lesion? Absence of transtentorial pressure gradients in an animal model.

Previous studies with animal models of supratentorial ICP elevation have demonstrated a pressure gradient between the supratentorial and the infratentorial compartments. The present study was designed to investigate the possible presence of such a gradient in the case of infratentorial ICP elevation. An inflatable infratentorial balloon catheter was implanted in seven domestic pigs. The infratentorial ICP (ICPi) was measured in the left cerebellar hemisphere, and the supratentorial ICP (ICPs) was measured in the left cerebral hemisphere. The corresponding pulse amplitudes (ICPi-PA, ICPs-PA) were recorded in both compartments, and the cerebral perfusion pressure (CPP) was calculated. ICPi and ICPs values prior to balloon inflation were 4.4 (SD 2.2) and 4.1 (SD 2.3) mm Hg, respectively, and increased to 63.1 (SD 32.6) and 62.3 (SD 28.1) mmHg after balloon inflation. ICPi-PA rose from 3.1 (SD 0.43) to 12.8 (SD 8.0) mmHg, and ICPs-PA rose from 3.2 (SD 0.63) to 13.0 (SD 7.1) mmHg. CPP decreased from 86.1 (SD 12.0) to 55.4 (SD 14.6) mm Hg. The paired difference between ICPi and ICPs values was 0.44 (SD 1.96) mmHg, and the paired difference of ICP amplitudes was 0.03 (SD 1.19) mmHg. All these differences in infratentorial and supratentorial values were statistically not significant. In conclusion, infratentorial ICP elevation in the presented pig model leads to a uniform ICP elevation in the intracranial space without development of a considerable pressure gradient below and above the tentorium. In the low pressure part of the ICP curve, cerebrospinal fluid connects the compartments and contributes to the pressure equilibrium. The early obstruction of the foramen magnum by intruding cerebellar tissue seems to isolate the infratentorial from the spinal compartment. In the high-pressure part of the curve, the upwards cerebellar transtentorial herniation takes over the pressure transfer, and the whole intracranial space can be considered as a single compartment in the pig.

Continuous monitoring of the partial pressure of oxygen in cerebral venous blood.

OBJECTIVE: Clinical oxygen monitoring in the injured brain is somewhat difficult. However, ischemia is one of the major factors responsible for secondary tissue damage after head injury or subarachnoid hemorrhage. Therefore, the aim of the present study was to investigate the value of continuously monitoring the partial pressure of oxygen in cerebral venous blood (PcvO2) during changes in intracranial pressure (ICP). METHODS: In eight domestic pigs with Clark type probes placed in the posterior third of the superior sagittal sinus, PcvO2 was continuously registered while ICP was stepwise elevated by an inflatable balloon placed below the tentorium. Arterial blood pressure was continuously monitored, cerebral perfusion pressure (CPP) was calculated, and arterial partial carbon dioxide pressure and partial pressure of oxygen were registered intermittently. RESULTS: The mean intraparenchymal ICP before the start of balloon inflation was 5 +/- 1 mm Hg, the mean CPP was 80 +/- 15 mm Hg, and the mean PcvO2 was 36 +/- 3 mm Hg. At maximum ICP elevation, CPP decreased to 20 +/- 12 mm Hg, PcvO2 decreased to 10 +/- 6 mm Hg, and ICP increased to 90 +/- 10 mm Hg. Strong linear correlations between ICP and PcvO2 and between CPP and PcvO2 were revealed, and mean correlation coefficients of 0.89 for ICP/PcvO2 and 0.73 for CPP/PcvO2 were calculated. CONCLUSION: The present study demonstrates that polarographic PcvO2 monitoring in the superior sagittal sinus is a reliable method for the early detection of reduced CPP during ICP elevation. This technique is capable of registering the global oxygen supply and oxygen consumption of the brain. It seems superior to jugular venous oxymetry and is better suited for clinical use because of a somewhat low artifact susceptibility.

[Cerebrovascular fiberoptic catheter oximetry in an intracranial pressure model in swine. New aspects of a clinical routine]. / Die zerebrovenöse fiberoptische Katheteroxymetrie im Hirndruckmodell des Schweins. Neue Aspekte für die klinische Routine.

UNLABELLED: The reliability of continuous fibreoptic oximetry in cerebral venous blood and its correlation with intracranial and cerebral perfusion pressures (pressure-volume curve) were examined in an experimental porcine study. METHODS: The pressure in the infratentorial compartment of 13 domestic pigs (18-24 kg) was gradually increased by inflating a Fogarty balloon catheter placed on the surface of the right cerebellar hemisphere and below the tentorium. Single volumes of 0.4 ml saline were injected into the inflatable balloon at 1-min intervals up to a total volume of 7 ml. Intracranial pressure (ICP), arterial blood pressure, cerebral perfusion pressure (CPP), and cerebral venous saturation measured continuously by fibreoptic oximetry and intermittent blood-gas analyses (SjO2 superior sagittal sinus) were monitored during balloon inflation. All data were down-loaded onto a PC and evaluated off-line by a commercial statistical software package. RESULTS: Over the whole pressure-volume curve, two phases of SjO2 behaviour were registered by continuous fibreoptic oximetry (Oximetrix 3, Abbott) (Fig. 1). CPP ranges of less than 50% reduction from the initial value showed a linear correlation (rmittl. = 0.712, P < 0.01) between both parameters (CPP-SjO2). In CPP ranges below a crucial point of about 50 mmHg no such correlation was found (rmittl = 0.176, P < 0.5). In contrast, in 3 pigs a very good correlation was found between CPP and SjO2 over the whole pressure-volume curve as measured by blood-gas analyses of samples from the cerebrovenous catheter (rmittl. = 0.84, P < 0.05). DISCUSSION: We conclude that in physiological CPP ranges down to 50 mmHg, SjO2 measurement is a reliable method of detecting oxygen desaturation in cerebrovenous blood. Below that CPP value, the fibreoptic catheter showed repeated false-high oxygen saturation values. The accuracy of SjO2 measurement seems to depend on sufficient cerebral blood flow (CBF): with decreasing CBF the amount of cerebral venous outflow is diminished. We believe this is why we could not find a correlation in low CPP ranges with the oximetry catheter. This flow-dependency is a new aspect of fibreoptic cerebrovenous oximetry. The authors recommend that rising SjO2 values after desaturation events be confirmed by blood-gas analyses.

Factors predicting pituitary adenoma invasiveness in acromegalic patients.

Forty-four adult acromegalic patients carrying growth hormone-producing pituitary macroadenomas were investigated with neuroradiological and endocrinological techniques. Plasma growth hormone and somatomedin-C levels were repeatedly measured before surgical removal of tumors and during the follow-up period. Twenty-five patients presented preoperatively with an invasive adenoma that involved the cavernous sinus (CS). Diagnosis of tumor invasivity was made according to distinct neuroradiological criteria and was confirmed or rejected during surgery Significantly higher basal growth hormone levels were found in patients with CS invasion than in cases without tumor growth in the CS. Evidence is presented that plasma growth hormone level in acromegalics is a more sensitive indicator for predicting tumor invasiveness than somatomedin-C. Growth hormone basal values before surgery and the extent of their decrease after removal of tumor correlate with adenoma growth in the parasellar compartments and should be used as a prognostic factor to aid in planing adjuvant tumor treatment.

Dorsal spondylodesis of unstable thoracolumbar fractures by a far-lateral approach to the disc.

This paper describes a modified and less traumatic approach to the thoracolumbar spine and compares it with standard techniques for instrumented spinal fusion. Ten patients with unstable fractures of the thoracolumbar spine were included in the open prospective investigation, and were treated by a surgical technique consisting of a dorsolateral approach to the injured segment, filling the disk space and the fractured vertebra with autologous bone, and transpedicular fixation with an AO internal fixator. All patients were followed for 6 to 12 months after surgery by clinical tests and spinal X-rays. Excellent short-term and long-term results were obtained. A stable bony fusion was achieved in all cases, and a minimal mean decrease of 2 degrees in the kyphosis angle was found at late follow-up. No major complications related to the procedure were encountered, and no worsening of neurological deficits occurred after surgery. In conclusion, the far-lateral approach to the thoracolumbar spine yields results which are equivalent or better than those of standard techniques. Major advantages of our procedure, as evaluated in this rather small group of patients, are selective immobilization of the injured segment without involvement of functionally intact spinal levels, no manipulations within the spinal canal boundaries, and relatively limited exposure of the spine.

Ultrasound-guided endoscopic fenestration of the third ventricular floor for non-communicating hydrocephalus.

Conventional valve shunting for treatment of hydrocephalus has a high rate of long-term complications. Endoscopic ventriculostomy by fenestration of the third ventricular floor, a minimally-invasive technique, avoids many of the drawbacks of extracranial shunting. Endoscopy was performed in 12 hydrocephalic patients with MRI-diagnosed aqueductal stenosis and neurological signs. Intraoperative ultrasound guidance allowed aiming the tip of the rigid endoscope to the foramen of Monro, and direct entering of the enlarged third ventricle. This technique is as exact as stereotaxy but is faster and easier. No complications were seen due to the surgical procedure. Nine patients were cured from their complaints, in 3 cases there was a subjective improvement of neurology. Long-term patency of the third ventriculostomy was confirmed by movement-sensitive MRI.