Pressure indicating bag for monitoring intracranial pressure. Technical note

Sagittal synostosis--its clinical significance and the results of three different methods of craniectomy

From 1973 to 1986, 50 infants with sagittal synostosis have been operated by three different methods of craniectomy (linear craniectomy and extended craniectomies, as proposed by Schut and Epstein et al.). Preoperatively, the mean cephalic index was 67 +/- 4, 35.5% had clinical findings as cerebral palsy, psychomotor retardation and/or neurological signs, and intraoperatively the epidural pressure was more than 200 mm H2O in 60% (recorded in the last 20 patients). The mean follow-up time was 4.7 (1-10.6) years. Postoperatively, only 14.5% had minor clinical signs, which were mostly not in relation to the former scaphocephaly. Half of the patients with increased ICP had clinical signs preoperatively, and none of the 20 patients had distinct findings postoperatively. Out of the 20 children operated on by linear craniectomy or by Schut's method up to 1980, two-thirds had no school problems and one-third some school problems; one-third had occasionally headaches and one-quarter ametropia. Concerning the aesthetic results, Epstein's method and, somewhat less Schut's method, were superior to linear craniectomy, as verified by craniometry and by the tracings of the outlines of the neurocranium 0.4-0.7 and 1.6-2.0 years postoperatively: mean cephalic indices 73 +/- 5 (normal in one-fourth), 74 +/- 7 (normal in half) and 79 +/- 4 (normal in nearly all patients). Epstein's method is superior to the other two methods because it renders it possible to increase the breadth the greatest during the period of greatest postnatal brain growth. In addition to the effect on the neurocranium, the extended craniectomies add to normalization of the base of the skull (in contrast to the natural history of scaphocephaly). In the long run, the results obtained remain the same. The disadvantage of residual skull defects (approximately 11% of the patients with extended craniectomies) can be avoided by performing surgery prior to 4-6 months of age or by preserving the removed bone in a deep-freeze for a limited time.

A clinical comparison of subarachnoid catheters to ventriculostomy and subarachnoid bolts: a prospective study

A subarachnoid catheter (SAC) technique of continuous intracranial pressure (ICP) monitoring is presented and compared to intraventricular catheters (IVC's) and subarachnoid bolts (SAB's) in 40 neurosurgical patients. Thirty-one patients were monitored simultaneously with SAC's and IVC's and nine patients with SAC's and SAB's, and the ICP waveforms and measurements were compared. The duration of monitoring ranged from 15 hours to 11 days, and the initial ICP from 2 to 117 torr. A total of 42 SAC's were placed; two that entered brain parenchyma were redirected. One SAC placement was associated with an intracerebral hematoma. There were no infections. For the 31 patients with SAC's and IVC's, there were 2706 pairs of ICP measurements with a mean difference of -0.12 torr and a standard deviation of 5.29 torr. The waveforms from the SAC's and IVC's were indistinguishable. For the nine patients with SAC's and SAB's, there were 773 pairs of ICP measurements with a mean difference of 1.24 torr and a standard deviation of 32.83 torr. The SAB waveforms were of varying quality and all dampened with time. The paired t-test (ts) demonstrated no statistically significant difference between SAC's and IVC's (ts = - 1.19). An analysis of variance demonstrated the scatter of the measurements obtained from SAB's to be 38.5 times that of SAC's, p less than 0.00005. The SAB is shown to be relatively inaccurate with a wide range of variance, while the SAC is demonstrated to be an accurate, reliable, and safe method of continuous ICP measurement and an acceptable alternative to ventriculostomy.

Intracranial pressure: a review of clinical problems, measurement techniques and monitoring methods

Intracranial hypertension is a dangerous condition and is common in patients suffering from a severe head injury or from a variety of pathological problems. Measurement of intracranial pressure (ICP) is considered by many to be a valuable aid in the management of such patients. Despite the invasive nature of the more widely-used measurement techniques, and hence their associated risks, results from many centres have convincingly shown that ICP measurement enables management of intracranial hypertension to be rationally approached, and a direct measure of the progress and outcome of treatment to be obtained. This paper begins with a description of normal cerebrospinal fluid (c.s.f.) pressure. This is followed by an account of the pressure-volume relationship of the intracranial system, and the control mechanisms that regulate the ICP during limited increases in mass volume within the cranium. The consequences of these for patient management are discussed. Reasons why ICP is monitored, and the benefits arising, are described. The paper then concentrates upon the methods of measuring ICP and discusses their relative merits and limitations. A selection of typical pressure sensors is described. Finally, methods that have been devised to monitor ICP and to anticipate intracranial hypertension are reviewed, and the direction of work in this area is assessed.

Intracranial pressure monitoring by flaccid-cuff catheter in an animal model

Several methods of monitoring intracranial pressure (ICP) are in current use, each with its own advantages and disadvantages. The intraventricular line has been most useful because of the ability to withdraw cerebrospinal fluid to assist in control of elevated ICP. However, masses within the brain or generalized increased ICP may compress the lateral ventricle, making insertion of the catheter difficult or impossible. The intracerebral wick records hydrostatic changes too slowly to be used clinically. Swollen cerebral tissue may occlude the subarachnoid bolt thereby dampening the recorded pressure, and epidural monitors may give falsely high recordings because of irregularities of dura or bone. The authors have developed a flaccid-cuff catheter which has proven in animals to be an effective ICP monitor. There are several advantages, such as easy insertion into the centrum semiovale, rapid response to acute pressure changes, and continued sensitivity for periods of up to 3 weeks. The flaccid catheter cuff has no tension so that the pressure across the membrane is equal to zero, simplifying calibration. This type of cuff is necessary for maximum sensitivity to interstitial, brain-tissue, and gross ICP changes. The flaccid-cuff catheter may prove to be useful in a variety of situations such as after closed head trauma or intracranial surgery to assess elevated ICP caused by edema or evolving hematoma.

Brain tissue pressure: physiological observations in anesthetized cats

This study of direct tissue pressure measurement from brain parenchyma in 25 anesthetized cats focuses on steady-state observations and responses to some common physiological manipulations. Tissue pressure recording by a needle system can be done accurately without significant alterations of the blood-brain barrier, brain water content, regional cerebral blood flow, and cerebrovascular reactivity to changes in PaCO2 and cerebral perfusion pressure. Methodological details, including in vitro and in vivo validation, are described.

Chronic measurement of epidural pressure with an induction-powered oscillator transducer

An induction-powered oscillator transducer (IPOT) was designed for the chronic measurement of epidural pressure. The transducer was completely implantable so all pressure measurements were made through the intact skin. The IPOT had a linear pressure range from -50 to +200 cm H2O, was sensitive to 1 mm H2O and had a zero drift of less than 1 mm H2O/day under full load. Zero drift was minimized by using a hermetically-sealed metal bellows transducing element which was chemically treated to prevent corrosion and creep. The correlation between epidural pressure and intraventricular pressure was determined during the first 24 hours after implantation in six dogs. Epidural pressure was found to be a linear function of intraventricular fluid pressure. Epidural pressure and intraventricular pressure were essential equal provided the epidural wedge pressure was minimized by proper insertion of the transducer. The correlation between epidural pressure and intraventricular pressure was determined after chronic implantation in five dogs. Epidural pressure was a linear function of intraventricular pressure in the chronically implanted dogs, but epidural pressure was not equal to intraventricular pressure. After chronic implantation, the epidural pressure transducer was not responsive to changes in intraventricular pressure because of mechanical changes in the dura. The dura became stiff and non-compliant. Maximum correlation between epidural pressure and intraventricular fluid pressure in chronic implantations will depend on judicious material selection and mechanical design at the transducer-dura interface.

Changes of epidural pressures after experimental occlusion of one middle cerebral artery in cats

Epidural pressures (EDP) were measured in 29 cats. Twenty cats had the left middle cerebral artery (MCA) occluded; pentobarbital was used for anesthesia for 10 of these, and halothane was used for the other 10. Two cats had sham operations: the MCA was manipulated but not occluded. Seven cats were used for testing the reliability of the EDP devices. EDP was measured successfully and was directly related to the swelling of the brain and to the size of the cerebral infarct resulting from MCA occlusion. Side-to-side pressure gradients were demonstrated in 7 cats with marked increases of EDP after occlusion; in these cats, EDP may have reflected the pressure of compressed cerebral tissue rather than the pressure of cerebrospinal fluid. Cats anesthetized with pentobarbital had greater increases of EDP and died before the end of the period of observation more frequently than cats anesthetized with halothane, probably because of respiratory depression and slower recovery with pentobarbital. Measurements of EDP may be useful for studies of the treatment of cerebral edema in experimental models of acute cerebral ischemia.