Intracranial pressure and cerebral haemodynamics

Study of the effect of anaesthesia on the canine ultrasonographic optic nerve sheath diameter

OBJECTIVES

To investigate the effects of anaesthetic duration and serial anaesthetic events on optic nerve sheath diameter in a population of dogs without intracranial disease using point-of-care ultrasonography.

MATERIALS AND METHODS

Client-owned dogs requiring advanced head imaging were prospectively enrolled. Exclusion criteria included signs of elevated intracranial pressure, glaucoma and optic nerve disease. Using a transpalpebral technique, two optic nerve sheath diameter measurements were recorded for each eye at three timepoints: following premedication, after induction within 7 minutes and before discontinuing isoflurane. Mixed model analysis was used to characterise optic nerve sheath diameter behaviour and investigate the effects of anaesthetic duration, bodyweight and anaesthetic protocol, age and sex.

RESULTS

Fourteen dogs of various ages, breeds and bodyweights were enrolled. A positive linear relationship was detected between body weight and optic nerve sheath diameter. In 12 of 14 dogs, the optic nerve sheath diameter increased from measurements taken after premedication when compared to measurements taken after induction within 7 minutes. In a subset of patients, measurements subsequently decreased when anaesthetic duration exceeded 120 minutes. Age, side, sex, final body temperature, blood pressure and anaesthetic protocol did not significantly affect optic nerve sheath diameter. No significant association was noted between optic nerve sheath diameter and end-tidal carbon dioxide after induction and before discontinuing isoflurane.

CLINICAL SIGNIFICANCE

When using point-of-care ultrasound, a transient increase in optic nerve sheath diameter occurs between premedication and within 7 minutes following induction, regardless of bodyweight. This should be taken into consideration when serial monitoring is performed.

Automated Detection and Screening of Traumatic Brain Injury (TBI) Using Computed Tomography Images: A Comprehensive Review and Future Perspectives

Traumatic brain injury (TBI) occurs due to the disruption in the normal functioning of the brain by sudden external forces. The primary and secondary injuries due to TBI include intracranial hematoma (ICH), raised intracranial pressure (ICP), and midline shift (MLS), which can result in significant lifetime disabilities and death. Hence, early diagnosis of TBI is crucial to improve patient outcome. Computed tomography (CT) is the preferred modality of choice to assess the severity of TBI. However, manual visualization and inspection of hematoma and its complications from CT scans is a highly operator-dependent and time-consuming task, which can lead to an inappropriate or delayed prognosis. The development of computer aided diagnosis (CAD) systems could be helpful for accurate, early management of TBI. In this paper, a systematic review of prevailing CAD systems for the detection of hematoma, raised ICP, and MLS in non-contrast axial CT brain images is presented. We also suggest future research to enhance the performance of CAD for early and accurate TBI diagnosis.

Cerebrovascular Compliance Within the Rigid Confines of the Skull

Pulsatile blood flow is generally mediated by the compliance of blood vessels whereby they distend locally and momentarily to accommodate the passage of the pressure wave. This freedom of the blood vessels to exercise their compliance may be suppressed within the confines of the rigid skull. The effect of this on the mechanics of pulsatile blood flow within the cerebral circulation is not known, and the situation is compounded by experimental access difficulties. We present an approach which we have developed to overcome these difficulties in a study of the mechanics of pulsatile cerebral blood flow. The main finding is that while the innate compliance of cerebral vessels is indeed suppressed within the confines of the skull, this is compensated somewhat by compliance provided by other “extravascular” elements within the skull. The net result is what we have termed “intracranial compliance,” which we argue is more pertinent to the mechanics of pulsatile cerebral blood flow than is intracranial pressure.