Transcranial Doppler-derived indices of cerebrovascular haemodynamics are independent of depth and angle of insonation

Continuous measurement of cerebral blood flow velocity (CBFV) of the middle cerebral artery (MCA) using transcranial Doppler (TCD) and arterial blood pressure (ABP) monitoring enables assessment of cerebrovascular haemodynamics. Further indices describing cerebrovascular function can be calculated from ABP and CBFV, such as the mean index (Mxa) of cerebrovascular autoregulation, the 'time constant of the cerebral arterial bed' (tau), the 'critical closing pressure' (CrCP) and a 'non-invasive estimator of ICP' (nICP). However, TCD is operator-dependent and changes in angle and depth of MCA insonation result in different readings of CBFV. The effect of differing CBFV readings on the calculated secondary indices remains unknown. The aim of this study was to investigate variation in angle and depth of MCA insonation on these secondary indices. In eight patients continuous ABP and ipsilateral CBFV monitoring was performed using two different TCD probes, resulting in four simultaneous CBFV readings at different angles and depths per patient. From all individual recordings, the K-means clustering algorithm was applied to the four simultaneous longitudinal measurements. The average ratios of the between-clusters, sum-of-squares and total sum-of-squares were significantly higher for CBFV than for the indices Mxa, tau and CrCP (p < 0.001, p = 0.007 and p = 0.016) but not for nICP (p = 0.175). The results indicate that Mxa, tau and CrCP seemed to be not affected by depth and angle of TCD insonation, whereas nICP was.

Outcomes following grade V subarachnoid haemorrhage: A single-centre retrospective study

SummaryGrade V subarachnoid haemorrhage is associated with high mortality and morbidity, yet there are few contemporary reports on the treatment provided and outcomes of these patients. In this single-centre retrospective cohort study, we primarily sought to determine the 12-month mortality of patients admitted to the Royal Adelaide Hospital intensive care unit between 2006 and 2016 with grade V subarachnoid haemorrhage. Secondary objectives were to describe treatments provided, patient destination following hospital discharge, organ donation and hospital financial costs. Over the 11-year study period, there were 139 patients admitted with grade V subarachnoid haemorrhage. The annual number of admissions did not change over time. The median age was 56 (interquartile range 48-70) years, 88 (63%) were female and 77 (55%) had a procedure to isolate an aneurysm. There were 77 (55%) patients who died in the intensive care unit, 87 (63%) died in hospital and 89 (64%) had died at 12 months. Of the 52 patients who survived to hospital discharge, 33 (63%) were transferred to a rehabilitation facility, 17 (33%) to another acute care hospital and two (4%) were discharged. Of the 87 patients who died in hospital, 45 (52%) donated organs. The total hospital cost of managing this cohort was A$8.3 million, with a median cost of A$41,824 (interquartile range A$9,933-A$97,332) per patient. Grade V subarachnoid haemorrhage has a high mortality rate, with one-third of patients alive after one year.

Home telemonitoring of intracranial pressure

BACKGROUND

As technical progress advances, telemonitoring has become an important part of patient care in many areas of medical treatment. However, distanced surveillance of intracranial pressure (ICP) could not be established so far. With the recent introduction of a telemetric ICP measurement probe, new possibilities arise. Here, we report on a new home setup enabling home telemonitoring of intracranial pressure.

METHODS

Twenty patients suffering from disturbances of cerebrospinal fluid circulation, who underwent insertion of a telemetric ICP measurement probe, were provided with medical equipment to read ICP at home and save the data on an internet-enabled computer. Training in handling the equipment was performed during in-patient stay; recorded and uploaded ICP data was then analyzed online. Therefore, the treating medical team was able to access the ICP data via a secure internet connection while telephone conferencing with the patient.

RESULTS

Almost 7400 h of ICP data were recorded at home and evaluated via an internet connection according to the telemonitoring setup. This corresponds to an average record time of about 370 h per patient. ICP profiles were observed following endoscopic treatment, shunting procedures, or valve adjustments. The mean distance between the patients' residence and the consulting hospital was 172 km (range, 16-649 km).

CONCLUSIONS

ICP measurements have become accessible for telemonitoring purposes. This new management of hydrocephalus reflects an alternative method in patient care, especially for those who live far away from specialized centers.

What neurosurgeons need to know about dabigatran etexilate (pradax(®)/pradaxa(®)/prazaxa(®))

Dabigatran etexaliate is a novel oral anticoagulant that directly inhibits thrombin. It offers a number of substantial medical benefits over other oral and parenteral anticoagulants but its advent raises important neurosurgical considerations. Dabigatran has important potential benefits. Unlike warfarin, it does not require routine blood tests to monitor its anticoagulative effect and there is no need for dose titration. Drug interactions are greatly simplified when compared to warfarin as dabigatran is not metabolized by cytochrome p450 isoenzymes. As a result, dabigatran has been approved in many jurisdictions for DVT prophylaxis after orthopaedic surgery and also for the prevention of embolic events associated with non-valvular atrial fibrillation. There are, however, important neurosurgical challenges associated with regular dabigatran use. Unlike current anti-coagulants, there is no specific reversal agent for dabigatran. Known reversal options include activated charcoal (within one to two hours of intake) and renal dialysis. Protamine sulfate and vitamin K are unlikely to affect the activity of dabigatran. Platelet concentrates will not inactivate dabigatran's anti-thrombin properties. Assessing the degree of anticoagulation is difficult as conventional markers of serum coagulability are typically normal in patients taking dabigatran. The potential neurosurgical challenges of dabigatran were cast in sharp relief by a recent case report from the United States that is considered in this note. In the absence of a clear reversal pathway, we propose a treatment algorithm for chronic dabigatran use based on the replacement of any deficient factors and rapid access to renal dialysis.

Palmitoylation of rhodopsin with S-protein acyltransferase: enzyme catalyzed reaction versus autocatalytic acylation

Protein palmitoylation in vitro was studied using bovine rhodopsin as the substrate and a partially purified acylating enzymatic activity (PAT) from placental membranes. PAT incorporates fatty acid into rhodopsin with higher efficiency (10 times higher initial rate), as compared to autoacylation. The activity is sensitive to heat and trypsin, indicating a protein-mediated enzymatic process and requires the native conformation of rhodopsin. The presence of deacylated, free cysteine residues in dark-adapted rhodopsin increases palmitoylation via PAT. The sites for non-enzymatic and enzymatic palmitoylation could not be distinguished by peptide mapping. The reversible palmitoylation described here will provide a tool for the study of the role of palmitoylation in photoreceptor function.