Are we meeting the standards set for informed consent in spinal surgery?

INTRODUCTION: Informed consent empowers patients to exercise their autonomy and actively participate in their medical care. Guidance published by the British Association of Spine Surgeons (BASS) lists three components of consent: provision of information booklets, patient-centred dialogue and completion of appropriate consent forms. The aim of the study was to review the quality of the spinal surgery consent process against the BASS guidance in a single tertiary neurosurgery centre in London. METHODS: Retrospective review of clinic letters and consent forms was performed for 100 consecutive cases of elective, non-instrumented spinal decompression surgeries performed in 2019. Documentation was graded for inclusion of the intended benefit (improvement of pain/prevention of neurological deterioration), alternative management options (including no treatment), surgical options and risks (infection, bleeding, paralysis, sphincter disturbances, dural tear and recurrence). Provision of supplementary information booklets was recorded. Two-tailed Fisher exact test was used to calculate statistical significance where appropriate. RESULTS: Documentation of indications and risks of elective spinal surgery, specifically risk of recurrence (62%) and sphincter disturbance (85%), was suboptimal on the consent forms. Documentation of these risks was also poor in clinic letters (<50%). Alternative treatment options were explained in less than half of the clinic letters, and there was no documentation of information booklet provision prior to elective surgeries. CONCLUSION: Lack of informed consent plays a major role in medical malpractice claims in spinal surgery. Poor documentation puts the surgeon in a liable position. BASS guidance could be implemented to create a more standardised process of consent in spinal surgery.

Intrathecal baclofen overdose mimicking brainstem death during deep brain stimulation surgery for pain.

We describe a unique case of intrathecal baclofen overdose mimicking brainstem death, during bilateral anterior cingulate cortex deep brain stimulation (DBS) for pain. A 37-year-old man with chronic regional pain syndrome requiring an intrathecal baclofen pump underwent DBS under general anaesthesia and experienced an intraoperative generalised tonic-clonic seizure on dural opening. Once the operation was completed, the patient was noted to have fixed, dilated pupils bilaterally and was transferred for an emergency computed tomography scan of the head, which did not reveal any acute intracranial pathology. The patient was transferred to the intensive care unit for management of concurrent hypotension, bradycardia and supportive management of his low Glasgow Coma Scale (GCS) score. A trial of atropine to counter the bradycardia was unsuccessful. Intrathecal baclofen toxicity was suspected as a diagnosis of exclusion, necessitating urgent aspiration of the baclofen pump. The patient's GCS score improved after pump aspiration and he was discharged home several days later. It was noted that the intrathecal baclofen pump had been refilled several days previously and the patient had reported intermittent episodes of somnolence. In perioperative patients with intrathecal baclofen pumps in situ, baclofen toxicity should always be considered as a differential in perioperative complications, even if it is considered a rare event.

Fulminant intracranial hypertension secondary to oxytetracycline requiring urgent ventriculo-peritoneal shunt insertion.

Idiopathic intracranial hypertension is a syndrome that presents with headaches and visual loss. Its pathogenesis is unknown. Treatment options include acetazolamide, therapeutic lumbar punctures or permanent CSF diversion. We present the only reported case of acute drug-induced intracranial hypertension secondary to oxytetracycline requiring urgent cerebrospinal fluid diversion. The patient's rapid visual failure progressed daily despite discontinuation of the drug and required an urgent ventriculo-peritoneal (VP) shunt insertion. Patients should be counselled about the rare potential risk of developing intracranial hypertension when commencing oxytetracycline. Rapid visual failure in IIH is a neurosurgical emergency necessitating urgent ventriculoperitoneal shunt insertion.

Subthalamic deep brain stimulation induces finely-tuned gamma oscillations in the absence of levodopa.

Finely-tuned gamma (FTG) oscillations can be recorded from cortex or the subthalamic nucleus (STN) in patients with Parkinson's disease (PD) on dopaminergic medication, and have been associated with dyskinesias. When recorded during deep brain stimulation (DBS) on medication the FTG is entrained to half the stimulation frequency. We investigated whether these characteristics are shared off medication by recording local field potentials (LFP) from the STN from externalised DBS leads in 14 PD patients after overnight withdrawal of medication. FTG was induced de-novo by DBS in the absence of dyskinesias in a third of our cohort. The FTG could outlast stimulation or arise only after DBS ceased. FTG frequencies decreased during and across consecutive DBS blocks, but did not shift with changing stimulation frequency off medication. Together with the sustained after-effects this argues against simple entrainment by DBS in the off medication state. We also found significant coherence between STN-LFP and electroencephalogram (EEG) signals at FTG frequencies. We conclude that FTG is a network phenomenon that behaves differently in the off medication state, when it is neither associated with dyskinesias nor susceptible to entrainment.

Local field potential activity dynamics in response to deep brain stimulation of the subthalamic nucleus in Parkinson's disease.

Local field potentials (LFPs) may afford insight into the mechanisms of action of deep brain stimulation (DBS) and potential feedback signals for adaptive DBS. In Parkinson's disease (PD) DBS of the subthalamic nucleus (STN) suppresses spontaneous activity in the beta band and drives evoked resonant neural activity (ERNA). Here, we investigate how STN LFP activities change over time following the onset and offset of DBS. To this end we recorded LFPs from the STN in 14 PD patients during long (mean: 181.2 s) and short (14.2 s) blocks of continuous stimulation at 130 Hz. LFP activities were evaluated in the temporal and spectral domains. During long stimulation blocks, the frequency and amplitude of the ERNA decreased before reaching a steady state after ~70 s. Maximal ERNA amplitudes diminished over repeated stimulation blocks. Upon DBS cessation, the ERNA was revealed as an under-damped oscillation, and was more marked and lasted longer after short duration stimulation blocks. In contrast, activity in the beta band suppressed within 0.5 s of continuous DBS onset and drifted less over time. Spontaneous activity was also suppressed in the low gamma band, suggesting that the effects of high frequency stimulation on spontaneous oscillations may not be selective for pathological beta activity. High frequency oscillations were present in only six STN recordings before stimulation onset and their frequency was depressed by stimulation. The different dynamics of the ERNA and beta activity with stimulation imply different DBS mechanisms and may impact how these activities may be used in adaptive feedback.

Mechanisms of reinforcement in polymer nanocomposites.

Coarse-grained molecular dynamics simulations are used to elucidate molecular mechanisms responsible for different mechanical behaviours of elastomers containing spherical particles with different volume fractions. We observe that different filler volume fractions result in qualitatively different responses of the polymer nanocomposite to tensile strain. At relatively low filler volume fraction a yield drop appears in the stress-strain curve. As the filler volume fraction increases there is a reduction in the rate of plastic hardening, becoming plastic softening at sufficiently high filler volume fraction. We demonstrate that these behaviours are a result of the network formed by the polymer chains and filler particles. We identify three distinct molecular structural motifs between polymer and filler particles whose relative prevalence varies with the filler volume fraction and as the system is dynamically strained. We show how this evolution in molecular structure is directly linked to the observed mechanical response.

Molecular Simulation of Gas Solubility in Nitrile Butadiene Rubber.

Molecular simulation is used to compute the solubility of small gases in nitrile butadiene rubber (NBR) with a Widom particle-insertion technique biased by local free volume. The convergence of the method is examined as a function of the number of snapshots upon which the insertions are performed and the number of insertions per snapshot and is compared to the convergence of the unbiased Widom insertion technique. The effect of varying the definition of local free volume is also investigated. The acrylonitrile content of the polymer is altered to examine its influence on the solubility of helium, CO2, and H2O, and the solubilities of polar gases are found to be enhanced relative to those of nonpolar gases, in qualitative agreement with experiment. To probe this phenomenon further, the solubilities are decomposed into contributions from the neighborhoods of different atoms, using a Voronoi cell construction, and a strong bias is found for CO2 and H2O in particular to be situated near nitrogen sites in the elastomer. Temperature is shown to suppress the solubility of CO2 and H2O but to increase that of helium. Increasing pressure is found to suppress the solubility of all gases but at different rates, according to a balance between their molecular sizes and electrostatic interactions with the polymer. These results are relevant to the use of NBR seals at elevated temperatures and pressures, such as in oil and gas wells.

Molecular Model for HNBR with Tunable Cross-Link Density.

We introduce a chemically inspired, all-atom model of hydrogenated nitrile butadiene rubber (HNBR) and assess its performance by computing the mass density and glass-transition temperature as a function of cross-link density in the structure. Our HNBR structures are created by a procedure that mimics the real process used to produce HNBR, that is, saturation of the carbon-carbon double bonds in NBR, either by hydrogenation or by cross-linking. The atomic interactions are described by the all-atom "Optimized Potentials for Liquid Simulations" (OPLS-AA). In this paper, first, we assess the use of OPLS-AA in our models, especially using NBR bulk properties, and second, we evaluate the validity of the proposed model for HNBR by investigating mass density and glass transition as a function of the tunable cross-link density. Experimental densities are reproduced within 3% for both elastomers, and qualitatively correct trends in the glass-transition temperature as a function of monomer composition and cross-link density are obtained.

The potential of imogolite nanotubes as (co-)photocatalysts: a linear-scaling density functional theory study.

We report a linear-scaling density functional theory (DFT) study of the structure, wall-polarization absolute band-alignment and optical absorption of several, recently synthesized, open-ended imogolite (Imo) nanotubes (NTs), namely single-walled (SW) aluminosilicate (AlSi), SW aluminogermanate (AlGe), SW methylated aluminosilicate (AlSi-Me), and double-walled (DW) AlGe NTs. Simulations with three different semi-local and dispersion-corrected DFT-functionals reveal that the NT wall-polarization can be increased by nearly a factor of four going from SW-AlSi-Me to DW-AlGe. Absolute vacuum alignment of the NT electronic bands and comparison with those of rutile and anatase TiO2 suggest that the NTs may exhibit marked propensity to both photo-reduction and hole-scavenging. Characterization of the NTs' band-separation and optical properties reveal the occurrence of (near-)UV inside-outside charge-transfer excitations, which may be effective for electron-hole separation and enhanced photocatalytic activity. Finally, the effects of the NTs' wall-polarization on the absolute alignment of electron and hole acceptor states of interacting water (H2O) molecules are quantified and discussed.

Linear-scaling density-functional simulations of charged point defects in Al2O3 using hierarchical sparse matrix algebra.

We present calculations of formation energies of defects in an ionic solid (Al(2)O(3)) extrapolated to the dilute limit, corresponding to a simulation cell of infinite size. The large-scale calculations required for this extrapolation are enabled by developments in the approach to parallel sparse matrix algebra operations, which are central to linear-scaling density-functional theory calculations. The computational cost of manipulating sparse matrices, whose sizes are determined by the large number of basis functions present, is greatly improved with this new approach. We present details of the sparse algebra scheme implemented in the ONETEP code using hierarchical sparsity patterns, and demonstrate its use in calculations on a wide range of systems, involving thousands of atoms on hundreds to thousands of parallel processes.