Treatment threshold for intra-operative hypotension in clinical practice-a prospective cohort study in older patients in the UK.

Intra-operative hypotension frequently complicates anaesthesia in older patients and is implicated in peri-operative organ hypoperfusion and injury. The prevalence and corresponding treatment thresholds of hypotension are incompletely described in the UK. This study aimed to identify prevalence of intra-operative hypotension and its treatment thresholds in UK practice. Patients aged ≥ 65 years were studied prospectively from 196 UK hospitals within a 48-hour timeframe. The primary outcome was the incidence of hypotension (mean arterial pressure <65 mmHg; systolic blood pressure reduction >20%; systolic blood pressure <100 mmHg). Secondary outcomes included the treatment blood pressure threshold for vasopressors; incidence of acute kidney injury; myocardial injury; stroke; and in-hospital mortality. Additionally, anaesthetists providing care for included patients were asked to complete a survey assessing their intended treatment thresholds for hypotension. Data were collected from 4750 patients. Hypotension affected 61.0% of patients when defined as mean arterial pressure <65 mmHg, 91.3% of patients had >20% reduction in systolic blood pressure from baseline and 77.5% systolic blood pressure <100 mmHg. The mean (SD) blood pressure triggering vasopressor therapy was mean arterial pressure 64.2 (11.6) mmHg and the mean (SD) stated intended treatment threshold from the survey was mean arterial pressure 60.6 (9.7) mmHg. A composite adverse outcome of myocardial injury, kidney injury, stroke or death affected 345 patients (7.3%). In this representative sample of UK peri-operative practice, the majority of older patients experienced intra-operative hypotension and treatment was delivered below suggested thresholds. This highlights both potential for intra-operative organ injury and substantial opportunity for improving treatment of intra-operative hypotension.

Influence of study design on effects of mask wearing on fMRI BOLD contrast and systemic physiology - A comment on Law et al. (2021).

In a study by Law and colleagues recently published in Neuroimage, the authors reported that wearing a surgical mask during an fMRI scan leads to a statistically significant subject-specific change (30%) in the baseline BOLD level in gray matter, although the response to a sensory-motor task was unaffected. An average increase in end-tidal CO2 of 7.4% was found when wearing a mask, despite little support in the literature for major effects of mask wearing on blood gas levels. We comment on these findings, point out a several relevant limitations of the study design and provide alternative interpretations of these data.

A Fibreless Multiwavelength NIRS System for Imaging Localised Changes in Cerebral Oxidised Cytochrome C Oxidase.

Measurement of the oxidation state of cytochrome c oxidase (oxCCO) can inform directly on neuronal metabolism. Conventionally this has been measured in vivo using benchtop broadband near infrared spectroscopy (NIRS) systems. Spatially resolved measures of oxCCO have recently been made possible using a multichannel fibre-based broadband NIRS system. We describe the use of a fibreless multiwavelength NIRS system using light emitting diodes (LED) designed specifically to image localised changes in oxCCO and hence neuronal metabolism. A fibreless system consisting of four modules, each containing two LED sources and four photodiode detectors, was developed. Each LED source contained eight LED dies (780, 811, 818, 842, 850, 882, 891 and 901 nm) assembled in an area of 1.5 × 1.5 mm. A well-established hyperoxia protocol was used to evaluate the oxCCO spatially resolved measurement capabilities of the system and, subsequently, its imaging capabilities were tested using a functional activation paradigm. A multi-spectral image reconstruction approach was used to provide images of Δ[HbO2], Δ[HHb] and Δ[oxCCO] from the multi-distance, multi-channel optical datasets. This novel fibreless multiwavelength NIRS system allows imaging of localised changes in oxCCO in the human brain, and has potential for development as an inexpensive, wearable, continuous monitor of cerebral energetics in a range of experimental and clinical scenarios.

Spatial Distribution of Changes in Oxidised Cytochrome C Oxidase During Visual Stimulation Using Broadband Near Infrared Spectroscopy Imaging.

Functional hyperaemia, characterised as an increase in concentration of oxyhaemoglobin [HbO2] and a decrease in concentration of deoxyhaemoglobin [HHb] in response to neuronal activity, can be precisely mapped using diffuse optical spectroscopy. However, such techniques do not directly measure changes in metabolic activity during neuronal activation. Changes in the redox state of cerebral oxidised cytochrome c oxidase Δ[oxCCO] measured by broadband spectroscopy may be a more specific marker of neuronal metabolic activity. This study aims to investigate the spatial distribution of Δ[oxCCO] responses during the activation of the visual cortex in the healthy adult human brain, and reconstruct images of these changes.Multi-channel broadband NIRS measurements were collected from the left visual cortex of four healthy volunteers using an in-house broadband spectrometer during an inverting checkerboard visual stimulation paradigm. Δ[HbO2], Δ[HHb] and Δ[oxCCO] were calculated by fitting the broadband spectra between 780 and 900 nm using the UCLn algorithm. Centre of gravity analysis was applied to the concentration data to determine the centres of activation for [HbO2], [HHb] and [oxCCO].All four subjects showed similar changes in [oxCCO] in the presence of a typical visual-evoked haemodynamic response in channels overlying the visual cortex. Image reconstruction of the optical data showed a clear and spatially localized activation for all three chromophores. Centre of gravity analysis showed different localisation of the changes in each of the three chromophores across the visual cortex with the x-y coordinates of the mean centres of gravity (across 4 subjects) of HbO2, HHb and oxCCO at (63.1 mm; 24.8 mm), (56.2 mm; 21.0 mm) and (63.7 mm; 23.8 mm), respectively.The spatial distribution of Δ[oxCCO] response appears distinct from the haemodynamic response in the human visual cortex. Image reconstruction of Δ[oxCCO] shows considerable promise as a technique to visualise regional variation in [oxCCO] in a range of scenarios.

Effect of blood in the cerebrospinal fluid on the accuracy of cerebral oxygenation measured by near infrared spectroscopy.

Near infrared spectroscopy (NIRS) is an optical technique used to examine the oxygenation state of tissues such as the brain in patients, including those with brain injury. We have examined the effect of a cerebrospinal fluid (CSF) contaminant, specifically haemoglobin, on the sensitivity of cerebral NIRS signals through computer simulation. Previous models of light transport in the head have shown that the clear CSF layer has a profound effect on the sensitivity profile of the NIRS signal due to its low absorbing, low scattering qualities. In subarachnoid haemorrhage, which may accompany brain injury, the principal near infrared chromophore, haemoglobin, is released into the CSF. Sensitivity was measured through forward modeling and the presence of haemoglobin within the CSF was modeled by increasing the absorption coefficient of the layer, with sensitivity quantified in terms of the partial pathlength of light within the brain. The model demonstrated that increases in the CSF absorption led to a marked decrease in the sensitivity to changes in the brain layer. This suggests that blood or other contaminants in the CSF may have a significant effect on the utility of NIRS for measurement of cerebral oxygenation, and merits further investigation.

What do I want from a clinical director?

There are strong arguments for the effective involvement of clinicians in management and the need for a positive interface between medical staff and managers. There are three major dimensions of different management models for the involvement of clinicians in management. There are a number of key deliverables expected from an effective clinical director, and a series of characteristics which the ideal clinical director should possess.