Advances in Neuroimaging and Monitoring to Defend Cerebral Perfusion in Noncardiac Surgery.

Noncardiac surgery conveys a substantial risk of secondary organ dysfunction and injury. Neurocognitive dysfunction and covert stroke are emerging as major forms of perioperative organ dysfunction, but a better understanding of perioperative neurobiology is required to identify effective treatment strategies. The likelihood and severity of perioperative brain injury may be increased by intraoperative hemodynamic dysfunction, tissue hypoperfusion, and a failure to recognize complications early in their development. Advances in neuroimaging and monitoring techniques, including optical, sonographic, and magnetic resonance, have progressed beyond structural imaging and now enable noninvasive assessment of cerebral perfusion, vascular reserve, metabolism, and neurologic function at the bedside. Translation of these imaging methods into the perioperative setting has highlighted several potential avenues to optimize tissue perfusion and deliver neuroprotection. This review introduces the methods, metrics, and evidence underlying emerging optical and magnetic resonance neuroimaging methods and discusses their potential experimental and clinical utility in the setting of noncardiac surgery.

Management of the patient presenting with anaemia in the preoperative setting.

Preoperative anaemia is common, seen in a third of patients before major surgery. Both preoperative anaemia and blood transfusion are associated with increased patient risk and adverse outcome. Patient Blood Management (PBM) is the multidisciplinary, multimodal approach to optimising the care of patients who may require blood transfusion. Guidelines exist with many recommendations throughout the perioperative pathway. However, the efficacy of individual recommendations as an intervention in terms of clinical outcome can be confusing. In the UK the first national audit of PBM in surgery was carried out in 2015. This reviewed the use and impact of PBM recommendations in hospitals throughout the UK where major surgery was undertaken. The current evidence base for these PBM recommendations was reviewed and the patient outcome in terms of blood transfusion use and length of hospital stay assessed in those where PBM interventions were followed. For the patient who presents with preoperative anaemia, 'quick wins' were identified that reduced blood transfusion use and reduced length of stay in hospital; preoperative discontinuation of anticoagulation or antiplatelet therapy, and intraoperative use of tranexamic acid and cell salvage.

Pressure passivity of cerebral mitochondrial metabolism is associated with poor outcome following perinatal hypoxic ischemic brain injury.

Hypoxic ischemic encephalopathy (HIE) leads to significant morbidity and mortality. Impaired autoregulation after hypoxia-ischaemia has been suggested to contribute further to injury. Thalamic lactate/N-Acetylasperate (Lac/NAA) peak area ratio of > 0.3 on proton (1H) magnetic resonance spectroscopy (MRS) is associated with poor neurodevelopment outcome following HIE. Cytochrome-c-oxidase (CCO) plays a central role in mitochondrial oxidative metabolism and ATP synthesis. Using a novel broadband NIRS system, we investigated the impact of pressure passivity of cerebral metabolism (CCO), oxygenation (haemoglobin difference (HbD)) and cerebral blood volume (total haemoglobin (HbT)) in 23 term infants following HIE during therapeutic hypothermia (HT). Sixty-minute epochs of data from each infant were studied using wavelet analysis at a mean age of 48 h. Wavelet semblance (a measure of phase difference) was calculated to compare reactivity between mean arterial blood pressure (MABP) with oxCCO, HbD and HbT. OxCCO-MABP semblance correlated with thalamic Lac/NAA ( r = 0.48, p = 0.02). OxCCO-MABP semblance also differed between groups of infants with mild to moderate and severe injury measured using brain MRI score ( p = 0.04), thalamic Lac/NAA ( p = 0.04) and neurodevelopmental outcome at one year ( p = 0.04). Pressure passive changes in cerebral metabolism were associated with injury severity indicated by thalamic Lac/NAA, MRI scores and neurodevelopmental assessment at one year of age.

Impact of postoperative intravenous fluid administration on complications following elective hepato-pancreato-biliary surgery.

BACKGROUND: The impact of perioperative intravenous fluid administration on surgical outcomes has been documented in literature, but not specifically studied in the context of hepato-pancreato-biliary (HPB) surgery. This study aimed to investigate the impact of postoperative intravenous fluid administration on intensive care unit (ICU), in this subgroup of patients. METHODS: A single-center retrospective cohort of 241 HPB patients was assessed, focusing on intravenous fluid administration in ICU, during the first 24 h. Intravenous fluid variables were compared to hospital stay and postoperative complications. Data were assessed using Spearman's correlation test for bivariate correlations and logistic regression for multivariate analysis. RESULTS: The median volume of intravenous fluid administered in the first 24 h postoperatively was 4380 mL, of which 2200 mL was crystalloid, 1500 mL colloid and 680 mL "other" fluid. Patients with one or more complications had a higher median total intravenous fluid input (4790 vs. 4300 mL), higher colloid volume (2000 vs. 1500 mL), lower urine output (1595 vs. 1900 mL) and greater overall fluid balance (+3040 vs.+2553 mL) than those without complications. There were correlations between total intravenous fluid volume administered (r = 0.278, P < 0.001), intravenous colloid input (r = 0.278, P < 0.001), urine output (r = -0.295, P < 0.001), positive fluid balance (r = 0.344, P < 0.001) and length of hospital stay. Logistic regression model was constructed to predict the occurrence of one or more complications; total intravenous fluid volume and overall fluid balance were both independent significant predictors (OR = 2.463, P = 0.007; OR = 1.001, P = 0.011; respectively). CONCLUSIONS: Administration of high volumes of intravenous fluids in the first 24 hours post-HPB surgery, along with higher positive fluid balance is associated with a higher rate of complications and longer hospital stay. Moreover, lower urine output is associated with longer hospital stay. Whether these are the cause of complications or the result of them remains unclear.

Care of elderly patients: a prospective audit of the prevalence of hypotension and the use of BIS intraoperatively in 25 hospitals in London.

BACKGROUND: Anaesthesia is frequently complicated by intraoperative hypotension (IOH) in the elderly, and this is associated with adverse outcome. The definition of IOH is controversial, and although management guidelines for IOH in the elderly exist, the frequency of IOH and typical clinically applied treatment thresholds are largely unknown in the UK. METHODS: We audited frequency of intraoperative blood pressure against national guidelines in elderly patients undergoing surgery. Depth of anaesthesia (DOA) monitoring was also audited due to the association between low DOA values and IOH with increased mortality (as part of "double" and "triple low" phenomena) and because it is a suggested management strategy to reduce IOH. RESULTS: Twenty-five hospitals submitted data on 481 patients. Hypotension varied depending on the definition, but affected 400 patients (83.3 %) using the AAGBI standard. Furthermore, 2.9, 13.5, and 24.6 % had mean arterial blood pressures <50, <60, and <70 mmHg for 20 min, respectively, and 136 (28.4 %) had systolic blood pressure decrease by 20 % for 20 min. DOA monitors were used for 45 (9.4 %) patients. CONCLUSIONS: IOH is common and use of DOA monitors is less than implied by guidelines. Improved management of IOH may be a simple intervention with real potential to reduce morbidity in this vulnerable group.

Reduction of cytochrome C oxidase during vasovagal hypoxia-ischemia in human adult brain: a case study.

Near-infrared spectroscopy (NIRS)-derived measurement of oxidized cytochrome c oxidase concentration ([oxCCO]) has been used as an assessment of the adequacy of cerebral oxygen delivery. We report a case in which a reduction in conscious level was associated with a reduction in [oxCCO]. Hypoxaemia was induced in a 31-year-old, healthy male subject as part of an ongoing clinical study. Midway through the hypoxaemic challenge, the subject experienced an unexpected vasovagal event with bradycardia, hypotension and reduced cerebral blood flow (middle cerebral artery blood flow velocity decrease from 70 to 30 cm s(-1)) that induced a brief reduction in conscious level. An associated decrease in [oxCCO] was observed at 35 mm (-1.6 µM) but only minimal change (-0.1 µM) at 20-mm source-detector separation. A change in optical scattering was observed, but path length remained unchanged. This unexpected physiological event provides an unusual example of a severe reduction in cerebral oxygen delivery and is the first report correlating change in clinical status with changes in [oxCCO].