The Role of Inflammation after Surgery for Elders (RISE) study: Study design, procedures, and cohort profile

Biomarkers of neurodegeneration and neural injury as potential predictors for delirium

OBJECTIVES

Determine if biomarkers of Alzheimer's disease and neural injury may play a role in the prediction of delirium risk.

METHODS

In a cohort of older adults who underwent elective surgery, delirium case-no delirium control pairs (N = 70, or 35 matched pairs) were matched by age, sex and vascular comorbidities. Biomarkers from CSF and plasma samples collected prior to surgery, including amyloid beta (Aβ)42 , Aβ40 , total (t)-Tau, phosphorylated (p)-Tau181 , neurofilament-light (NfL), and glial fibrillary acid protein (GFAP) were measured in cerebrospinal fluid (CSF) and plasma using sandwich enzyme-linked immunosorbent assays (ELISAs) or ultrasensitive single molecule array (Simoa) immunoassays.

RESULTS

Plasma GFAP correlated significantly with CSF GFAP and both plasma and CSF GFAP values were nearly two-fold higher in delirium cases. The median paired difference between delirium case and control without delirium for plasma GFAP was not significant (p = 0.074) but higher levels were associated with a greater risk for delirium (odds ratio 1.52, 95% confidence interval 0.85, 2.72 per standard deviation increase in plasma GFAP concentration) in this small study. No matched pair differences or associations with delirium were observed for NfL, p-Tau 181, Aβ40 and Aβ42 .

CONCLUSIONS

These preliminary findings suggest that plasma GFAP, a marker of astroglial activation, may be worth further investigation as a predictive risk marker for delirium.

Patterns and Persistence of Perioperative Plasma and Cerebrospinal Fluid Neuroinflammatory Protein Biomarkers After Elective Orthopedic Surgery Using SOMAscan

BACKGROUND

The neuroinflammatory response to surgery can be characterized by peripheral acute plasma protein changes in blood, but corresponding, persisting alterations in cerebrospinal fluid (CSF) proteins remain mostly unknown. Using the SOMAscan assay, we define acute and longer-term proteome changes associated with surgery in plasma and CSF. We hypothesized that biological pathways identified by these proteins would be in the categories of neuroinflammation and neuronal function and define neuroinflammatory proteome changes associated with surgery in older patients.

METHODS

SOMAscan analyzed 1305 proteins in blood plasma (n = 14) and CSF (n = 15) samples from older patients enrolled in the Role of Inflammation after Surgery for Elders (RISE) study undergoing elective hip and knee replacement surgery with spinal anesthesia. Systems biology analysis identified biological pathways enriched among the surgery-associated differentially expressed proteins in plasma and CSF.

RESULTS

Comparison of postoperative day 1 (POD1) to preoperative (PREOP) plasma protein levels identified 343 proteins with postsurgical changes ( P < .05; absolute value of the fold change [|FC|] > 1.2). Comparing postoperative 1-month (PO1MO) plasma and CSF with PREOP identified 67 proteins in plasma and 79 proteins in CSF with altered levels ( P < .05; |FC| > 1.2). In plasma, 21 proteins, primarily linked to immune response and inflammation, were similarly changed at POD1 and PO1MO. Comparison of plasma to CSF at PO1MO identified 8 shared proteins. Comparison of plasma at POD1 to CSF at PO1MO identified a larger number, 15 proteins in common, most of which are regulated by interleukin-6 (IL-6) or transforming growth factor beta-1 (TGFB1) and linked to the inflammatory response. Of the 79 CSF PO1MO-specific proteins, many are involved in neuronal function and neuroinflammation.

CONCLUSIONS

SOMAscan can characterize both short- and long-term surgery-induced protein alterations in plasma and CSF. Acute plasma protein changes at POD1 parallel changes in PO1MO CSF and suggest 15 potential biomarkers for longer-term neuroinflammation that warrant further investigation.

Plasma and cerebrospinal fluid inflammation and the blood-brain barrier in older surgical patients: the Role of Inflammation after Surgery for Elders (RISE) study

Background

Our understanding of the relationship between plasma and cerebrospinal fluid (CSF) remains limited, which poses an obstacle to the identification of blood-based markers of neuroinflammatory disorders. To better understand the relationship between peripheral and central nervous system (CNS) markers of inflammation before and after surgery, we aimed to examine whether surgery compromises the blood-brain barrier (BBB), evaluate postoperative changes in inflammatory markers, and assess the correlations between plasma and CSF levels of inflammation.

Methods

We examined the Role of Inflammation after Surgery for Elders (RISE) study of adults aged ≥ 65 who underwent elective hip or knee surgery under spinal anesthesia who had plasma and CSF samples collected at baseline and postoperative 1 month (PO1MO) (n = 29). Plasma and CSF levels of three inflammatory markers previously identified as increasing after surgery were measured using enzyme-linked immunosorbent assay: interleukin-6 (IL-6), C-reactive protein (CRP), and chitinase 3-like protein (also known as YKL-40). The integrity of the BBB was computed as the ratio of CSF/plasma albumin levels (Qalb). Mean Qalb and levels of inflammation were compared between baseline and PO1MO. Spearman correlation coefficients were used to determine the correlation between biofluids.

Results

Mean Qalb did not change between baseline and PO1MO. Mean plasma and CSF levels of CRP and plasma levels of YKL-40 and IL-6 were higher on PO1MO relative to baseline, with a disproportionally higher increase in CRP CSF levels relative to plasma levels (CRP tripled in CSF vs. increased 10% in plasma). Significant plasma-CSF correlations for CRP (baseline r = 0.70 and PO1MO r = 0.89, p < .01 for both) and IL-6 (PO1MO r = 0.48, p < .01) were observed, with higher correlations on PO1MO compared with baseline.

Conclusions

In this elective surgical sample of older adults, BBB integrity was similar between baseline and PO1MO, plasma-CSF correlations were observed for CRP and IL-6, plasma levels of all three markers (CRP, IL-6, and YKL-40) increased from PREOP to PO1MO, and CSF levels of only CRP increased between the two time points. Our identification of potential promising plasma markers of inflammation in the CNS may facilitate the early identification of patients at greatest risk for neuroinflammation and its associated adverse cognitive outcomes.

Preoperative red cell distribution width predicts postoperative cognitive dysfunction after coronary artery bypass grafting

We assessed the relationship between red blodd cell distribution width (RDW) and postoperative cognitive dysfunction (POCD) after coronary artery bypass grafting (CABG) in patients who usually had obvious hemodynamic changes. We enrolled 362 coronary heart disease patients who received CABG. POCD was assessed through neuropsychological examination at 21 days after operation. Demographics, history of diseases, blood biochemical parameters and perioperative data were collected. The receiver operating characteristic (ROC) curve was used to find the best cut-off value of RDW for diagnosis of POCD. Logistic regression was used to explore the relationship between RDW and POCD. The 21-day incidence of POCD in patients receiving CABG was 27.1% (98/362). The RDW of POCD patients was significantly higher than in the non-POCD patients (17.4 vs. 13.2). The sensitivity and specificity of RDW for predicting POCD were 82.7 and 64.8%, respectively. The POCD patients also tended to be older and had higher fasting plasma glucose, hypersensitive c-reactive protein, tumor necrosis factor-α, white blood cell levels and longer surgery time. No significant differences were found in other parameters. The 21-day neuropsychological test results were better in the POCD patients than the non-POCD patients. After adjustment of potential factors, the preoperative high RDW was still associated with an increased risk of POCD (odds ratio (OR) = 2.52, 95% confidence interval (CI): 1.28–4.31). Our study indicates that preoperative RDW is significantly elevated in POCD patients receiving CABG. The elevated preoperative RDW is associated with an increased risk of POCD and preoperative RDW can be an independent predictor of POCD.

Association of CSF Alzheimer's disease biomarkers with postoperative delirium in older adults

INTRODUCTION

The interaction between delirium and dementia is complex. We examined if Alzheimer's disease (AD) biomarkers in patients without clinical dementia are associated with increased risk of postoperative delirium, and whether AD biomarkers demonstrate a graded association with delirium severity.

METHODS

Participants (n = 59) were free of clinical dementia, age ≥ 70 years, and scheduled for elective total knee or hip arthroplasties. Cerebrospinal fluid (CSF) was collected at the time of induction for spinal anesthesia. CSF AD biomarkers were measured by enzyme-linked immunosorbent assay (ELISA) (ADX/Euroimmun); cut points for amyloid, tau, and neurodegeneration (ATN) biomarker status were A = amyloid beta (Aβ)42 <175 pg/mL or Aβ42/40 ratio <0.07; T = p-tau >80 pg/mL; and N = t-tau >700 pg/mL. Confusion Assessment Method (CAM) and CAM-Severity (CAM-S) were rated daily post-operatively for delirium and delirium severity, respectively.

RESULTS

Aβ42, tau, and p-tau mean pg/mL (SD) were 361.5 (326.1), 618.3 (237.1), and 97.1 (66.1), respectively, for those with delirium, and 550.4 (291.6), 518.3 (213.5), and 54.6 (34.5), respectively, for those without delirium. Thirteen participants (22%) were ATN positive. Delirium severity by peak CAM-S [mean difference (95% confidence interval)] was 1.48 points higher (0.29-2.67), P = 0.02 among the ATN positive. Delirium in the ATN-positive group trended toward but did not reach statistical significance (23% vs. 7%, p = 0.10). Peak CAM-S [mean (SD)] in the delirium group was 7 (2.8) compared to no delirium group 2.5 (1.3), but when groups were further classified by ATN status, an incremental effect on delirium severity was observed, such that patients who were both ATN and delirium negative had the lowest mean (SD) peak CAM-S scores of 2.5 (1.3) points, whereas those who were ATN and delirium positive had CAM-S scores of 8.7 (2.3) points; other groups (either ATN or delirium positive) had intermediate CAM-S scores.

DISCUSSION

The presence of AD biomarkers adds important information in predicting delirium severity. Future studies are needed to confirm this relationship and to better understand the role of AD biomarkers, even in pre-clinical phase, in delirium.

Intraoperative periarticular injection can alleviate the inflammatory response and enhance joint function recovery after hip arthroplasty in elderly patients with osteoporotic femoral neck fractures

PURPOSE

This study aimed to investigate the potential beneficial effects of periarticular injection (PAI) of multimodal drugs on the inflammatory response and joint function after hip arthroplasty in elderly patients with osteoporotic femoral neck fractures.

METHODS

Fifty six elderly patients with unilateral osteoporotic femoral neck fractures were randomly allocated to 2 groups: the PAI group, which received the multimodal drug PAI intraoperatively before incision closure, and the control group, which received an injection of saline at the same time as placebo. The C-reactive protein (CRP), interleukin-1β (IL-1β), and IL-6 levels as well as the erythrocyte sedimentation rate (ESR) in peripheral venous blood samples were measured, along with the Visual Analogue Scale (VAS) score with activity and Harris hip score preoperation at 1, 2, 4, 7, and 14 days as well as 1 and 3 months post-operation.

RESULTS

The 2 groups were comparable in sex and age, and no significant differences were observed in the preoperative CRP, IL-1β, and IL-6 levels, ESR, VAS score, or Harris hip score between the 2 groups (all P > .05). However, during the postoperative period, the PAI group exhibited significantly lower levels of CRP, IL-1β, and IL-6 as well as a lower ERS and VAS score compared with the control group (P < .05), while the Harris hip score was significantly higher postoperatively in the PAI group (P < .05).

CONCLUSION

Multimodal drug PAI can alleviate the inflammatory response and enhance hip function recovery after hip arthroplasty in elderly patients with osteoporotic femoral neck fractures.

The Potential Role of Lung-Protective Ventilation in Preventing Postoperative Delirium in Elderly Patients Undergoing Prone Spinal Surgery: A Preliminary Study

Background

Postoperative delirium (POD) is a frequent complication in elderly patients, usually occurring within a few days after surgery. This study investigated the effect of lung-protective ventilation (LPV) on POD in elderly patients undergoing spinal surgery and the mechanism by which LPV suppresses POD.

Material/Methods

Seventy-one patients aged ≥65 years were randomized to receive LPV or conventional mechanical ventilation (MV), consisting of intermittent positive pressure ventilation following induction of anesthesia. The tidal volume in patients who received MV was 8 ml/kg predicted body weight (PBW), and the ventilation frequency was 12 times/min. The tidal volume in patients who received LPV was 6 ml/kg PBW, the positive end-expiratory pressure was 5 cmH₂O, and the ventilation frequency was 15 times/min, with a lung recruitment maneuver performed every 30 min. Blood samples were collected immediately before anesthesia induction (T₀), 10 min (T₁) and 60 min (T₂) after turning over, immediately after the operation (T₃), and 15 min after extubation (T₄) for blood gas analysis. Simultaneous cerebral oxygen saturation (rSO₂) and cerebral desaturation were recorded. Preoperative and postoperative serum concentrations of interleukin (IL)-6, IL-10 and glial fibrillary acidic protein (GFAP) were measured by ELISA. POD was assessed by nursing delirium screening score.

Results

Compared with the MV group, pH was lower and PaCO₂ higher in the LPV group at T₂. In addition PaO₂, SaO₂, and PaO₂/FiO₂ were higher at T₁, and T₄, and rSO₂ was higher at T₃, and T₄ in the LPV than in the MV group (P<0.05 each). Postoperative serum GFAP and IL-6 were lower and IL-10 higher in the LPV group. The incidences of cerebral desaturation and POD were significantly lower in the LPV group (P<0.05).

Conclusions

LPV may reduce POD in elderly patients undergoing spinal surgery by inhibiting inflammation and improving cerebral oxygen metabolism.

The Role of Inflammation after Surgery for Elders (RISE) study: Examination of [11C]PBR28 binding and exploration of its link to post-operative delirium

Major surgery is associated with a systemic inflammatory cascade that is thought, in some cases, to contribute to transient and/or sustained cognitive decline, possibly through neuroinflammatory mechanisms. However, the relationship between surgery, peripheral and central nervous system inflammation, and post-operative cognitive outcomes remains unclear in humans, primarily owing to limitations of in vivo biomarkers of neuroinflammation which vary in sensitivity, specificity, validity, and reliability. In the present study, [11C]PBR28 positron emission tomography, cerebrospinal fluid (CSF), and blood plasma biomarkers of inflammation were assessed pre-operatively and 1-month post-operatively in a cohort of patients (N = 36; 30 females; ≥70 years old) undergoing major orthopedic surgery under spinal anesthesia. Delirium incidence and severity were evaluated daily during hospitalization. Whole-brain voxel-wise and regions-of-interest analyses were performed to determine the magnitude and spatial extent of changes in [11C]PBR28 uptake following surgery. Results demonstrated that, compared with pre-operative baseline, [11C]PBR28 binding in the brain was globally downregulated at 1 month following major orthopedic surgery, possibly suggesting downregulation of the immune system of the brain. No significant relationship was identified between post-operative delirium and [11C]PBR28 binding, possibly due to a small number (n = 6) of delirium cases in the sample. Additionally, no significant relationships were identified between [11C]PBR28 binding and CSF/plasma biomarkers of inflammation. Collectively, these results contribute to the literature by demonstrating in a sizeable sample the effect of major surgery on neuroimmune activation and preliminary evidence identifying no apparent associations between [11C]PBR28 binding and fluid inflammatory markers or post-operative delirium.

Neurovascular and immune mechanisms that regulate postoperative delirium superimposed on dementia

Objective

The present work evaluates the relationship between postoperative immune and neurovascular changes and the pathogenesis of surgery‐induced delirium superimposed on dementia.

Background and rationale

Postoperative delirium is a common complication in many older adults and in patients with dementia including Alzheimer's disease (AD). The course of delirium can be particularly debilitating, while its pathophysiology remains poorly defined.

Historical evolution

As of 2019, an estimated 5.8 million people of all ages have been diagnosed with AD, 97% of whom are >65 years of age. Each year, many of these patients require surgery. However, anesthesia and surgery can increase the risk for further cognitive decline. Surgery triggers neuroinflammation both in animal models and in humans, and a failure to resolve this inflammatory state may contribute to perioperative neurocognitive disorders as well as neurodegenerative pathology.

Updated hypothesis

We propose an immunovascular hypothesis whereby dysregulated innate immunity negatively affects the blood‐brain interface, which triggers delirium and thereby exacerbates AD neuropathology.

Early experimental data

We have developed a translational model to study delirium superimposed on dementia in APPSwDI/mNos2^−/− AD mice (CVN‐AD) after orthopedic surgery. At 12 months of age, CVN‐AD showed distinct neuroimmune and vascular impairments after surgery, including acute microgliosis and amyloid‐β deposition. These changes correlated with attention deficits, a core feature of delirium‐like behavior.

Future experiments and validation studies

Future research should determine the extent to which prevention of surgery‐induced microgliosis and/or neurovascular unit dysfunction can prevent or ameliorate postoperative memory and attention deficits in animal models. Translational human studies should evaluate perioperative indices of innate immunity and neurovascular integrity and assess their potential link to perioperative neurocognitive disorders.

Major challenges for the hypothesis

Understanding the complex relationships between delirium and dementia will require mechanistic studies aimed at evaluating the role of postoperative neuroinflammation and blood‐brain barrier changes in the setting of pre‐existing neurodegenerative and/or aging‐related pathology.

Linkage to other major theories

Non‐resolving inflammation with vascular disease that leads to cognitive impairments and dementia is increasingly important in risk stratification for AD in the aging population. The interdependence of these factors with surgery‐induced neuroinflammation and cognitive dysfunction is also becoming apparent, providing a strong platform for assessing the relationship between postoperative delirium and longer term cognitive dysfunction in older adults.