Low preoperative regional cerebral oxygen saturation in hemodialysis patients

Association between white matter hyperintensities and altered cerebral blood flow in maintenance hemodialysis patients: a longitudinal study

OBJECTIVES

To explore changes in cerebral blood flow (CBF) and white matter in hemodialysis patients.

METHODS

Thirty-three hemodialysis patients who underwent two brain MRI at an interval of three years and 33 age- and sex-matched healthy controls (HC) underwent structural and arterial spin-labeling MRI examinations. Intergroup differences in CBF in the gray matter, white matter, and whole matter, and regional white matter hyperintensities (WMH) were analyzed. Based on the changes in CBF between the baseline and follow-up groups, the hemodialysis patients were divided into two subgroups: an increased CBF group and a decreased CBF group. Differences in CBF and WMH between the subgroups and HC were analyzed.

RESULTS

Patients undergoing hemodialysis exhibited increased cerebral watershed (CW) WMH, deep WMH, and periventricular WMH (P < 0.01). The CBF of patients with decreased CBF was higher than that of HC at baseline (,P < 0.01) and lower than that of HC at follow-up (P < 0.01). Compared with the increased CBF group, obvious development of deep WMH was found in the decreased CBF group for the gray matter, white matter, and whole matter (P < 0.01).

CONCLUSIONS

WMH in hemodialysis patients were distributed in the deep white matter, periventricular white matter and CW, and progressed with the extension of hemodialysis duration. CBF in hemodialysis patients could manifest as both increased and decreased, and WMH in patients with decreased CBF developed severely with prolongation of hemodialysis duration.

ADVANCES IN KNOWLEDGE

These findings provide a basis for exploring neuropathological changes of hemodialysis patients.

Long-term hemodialysis may affect enlarged perivascular spaces in maintenance hemodialysis patients: evidence from a pilot MRI study

BACKGROUND

Hemodialysis (HD) causes various nervous system abnormalities. Alterations in white matter (WM) microstructure after long-term HD have been reported in a few previous studies; however, no studies have been performed to investigate enlarged perivascular spaces (PVS) in WM regions. We measured cerebral blood flow (CBF) and white matter volume (WMV) in HD patients to assess enlarged PVS severity in the WM across the whole brain and suggest possible explanations for this.

METHODS

Fifty-one HD patients and 51 age-, sex-, and education-matched healthy controls (HCs) were recruited. The number of enlarged PVS in the centrum semiovale (CS), cerebral watershed (CW), and basal ganglia (BG) regions were assessed by T2-weighted MRI. CBF was estimated by arterial spin labeling (ASL), which is a non-invasive perfusion imaging technique. WMV was assessed by the computational anatomy toolbox (CAT12), which is a statistical analysis package. Differences in descriptive variables (two-tailed t-tests, χ² tests, Mann-Whitney U tests, and Friedman M tests), an intra-class correlation between radiologists, the relationship between enlarged PVS number and HD duration, normalized CBF and WMV (multiple regression), and group differences in CBF and WMV {voxel-wise t-tests with age and sex as covariates [cluster size >50 voxels, false discovery rate (FDR) corrected, P<0.05]} were assessed.

RESULTS

HD patients displayed a more significant number of CS-PVS and CW-PVS in WM regions compared with the HCs, but there was no significant difference in the number of BG-PVS. The number of CS-PVS and CW-PVS were positively associated with HD duration. The number of CW-PVS was positively associated with CBF changes and WMV alteration in HD patients. Meanwhile, significant differences in the blood pressure (BP) readings pre-HD, intra-HD, and post-HD were observed in HD patients. Compared with the HCs, the HD patients showed higher CBF in the CS, CW, and BG regions (P<0.05). Hence, decreased WMV in the CS, CW, and BG regions were shown in the HD patients compared with the HCs (P<0.05).

CONCLUSIONS

Enlarged CS-PVS and CW-PVS on MRI might be a feature of long-term HD patients. Enlarged CW-PVS number is associated with higher CBF in the CW region and lower WMV in the CW region in HD patients.

Εndothelial and microvascular function in CKD: Evaluation methods and associations with outcomes

BACKGROUND

Cardiovascular disease is the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Endothelial dysfunction, the hallmark of atherosclerosis, is suggested to be involved pathogenetically in cardiovascular and renal disease progression in these patients.

METHODS

This is a narrative review presenting the techniques and markers used for assessment of microvascular and endothelial function in patients with CKD and discussing findings of the relevant studies on the associations of endothelial dysfunction with co-morbid conditions and outcomes in this population.

RESULTS

Venous Occlusion Plethysmography was the first method to evaluate microvascular function; subsequently, several relevant techniques have been developed and used in patients with CKD, including brachial Flow-Mediated Dilatation, and more recently, Near-Infrared Spectroscopy and Laser Speckle Contrast Analysis. Furthermore, several circulating biomarkers are commonly used in clinical research. Studies assessing endothelial function using the above techniques and biomarkers suggest that endothelial dysfunction occurs early in CKD and contributes to the target organ damage, cardiovascular events, death and progression towards end-stage kidney disease.

CONCLUSIONS

Older and newer functional methods and several biomarkers have assessed endothelial dysfunction in CKD; accumulated evidence supports an association of endothelial dysfunction with outcomes. Future research with new, non-invasive and easily applicable methods could further delineate the role of endothelial dysfunction on cardiovascular and renal disease progression in patients with CKD.

Assessment of Endothelial and Microvascular Function in CKD: Older and Newer Techniques, Associated Risk Factors, and Relations with Outcomes

BACKGROUND

Endothelium is the inner cellular lining of the vessels that modulates multiple biological processes including vasomotor tone, permeability, inflammatory responses, hemostasis, and angiogenesis. Endothelial dysfunction, the basis of atherosclerosis, is characterized by an imbalance between endothelium-derived relaxing factors and endothelium-derived contracting factors.

SUMMARY

Starting from the semi-invasive venous occlusion plethysmography, several functional techniques have been developed to evaluate microvascular function and subsequently used in patients with CKD. Flow-mediated dilatation of the forearm is considered to be the "gold standard," while in the last years, novel, noninvasive methods such as laser speckle contrast imaging and near-infrared spectroscopy are scarcely used. Moreover, several circulating biomarkers of endothelial function have been used in studies in CKD patients. This review summarizes available functional methods and biochemical markers for the assessment of endothelial and microvascular function in CKD and discusses existing evidence on their associations with comorbid conditions and outcomes in this population. Key Messages: Accumulated evidence suggests that endothelial dysfunction occurs early in CKD and is associated with target organ damage, progression of renal injury, cardiovascular events, and mortality. Novel methods evaluating microvascular function can offer a detailed, real-time assessment of underlying phenomena and should be increasingly used to shed more light on the role of endothelial dysfunction on cardiovascular and renal disease progression in CKD.

Cerebral blood flow regulation in end-stage kidney disease

Patients with chronic kidney disease (CKD) and end-stage kidney disease (ESKD) experience an increased risk of cerebrovascular disease and cognitive dysfunction. Hemodialysis (HD), a major modality of renal replacement therapy in ESKD, can cause rapid changes in blood pressure, osmolality, and acid-base balance that collectively present a unique stress to the cerebral vasculature. This review presents an update regarding cerebral blood flow (CBF) regulation in CKD and ESKD and how the maintenance of cerebral oxygenation may be compromised during HD. Patients with ESKD exhibit decreased cerebral oxygen delivery due to anemia, despite cerebral hyperperfusion at rest. Cerebral oxygenation further declines during HD due to reductions in CBF, and this may induce cerebral ischemia or "stunning." Intradialytic reductions in CBF are driven by decreases in cerebral perfusion pressure that may be partially opposed by bicarbonate shifts during dialysis. Intradialytic reductions in CBF have been related to several variables that are routinely measured in clinical practice including ultrafiltration rate and blood pressure. However, the role of compensatory cerebrovascular regulatory mechanisms during HD remains relatively unexplored. In particular, cerebral autoregulation can oppose reductions in CBF driven by reductions in systemic blood pressure, while cerebrovascular reactivity to CO₂ may attenuate intradialytic reductions in CBF through promoting cerebral vasodilation. However, whether these mechanisms are effective in ESKD and during HD remain relatively unexplored. Important areas for future work include investigating potential alterations in cerebrovascular regulation in CKD and ESKD and how key regulatory mechanisms are engaged and integrated during HD to modulate intradialytic declines in CBF.

Factors responsible for cerebral hypoxia in hemodialysis population

Brain tissue oxygenation (rSO(2)) measured by near-infrared spectroscopy (NIRS) is lower in hemodialysis patients than in the healthy population and is associated with cognitive dysfunction. The involved mechanisms are not known. We conducted this study to identify the factors that influence the rSO2 values in end-stage renal disease (ESRD) patients and to describe rSO2 changes during hemodialysis. We included a cohort of ESRD patients hemodialyzed in our institution. We recorded rSO2 using INVOS 5100C oximetry system (Medtronic, Essex, U.K.) and analyzed changes in basic laboratory values and hemodynamic fluctuations. Baseline rSO2 was lower in patients with heart failure (45.2±8.3 % vs. 54.1±7.8 %, p=0.006) and was significantly linked to higher red cell distribution width (RDW) (r=-0.53, p?0.001) and higher BNP level (r=-0.45, p=0.01). The rSO(2) value decreased in first 15 min of hemodialysis, this decrease correlated with drop in white blood count during the same period (r=0.43, p=0.02 in 10 min, r=0.43, p=0.02 in 20 min). Lower rSO(2) values in patients with heart failure and higher RDW suggest that hemodynamic instability combined with vascular changes probably leads to worse cerebral oxygenation in these patients. Decrease of rSO(2) in 15th minute of hemodialysis accompanied with a significant drop in leukocyte count could be explained by complement activation.

Near-infrared spectroscopy underestimates cerebral oxygenation in hemodialysis patients

Regional cerebral oxygen saturation (rSO₂) measured using near-infrared spectroscopy has been reported to be significantly lower in hemodialysis (HD) patients than in non-HD ones, but the mechanisms are unknown. The aim of this prospective study was to assess the accuracy of near-infrared spectroscopy to estimate cerebral oxygenation in HD patients undergoing cardiovascular surgery. Our hypothesis was that rSO₂ values would underestimate cerebral oxygenation in HD patients. This study included 113 patients (7 HD patients and 106 non-HD ones) undergoing cardiac or major aortic surgery between December 2015 and November 2017. We evaluated the validity of rSO₂ by comparing it with ipsilateral jugular venous oxygen saturation (SjvO₂). In HD and non-HD patients, rSO₂ and SjvO₂ showed a weak correlation (R²: 0.46 and 0.28 in HD and non-HD patients, respectively). Bland-Altman analysis revealed that bias (95% limits of agreement) of rSO₂ compared to SjvO₂ was - 19.2% ( - 41.7-3.3%) in HD patients and - 1.9% (- 19.3-15.5%) in non-HD ones. The large negative bias suggests that the rSO₂ values measured using near-infrared spectroscopy substantially underestimate cerebral oxygenation in HD patients.